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KISS Amp Score Card
I have scored the three current entrants in the KISS amp design competition in accordance with the design parameters that Andre originally set down. As you would expect Andre's original "KISS" design scored the full 100 points, my KISSASS design scored 83 points, and Stewart's KISASS design brought up the rear with only 50 points. The scoring was based on meeting the following 6 design goals established by Andre. 1. KISS 2. All Class A 3. Zero Negative Feedback 4. Single Ended Output Stage 5. 3 Watt Power Output 6. 2 Volt Input Sensitivity Andre explicitly stated all but the first goal which was implicit. Each goal that was meet garnered 1/6 of the maximum 100 points. Most of the goals are obvious, except the first which was scored based on the total parts count not being more than 10% greater than the parts count of Andre's reference design, which I assumed has 22 parts. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. The following table shows how the scoring broke down. Andre's John's Stewart's KISS 300B KISSASS KISASS 1. KISS YES YES NO 2. All Class A YES YES YES 3. Zero NFB YES NO NO 4. SE Output YES YES NO 5. 3 Watts Out YES YES YES 6. 2 Volt Sens YES YES YES Score 6/6 5/6 3/6 Parts Count 22 21 33 Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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On Sun, 13 Mar 2005 08:00:24 +0100 (CET), George Orwell
wrote: John: Congratulations on coming so close. I think that as the trophyholder I should have just marginally less than a unit of points to distribute within my discretion for some facet beyond the rules. (Not quite a full unit, so that any discretionary bonus cannot unfairly change a close contest.) There is no trophy, if there was you wouldn't be holding it, and why all the pathetic sockpuppets? BROWNIE POINTS This contest was for arriving at a tube-like sound with transistors. It's not a contest, but that is indeed the design target. I have already explained elsewhere that I don't actually believe in a DHT sound or an SE sound, that I believe that the ultrafi sound (widely ascribed to DHT with 300B as the paradigm) is largely created by ZNFB Class A. That will be true too in transistors, where it is much more difficult to arrange. Depends how you define 'feedback'................ For arranging your transistor KISSass amp to produce all its output in SE Class A, and for a certain restraint which is essential in ultrafi amps, I therefore award you 8 of the discretionary points to bring your total up to 91. WHAT WE OVERLOOKED: HARMONICS DISTRIBUTION Looking back on it, I think we didn't set the rules closely enough. There is a major determinant of the sound of a ultrafi 300B for which we did not regulate. We overlooked it because at the time Pinkerton promised to provide a proper design that people would want to build or that at least he built and measured, so that physical comparisons could be made with my KISS 300B. What KISS 300B? We've seen no sign of your vapourware flea-power abomination, just lots of handwaving and wrong-headed ranting about the underlying principles. Now Pinkerton has turned in a piece of crap strictly on paper, which he is not building and which he has announced to be rubbish on, for instance, ABSE, so I do not see anyone building the Pinkytron Abomination and sending it to me or you for comparison. Interesting that you would pass judgement on something which you have not built, and whose design principles you clearly do not understand. The ultrafi sound of my 300B depends, beyond the absence of negative feedback, beyond being in Class A, on a favourable distribution of harmonics. We have been through this before, but it may be as well to have on it on record in this context. A much detuned version of my KISS 300B, called the Hedonist's Delight and drawn in compromised form to make it directly comparable to the Bubbaland 300B with which some earlier wannabe swinging dick challenged me, showed 1.83% of second harmonic at full power of near enough 8W and vanishingly small third and higher harmonics also at full power. The other guy's amp was so noisy, it wasn't even worth calculating noise at 1W because everyone knew I had annihilated the challenger. (Deja vu.) Still with the self-appointed 'winning', eh? You really are a sad sack of ****. The KISS 300B will put out half as much power over a higher impedance than the Hedonist. It is therefore reasonable to suppose that at full power of 3.8W my KISS 300B will have second harmonic well below 1.83% and zero third or higher harmonics. The distortion at the normal intended use of a fraction of a watt is unlikely to rise to 0.1% THD, which will be all second harmonic with zero third, odd or higher harmonics. Pinkerton says of his amp, "THD will be several percent above 5 watts". Unless this is some kind of a misprint, it is unacceptable even if it is all 2HD. Sez who? But we know it won't be... But even worse is the fact that in Pinkerton's amp the NFB will even at lower output create a harmonics mix in which the third, odd and higher harmonics will feature to a much larger extent than is acceptable in an ultrafi amp, and than I have demonstrably repeatedly achieved in tube amps, and will clearly improve upon in the KISS 300. There is no loop NFB in KISASS, and below 1 watt output, it will have no significant distortion products of any sort. It's certainly as 'ultrafi' as KISS, probably more so. Indeed, I challenge anyone to tell the difference under level-matched blind conditions - unless of course KISS has a horribly noisy and hummy output at low levels. This botch by Pinkerton was specifically "designed" to sound like a tube amp. Pinkerton claims it *will* sound like a tube amp if anyone wants to waste his time building it. I see no evidence of that and Pinkerton doesn't offer any evidence, nor is there any sign of thought or understanding of harmonic distribution by him. (I explained all this before putting my KISS 300B project on hold to give the challenger space to work but Pinkerton, like the other little irrationals, reflexively rejects whatever I say, "true or not" in Yaeger's phrase, because he doesn't like me.) Don't flatter yourself, I merely despise you. Pinkerton's travesty of a KISSass amp is hereby rejected because, in consideration of its likely harmonics distribution, I don't believe it will sound remotely like my KISS 300B or any other amp with ultra-fi pretentions. Unfortunately for your overinflated ego, I don't give a rat's as what *you* think of anything, and particularly of KISASS. Sure, it will have a sonic signature, as Pinkerton says. But it will be altogether the wrong sonic signature. Like Pinkerton's mind it will be arid and confused. Who could possibly want an amp with Pinkerton's manners? Certtainly more than would want one with your deranged personality. COMPONENT NUMBERS As an aside, irrelevant in the present context because it will make no difference to the outcome, but perhaps good to have on record, my KISS 300B will be presented as a linestage integrated and therefore will use up to 20-25 components depending on configuration and whether one assumes a custom power transformer or voltage droppers for the filaments of a catalogued transformer. I would thus be inclined to be generous about the number of components, say up to 28 including your 10 percent overage before a penalty is incurred. Andre Jute Special Plinkytron edition of KISSass amp rules: Rule 1: Talent is required. Rule 2: Andre already told you how to do it. Next time listen up. Rule 3. Grab your ankles. Andy baby, you have no idea how to do it, and you're certainly not the real McCoy. Furthermore, until you provide some evidence of both its existence and its circuitry, KISS is just another of your deranged fantasies. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Sun, 13 Mar 2005 01:57:31 -0500, Jon Yaeger
wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition What 'competition' is this? And who elected you judge? in accordance with the design parameters that Andre originally set down. As you would expect Andre's original "KISS" design scored the full 100 points, my KISSASS design scored 83 points, and Stewart's KISASS design brought up the rear with only 50 points. The scoring was based on meeting the following 6 design goals established by Andre. 1. KISS 2. All Class A 3. Zero Negative Feedback 4. Single Ended Output Stage 5. 3 Watt Power Output 6. 2 Volt Input Sensitivity Andre explicitly stated all but the first goal which was implicit. Each goal that was meet garnered 1/6 of the maximum 100 points. Most of the goals are obvious, except the first which was scored based on the total parts count not being more than 10% greater than the parts count of Andre's reference design, which I assumed has 22 parts. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. That is incorrect. The following table shows how the scoring broke down. Andre's John's Stewart's KISS 300B KISSASS KISASS 1. KISS YES YES NO 2. All Class A YES YES YES 3. Zero NFB YES NO NO 4. SE Output YES YES NO 5. 3 Watts Out YES YES YES 6. 2 Volt Sens YES YES YES Score 6/6 5/6 3/6 Parts Count 22 21 33 Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ Well, I guess it ain't no secret who one the ass kissin' contest . . . . Shame that you missed the point of my design. This isn't a competition, and Andre (or Turner) doesn't get to make up rules. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Jon Yaeger wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition in accordance with the design parameters that Andre originally set down. As you would expect Andre's original "KISS" design scored the full 100 points, my KISSASS design scored 83 points, and Stewart's KISASS design brought up the rear with only 50 points. The scoring was based on meeting the following 6 design goals established by Andre. 1. KISS 2. All Class A 3. Zero Negative Feedback 4. Single Ended Output Stage 5. 3 Watt Power Output 6. 2 Volt Input Sensitivity Andre explicitly stated all but the first goal which was implicit. Each goal that was meet garnered 1/6 of the maximum 100 points. Most of the goals are obvious, except the first which was scored based on the total parts count not being more than 10% greater than the parts count of Andre's reference design, which I assumed has 22 parts. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. The following table shows how the scoring broke down. Andre's John's Stewart's KISS 300B KISSASS KISASS 1. KISS YES YES NO 2. All Class A YES YES YES 3. Zero NFB YES NO NO 4. SE Output YES YES NO 5. 