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#1
Posted to rec.audio.tubes
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S-30 Mk III circuit help
Hello Everyone
I am new to this news group and need some help. I need a circuit for Atma-Sphere S-30 MKIII amplifier I have done a google search but could not find anything. Is there someone on this newgroup with a circuit or a URL for one? I am just getting back into tube amps after 30 years and have forgotten most of my tube theory. Thanks |
#2
Posted to rec.audio.tubes
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S-30 Mk III circuit help
in article , spock at
wrote on 7/25/07 11:17 PM: Hello Everyone I am new to this news group and need some help. I need a circuit for Atma-Sphere S-30 MKIII amplifier I have done a google search but could not find anything. Is there someone on this newgroup with a circuit or a URL for one? I am just getting back into tube amps after 30 years and have forgotten most of my tube theory. Thanks If you contact the OEM they are usually happy to sell you an operator's manual with schematic. http://www.atma-sphere.com/ I think I called them the last time I bought a manual. Jon |
#3
Posted to rec.audio.tubes
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S-30 Mk III circuit help
I just want a circuit so I can see how I can avoid using an
output transformer. firstly they are expensive and they add distortion to the output. So if you know someone else that uses this method and you have a circuit I would like to hear from you. Thanks. "Bret Ludwig" wrote in message oups.com... I am new to this news group and need some help. I need a circuit for Atma-Sphere S-30 MKIII amplifier I have done a google search but could not find anything. Is there someone on this newgroup with a circuit or a URL for one? I am just getting back into tube amps after 30 years and have forgotten most of my tube theory. Thanks If you contact the OEM they are usually happy to sell you an operator's manual with schematic. http://www.atma-sphere.com/ AtmaSphere can be difficult to deal with from what I have heard. These are unconventional amps and are not the thing to learn on if you do not thoroughly understand the circuit. However, they do perform pretty well. |
#4
Posted to rec.audio.tubes
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S-30 Mk III circuit help
If saving money is your goal, it will be cheaper to buy an output
transformer than to construct and maintain OTL amplifiers. Performance is subjective. "spock" wrote in message ... I just want a circuit so I can see how I can avoid using an output transformer. firstly they are expensive and they add distortion to the output. So if you know someone else that uses this method and you have a circuit I would like to hear from you. Thanks. "Bret Ludwig" wrote in message oups.com... I am new to this news group and need some help. I need a circuit for Atma-Sphere S-30 MKIII amplifier I have done a google search but could not find anything. Is there someone on this newgroup with a circuit or a URL for one? I am just getting back into tube amps after 30 years and have forgotten most of my tube theory. Thanks If you contact the OEM they are usually happy to sell you an operator's manual with schematic. http://www.atma-sphere.com/ AtmaSphere can be difficult to deal with from what I have heard. These are unconventional amps and are not the thing to learn on if you do not thoroughly understand the circuit. However, they do perform pretty well. |
#5
Posted to rec.audio.tubes
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S-30 Mk III circuit help
"spock" wrote in message ... I just want a circuit so I can see how I can avoid using an output transformer. firstly they are expensive and they add distortion to the output. So if you know someone else that uses this method and you have a circuit I would like to hear from you. Thanks. Check out Bruce Rozenblit's Transcendent Sound http://www.transcendentsound.com/ Fred "Bret Ludwig" wrote in message oups.com... I am new to this news group and need some help. I need a circuit for Atma-Sphere S-30 MKIII amplifier I have done a google search but could not find anything. Is there someone on this newgroup with a circuit or a URL for one? I am just getting back into tube amps after 30 years and have forgotten most of my tube theory. Thanks If you contact the OEM they are usually happy to sell you an operator's manual with schematic. http://www.atma-sphere.com/ AtmaSphere can be difficult to deal with from what I have heard. These are unconventional amps and are not the thing to learn on if you do not thoroughly understand the circuit. However, they do perform pretty well. |
#6
Posted to rec.audio.tubes
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S-30 Mk III circuit help
spock wrote: Hello Everyone I am new to this news group and need some help. I need a circuit for Atma-Sphere S-30 MKIII amplifier I have done a google search but could not find anything. Is there someone on this newgroup with a circuit or a URL for one? I am just getting back into tube amps after 30 years and have forgotten most of my tube theory. Thanks OTL amps can be somewhat unreliable. The reason is that the load match for the tubes is so very poor. Triodes like to have a load which is at least twice the dynamic anode resistance listed in the data sheets as Ra. With the 5 x 6AS7 tubes, there are 2 triodes per tube making a total of 5 triodes for each half of a PP circuit. The Ra for a single triode is 280 ohms, so 5 in parallel amounts to 56 ohms. The PP circuit must work in very close to class B condition of low bias current levels because the load of the tubes, say 8 ohms is much lower than the 56 ohms of Ra of the tubes. The peak current ability of the 5 triodes driven into class AB conditions is maybe about 1/2 amp each, so about 1.8 amps rms is possible, generating 14.4Vrms, giving 25 watts of power. The anode dissipation = average anode voltage x average anode current, and this usually is much more than max PO to the load, so when run with a sine wave at full PO, the amp will overheat the output tubes. Using a 4 ohm load makes matters a lot worse. The linearity of the triodes is poor when used in near class B and with a load that is 1/20 times the recommended load as would be arranged when using an OPT. Thus a large amount of NFB must be applied to reduce the THD/IMD, and output resistance, so what ppl are