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Heathkit AA-151 cathode resistor mod
Hi All,
As an added bonus of asking RAT's about adding a choke to my Heathkit aa-151 power supply, Patrick Turner had a once-over of the schematic and made a few excellent suggestions. The next one I'm going to tackle is changing the single cathode- resitor-bypass-cap to the 6BQ5's. The aa-151 is a PP 6BQ5 "ultra linear" integrated with a 5AR4 rectifier and cathode biasing, and aside from 6EU7's instead of 12AX7's is like the Heathkit SA-2; http://www.mods.com/heath-hifi/sa2ma...2schematic.gif I've done the obligatory newsgroup search for this topic. Maybe surprising, but some people have experienced negative effects from going from one cathode resistor-cap to four separate ones. The general argument being about improved DC balancing with shared resistor-caps per channel (in PP). So... I'm going to go half way, changing the one resistor-cap into two, one for left, one for right. Currently, shared between all four 6BQ5's cathodes is a 100ohm- 7watt resistor and a 50uf-25V bypass-cap. Patrick suggested four separate pairs with 200ohm and 1000uf, a BIG change! The 6BQ5 spec-sheet states for PP class AB two tubes, a typical cathode-bias resistor of 130ohm. What I'm wondering is the RAT's-eye-view of the values for these resistor-cap pairs. I'm thinking 165ohm-5W and 80uf would be OK, but maybe a bit conservative. Thanks! |
#2
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Hi:
You note that the 6BQ5 spec sheet shows 130 ohm cathode resistor for 2 tubes, class AB PP. Be aware that this is for designs at approx max ratings of 300V A-K: the AA151 runs the 6BQ5s WAY over max plate voltage at something like 360V A-K (similar to Dyna ST/SCA35). It seems reasonable to assume that if the original design used 100 ohms for four cathodes, equivalent for two pairs of two cathodes ea would be 200 ohms and this is still running the BQ5s pretty hot. I'd be inclined to run more like 220-250 ohm @10W ea. A real benefit of separating the common K resistor is that a matched quad of BQ5s is no longer required, just two matched pairs. Heath (and Dyna) don't really do a good job of alerting the user to this issue. Individual K resistors reduce the need for matched pairs but if it were my amp, I'd still go for them. -- Steve |
#3
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"Steve O'Neill" wrote in
: Hi: You note that the 6BQ5 spec sheet shows 130 ohm cathode resistor for 2 tubes, class AB PP. Be aware that this is for designs at approx max ratings of 300V A-K: the AA151 runs the 6BQ5s WAY over max plate voltage at something like 360V A-K (similar to Dyna ST/SCA35). It seems reasonable to assume that if the original design used 100 ohms for four cathodes, equivalent for two pairs of two cathodes ea would be 200 ohms and this is still running the BQ5s pretty hot. I'd be inclined to run more like 220-250 ohm @10W ea. A real benefit of separating the common K resistor is that a matched quad of BQ5s is no longer required, just two matched pairs. Heath (and Dyna) don't really do a good job of alerting the user to this issue. Individual K resistors reduce the need for matched pairs but if it were my amp, I'd still go for them. -- Steve Good point! I was wondering about the reduced current sharing the resistor 4 ways... |
#4
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Hi:
Has it occurred to you that these design teams you cite had many conflicting constraints they had to balance and OA sonic performance was just one of them and maybe not the most important one. In the case of the AA151, low cost was clearly a consideration. Surely, having been the owner of one of these amps for 40 years you're intimately familiar with the strange line level input design on this amp. For those who aren't, the line level inputs are padded down by 24 dB at the input sockets and then fed thru the input selector switch to what amounts to the second stage of the magnetic phono preamp. I know of no sonic advantage to this scheme but it does result in simpler (cheaper) input switching. The price is additional noise on the line level inputs. Then there's the single cathode bias resistor for the four output tubes. I know of no sonic benefit to this biasing scheme but it does save the cost of an additional power resistor and cathode bypass cap. It also just about demands a matched quad of output tubes to prevent one tube from going ballistic. As you know, the conventional approach would be to put each pair of output tubes on their own bias resistor. As you also know, some of the top classic designs such as by Mullard even went as far as individual cathode bias resistors for each output tube. By inference, you are a professional engineer and as such, being an amateur, I'd really appreciate hearing your opinions regarding the sonic advantages of the line level input scheme and the four into one cathode bias arrangement for the output tubes. To me the bottom line here is that today's hobbiest doesn't have to deal with the cost issues that constrained the original designers. In a cost-no-object environment I'm certain that the original AA151 design team would have done things a lot differently in many areas including the addition of a filter choke or