3 Watts Out YES YES YES 6. 2 Volt Sens YES YES YES Score 6/6 5/6 3/6 Parts Count 22 21 33 Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ Well, I guess it ain't no secret who one the ass kissin' contest . . . . I don't really want to comment on who is kissin who's ace, or focus too much on the above "score" from such an illustrious but perhaps nevetheless "imaginitive referee" as JB. At the end of the day, what "score" of music sounds best is the final decider, surely. I have just had a geek at Pinky's provisional SS amp......... OK, we have a complementary emitter follower pair of class A bjts presumably biased with a couple of amps idle current from an RC smoothed supply, so they'll run in class A. Let us suppose the current gain was 30 between the output current and the base inputs. Therefore if there is 1 amp rms in the output current load, threre will have to be 0.033 amps base input current. Now the Gm of the output bjts would be about the usual 30A/V, and open loop gain would be approx Gm x RL, so if the load is 8 ohms, each output bjt sees approximately 16 ohms, depending on the current sharing between the two bjts. Therefore open loop voltage gain of the output bjts is 30 x 16, or 480. But because Pinky has a EF output stage, closed loop voltage gain is 480 / (1 + 480 x beta), or very close to 1.0. So there is a gain reduction due to NFB = approximately 1/480 times So providing the input voltage can be kept linear, thd should also be reduced from say 10% for common emitter connection to 0.021% for emitter follower connection, and at 8 watts. So the amount of series voltage NFB applied in the output stage is 20 log 480, so about 54 dB of NFB is applied locally in the output stage. Its not uncommon for the emitter follower connection to automatically give between 30 and 60 db of series voltage NFB. We can neglect the 0.22 ohm emitter bias stabilizing resistors for the present. For an 8 volt swing on the output, there is just slightly more than 8v applied to the output bases, and a 0.033 amp swing, so the Rin of the output stage is 8 / 0.033 = 242 ohms. One has to remember that with BJT output stages, the Rin to an output stage varies in proportion to the output load, so that if 4 ohms were connected, Iin would be 0.066 amps, if the voltage swing was the same, and Rin would be 8 / 0.066 = 121 ohms. Now the driver transistor will have a much higher Rc than the load, so the only thing that tends to keep the drive voltage constant is the R5, 150 ohms. Now the open loop gain of the driver stage also = Gm x RL, since it is a *current* source, and RL with 8 ohms is 150 // 242 = 93 ohms, and with 4 ohms its 67 ohms So the gain of the driver with 8 ohms will be nearly 3 dB greater than when 4 ohms is connected, and a rough calculation makes me think the output resistance of the amp will be 6 ohms, due to the huge variation in driver gain due to reflected load variation.. This is a perfectly lousy result, and well below what the 300B is capable of. Also, if any load caused distortion currents are generated, they too escape the voltage emitter follower FB clean up, because they flow through to the bases, and appear in the input wave form largely unsupressed by any NFB action. But let us consider the driver stage, a lone transistor, presumably some sort of T0220 driver type of bjt with a current gain of maybe a 100, and Gm = 20 A/V, typical of what is available. Since its collector load is 93 ohms when 8 ohms is at the output, then its gain with the 24 ohm emitter load will be about 93/24 = about 4, so 2 vrms is about what's needed to produce 8vrms at the collector to drive the output bases.. 8v into 93 ohms gives 86 mA I change, so if driver hfe = 100, then there is about 0.86 mA change in the base current for the 2v input needed, so Ri to the driver = 2 / 0.00086 = 2.35kohms. This is still very low for any preamp, so Pinky has added the input buffer, and with its current gain the 2.35k will be increased to around 235k, and small in comparison to the bias nework at the input of 100k and 36k in parallel. But nevertheless, variations in the output load value transmit themselves all the way forward to the input, and this is the ****tiest thing about BJTs when you don't wanna use many of them or any NFB. To reduce this current transfer effect, most designers ues darlington pairs or triples in the output stage. But alas, the hfe of the P and N devices used even with such local output buffers can vary so much that the output stage base input impedance for each 1/2 of the cycle in a typical class B output emitter follower can vary by so much to cause distortion up to 40%. I have seen it myself in many designs, hence the use of a darlington triple, which uses the first of the darlington transistors in class A, and the Ro is so low it shunts the non linear input R of a class B output stage. Now in Pinky's output, the outputs are in class A, so the Rin will only vary during the cycle by the mismatch between N and P transistors. Seen the Ic vs Vc curves for N and P devices? Usually they are about as different as an EL34 is to a 6L6. Its not a happy situation though, and mosfets with high Rin to their gates would have been a natural better choice for a trouble free low parts count, and give an output stage without the current reflection effects I have outlined. A pair of mosfets in source follower will also each see 16 ohms each, but their Gm is only about 0.8 amps/V, far less than the BJTs, so their open loop gain = 0.8 x 16 = 12.8, so with the source follower connection, closed loop gain is about 12.8 / (1 + 12.8), so about 0.93, so the amount of applied series voltage NFB is far less than the BJT EF stage, but it still amounts to about 23 dB. In tests I have done with class A SF comp pairs expect thd to be about 0.5% 8 watts, but declining nicely as power is reduced, so that no other NFB is needed apart from the follower connection since the output devices are in class A and there are no switching distortions, and we hope we can design a one stage j-fet or bjt input stage to make about 9 vrms at below 0.1% thd. Since there is no current change of the output load transferred to the gate drive with mosfets, the use of a pair of class A output mosfets gives a far more easiliy drivable stage, and Rout is usually around an ohm or less, and no buffer is needed, so the input stage can be just one signal fet or one signal BJT with local current FB to get the wanted drive voltage to the output gates. Thus we could build an output stage with 2 mosfets in source follower mode, and one driver transistor, and this would be 3 devices only, instead of Pinky's 4 devices.. If we were to think a little more we could use a mosfet as an SE device, and use a choke to supply the idle current to the drain, then cap couple the load off the drain via the 4,700 uF cap Pinky is using in his amp, and there isn't much wrong with a parafeed amp. One mosfet can safely dissipate exactly what we consider safe with a 300B, ie, 32 watts, and since efficiency is up to about 45%, we can easily get 15 watts of output power if RL is about 32 ohms. But instead of choke, it could have a secondary winding to make it an SE OPT, and then that gets rid of the cap coupling, and provides us with a grounded potential winding from which we can take series voltage NFB back to a single input bjt or j-fet, like one might with a pentode plus triode driver tube. Thus the active device count could be reduced to 2. There are advantages of the SE mosfet amp with a transformer coupled load. One is that we can have the load seen by the mosfet to = say 32 ohms, which may be an ideal load for the mosfet if Ia at idle is 1 amp. If the OPT TR = 2:1, then ZR = 4:1, and the load at the output is 8 ohms. But we can nicely match to other loads if we use the brain to design suitable winding configs. Then this common source output stage needs less than 1 vrms drive to make 8 vrms at the output. This is far more easily achieved by a signal bjt or j-fet because whenever we increase signal voltage above a volt for bjts or j-fets the thd increases alarmingly compared to triodes, and we are compelled to use enormous dB of local current NFB to control distortion. Now I maintain that NFB is *NOT* inherently evil. It has been my experience to have prooved definately to several gatherings of witheringly critical audiophiles that NFB does not suck, and it does not suck the life from music, but then I will offer two conditions; not too much NFB, and what there is must be effective, not like Pinky's amp, where you'd expect 54 db of series voltage NFB to radically reduce Rout to very low figures, but it can't and Rout is 6 ohms, and the other condition is that the circuit be fast enough, and this means that the OPT if there is one should have around 60 khz of open loop BW. The demos to audiophiles were on repeated occasions, and in one memorable one a system with 4 x 6550 in triode with 6 db of global NFB was regarded as worse than mine with 16 db and two 6550 in UL for each channel, same speakers, same sources, same tunes. SE amps with 16 db global NFB were also well accepted in comparison with other amps with far less NFB. And i say that with several flame proof suits on, so please, all of you just stay calm, and alow some explanation. Where we have an output SE mosfet with a single fet driver, there will be some cancellation of the 2H produced but at large output voltages, the odd order thd is going to be similar to a 6L6 in beam power mode. Alas we cannot connect as triode or in UL, the mosfet has no screen and its is like a beam tube..... But if we did apply the same 23 dB of global NFB from the secondary of the OPT back to the source of the driver j-fet, then we would reduce Ro to the same or better than the source follower output connection, and reduce thd substantially to acceptable levels, and more effectively than just using a source follower output. The mosfet such as a 2SK134 can be considered similarly as a tube, because its a transconductance device, but at 1 amp of idle current Rd = 220 ohms, Gm = 0.9 A/V, and so U = 198. At an amp of idle current, its surprising just how linear the mosfet can be without ANY kind of NFB at all, and so much more linear than a bog standard output BJT, in terms of voltage linearity. BJTs have current linearity, but make poor voltage amps unless huge amounts of current NFB are used, and as I have explained above, Pinky needs both lots of current AND voltage NFB to make his 4 stage amp work far better. He really needs to have a a pair of darlington connected N