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Soon I will be trying fixed bias on my power tube (6P45S) again. This time I'd like to build it very high-end-ish with good resistors, good filter capacitors, tube rectifiers and wire. I will be comparing them next to the cathode bias with MILLS MRA12 and Elna cerafine.The bias PSU will be a classic LCRC filtered power supply.
Edits: 04/05/16Follow Ups:
May I ask what the advantage of fixed bias would be in a Class A amplifier?
Phil
"May I ask what the advantage of fixed bias would be in a Class A amplifier?"
I think one advantage is that you don't need a cathode resistor that dissipates a lot of heat.
Chris
And a high current audio signal doesn't pass through a high value capacitor. The fixed bias decoupling capacitor can be much smaller, so cheaper and of a higher quality.
I have heard these, and they sound wonderful.
Failure of that tube could lead to catastrophic damage to the output stage. I'd go with quality UF4007 bridge. As I don't think solid-state in the bias supply effects the final tonal quality. Quiet, steady, & reliable is all you need.
Good luck with the project!
I'm very sure I want to, no matter the failure potential. Everything on the bias circuit is audible and I do not want sand there.
...and they use Teflon-film caps bypassing 'propylenes in the bias supplies and the main HV supplies of their premium amps.
----------
Tin-eared audiofool, large-scale-Classical music lover, and damned-amateur fotografer.
William Bruce Cameron: "...not everything that can be counted counts, and not everything that counts can be counted."
Only in the sense that everything is audible. In this case, the only goal of the bias supply is to create a negative voltage reference of almost no current. Your tube will actually sound worse than a simple UF4007 as the tube will add noise with its heater. The choke will pick up noise as well. One can get into a lot of trouble constructing a self-reasoned personal audio belief system. :-)
Well, a long time ago I came to the conclusion that one of the worst enemies in hi-fi audio equipment building is to standardize and simplify, especially by simple textbook physics and electronics. Sorry, but to progress to a higher level of sounding, the constructor has to open his mind and ears. A fixed bias circuit is something much more than a negative DC source to your tube grid, it's a combination of elements and each element has its own sound signature. The wire, the resistors, the capacitors, the choke, the rectifier, the transformer and the power cord. The combinations of these elements + the well engineered schematic + the tube operating point will give you a certain sound that you may have to tweak further.
I mean no offense by this post, I just share my personal opinion.
But if I have to go into this kind of debate again, I prefer to stop typing.
"A fixed bias circuit is something much more than a negative DC source to your tube grid, it's a combination of elements and each element has its own sound signature. The wire, the resistors, the capacitors, the choke, the rectifier, the transformer and the power cord. The combinations of these elements + the well engineered schematic + the tube operating point will give you a certain sound that you may have to tweak further."
I can see how some of those elements might make their presence audibly noticeable if the bias supply were poorly designed, but it is really not that complicated to make a supply that lives up to its name of "fixed bias." Namely, it should simply produce a voltage that is fixed, i.e. constant in time.
Chris
"...higher level of sounding..."
What do you mean?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
There is a certain level where the builder becomes aware that most electronic measurements and theory don't correlate with the resulting sound quality. So he starts looking elsewhere.
From my experience, people who don't look further always build limited devices that are trapped by their own boundaries.
"There is a certain level where the builder becomes aware that most electronic measurements and theory don't correlate with the resulting sound quality. So he starts looking elsewhere.From my experience, people who don't look further always build limited devices that are trapped by their own boundaries."
I don't see precise enough statements here to be able to evaluate them properly. In the case under discussion, of fixed bias supplies, I was assuming that by "fixed bias" you meant a supply that was of constant voltage.
It is easy enough to arrange such a supply to be essentially of any arbitrarily desired degree of constancy. If you are saying that you have found that by playing with the various components in such an "ideal" supply you can obtain sounds that you find more pleasing to the ear, then that is certainly logically possible. It might be, for example, that a bit of mains ripple superimposed on the bias supply might be more appealing to some listeners. Or a frequency-dependent colouration caused by insufficient smoothing capacitance for achieving constant voltage across the spectrum.
But any such deviations from a truly fixed voltage bias supply would easily be measurable by using suitable test equipment. Whether "most electronic measurements" would be able to pick up the effects would be dependent on how you define or quantify "most." I could easily believe that many measurements performed around the world might be of insufficient accuracy to pick up the effects at the necessary level of precision. But that is quite different from the implication that is tacitly, I think, suggested by your statement, namely that no possible measurements could be made that would be able to correlate the sounds with the measurements.