two, a more optimum output stage bias scheme and definitely a different line level input circuit. Just because their hands were tied doesn't dictate that ours should be now. If you want to own and listen to a piece of equipment that would not be out of place in a museum, that's fine. Others want to try for improved performance and on the AA151 that's relatively easy to do. And since it's relatively uncollectable and cheap to obtain, why not? -- Steve firedome wrote in message ... I'd leave this amp alone...it sounds extremely good just as it is, IF properly restored...I'm constantly amazed at the amateur engineers who think they know better than the original design teams responsible for creating many of the best of the vintage amps...I've had one of these amps for 40 yrs. and it still sounds great...leave it be! Roger in NY |
#5
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Steve O'Neill wrote: Hi: Has it occurred to you that these design teams you cite had many conflicting constraints they had to balance and OA sonic performance was just one of them and maybe not the most important one. [... snip for brevity] Others want to try for improved performance and on the AA151 that's relatively easy to do. And since it's relatively uncollectable and cheap to obtain, why not? -- Steve Bravo! Very well stated. Cheers, Fred -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects, Vacuum Tubes & other stuff: | | http://www.dogstar.dantimax.dk | +--------------------------------------------+ |
#6
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Hi:
John does indeed present an interesting (although not compelling to me at least) case for the common cathode bias resistor. Don't have time for a lot of discussion here but note that he didn't get around to actually verifying his theories in a practical sense. Overall, I'd agree that if taken to the extreme of an infinite number of tubes, the single bias resistor may have benefit in eliminating what amounts to undesirable positive DC bias feedback. It might also be argued that it converges on fixed bias with it's improved power capabilities in AB operation. However, four tubes is very different from infinite and I found from actual measurement that the need for a matched quad (in terms of bias current) remains (positive bias feedback remains). The fact that Dyna even recommends matched quads for the ST/SCA35 is evidence that they were aware of the practical limitations of the scheme. Regarding power output capabilities, I measured no practical difference between four tubes on a bias resistor vs two tubes per resistor. This was on an ST35 with continuous signal, measuring both one channel driven and both channels driven. Transients like music may provide different results. However, with two tubes on a resistor I was able to achieve much better DC balance which probably contributed to a little better low end performance because OPT core saturation effects were reduced. If you read the other archived posts I think you'll conclude like I did that this is a controversial subject with theory on one side and practice on the other. Fortunately the cathode resistor mod is really easy on the AA151 so all you need to do is try it and trust your ears. Interestingly I ended up with the single cathode resistor on my 151 but increased the bypass cap to 220uF AND use a quad of tightly matched EL84s. On my ST35 I ended up with a cathode resistor for each pair of matched output tubes each bypassed by 220uF. On this one I tried everything inc fixed bias for four tubes, for each pair and individually for each tube. Still came back to cathode bias because of sound even though the fixed bias schemes produced a lot more power. I also added a filter choke to the PS which made a huge difference in hum and noise when using efficient speakers. -- Over and out Steve |
#7
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Actually I'm a scientist, not a PE, big difference. Stating that alot
of these mods are proposed by amateurs does not infer I'm a PE, that is simple logic...however one can presume the AA-151 designers were. If you are talking subjective sound, I'd like to see the resulting data from a proper double blind randomized comparison of these modded units with the original design... The cost savings you mentioned are relatively trivial, it's not like you are eliminating transformers . What were OEM caps and resisitors then, a few cents? The production/yr #s wouldn't justify it either. I believe it's a case of some compulsive folks who can't leave anything alone - let's face it there is a mod out there for every vintage piece ever made, did no one get it right? If you are talking measurable parameters, have you quantified the increased noise in the line level inputs and from the original cathode bias arrangement? In empirical terms, just what are the sonic disadvantages of the original design...and what is the data base? AA-151s are common, and if one wants to play with the circuit, have at it. My point is that such re-arranging deck chairs is basically a waste of time IMHO. Roger in NY "Steve O'Neill" wrote in message ... Hi: Has it occurred to you that these design teams you cite had many conflicting constraints they had to balance and OA sonic performance was just