and P devices for the class A output, then perhaps another darlington pair connected gain stage fro the input. That'd be 6 devices. Now Anrdre's amp uses a lone 300B to do the business, and as I have explained to all before, there is local electrostatic NFB acting at all AF within the tube. Its about as local and inimtate an application of NFB as one could ever wish for, and it was put there by the God Of Triodes when the tube was made, and lets not argue with a God in charge of so much high voltage. If we remove the NFB from a triode by placing a screen grid into a triode, we get a beam tetrode or pentode, and no NFB and the distortion not only increases but its spectra degenerates and both odd and even orderered harmonics are present, and the output resistance of the tube increases dramatically. The benefit is twice the triode power for a given amount of plate dissipation. The necessary thing we must then do to restore such an amp is to provide some external loop of NFB to compensate for the presence of the NFB stopping screen grid. hence global or other loops of NFB. With mosfets or BJTs, the current flow is high compared to the voltage fields in the device, so the electrostatic FB effect in three terminal SS devices isn't large. That is an overly simplistic explanation, but the fact is that for most SS devices the voltage linearity with no external FB loops is poor, and the Rout high in comparison with the loads we want to drive, so the bjt and fet is as bad a device to begin with as a pentode or beam tetrode. With a beam tetrode or pentode, we can use the UL connection to make the thd resemble that of a triode, ie, mainly 2H, with little 3H, 4H or 5H. 2H is more tolerable than the rest, so not much NFB is needed with a triode, and if we are careful, enough NFB is within the triode to do the trick of making the music not just acceptable, but wonderful. Therefore with NFB applied to a pentode or beam tube the 2H, 3H, 4H, 5H all stay there after FB is applied, so we need to apply more NFB than what is naturally within a triode, and 20 dB is generally used with a pentode to make it as acceptable as a triode without any. But just how one rigs such NFB is beyond this post now, because many ways are possible, and some ways are more effective than others. The mosfet SE amp with OPT will be able to easily make 8 watts, and with only 23 db of series voltage NFB it will have a very good DF, and low thd, and measure better than the 300B amp. The Nelson Pass Zen amp pushes things harder by making a single mosfet dissipate 50 watts from which 17 audio watts are available, and then another mosfet is a CCS also dissipating 50 watts, but producing no power. There is 12 dB of shunt voltage NFB applied, and the result in terms of Ro and thd about resembles the triode amp with no NFB. A friend got nothing but smoky silence from his Zen attempt, and after 3 expensive mosfet changes he gave up. Expecting any T03 device to safely dissipate 50 watts is total BS imho. Its like saying an EL34 is happy dissipating 32 watts. It will, but sooner rather than later it will fail. In my AM radio I use in the kitchen, I have an SE EL34 in triode with a paralleled 12AX7 driver tube and 12 db of global NFB. I have a sensitive speaker, and about all I use is around 1/2 a watt max average power. The sound is utterly blameless. The rule for simple *low power* power amps is that the average levels should be 1/10 the maximum levels for clipping, so if an amp clips at 5 watts, then only expect a nice average 0.5 watts and no more. 0.5 watts into a speaker with 95 db efficiency with 1 watt means you get 92 dB, and that's way too loud for me, so 0.05 watts for 82 db is about all I need. 5 watts allows a 102 db ceiling, quite enough in the kitchen. Andre's requirement for 3? watts is a bit low, but he intends for horns, so its OK. But a simple amp is still simple if it merely means that to quadruple the power we just use 4 parallel output devices and use a more current able driver device, or use a much larger output tube. AFAIK, there are not many cheap easily available gigantic transistors or mosfets rated for safe continuous dissipation of 200 watts. Patrick Turner. |
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Yon yeager remarked that ...
Well, I guess it ain't no secret who one the ass kissin' contest . . . . Pinky retorted.... Shame that you missed the point of my design. This isn't a competition, and Andre (or Turner) doesn't get to make up rules. -- Well who does make up the rules? Yer canna have lyfe without rules.... Anyway, so damn what. Its men's business to spend just about all their lives competing with each other, and makin up rules as they go along. So even when we try to care to share something, we soon start competing, and soon the dismissals of individuals as idiots and fools begins.... But I'll be kind, I won't be slightly tempted to dismiss anything right now. But I don't wanna build your Kissass amp for a long while, dat fo sure. In the words of the famous immortalist, "I'll do it my way". Patrick Turner |
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"François Yves Le Gal" wrote: On Sun, 13 Mar 2005 14:01:19 GMT, Patrick Turner wrote: But instead of choke, it could have a secondary winding to make it an SE OPT, http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm Yep, also if PP action is needed, but with no regard for simplicity, http://www.turneraudio.com.au/htmlwe...5050mosfet.htm Patrick Turner. |
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On Sun, 13 Mar 2005 14:01:19 +0000, Patrick Turner wrote:
snip I have just had a geek at Pinky's provisional SS amp......... snip Thanks for your comments Patrick. Very informative - keep up the good work. :-) -- Mick (no M$ software on here... :-) ) Web: http://www.nascom.info Web: http://projectedsound.tk |
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On Mon, 14 Mar 2005 01:30:24 +1100, Patrick Turner
wrote: Yon yeager remarked that ... Well, I guess it ain't no secret who one the ass kissin' contest . . . . Pinky retorted.... Shame that you missed the point of my design. This isn't a competition, and Andre (or Turner) doesn't get to make up rules. Well who does make up the rules? Yer canna have lyfe without rules.... Yes, but since it isn't a competition, it doesn't *need* rules. Anyway, so damn what. Its men's business to spend just about all their lives competing with each other, and makin up rules as they go along. So even when we try to care to share something, we soon start competing, and soon the dismissals of individuals as idiots and fools begins.... But I'll be kind, I won't be slightly tempted to dismiss anything right now. But I don't wanna build your Kissass amp for a long while, dat fo sure. It's KISASS, but no problem - neither do I. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Sun, 13 Mar 2005 14:01:19 GMT, Patrick Turner
wrote: At the end of the day, what "score" of music sounds best is the final decider, surely. Indeed, although if as claimed 'the first watt is the most important', I'll lay odds that the various options are sonically indistinguishable up to that limit. I have just had a geek at Pinky's provisional SS amp......... OK, we have a complementary emitter follower pair of class A bjts presumably biased with a couple of amps idle current from an RC smoothed supply, so they'll run in class A. 1 amp quiescent current, giving a maximum output into 4 ohms of 8 watts. The voltage limitation also dictates a maximum of about 8 watts into 8 ohms. Let us suppose the current gain was 30 between the output current and the base inputs. Therefore if there is 1 amp rms in the output current load, threre will have to be 0.033 amps base input current. It's typically about 200 for the MJL4281A/MJL4302A devices chosen for this design, hence about 5mA base current. Now the Gm of the output bjts would be about the usual 30A/V, It is in fact something like 150 A/V at 1 amp for these devices, so far as can be seen from the Vbe/Ic curves. and open loop gain would be approx Gm x RL, so if the load is 8 ohms, each output bjt sees approximately 16 ohms, depending on the current sharing between the two bjts. Therefore open loop voltage gain of the output bjts is 30 x 16, or 480. Actually, about 2500. But because Pinky has a EF output stage, closed loop voltage gain is 480 / (1 + 480 x beta), or very close to 1.0. So there is a gain reduction due to NFB = approximately 1/480 times So providing the input voltage can be kept linear, thd should also be reduced from say 10% for common emitter connection to 0.021% for emitter follower connection, and at 8 watts. I'd say closer to 0.0015%, but let's just agree that it's negligible. So the amount of series voltage NFB applied in the output stage is 20 log 480, so about 54 dB of NFB is applied locally in the output stage. Its not uncommon for the emitter follower connection to automatically give between 30 and 60 db of series voltage NFB. We can neglect the 0.22 ohm emitter bias stabilizing resistors for the present. You can? Without loop NFB? Intriguing.................. For an 8 volt swing on the output, there is just slightly more than 8v applied to the output bases, and a 0.033 amp swing, so the Rin of the output stage is 8 / 0.033 = 242 ohms. More like 8/0.005 = 1600 ohms. One has to remember that with BJT output stages, the Rin to an output stage varies in proportion to the output load, so that if 4 ohms were connected, Iin would be 0.066 amps, if the voltage swing was the same, and Rin would be 8 / 0.066 = 121 ohms. Actually, about 800 ohms. Now the driver transistor will have a much higher Rc than the load, so the only thing that tends to keep the drive voltage constant is the R5, 150 ohms. Correct. Now the open loop gain of the driver stage also = Gm x RL, since it is a *current* source, and RL with 8 ohms is 150 // 242 = 93 ohms, and with 4 ohms its 67 ohms Actually, about 150//1600 = 137 ohms, and about 126 ohms for a 4 ohm load. So the gain of the driver with 8 ohms will be nearly 3 dB greater than when 4 ohms is connected, and a rough calculation makes me think the output resistance of the amp will be 6 ohms, due to the huge variation in driver gain due to reflected load variation.. No, in fact it will be more like 0.72dB, and the Zo of the amp will be less than 1 ohm. This is a perfectly lousy result, and well below what the 300B is capable of. Bull****, since your assumptions are incorrect. Check your facts. Also, if any load caused distortion currents are generated, they too escape the voltage emitter follower FB clean