raving about when they say how marvellous OTL are is the simple combination of non linear devices and enormous amounts of NFB, almost similar to the case of using a couple of mosfets in class B. OTL amps are renowned for producing smoke when the volume is turned up, and or 4 ohm loads or less are used. What you could do if you have the money, is invest in a pair of impedance matching transformers, such as the types supplied at http://www.zeroimpedance.com/ There are two guys here who have bought them and found them to have a beneficial effect on the music. However, one complains that his SE 25 watt OPT coupled amp runs out of head room. When the 32ohm to 8 ohm match is employed, the amp has to produce twice the output voltage at the 32 ohm input to give the same volume as when 8 ohms is directly connected to the amp. So twice the input level is needed. But when not out of headroom, he says the music is better with the matching tranny included. The THD is nearly halved, IMD much reduced, Rout effectively raised, and partially because the mild amount of global NFB is increased towards its maxima of when no oad at all is connected. The other guy has a 56 watt VAC amp with 4 x 300B per channel, OTP coupled, and he isn't so prone to having headroom problems. I measured the response of the Zero Impedance Xformers, and found it extremely wide, and the distortion contribution was negligible. The transformer that is connected to the output of the amp like a speaker has ONE winding, as it is an auto transformer. There are 6 terminals, one at each end of the winding, and two pairs located along the winding. If you connect the amp to the total winding, and use the inner pair of terminals for an 8 ohm speaker, there is a 4:1 impedance ratio load change, so that 8 ohms is experienced by the amplifier exactly if it was a 32 ohm load, which would be a far better load for your amp. There is more at the technical page at the 'zero' site, http://www.zeroimpedance.com/multiplier.html A 32 ohm load connected to an OTL will slightly increase the internal gain of the output tubes, and thus make the NFB applied more effective. The load seen by each triode becomes 5 x 32 = 160 ohms, and is far better than the 40 ohms. So the natural THD/IMD even before any NFB is applied will become a lot lower. The technical information supplied by AtmaSphere is quite UNACCEPTABLE AND INADEQUATE because it omits to say what the output resistance of ther amp actually is, and gives what I think is the wrong amount of NFB applied. They don't want anyone to know what the output resistance of the amp is. They say there is 2dB of NFB, yes, only TWO lousy db of NFB. They claim 1% THD at full power. But assuming what they do say to be be correct and factual, the Rout would be perhaps be 40 ohms because of the extremely low amount of NFB. One normally expects 40 dB of global NFB to be able to get the typical and attrociously HIGH Rout of most OTL amps down to around 1 ohm, itself a lousy high figure when compared to most normal transformer coupled amps with a typical 16 to 22db of NFB. And most triode amps without global NFB have Rout of about 2 ohms if really well designed, and 4 ohms in most ordinary cases of average designs by accountants. When Rout is well ove the nominal speaker Z the amp becomes a current source, not a voltage source, and speaker response is dependant on the varying Z of the speaker at the various frequencies, and the sound is usually quite dismal when the Rout is high. Let's assume the Rout is 40 ohms because whe have no information from Atma-Shere to suggest otherwise. The damping factor is thus 8 / 40 = 0.2, which is next to zero damping, and perfectly horrible! If you have a matching tranny to change the speaker Z from 8 ohms to 32 ohms, then the the DF = 32 / 40 = 4/5 = 0.8, which means the load is nearly the same impedance as the output resistance of the amp. Its far better than 0.2. Most amps aim for a DF = 5 at least, and most achieve DF = 10, and it isn't much use going any higher, but SS amps typically have DF = 100, because there is a total amount of output stage and global NFB which sums to an effective 100dB, which is a large amount. Missing entirely from the Atma-Sphere site is any load line analysis of the tubes involved in their amps. Why? Because they don't want anyone to know the serious limitations of tubed OTL amplifiers. The truth would hurt the sales, and they like to sell plenty of product. The OPT is the most expensive single component in most tube amps. Atma-Sphere fail dismally to give their customers the discount benefits of a product with the vital OPT missing. They just give a box of tubes with PS without OPT for the same price as an amp with an OTL. They don't fool me. Most people would not drive the OTLs very hard, and so the tubes will last OK. But if an amp is left running into a defective speaker, or a load that's too low, OTL generate smoke pretty fast. You have been warned. The matching tranny does ameliorate the problem to some extent. Assume you have the matching tranny set so each full winding end is at the amp output terminals. Suppose we label the remaining 6 terminals along the winding ABCDEF. Suppose A-F = 400 turns. C-D is 200 turns, and B-E = 280 turns, giving ZR = 4:1 and 2:1 respectively. If 8 ohms is connected at C-D, 32 ohms is the load at A-F. If 8 ohms is connected at C-D, 16 ohms is the load at A-F. But other matches are available, amp to A-F, and speaker to A-B, this is 400turns to 60turns, or 44.4:1, which converts 8 ohms to 355 ohms. Other matching impedances are available from the 6 terminal winding. The Zero Impedance trannies are not particularly cheap especially if bought with the nice wooden box. To make your own, use a 500VA mains toroidal transformer core, and use 1.5mm wire and place 400 turns total with from one end at taps at 60 turns, 40turns, 300 turns, 340 turns and then end the winding at 400 turns. Two identical windings wound on top of each other will give low winding losses. One can also use E&I laminations for excellent results, using a 50mm stack of 51mm tongue grain oriented material. 1.0 mm wire can be used to get 66 turns per layer and about 20 layers total for 1,320 turns total which then need to be carefully subdivided and tapped at layer ends and interleaved to get a wide F response. Not easy to design for the beginner!!!!. Good Luck. Patrick Turner. |
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