one of them and maybe not the most important one. In the case of the AA151, low cost was clearly a consideration. Surely, having been the owner of one of these amps for 40 years you're intimately familiar with the strange line level input design on this amp. For those who aren't, the line level inputs are padded down by 24 dB at the input sockets and then fed thru the input selector switch to what amounts to the second stage of the magnetic phono preamp. I know of no sonic advantage to this scheme but it does result in simpler (cheaper) input switching. The price is additional noise on the line level inputs. Then there's the single cathode bias resistor for the four output tubes. I know of no sonic benefit to this biasing scheme but it does save the cost of an additional power resistor and cathode bypass cap. It also just about demands a matched quad of output tubes to prevent one tube from going ballistic. As you know, the conventional approach would be to put each pair of output tubes on their own bias resistor. As you also know, some of the top classic designs such as by Mullard even went as far as individual cathode bias resistors for each output tube. By inference, you are a professional engineer and as such, being an amateur, I'd really appreciate hearing your opinions regarding the sonic advantages of the line level input scheme and the four into one cathode bias arrangement for the output tubes. To me the bottom line here is that today's hobbiest doesn't have to deal with the cost issues that constrained the original designers. In a cost-no-object environment I'm certain that the original AA151 design team would have done things a lot differently in many areas including the addition of a filter choke or two, a more optimum output stage bias scheme and definitely a different line level input circuit. Just because their hands were tied doesn't dictate that ours should be now. If you want to own and listen to a piece of equipment that would not be out of place in a museum, that's fine. Others want to try for improved performance and on the AA151 that's relatively easy to do. And since it's relatively uncollectable and cheap to obtain, why not? -- Steve firedome wrote in message ... I'd leave this amp alone...it sounds extremely good just as it is, IF properly restored...I'm constantly amazed at the amateur engineers who think they know better than the original design teams responsible for creating many of the best of the vintage amps...I've had one of these amps for 40 yrs. and it still sounds great...leave it be! Roger in NY |
#8
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Hi All, Since I saw my name mentioned I thought I would throw my two cents into this thread and also comment on the other AA-151 thread. I am not sure exactly what you want me to do to verify my theory in a "practical sense"? It seems to me that the main "practical" effort that would be required is to collect and measure a large number of 6BQ5/EL84s, to characterize their variations. This is not something I want to do, maybe one of the tube vendors would like to do this for us? Once you have an handle on the statistics of the tube characteristics, the rest is mostly math, to compare the different cathode resistor schemes for balance with different random selections of tubes. All I can say is that I put my money where my mouth is, for example see my 25L6 amplifier on my web pages. I am not obsessive about tube balance, some people even tolerate single ended amplifiers, the ultimate in unbalance. I do not like to even bother with matched pairs. It is of course desirable that the output transformer be designed to handle any likely unbalance. For unmatched, randomly selected tubes, four separate cathode resistors will give the best balance, the single cathode resistor shared by four tubes is next best, and two cathode resistors, one for each channel, is the worst choice if you aren't using matched tubes. Of course if you are really obsessive about balancing the DC in the transformers, it is easy enough to add a couple of DC balance pots to the circuit, then you can set the balance in each channel right on, even with four tubes sharing a single cathode resistor. As far as the power supply chokes go, that were mentioned in the other thread, I suspect that in general it wasn't entirely a matter of economics, as even many higher end amplifiers didn't use chokes in the power supply. I suspect this was because they were all trying to cram a stereo amplifier into a low profile cabinet that was as small as possible. Of course in the case of the AA-151, economics would have prevented the inclusion of a choke even if there was space for it. Anyone know if there is space in the AA-151 to do a neat job of adding a choke? I would add one if it could be done so that it looked like it came from the factory that way. As far as tone control modifications go, I like tone controls, so I would keep them. If I could find suitable switches, of about 11 positions, with enough poles, that would work with the stock Heathkit knobs, I would get rid of the pots, and go to switched tone control networks. As far as the phono preamp goes, I would put DC on the phono preamp heaters by putting the two preamp tube heaters in series and using them to