up, because they flow through to the bases, and appear in the input wave form largely unsupressed by any NFB action. But let us consider the driver stage, a lone transistor, presumably some sort of T0220 driver type of bjt with a current gain of maybe a 100, and Gm = 20 A/V, typical of what is available. It's already been specified as a MJL4281A, with typical current gain of 200 at the quiescent operating point of 100mA, and even higher Gm than at 1 amp. Since its collector load is 93 ohms when 8 ohms is at the output, then its gain with the 24 ohm emitter load will be about 93/24 = about 4, so 2 vrms is about what's needed to produce 8vrms at the collector to drive the output bases.. Nope, your assumptions are incorrect, and it has a voltage gain of pretty close to 6. snip of lots of handwaving and false assumptions BJTs have current linearity, but make poor voltage amps unless huge amounts of current NFB are used, and as I have explained above, Pinky needs both lots of current AND voltage NFB to make his 4 stage amp work far better. He really needs to have a a pair of darlington connected N and P devices for the class A output, then perhaps another darlington pair connected gain stage fro the input. That'd be 6 devices. Nope, it will work just fine as designed, for the reasons given above. Get your head out of RDH4 and look at what modern multiple-emitter poer BJTs can do. Now Anrdre's amp uses a lone 300B to do the business, and as I have explained to all before, there is local electrostatic NFB acting at all AF within the tube. Its about as local and inimtate an application of NFB as one could ever wish for, and it was put there by the God Of Triodes when the tube was made, and lets not argue with a God in charge of so much high voltage. **** 'Im, if for some deranged reason you want a *real* SET amp, use an 845 or 211, and play with proper Frankensteinian voltages! :-) The mosfet SE amp with OPT will be able to easily make 8 watts, and with only 23 db of series voltage NFB it will have a very good DF, and low thd, and measure better than the 300B amp. The Nelson Pass Zen amp pushes things harder by making a single mosfet dissipate 50 watts from which 17 audio watts are available, and then another mosfet is a CCS also dissipating 50 watts, but producing no power. There is 12 dB of shunt voltage NFB applied, and the result in terms of Ro and thd about resembles the triode amp with no NFB. A friend got nothing but smoky silence from his Zen attempt, and after 3 expensive mosfet changes he gave up. There's no substitute for skill! :-) If properly built, the Zen does what it says on the tin, and the magic blue smoke stays inside the tin. Expecting any T03 device to safely dissipate 50 watts is total BS imho. Agreed, without heroic and costly cooling arrangements. Its like saying an EL34 is happy dissipating 32 watts. It will, but sooner rather than later it will fail. In my AM radio I use in the kitchen, I have an SE EL34 in triode with a paralleled 12AX7 driver tube and 12 db of global NFB. I have a sensitive speaker, and about all I use is around 1/2 a watt max average power. The sound is utterly blameless. Aside from the speaker, of course.......... :-) The rule for simple *low power* power amps is that the average levels should be 1/10 the maximum levels for clipping, so if an amp clips at 5 watts, then only expect a nice average 0.5 watts and no more. Except of course properly conceived amps like the 1969 Linsley Hood 10-watter, which is just fine all the way from half-power downwards. 0.5 watts into a speaker with 95 db efficiency with 1 watt means you get 92 dB, and that's way too loud for me, so 0.05 watts for 82 db is about all I need. 5 watts allows a 102 db ceiling, quite enough in the kitchen. Shame that there are *very* few decent 95dB/w/m speakers, and they tend to cost many thoiusands of dollars. Andre's requirement for 3? watts is a bit low, but he intends for horns, so its OK. But a simple amp is still simple if it merely means that to quadruple the power we just use 4 parallel output devices and use a more current able driver device, or use a much larger output tube. AFAIK, there are not many cheap easily available gigantic transistors or mosfets rated for safe continuous dissipation of 200 watts. As you point out, not a problem if you just parallel them up. Alternatively, grow a brain and build a 100 watt Class AB BJT design with negligible distortion at *any* level up to 3/4 of full power. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Sun, 13 Mar 2005 15:28:26 +0100, François Yves Le Gal
wrote: On Sun, 13 Mar 2005 14:01:19 GMT, Patrick Turner wrote: But instead of choke, it could have a secondary winding to make it an SE OPT, http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm Undeniably a KISS design, and arguably superior to Zen, if the OPT is of high quality. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Sun, 13 Mar 2005 18:46:15 +0000 (UTC), Stewart Pinkerton
wrote: http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm Undeniably a KISS design, and arguably superior to Zen, if the OPT is of high quality. 845's and now this? Sure you're not suffering from (what's the name of that syndrome where the captive starts to sympathize with the captors?) syndrome? Arf! What seems strange to me in both designs are the original design goals. Why Oh Why not incorporate the required "line" stage and volume control? Seeing these three things together allows better choices for all and can minimize the number of components in the signal path. Thanks for your thoughts, Chris Hornbeck |
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Stewart Pinkerton wrote: On Sun, 13 Mar 2005 14:01:19 GMT, Patrick Turner wrote: At the end of the day, what "score" of music sounds best is the final decider, surely. Indeed, although if as claimed 'the first watt is the most important', I'll lay odds that the various options are sonically indistinguishable up to that limit. I have just had a geek at Pinky's provisional SS amp......... OK, we have a complementary emitter follower pair of class A bjts presumably biased with a couple of amps idle current from an RC smoothed supply, so they'll run in class A. 1 amp quiescent current, giving a maximum output into 4 ohms of 8 watts. The voltage limitation also dictates a maximum of about 8 watts into 8 ohms. Let us suppose the current gain was 30 between the output current and the base inputs. Therefore if there is 1 amp rms in the output current load, threre will have to be 0.033 amps base input current. It's typically about 200 for the MJL4281A/MJL4302A devices chosen for this design, hence about 5mA base current. Then if that is the case, and the device numbers were not shown on the schematic I got, then the base current will have 6 times less effect than I predicted. Now the Gm of the output bjts would be about the usual 30A/V, It is in fact something like 150 A/V at 1 amp for these devices, so far as can be seen from the Vbe/Ic curves. This means the open loop gain would be many times greater than what I had guessed. and open loop gain would be approx Gm x RL, so if the load is 8 ohms, each output bjt sees approximately 16 ohms, depending on the current sharing between the two bjts. Therefore open loop voltage gain of the output bjts is 30 x 16, or 480. Actually, about 2500. But because Pinky has a EF output stage, closed loop voltage gain is 480 / (1 + 480 x beta), or very close to 1.0. So there is a gain reduction due to NFB = approximately 1/480 times So providing the input voltage can be kept linear, thd should also be reduced from say 10% for common emitter connection to 0.021% for emitter follower connection, and at 8 watts. I'd say closer to 0.0015%, but let's just agree that it's negligible. If your gain figures are correct, then indeed the amount of applied series voltage FB is far greater than I said. So the amount of series voltage NFB applied in the output stage is 20 log 480, so about 54 dB of NFB is applied locally in the output stage. Its not uncommon for the emitter follower connection to automatically give between 30 and 60 db of series voltage NFB. We can neglect the 0.22 ohm emitter bias stabilizing resistors for the present. In this case, about 70 dB of NFB is applied in the emitter follower output stage. You can? Without loop NFB? Intriguing.................. The two 0.22 ohm resistors parallel to 0.11 ohms, and these are outside you local eitter follower FB loop. So the Rout will at least be 0.11 ohms.... I have neglected the 0.22 ohms because I wanted the analysis to be simple. For an 8 volt swing on the output, there is just slightly more than 8v applied to the output bases, and a 0.033 amp swing, so the Rin of the output stage is 8 / 0.033 = 242 ohms. More like 8/0.005 = 1600 ohms. One has to remember that with BJT output stages, the Rin to an output stage varies in proportion to the output load, so that if 4 ohms were connected, Iin would be 0.066 amps, if the voltage swing was the same, and Rin would be 8 / 0.066 = 121 ohms. Actually, about 800 ohms. Now the driver transistor will have a much higher Rc than the load, so the only thing that tends to keep the drive voltage constant is the R5, 150 ohms. Correct. Now the open loop gain of the driver stage also = Gm x RL, since it is a *current* source, and RL with 8 ohms is 150 // 242 = 93 ohms, and with 4 ohms its 67 ohms Actually, about 150//1600 = 137 ohms, and about 126 ohms for a 4 ohm load. So the gain of the driver with 8 ohms will be nearly 3 dB greater than when 4 ohms is connected, and a rough calculation makes me think the output resistance of the amp will be 6 ohms, due to the huge variation in driver gain due to reflected load variation.. No, in fact it will be more like 0.72dB, and the Zo of the amp will be less than 1 ohm. This is a perfectly lousy result, and well below what the 300B is capable of. Bull****, since your assumptions are incorrect. Check your facts. Without being told what transistors you are using, I was left to assume whatever I cared to. When posting schematics, be prepared to be made to look a fool if you are sloppy with your presentation. But from what you have now suggested about the chosen transistors, you are indeed correct, I have no argument. Add about 0.11 ohms to the Rout you got. So Rout would still be just less than 1 ohm, and is acceptable imho, but does not the 70 dB of series voltage FB render itself rather ineffective because of the "current reflection" to the input stages? Also, if any load caused distortion currents are generated, they too escape the voltage emitter follower FB clean up, because they flow through to the bases, and appear in the input wave form largely unsupressed by any NFB action. But let us consider the driver stage, a lone transistor, presumably some sort of T0220 driver type of bjt with a current gain of maybe a 100, and Gm = 20 A/V, typical of what is available. It's already been specified as a MJL4281A, with typical current gain of 200 at the quiescent operating point of 100mA, and even higher Gm than at 1 amp. Since its collector load is 93 ohms when 8 ohms is at the output, then its gain with the 24 ohm emitter load will be about 93/24 = about 4, so 2 vrms is about what's needed to produce 8vrms at the collector to drive the output bases.. Nope, your assumptions are incorrect, and it has a voltage gain of pretty close to 6. With your full information, the driver has a gain of about = collector load divided by emitter load, so 6 is about right. snip of lots of handwaving and false assumptions BJTs have current linearity, but make poor voltage amps unless huge amounts of current NFB are used, and as I have explained above, Pinky needs both lots of current AND voltage NFB to make his 4 stage amp work far better. He really needs to have a a pair of darlington connected N and P devices for the class A output, then perhaps another darlington pair connected gain stage fro the input. That'd be 6 devices. Nope, it will work just fine as designed, for the reasons given above. Get your head out of RDH4 and look at what modern multiple-emitter poer BJTs can do. Get you head into RDH4, and see what tubes can do. Now Anrdre's amp uses a lone 300B to do the business, and as I have explained to all before, there is local electrostatic NFB acting at all AF within the tube. Its about as local and inimtate an application of NFB as one could ever wish for, and it was put there by the God Of Triodes when the tube was made, and lets not argue with a God in charge of so much high voltage. **** 'Im, if for some deranged reason you want a *real* SET amp, use an 845 or 211, and play with proper Frankensteinian voltages! :-) I prefer a 13E1, or perhaps a QE08, far less common, but such tetrodes make excellent triodes, and run at normal 300B type voltages. a single 13E1 can make 25 watts in UL mode, Ea only 375v. The mosfet SE amp with OPT will be able to easily make 8 watts, and with only 23 db of series voltage NFB it will have a very good DF, and low thd, and measure better than the 300B amp. The Nelson Pass Zen amp pushes things harder by making a single mosfet dissipate 50 watts from which 17 audio watts are available, and then another mosfet is a CCS also dissipating 50 watts, but producing no power. There is 12 dB of shunt voltage NFB applied, and the result in terms of Ro and thd about resembles the triode amp with no NFB. A friend got nothing but smoky silence from his Zen attempt, and after 3 expensive mosfet changes he gave up. There's no substitute for skill! :-) He isn't use to have to praying to the GOT before farnarkling with voltages. If properly built, the Zen does what it says on the tin, and the magic blue smoke stays inside the tin. I don't like the Zen. Expecting any T03 device to safely dissipate 50 watts is total BS imho. Agreed, without heroic and costly cooling arrangements. Its like saying an EL34 is happy dissipating 32 watts. It will, but sooner rather than later it will fail. In my AM radio I use in the kitchen, I have an SE EL34 in triode with a paralleled 12AX7 driver tube and 12 db of global NFB. I have a sensitive speaker, and about all I use is around 1/2 a watt max average power. The sound is utterly blameless. Aside from the speaker, of course.......... :-) The speaker measures and sounds very well. I use microscopic amounts of power most days. I don't expect the radio to reproduce the effect of standing in the middle of the LSO at full bore. The rule for simple *low power* power amps is that the average levels should be 1/10 the maximum levels for clipping, so if an amp clips at 5 watts, then only expect a nice average 0.5 watts and no more. Except of course properly conceived amps like the 1969 Linsley Hood 10-watter, which is just fine all the way from half-power downwards. A williamson also is fine on the same basis. And that basis is for a sine wave to R load. And evan at full 16 watts, the W makes only 0.1% thd. Average power for music is quite different. 1/10 full power means the output voltage is about 1/3 the full clipping voltage. Much pop music from radio stations has an average voltage level only 6 db below the maximum voltage level transmitted. If you monitor a radio stations's signal just have a dummy load and take the music up to where it begins to clip as shown on a CRO with a signal which is rap, bebop, rock or whatever, and you will measure an RMS voltage about 1/2 the sine wave voltage for full power and clipping. But one has to allow for much more headroom for classical or un compressed music, and a 10 dB voltage headroom is a minimum; more headroom is better. 0.5 watts into a speaker with 95 db efficiency with 1 watt means you get 92 dB, and that's way too loud for me, so 0.05 watts for 82 db is about all I need. 5 watts allows a 102 db ceiling, quite enough in the kitchen. Shame that there are *very* few decent 95dB/w/m speakers, and they tend to cost many thoiusands of dollars. Its easier to use 4 tubes instead of 1 and use 89 db speakers than be compelled to use 95 dB speakers with one tube imho, unless the tube is a biggun. Andre's requirement for 3? watts is a bit low, but he intends for horns, so its OK. But a simple amp is still simple if it merely means that to quadruple the power we just use 4 parallel output devices and use a more current able driver device, or use a much larger output tube. AFAIK, there are not many cheap easily available gigantic transistors or mosfets rated for safe continuous dissipation of 200 watts. As you point out, not a problem if you just parallel them up. Alternatively, grow a brain and build a 100 watt Class AB BJT design with negligible distortion at *any* level up to 3/4 of full power. Yes but I have customers who have such amps, and they still prefer the tubes. They sometimes go back to the SS just for an hour every few months. Last month one told me that when he tried this for a couple of hours, he thought the musicians were all playing separately. Then when he goes back to the tubes he says they all sounded like they were together. I don't argue with them. I build amps that Andre and many others don't like. Too much power, vanishingly low thd, even the SE35 amps with a quad of 6CA7 make 10 watts into any load between 3 and 12 ohms at less than 0.1% thd. the ceiling is 35 watts. Many other SE amps are up there with well over 1%. I have built/restored 3 watt amps, and tried to use test them on my 89 dB speakers, and they just don't have the power. I have a 2A3 project under way for someone who does have some 95 db speakers. He does not use much volume. Most people with excellent and undamaged hearing don't need high volume and huge powers. But if only 1/3 of a watt is the maximum average power, then a 300B is very hard to beat, and the NFB within it is sufficient. A colleage of mine used 8 x 300B for 80 watts max for a cane farmer's amp ( 16 tubes for two channels ). At a watt there was not a lot of measurable problems, and the sound was OK. You could ask why he didn't buy an 80 watt SS amp for 1/10 of the price and weight, but some folks just ain't interested. They could always buy a cheap car, cheap shoes, cheap house, marry a cheap lady, but they ain't interested. I'd still wanna build an SE mosfet amp rather than yours. You snipped out the juicy bits from my post, so it wasn't worth your while to comment. Patrick Turner. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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In article , Stewart Pinkerton
wrote: On Sun, 13 Mar 2005 01:57:31 -0500, Jon Yaeger wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. What 'competition' is this? And who elected you judge? Everyone else took a step backwards, so I was elected. Somebody had to compare the various designs, your comments/criticisms on my judging are welcome. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. That is incorrect. How so? Are you saying that my judging criterion relative to NFB around two or more stages is incorrect, or that your KISASS design doesn't have NFB around two stages? Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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In article , Patrick Turner
wrote: If we were to think a little more we could use a mosfet as an SE device, and use a choke to supply the idle current to the drain, then cap couple the load off the drain via the 4,700 uF cap Pinky is using in his amp, and there isn't much wrong with a parafeed amp. One mosfet can safely dissipate exactly what we consider safe with a 300B, ie, 32 watts, and since efficiency is up to about 45%, we can easily get 15 watts of output power if RL is about 32 ohms. But instead of choke, it could have a secondary winding to make it an SE OPT, and then that gets rid of the cap coupling, and provides us with a grounded potential winding from which we can take series voltage NFB back to a single input bjt or j-fet, like one might with a pentode plus triode driver tube. Thus the active device count could be reduced to 2. Couldn't the circuit be arranged with one end of the choke grounded so that "we can take series voltage NFB back to a single input bjt or j-fet"? This circuit is very similar to my KISSASS two bjt design which uses one PNP and one NPN transistor in what I call a "reverse amplified emitter follower" circuit. The output is taken through a transformer, with feedback taken from the primary side of the transformer. Since one end of the output transformer primary is grounded, if desired the output can be taken directly across the primary, serving as an inductor. Another alternative is to use an output autotransformer. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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John Byrns wrote: In article , Stewart Pinkerton wrote: On Sun, 13 Mar 2005 01:57:31 -0500, Jon Yaeger wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. What 'competition' is this? And who elected you judge? Everyone else took a step backwards, so I was elected. Somebody had to compare the various designs, your comments/criticisms on my judging are welcome. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. That is incorrect. How so? Are you saying that my judging criterion relative to NFB around two or more stages is incorrect, or that your KISASS design doesn't have NFB around two stages? Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. There is 70 dB of series voltage NFB in the output stage from the follower connection alone. The NFB in the output stage is not 100% effective because part of the output load current current appears in the bases of the output transistors, and thus this current is subject to the series current NFB in the driver stage. Its not as much as i first assumed though, and really, very little NFB is applied over more than 1 stage. I'd still prefer to build a mosfet amp with an OPT if i wanted simplicity due to a small number of devices. Patrick Turner. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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John Byrns wrote: In article , Patrick Turner wrote: If we were to think a little more we could use a mosfet as an SE device, and use a choke to supply the idle current to the drain, then cap couple the load off the drain via the 4,700 uF cap Pinky is using in his amp, and there isn't much wrong with a parafeed amp. One mosfet can safely dissipate exactly what we consider safe with a 300B, ie, 32 watts, and since efficiency is up to about 45%, we can easily get 15 watts of output power if RL is about 32 ohms. But instead of choke, it could have a secondary winding to make it an SE OPT, and then that gets rid of the cap coupling, and provides us with a grounded potential winding from which we can take series voltage NFB back to a single input bjt or j-fet, like one might with a pentode plus triode driver tube. Thus the active device count could be reduced to 2. Couldn't the circuit be arranged with one end of the choke grounded so that "we can take series voltage NFB back to a single input bjt or j-fet"? This circuit is very similar to my KISSASS two bjt design which uses one PNP and one NPN transistor in what I call a "reverse amplified emitter follower" circuit. The output is taken through a transformer, with feedback taken from the primary side of the transformer. Since one end of the output transformer primary is grounded, if desired the output can be taken directly across the primary, serving as an inductor. Another alternative is to use an output autotransformer. There are lotsa ways. Using a isolation transformer means there is no slight DC potential across winding to which one might connect a speaker, since the idle current is quite high. One dude i know does his mosfet amp using class A PP and with two PNP output fets, allowing a grounded CT of an auto transformer This means a speaker is slung between two taps on each 1/2 primary which are at equal DC potential. The tranny is easy to wind and about 200 turns are OK for the primary on a core with 38 tongue x 50 stack core. The driver is an LTP of NPN j-fets, and direct coupled, sort of like a pair of balanced zsiclai pairs. But the PP amp uses 4 devices. But no more complex than a Quad II. Patrick Turner. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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On Sun, 13 Mar 2005 23:54:44 GMT, Chris Hornbeck
wrote: On Sun, 13 Mar 2005 18:46:15 +0000 (UTC), Stewart Pinkerton wrote: http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm Undeniably a KISS design, and arguably superior to Zen, if the OPT is of high quality. 845's and now this? Sure you're not suffering from (what's the name of that syndrome where the captive starts to sympathize with the captors?) syndrome? Arf! No, I just suffer from logic, and a lack of bigotry. What seems strange to me in both designs are the original design goals. Why Oh Why not incorporate the required "line" stage and volume control? Seeing these three things together allows better choices for all and can minimize the number of components in the signal path. It's a pot and a switch - what's to design? -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Mon, 14 Mar 2005 00:49:21 -0600, (John Byrns) wrote:
In article , Stewart Pinkerton wrote: On Sun, 13 Mar 2005 01:57:31 -0500, Jon Yaeger wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. What 'competition' is this? And who elected you judge? Everyone else took a step backwards, so I was elected. Somebody had to compare the various designs, your comments/criticisms on my judging are welcome. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. That is incorrect. How so? Are you saying that my judging criterion relative to NFB around two or more stages is incorrect, or that your KISASS design doesn't have NFB around two stages? KISASS doesn't have feedback around two stages. Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. Yes. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. What? That's madness! Besides, Tr1 is only there to provide a conventionally high input impedance. If you have a CD player with a decent output stage, Tr1 can be removed. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Stewart Pinkerton wrote: On Mon, 14 Mar 2005 00:49:21 -0600, (John Byrns) wrote: In article , Stewart Pinkerton wrote: On Sun, 13 Mar 2005 01:57:31 -0500, Jon Yaeger wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. What 'competition' is this? And who elected you judge? Everyone else took a step backwards, so I was elected. Somebody had to compare the various designs, your comments/criticisms on my judging are welcome. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. That is incorrect. How so? Are you saying that my judging criterion relative to NFB around two or more stages is incorrect, or that your KISASS design doesn't have NFB around two stages? KISASS doesn't have feedback around two stages. Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. Yes. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. What? That's madness! Besides, Tr1 is only there to provide a conventionally high input impedance. If you have a CD player with a decent output stage, Tr1 can be removed. Why not use a j-fet? Patrick Turner. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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"Chris Hornbeck" wrote in message ... : On Sun, 13 Mar 2005 18:46:15 +0000 (UTC), Stewart Pinkerton : wrote: : : http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm : : Undeniably a KISS design, and arguably superior to Zen, if the OPT is : of high quality. : : 845's and now this? Sure you're not suffering from (what's : the name of that syndrome where the captive starts to : sympathize with the captors?) syndrome? Arf! - that would be the Stockholm syndrome - : : What seems strange to me in both designs are the original : design goals. Why Oh Why not incorporate the required : "line" stage and volume control? Seeing these three things : together allows better choices for all and can minimize : the number of components in the signal path. : : Thanks for your thoughts, : : Chris Hornbeck |
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On Mon, 14 Mar 2005 18:33:40 +1100, Patrick Turner
wrote: John Byrns wrote: In article , Stewart Pinkerton wrote: On Sun, 13 Mar 2005 01:57:31 -0500, Jon Yaeger wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. What 'competition' is this? And who elected you judge? Everyone else took a step backwards, so I was elected. Somebody had to compare the various designs, your comments/criticisms on my judging are welcome. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. That is incorrect. How so? Are you saying that my judging criterion relative to NFB around two or more stages is incorrect, or that your KISASS design doesn't have NFB around two stages? Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. There is 70 dB of series voltage NFB in the output stage from the follower connection alone. The NFB in the output stage is not 100% effective because part of the output load current current appears in the bases of the output transistors, and thus this current is subject to the series current NFB in the driver stage. Its not as much as i first assumed though, and really, very little NFB is applied over more than 1 stage. Quite so. John is really reaching to describe this as NFB. I'd still prefer to build a mosfet amp with an OPT if i wanted simplicity due to a small number of devices. Yes, but that's already been done, by Nelson Pass and Jean Hiraga. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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In article , Stewart Pinkerton
wrote: On Mon, 14 Mar 2005 00:49:21 -0600, (John Byrns) wrote: Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. Yes. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. What? That's madness! Besides, Tr1 is only there to provide a conventionally high input impedance. If you have a CD player with a decent output stage, Tr1 can be removed. Your claim that "Tr1 is only there to provide a conventionally high input impedance" is little more than a thinly disguised attempt to deflect the issue. It is obvious by inspection that the feedback voltage developed across R7, by the load current flowing through Tr2 & R7, is in series with the input voltage to Tr1, hence a feedback loop exists around two stages. This feedback loop can be easily seen if you delete R4 from the circuit. Of course the presence of R4 in the circuit does reduce the amount feedback from Tr2 back to Tr1, I will leave it to Patrick to calculate exactly how much R4 reduces the feedback, as he seems to be good at that. Holding my finger to the wind I will guess that the presence of R4 reduces the feedback by about 16 dB, depending on how you reckon it. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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On Mon, 14 Mar 2005 17:21:32 +1100, Patrick Turner