replace the common output stage cathode resistor. A resistive divider would be used across the preamp heater string to get the correct bias voltage for the output tube grids. I don't have the AA-151 schematic, but the SA-2 is similar and the schematic indicates that the total cathode current for the output tubes is 160 mA. A resistor in parallel with the preamp heaters could absorb the extra 10 mA, or the current could be backed off slightly which would make life easier for the output tubes. The extra 6.6 volt drop across the cathode "resistor" would also help the tubes a bit, although slightly reducing power output. Someone mentioned the input switching, and that is one of the things I dislike most about Heathkit amps. Assuming the switching in the AA-151 is the same as in the SA-2, the existing input selector switch could be used to switch the high level inputs directly into the volume control. I can't believe that with a pentode gain stage at that point, there isn't enough gain to feed the high level inputs in at the volume control, I suspect Heathkit provided and excess of gain in these amplifiers, or am I missing something? The only problem I see is that this would probably mess up the relative gain between the MM input and the high level inputs, so it might be necessary to reduce the gain of the phono preamp a bit. I have an AA-151 sitting under my workbench that I got for a bargain price, and have never even had the cover off. I was planing of selling it someday, when I happened on a likely buyer. Maybe instead I should get a schematic and try the choke, preamp heater, and input switching mods. Regards, John Byrns In article , "Steve O'Neill" wrote: Hi: John does indeed present an interesting (although not compelling to me at least) case for the common cathode bias resistor. Don't have time for a lot of discussion here but note that he didn't get around to actually verifying his theories in a practical sense. Overall, I'd agree that if taken to the extreme of an infinite number of tubes, the single bias resistor may have benefit in eliminating what amounts to undesirable positive DC bias feedback. It might also be argued that it converges on fixed bias with it's improved power capabilities in AB operation. However, four tubes is very different from infinite and I found from actual measurement that the need for a matched quad (in terms of bias current) remains (positive bias feedback remains). The fact that Dyna even recommends matched quads for the ST/SCA35 is evidence that they were aware of the practical limitations of the scheme. Regarding power output capabilities, I measured no practical difference between four tubes on a bias resistor vs two tubes per resistor. This was on an ST35 with continuous signal, measuring both one channel driven and both channels driven. Transients like music may provide different results. However, with two tubes on a resistor I was able to achieve much better DC balance which probably contributed to a little better low end performance because OPT core saturation effects were reduced. If you read the other archived posts I think you'll conclude like I did that this is a controversial subject with theory on one side and practice on the other. Fortunately the cathode resistor mod is really easy on the AA151 so all you need to do is try it and trust your ears. Interestingly I ended up with the single cathode resistor on my 151 but increased the bypass cap to 220uF AND use a quad of tightly matched EL84s. On my ST35 I ended up with a cathode resistor for each pair of matched output tubes each bypassed by 220uF. On this one I tried everything inc fixed bias for four tubes, for each pair and individually for each tube. Still came back to cathode bias because of sound even though the fixed bias schemes produced a lot more power. I also added a filter choke to the PS which made a huge difference in hum and noise when using efficient speakers. -- Over and out Steve Surf my web pages at, http://users.rcn.com/jbyrns/ |
#9
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Hi:
I'm the one that mentioned "practical sense". I was referring to two issues here. Issue #1: In your posts circa 1999 you speculated that the the common cathode resistor scheme might produce more power under certain conditions in an AB output stage (such as the AA151 or Dyna ST/SCA 35 are) which could be an advertising advantage at the time these amps were marketed. What I found by actual measurement was that there was no appreciable difference in max power output between two tubes on a cathode resistor vs all four tubes on a cathode resistor with either both channels driven or one channel driven. This was on Dyna ST35. Signal was a sine wave at various frequencies. Admittedly, music is not a continuous signal so the results might be different with transients or tone bursts. At any rate, I was unable to verify the theory that the common cathode resistor would allow more power in any of the various cathode bias schemes. Issue #2: You also state that best output tube balance is achieved with individual cathode resistors, next best with four to a resistor and worst with two to a resistor. By balance I assume you're referring to the relative equality of bias current at idle. My understanding and experience regarding the various biasing arrangements is that the ranking you give them is really more by order of the degree of influence one output tube has on the others tied to the common cathode resistor. Obviously, individual cathode resistors provide the greatest degree of isolation. Due to averaging, four tubes to a resistor is next with two to a resistor being worst. So if one inserts four randomly chosen tubes into the amp, tubes with the individual cathode resistors will bias up to some idle current value dictated by individual tube characteristics at the chosen operating point. However, each tube will probably idle at a different current. In the case of two randomly chosen tubes to a cathode resistor, the tube tending to draw more current at the operating point will tend to turn off it's lower current mate thus exacerbating any imbalance between the two. The case of four randomly chosen tubes to a cathode resistor is intermediate between the two cases in that the influence of any one tube on the others is reduced by averaging. However, aren't most PP amps designed on the assumption that current imbalance betw output tubes is minimized? While most OPTs will tolerate some degree of imbalance, on the whole, idle current balance is desirable. If one agrees that idle current balance is important then one will tend to used matched pairs in the output stage of a PP amp. This is where real world conditions may reduce the potential benefits of the four into one cathode resistor. Assume two matched pairs of tubes where matching betw tubes in a pair is close but matching betw the two pairs is not: a real world situation in my experience. If this set of tubes is inserted into a PP stereo amp with individual cathode resistors everything is fine. If these tubes are inserted into the same amp but with individual cathode resistors per pair of tubes, everything is still fine even though one pair draws more current than the other. Finally, if these tubes are inserted into the amp with all four tubes on a single cathode resistor, the hot pair will tend to turn off the cooler pair similar to the effect of two unbalanced tubes on one cathode resistor. The difference here is that presumably, tube to tube balance will be maintained on each PP pair although not at the expected values. I'm reasonably sure this is why Dyna recommended a matched quad of 6BQ5s for the ST/SCA35 although they stated that two matched pairs would work. By your statement "I am not obsessive about tube balance,some people even tolerate single ended amplifiers, the ultimate in unbalance." you obviously give output stage balance a lower priority than is traditional. As you're aware most higher end "golden age" PP designs had provisions for output stage bias balancing (inc those using cathode bias) as do most modern PP designs (notable exception is McIntosh). Also, although a single ended output stage may be the ultimate in imbalance, the circuit and/or magnetics are designed to handle the imbalance: most PP output stages assume a fairly good balance for best performance. The reason I used the term "practical sense" in the first place is that I more or less did what you suggested, I collected about 80 new mfg, NOS and "good used" 6BQ5s by various mfgrs and characterized bias at the ST35 and AA151 operating points. The idea here is that a mix like this is now what is available the the 21century tube user. All tested good or better on a gm type tube tester. What I found was that bias varied over a very wide range, even when gm was fairly closely matched. The results explained why one tube in a "matched" quad" I purchased from a reputable source would go red plate in my ST35. Obviously the quad had been matched for gm only. The hot tube would run at about 20 mA more than the others in the quad at operating conditions. I suppose it's debatable that a sample of 80 is statistically significant. OTOH, the quantity of tubes produced today is miniscule compare to the good ol days so maybe 80 is significant esp if considering the population of 6BQ5s available for my use. Summarizing, I fully understand what you were saying in you earlier posts about the theoretical advantages and disadvantages of the various cathode biasing schemes. No disrespect was intended when I stated that your theories were unverified. However, based on my experience, the real world variation in tubes combined with my understanding that PP output stage balance is desirable means that the theoretical advantages of four into one cathode biasing will probably not be realized: Power output capability is not increased and the requirement for bias matching remains. Therefore, I still contend that Heath's and Dyna's use of the single cathode resistor was driven primarily by cost considerations i.e save the cost of a cap and resistor and indirectly burden the end user with the additional costs of the matched quad nec. for optimum operation. Any functional advantages were incidental and secondary. As an aside, one poster commented that it was doubtful that a company like Heath or Dyna would attempt to save a few cents on the addl parts nec for individual bias resistor if that was a better way of doing things. My day job is with one of the few remaining manufacturers of "physical objects" in the US. I can assure you that a few cents per unit over a production run of thousands of units will get attention. As always, if my logic is warped I welcome enlightenment as to the error of my ways. -- Steve John Byrns wrote in message ... Hi All, Since I saw my name mentioned I thought I would throw my two cents into this thread and also comment on the other AA-151 thread. snip |