wrote: Stewart Pinkerton wrote: Patrick wrote: This is a perfectly lousy result, and well below what the 300B is capable of. Bull****, since your assumptions are incorrect. Check your facts. Without being told what transistors you are using, I was left to assume whatever I cared to. Had you troubled to check the thread, you'd have seen my recommended devices separately listed, no need to ass u me. When posting schematics, be prepared to be made to look a fool if you are sloppy with your presentation. Likewise, with false assumptions. But from what you have now suggested about the chosen transistors, you are indeed correct, I have no argument. Add about 0.11 ohms to the Rout you got. So Rout would still be just less than 1 ohm, and is acceptable imho, but does not the 70 dB of series voltage FB render itself rather ineffective because of the "current reflection" to the input stages? Yes, it does, but the circuit is simple to understand, should be nicely stable, and its transfer function is totally dominated by the voltage gain stage Tr2. Had I been attempting an *optimum* simple 10-watt 'sorta kinda single-ended' class A SS amp, I'd simply have pointed you to the classic 1969 Linsley Hood design, as I've mentioned several times. Get your head out of RDH4 and look at what modern multiple-emitter poer BJTs can do. Get you head into RDH4, and see what tubes can do. I did - forty years ago, when tubes were relevant technology, and RDH4 was still in print. Indeed, I still have my copy of Landee, Davis and Albrecht's 'Electronic Designers Handbook', a 1957 tome which I consider to be a somewhat superior reference. I've mentioned elsewhere that my very first 'hi-fi' amp was a single-ended 5-watt valve design - but audio has moved on a *long* way since then. The rule for simple *low power* power amps is that the average levels should be 1/10 the maximum levels for clipping, so if an amp clips at 5 watts, then only expect a nice average 0.5 watts and no more. Except of course properly conceived amps like the 1969 Linsley Hood 10-watter, which is just fine all the way from half-power downwards. A williamson also is fine on the same basis. And that basis is for a sine wave to R load. And evan at full 16 watts, the W makes only 0.1% thd. I was being overly cautious, checking the 1969 article reminds me that the original JLH amp remained well below 0.1% THD right up over 10 watts, almost to clipping at 12 watts. Average power for music is quite different. 1/10 full power means the output voltage is about 1/3 the full clipping voltage. Much pop music from radio stations has an average voltage level only 6 db below the maximum voltage level transmitted. If you monitor a radio stations's signal just have a dummy load and take the music up to where it begins to clip as shown on a CRO with a signal which is rap, bebop, rock or whatever, and you will measure an RMS voltage about 1/2 the sine wave voltage for full power and clipping. OTOH, when listening to pop music from a radio broadcast, is *amplifier* quality of much relevance? :-) But one has to allow for much more headroom for classical or un compressed music, and a 10 dB voltage headroom is a minimum; more headroom is better. Yes, I'd always seen 20-26dB peak to average SPL quoted as typical for classical music, which does require significant power to avoid clipping peaks, especially on solo piano. 0.5 watts into a speaker with 95 db efficiency with 1 watt means you get 92 dB, and that's way too loud for me, so 0.05 watts for 82 db is about all I need. 5 watts allows a 102 db ceiling, quite enough in the kitchen. Shame that there are *very* few decent 95dB/w/m speakers, and they tend to cost many thoiusands of dollars. Its easier to use 4 tubes instead of 1 and use 89 db speakers than be compelled to use 95 dB speakers with one tube imho, unless the tube is a biggun. You won't get any argument from me on that score! AFAIK, there are not many cheap easily available gigantic transistors or mosfets rated for safe continuous dissipation of 200 watts. As you point out, not a problem if you just parallel them up. Alternatively, grow a brain and build a 100 watt Class AB BJT design with negligible distortion at *any* level up to 3/4 of full power. Yes but I have customers who have such amps, and they still prefer the tubes. They sometimes go back to the SS just for an hour every few months. Last month one told me that when he tried this for a couple of hours, he thought the musicians were all playing separately. Then when he goes back to the tubes he says they all sounded like they were together. I don't argue with them. Arguing with one's customers is not generally advised, if business longevity is desired! I'd still wanna build an SE mosfet amp rather than yours. I'm not arguing on performance grounds, but others have already created such designs. I havent seen a BJT one recently, hence KISASS. You snipped out the juicy bits from my post, so it wasn't worth your while to comment. I do try to cut to the chase and to avoid rambling on - which general opinion seems to suggest is a weakness of yours. :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Mon, 14 Mar 2005 13:59:39 +0100, "Ruud Broens"
wrote: "Chris Hornbeck" wrote in message .. . : On Sun, 13 Mar 2005 18:46:15 +0000 (UTC), Stewart Pinkerton : wrote: : : http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm : : Undeniably a KISS design, and arguably superior to Zen, if the OPT is : of high quality. : : 845's and now this? Sure you're not suffering from (what's : the name of that syndrome where the captive starts to : sympathize with the captors?) syndrome? Arf! - that would be the Stockholm syndrome - Regrettably, Daddy is not a multi-millionaire, and I hardly ever sympathise with *anyone*! :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Mon, 14 Mar 2005 19:05:16 +0000, Stewart Pinkerton wrote:
snip I'm not arguing on performance grounds, but others have already created such designs. I havent seen a BJT one recently, hence KISASS. This thread prompted me to have another look at the JLH design. I found this build, which I thought was rather interesting: http://www.tcaas.btinternet.co.uk/jlhesl.htm think I'll stick with bottles - they're probably smaller.... ;-) -- Mick (no M$ software on here... :-) ) Web: http://www.nascom.info Web: http://projectedsound.tk |
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On Mon, 14 Mar 2005 00:49:21 -0600, John Byrns wrote:
snip The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. snip Not getting involved with any argument over competitions, but this page is interesting: http://sound.westhost.com/project36.htm The text accompanying Figure 3 points out that the design could be built with a lot of 2H distortion. This may sound more like a 300B than SP's design - but whether that is the point is something else... ;-) -- Mick (no M$ software on here... :-) ) Web: http://www.nascom.info Web: http://projectedsound.tk |
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On Mon, 14 Mar 2005 12:31:45 -0600, (John Byrns) wrote:
In article , Stewart Pinkerton wrote: On Mon, 14 Mar 2005 00:49:21 -0600, (John Byrns) wrote: Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. Yes. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. What? That's madness! Besides, Tr1 is only there to provide a conventionally high input impedance. If you have a CD player with a decent output stage, Tr1 can be removed. Your claim that "Tr1 is only there to provide a conventionally high input impedance" is little more than a thinly disguised attempt to deflect the issue. Not, it's reality. Remember that? I have never seen *anyone* attempt to suggest that an emitter follower is part of a feedback loop which includes the following common-emitter stage. Sounds like you're desperately attempting to exclude anything which doesn't look *exactly* like a 300B SET - and why the frell would anyone design a SS amp in the same fashion, since the technologies are totally different? It is obvious by inspection that the feedback voltage developed across R7, by the load current flowing through Tr2 & R7, is in series with the input voltage to Tr1, hence a feedback loop exists around two stages. This feedback loop can be easily seen if you delete R4 from the circuit. But R4 *is* in the circuit, which reduces your claimed 'feedback' to utterly negligible proportions. Without R4, it wouldn't *be* an emitter follower, it would be part of a Darlington pair, which I have never seen described as a feedback loop. What are you smoking? Of course the presence of R4 in the circuit does reduce the amount feedback from Tr2 back to Tr1, I will leave it to Patrick to calculate exactly how much R4 reduces the feedback, as he seems to be good at that. About 46dB, making any so-called 'feedback' not a primary effect, not even a secondary effect, but a mere tertiary effect at best. Can you get me some of that stuff you're smoking? Holding my finger to the wind I will guess that the presence of R4 reduces the feedback by about 16 dB, depending on how you reckon it. Well, you know what you can do with your finger............... -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Mon, 14 Mar 2005 20:30:15 GMT, mick wrote:
On Mon, 14 Mar 2005 00:49:21 -0600, John Byrns wrote: snip The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. snip Not getting involved with any argument over competitions, but this page is interesting: http://sound.westhost.com/project36.htm The text accompanying Figure 3 points out that the design could be built with a lot of 2H distortion. This may sound more like a 300B than SP's design - but whether that is the point is something else... ;-) I agree that Zen is likely to be more like KISS than is KISASS, but (noting that Fig 3 is specifically described as 'not a real circuit') to name a five-transistor amplifier as 'Death of Zen', is utterly hilarious! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Mon, 14 Mar 2005 20:19:25 GMT, mick wrote:
On Mon, 14 Mar 2005 19:05:16 +0000, Stewart Pinkerton wrote: snip I'm not arguing on performance grounds, but others have already created such designs. I havent seen a BJT one recently, hence KISASS. This thread prompted me to have another look at the JLH design. I found this build, which I thought was rather interesting: http://www.tcaas.btinternet.co.uk/jlhesl.htm think I'll stick with bottles - they're probably smaller.... ;-) Nah, just buy an old Quad 405 - doesn't cost much, and it was specifically designed to drive Quad speakers. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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Stewart Pinkerton wrote: On Mon, 14 Mar 2005 18:33:40 +1100, Patrick Turner wrote: John Byrns wrote: In article , Stewart Pinkerton wrote: On Sun, 13 Mar 2005 01:57:31 -0500, Jon Yaeger wrote: in article , John Byrns at wrote on 3/12/05 8:17 PM: I have scored the three current entrants in the KISS amp design competition The competition to see if a reasonable solid state facsimile of Andre's 300B KISS amp could be designed. What 'competition' is this? And who elected you judge? Everyone else took a step backwards, so I was elected. Somebody had to compare the various designs, your comments/criticisms on my judging are welcome. For scoring purposes I considered NFB to exist only if two or more stages were enclosed in a NFB loop, local NFB as in a triode tube or transistor emitter follower, was not counted as NFB. Stewart's KISASS design failed the NFB test because two stages, Tr1 & Tr2 were enclosed in the single NFB loop formed by R7. That is incorrect. How so? Are you saying that my judging criterion relative to NFB around two or more stages is incorrect, or that your KISASS design doesn't have NFB around two stages? Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. There is 70 dB of series voltage NFB in the output stage from the follower connection alone. The NFB in the output stage is not 100% effective because part of the output load current current appears in the bases of the output transistors, and thus this current is subject to the series current NFB in the driver stage. Its not as much as i first assumed though, and really, very little NFB is applied over more than 1 stage. Quite so. John is really reaching to describe this as NFB. I'd still prefer to build a mosfet amp with an OPT if i wanted simplicity due to a small number of devices. Yes, but that's already been done, by Nelson Pass and Jean Hiraga. Yeah, but transistor amps have been done to death... Even class A types. Not many mosfet amps with one power mosfet and a j-fet or small mosfet input. The necessary OPT is very easy to wind, since there are not many turns, and the wire is thick. Patrick Turner. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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John Byrns wrote: In article , Stewart Pinkerton wrote: On Mon, 14 Mar 2005 00:49:21 -0600, (John Byrns) wrote: Tr1 & Tr2 constitute a two stage amplifier with the load consisting of the 150 Ohm resistor R5 paralleled with the input of the output stage. Yes. The load current flows through the 24 Ohm resistor R7 in the emitter circuit of Tr2, R7 is also in series with the input signal driving the base emitter circuit of Tr1. This constitutes and obvious case of a NFB loop encompassing more than a single stage. What? That's madness! Besides, Tr1 is only there to provide a conventionally high input impedance. If you have a CD player with a decent output stage, Tr1 can be removed. Your claim that "Tr1 is only there to provide a conventionally high input impedance" is little more than a thinly disguised attempt to deflect the issue. It is obvious by inspection that the feedback voltage developed across R7, by the load current flowing through Tr2 & R7, is in series with the input voltage to Tr1, hence a feedback loop exists around two stages. This feedback loop can be easily seen if you delete R4 from the circuit. Of course the presence of R4 in the circuit does reduce the amount feedback from Tr2 back to Tr1, I will leave it to Patrick to calculate exactly how much R4 reduces the feedback, as he seems to be good at that. Holding my finger to the wind I will guess that the presence of R4 reduces the feedback by about 16 dB, depending on how you reckon it. R4 is in parallel with the Rout of the emitter Rout ot Tr1, an ohm or two. So the presence of R4 has almost no effect in the circuit whatsoever, except to discharge the capacitance at that point in the circuit when dealing with HF signal. Be careful with your finger left out in the wind John, it can blow hot sometimes. Tr1 can be eliminated entirely, and an EF buffer placed between Tr2 and the outputs. There is no buffer where there ought to be one. Patrick Turner. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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On Mon, 14 Mar 2005 07:50:00 +0000 (UTC), Stewart Pinkerton
wrote: 845's and now this? Sure you're not suffering from (what's the name of that syndrome where the captive starts to sympathize with the captors?) syndrome? Arf! No, I just suffer from logic, and a lack of bigotry. I'm a big fan of 845's; they solve a lot of speaker problems, which are much more intractible. 211's have even better curves, and three in parallel make 50 watts without grid current, and into an almost-practical 5K ohm load. Why not incorporate the required "line" stage and volume control? Seeing these three things together allows better choices for all and can minimize the number of components in the signal path. It's a pot and a switch - what's to design? Everything's to design, mon. It's not like we're working to end world hunger here. Shouldn't we be discussing arcania and trivial mysteries beyond the ken of mere mortals? Hobbies should be enjoyable and stimulating, but so often over Usenet degenerate into old-lady bickering. I know you're above that, so I feel confident in posting this plea in your thread. And to answer your question, the connection between the "line" stage and the "output" stage can be simplified if they're physically close (same box). Simpler is betterer. Chris Hornbeck "I just don't think it's right to have a club like this. It ain't in the Bible," said Gary Colwell, 18, a brick mason who grew up in the area. "We see them walking around holding hands, and it makes everybody feel uncomfortable." |
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On Mon, 14 Mar 2005 19:07:02 +0000 (UTC), Stewart Pinkerton
wrote: Regrettably, Daddy is not a multi-millionaire, and I hardly ever sympathise with *anyone*! :-) Arf! Chris Hornbeck |
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In article , Stewart Pinkerton
wrote: I have never seen *anyone* attempt to suggest that an emitter follower is part of a feedback loop which includes the following common-emitter stage. Sounds like you're desperately attempting to exclude anything which doesn't look *exactly* like a 300B SET - and why the frell would anyone design a SS amp in the same fashion, since the technologies are totally different? Nor have I, who has designed an SS amp in that fashion? For example my design, while quite different from yours, doesn't look anything like a 300B SET, the only similarity being that they both use an output transformer. It is obvious by inspection that the feedback voltage developed across R7, by the load current flowing through Tr2 & R7, is in series with the input voltage to Tr1, hence a feedback loop exists around two stages. This feedback loop can be easily seen if you delete R4 from the circuit. But R4 *is* in the circuit, which reduces your claimed 'feedback' to utterly negligible proportions. Without R4, it wouldn't *be* an emitter follower, it would be part of a Darlington pair, which I have never seen described as a feedback loop. You deleted the part where I specifically pointed out that R4 was present in the circuit, and has a significant effect. My point was simply to first consider the amplifier without R4 present, to make the basic topology clearer, before considering the effect of R4. I would describe a Darlington pair with an unbypassed emitter resistor as a feedback pair. If you don't believe it try this simple experiment with your amplifier. Feed a small signal voltage at say 1 kHz into the input and measure the signal voltage between the base of Tr1 and ground, and the signal current entering the base of Tr1. From the current and voltage you can calculate the input resistance of the amplifier at the base of Tr1, exclusive of the resistors, R1, R2, & R3. Next, take a spare 10m capacitor and connect it across resistor R7 in the emitter circuit of Tr2, and again measure the signal voltage between the base of Tr1 and ground, and the signal current entering the base of Tr1. Again calculate the input resistance of the amplifier at the base of Tr1, using the new voltage and current values. Now explain the substantial difference observed in the two input resistance values? The presence of resistor R7 in the emitter circuit of Tr2 effects not only Tr2, but also has a major impact on the resistance looking into the base of Tr1. The only way I can see to explain this effect is that the feedback loop created by R7 encompasses both Tr1 & Tr2, do you have an alternate explanation for this effect? Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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On Tue, 15 Mar 2005 11:35:18 +1100, Patrick Turner
wrote: Not many mosfet amps with one power mosfet and a j-fet or small mosfet input. The necessary OPT is very easy to wind, since there are not many turns, and the wire is thick. As I said, been done, way back in the '80s: http://www.bonavolta.ch/hobby/en/audio/2sk135se.htm Zen with a dash of Parisian style! :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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On Tue, 15 Mar 2005 02:40:50 GMT, Chris Hornbeck
wrote: On Mon, 14 Mar 2005 07:50:00 +0000 (UTC), Stewart Pinkerton wrote: 845's and now this? Sure you're not suffering from (what's the name of that syndrome where the captive starts to sympathize with the captors?) syndrome? Arf! No, I just suffer from logic, and a lack of bigotry. I'm a big fan of 845's; they solve a lot of speaker problems, which are much more intractible. 211's have even better curves, and three in parallel make 50 watts without grid current, and into an almost-practical 5K ohm load. Indeed, and they look really pretty, too! Why not incorporate the required "line" stage and volume control? Seeing these three things together allows better choices for all and can minimize the number of components in the signal path. It's a pot and a switch - what's to design? Everything's to design, mon. It's not like we're working to end world hunger here. Shouldn't we be discussing arcania and trivial mysteries beyond the ken of mere mortals? Hobbies should be enjoyable and stimulating, but so often over Usenet degenerate into old-lady bickering. I know you're above that, so I feel confident in posting this plea in your thread. And to answer your question, the connection between the "line" stage and the "output" stage can be simplified if they're physically close (same box). Simpler is betterer. Just stick a selector switch and a 20k pot on the front of KISASS, and you have a 'line level integrated amp'. If you need a phono stage, see my page on http://www.lurcher.org/ukra/ -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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"Patrick Turner" wrote in message ... Yeah, but transistor amps have been done to death... Even class A types. Not many mosfet amps with one power mosfet and a j-fet or small mosfet input. The necessary OPT is very easy to wind, since there are not many turns, and the wire is thick. Patrick Turner. Stewart states that he has not actually built his amp. Has anyone else? First impressions would be of interest. Iain |
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