#10
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Well, I know for sure that if I had an amp with an infinite number
of 6BQ5's... my wife would kill me... It might just about power all the speaker "projects" I got in the basement though! ) John, I've just done the choke-thing, and as suggested by Bob Fitzgerald, mine fit really nicely on top of the deck, in front of the aluminum plate by the power transformer, with a 100uf mini-can cap bolted to it. I added another 4.7uf Solen fastcap mounted to that aluminum separator, between the 6AU6's and the 6AN8's. This is meant to help "speed up" the bigger cap (I guess I've read TOO many RAT postings eh!). Anyrate, this mod I really like, reduced the "boominess" of the bass... nice! You should know it looks nothing like stock, but hey, the aa-151 has a face not even it's mother can luv... I ended up building a gloss black cage, and changing the front to black knobs and black tolex... still looks nothing like a Macintosh! I have backed off on the 4 or 2 separate cathode resistors, as I'm now not sure it will have that much possitive effect. I did add an extra 50uf to the bypass cap (mostly because I had one lying around). Next I plan to replace the last pf-range ceramic caps; at the AUX and TUNER inputs, the 56pf shunt for the 6AN8's and in the NFB. These first two are differnt than on the SA-2 schematic BTW. I'm also going to reduce the NFB a bit, and replace a few resistors that are wandering out of tolerance. All I can think to do after that is pluck up da' nerve to ask Patrick Turner how to do the 6AU6's as triodes mod in the preamp he mentioned, but I've got enuff to keep me busy for a bit! |
#11
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Hi RATs!
MTBF (Mean Time Between Failures) vs parts count is not the linear relationship direct logic might presume. As systems endure the rise and fall of the random ravages of time, larger parts populations exhibit more stable performance than smaller parts populations. Parallel resistors and other stupid wastes of time and money are not so stupid, statistically. The interesting thing to me about circuits is how they sound at this moment. All the rest is engineering mumbo-jumbo and only of interest to off world intellectuals and money grubbing employees. Each of us hears what we listen to and only learn anything epiphanally useful by happenstance and ironic cognitive dissonance. Pretending MTBF has any useful application relative to listening to Bach is simply posturing one's ego as greater than one's soul. A common pose, but, hardly noble. Just smug If you like what you hear, you are in the right place. If you think you know what others hear, you have your head in a dark, smelly place. If you know what others should hear, your head IS a dark, smelly place Listen and let listen! Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
#12
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Wow. Another great post, hopefully to appear in Al's "Zen in the Tube
Garden." I especially liked the line, "Each of us hears what we listen to and only learn anything epiphanally useful by happenstance and ironic cognitive dissonance." Thanks, Al. Live long and prosper! Cheers, Fred TubeGarden wrote: Hi RATs! MTBF (Mean Time Between Failures) vs parts count is not the linear relationship direct logic might presume. As systems endure the rise and fall of the random ravages of time, larger parts populations exhibit more stable performance than smaller parts populations. Parallel resistors and other stupid wastes of time and money are not so stupid, statistically. The interesting thing to me about circuits is how they sound at this moment. All the rest is engineering mumbo-jumbo and only of interest to off world intellectuals and money grubbing employees. Each of us hears what we listen to and only learn anything epiphanally useful by happenstance and ironic cognitive dissonance. Pretending MTBF has any useful application relative to listening to Bach is simply posturing one's ego as greater than one's soul. A common pose, but, hardly noble. Just smug If you like what you hear, you are in the right place. If you think you know what others hear, you have your head in a dark, smelly place. If you know what others should hear, your head IS a dark, smelly place Listen and let listen! Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects: http://dogstar.dantimax.dk | +--------------------------------------------+ |
#13
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Hi,
I think that much of what Al writes is not to be taken literally, rather just go with the flow and the intent will come across. Some of his writing reminds of John Lennon, one of the most illustrative and classic pieces is "I Am The Walrus." Applying the intellect to posts like this is using the wrong tool for the job. Read viscerally. The MTBF comment is, IMO, a reiteration of the idea that when you're listening to the system, (perhaps pondering your probable position on the composite MTBF bell-curve), you're not listening to Bach. Reminds of a story told by Peter Pringle, arguably the greatest thereminist alive today. He was visiting a friend, who happens to be a world-famous Japanese symphony conductor. As he arrived, this fellow was listening to a cassette tape on a crappy little table-top cassette recorder. Flabbergasted, Peter exclaimed, "Here you are, a world-famous conductor, what in Sam Hill are you doing listening to that thing?" Replied the conductor, "Oh, I'm not listening to the tape deck. I'm listening to Bach!" Whether we're listening to a crappy little cassette deck, or to a Macintosh or a homebrew or a Krell, almost doesn't matter. If we're aware that we're listening to a machine, then the machine isn't doing its job. If the machine is so "good" that we admire how realistic "it" sounds, we're still listening to "it"! Cheers, Fred Steve O'Neill wrote: Hi: I didn't understand most of the content of the original post and was too intimidated by the references to head locations to ask Al directly for an authors insight into the intended message. Many authors of profoundly philosophical statements such as this one seem to take offence when those of lesser reasoning abilities ask for elucidation. Apparently the very act of asking demonstrates a certain intellectual laziness. So...could you, not being the author AND clearly having achieved a certain intellectual resonance with the author please translate the entire passage for me? The one statement I mostly did understand "Pretending MTBF has any useful application relative to listening to Bach is simply posturing one's ego as greater than one's soul." strikes me as potentially wrong (pending translation). My experience indicates that if one intends to listen to Bach using electronic music reproduction devices, the concept of MTBF does indeed have useful application and may be the difference between listening and poring over a schematic. -- Steve Fred Nachbaur wrote in message 9Wu4b.118401$K44.58799@edtnps84... Wow. Another great post, hopefully to appear in Al's "Zen in the Tube Garden." I especially liked the line, "Each of us hears what we listen to and only learn anything epiphanally useful by happenstance and ironic cognitive dissonance." Thanks, Al. Live long and prosper! Cheers, Fred -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects: http://dogstar.dantimax.dk | +--------------------------------------------+ -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects: http://dogstar.dantimax.dk | +--------------------------------------------+ |
#14
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Hi RATs!
Well, it is true that extremely short MTBF would make listening to an entire CD impossible My position is simply that as audio experimenters, we can focus simply on sonics, and leave other engineering miracles for the production types. None of my circuits have died, they have all been murdered by me in the name of sonics. Oops, the 315A transmitter tubes for IFFR didn't last long as audio tubes, on the order of weeks, 24/7, but that was one out of hundreds. And, they did look cool as anything I have tried My point was using MTBF as some sense of quality in a private system is simply not very useful. Nor am I interested in watts consumed to produce the milliwatts that drive my speakers. Those are indeed real things, but, I only have ears for the music. The techno parallel universes are not of concern for me. I do not hope to leave this life with a place in history, just a smile Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
#15
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oooooooooooowow!
longggggg posssssssssst! they sing -or they not sing. pure facts we agree. -- Choky Prodanovic Aleksandar YU "TubeGarden" wrote in message ... Hi RATs! MTBF (Mean Time Between Failures) vs parts count is not the linear relationship direct logic might presume. As systems endure the rise and fall of the random ravages of time, larger parts populations exhibit more stable performance than smaller parts populations. Parallel resistors and other stupid wastes of time and money are not so stupid, statistically. The interesting thing to me about circuits is how they sound at this moment. All the rest is engineering mumbo-jumbo and only of interest to off world intellectuals and money grubbing employees. Each of us hears what we listen to and only learn anything epiphanally useful by happenstance and ironic cognitive dissonance. Pretending MTBF has any useful application relative to listening to Bach is simply posturing one's ego as greater than one's soul. A common pose, but, hardly noble. Just smug If you like what you hear, you are in the right place. If you think you know what others hear, you have your head in a dark, smelly place. If you know what others should hear, your head IS a dark, smelly place Listen and let listen! Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
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Hi RATs!
Perhaps one of us is wise? Happy Ears! Al we agree. Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
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