Chris
Edits: 04/08/16
"It is easy enough to arrange such a supply to be essentially of any arbitrarily desired degree of constancy. If you are saying that you have found that by playing with the various components in such an "ideal" supply you can obtain sounds that you find more pleasing to the ear, then that is certainly logically possible. It might be, for example, that a bit of mains ripple superimposed on the bias supply might be more appealing to some listeners. Or a frequency-dependent colouration caused by insufficient smoothing capacitance for achieving constant voltage across the spectrum."
And even more possibilities are present. Some of them are timbre characteristics of each element. Different resistors for example have different sonics, even if their value is the same.
Even if your schematic has the same level of output voltage, same level of ripple and the same values of smoothing capacitance, each element has its own signature.
I will be more than happy to own equipment that can measure "hidden" parameters of elements such as a resistor, a wire, a plug, a switch. If I do, I will be a rich man.
"But any such deviations from a truly fixed voltage bias supply would easily be measurable by using suitable test equipment. Whether "most electronic measurements" would be able to pick up the effects would be dependent on how you define or quantify "most." I could easily believe that many measurements performed around the world might be of insufficient accuracy to pick up the effects at the necessary level of precision. But that is quite different from the implication that is tacitly, I think, suggested by your statement, namely that no possible measurements could be made that would be able to correlate the sounds with the measurements."
I agree and I can think of some, for example: DC voltage value, AC ripple, harmonic spectrum on the output, output impedance, power supply filtering resonances and Qs, rectifier switching harmonics, mains noise.
Although great attention should be paid to those mentioned and I admit I do, I still defend my argument that each element has its own signature.
Good theory and engineering are needed, but practice has the final words and it is the ears that do so.
"Some of them are timbre characteristics of each element. Different resistors for example have different sonics......"
Why wouldn't that be measurable?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"Timbre is mainly determined by the harmonic content of a sound and the dynamic characteristics of the sound such as vibrato and the attack-decay envelope of the sound."
We can measure those.
I'm not saying that we know what all to measure but we can measure the above.
I believe a lot of the time when parts changes are made and differences are heard it is something we can measure.....we just don't.
Instead, the sound difference is chalked up to the great "unknown and unknowable".
It seems magic dust is more popular/fun than science.
Whatever.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
in our getting timbre, and expression.
This is unsurprising when you consider that lots of instruments - with timbre and expression, just don't do continuous tones, ever.
All this has been known for a long time.
I have heard a recording of an oboe with a clarinet attack replacing the original and we all thought it was a clarinet.
This is why matching rise and settle times into real loads are so important.
I lost interest in using valve rectifiers - anywhere - a long time ago.
Who wants sag / noise in a hi-fi PSU?
Even in a bias supply.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
"Who wants sag / noise in a hi-fi PSU?"
A tubed rectified, critical inductance power supply, with the appropriate amount of capacitance, feeding a Class A circuit will not sag and is as quiet as a power supply gets.
"In terms of ragged waveforms, solid-state diodes are the worst, followed by Schottky diodes and HEXFRED's, followed by conventional tube rectifiers, followed by TV damping diodes, which are the smoothest of all in terms of the AC waveform on the power trans secondary."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Also see my response to Jeff Behr, and look in reviews at AA for LEAK St 20s.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
"Conclusion: This is a set of personal preferences"I think Lynn meant the article as a whole.
Lynn has worked for major firms and is very versed in the science behind audio electronics.
What he says about power supply noise is not his opinion, it's fact.
There are plenty of things in this hobby that are purely subjective but physical facts are physical facts.
That doesn't mean that everyone will like the sound of a stable, noise free power supply but scientific fact will tell you which ones are stable and noise free and which ones aren't.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/14/16
"I lost interest in using valve rectifiers - anywhere - a long time ago."
How have you resolved the issue of instant-on B+, and the effect it has on amplifier tubes with cold filaments?
--------------------------
Buy Chinese. Bury freedom.
easy peasy.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Generally speaking, power tubes warm much more slowly than thermistors. I also suspect that whatever type(s) you're using, they're still degrading the dynamics of the supply.
--------------------------
Buy Chinese. Bury freedom.
.
----------
Tin-eared audiofool, large-scale-Classical music lover, and damned-amateur fotografer.
William Bruce Cameron: "...not everything that can be counted counts, and not everything that counts can be counted."
Typing too fast.We also snubbed the slow, soft recovery diodes.
I wanted maximum power, given cathode bias.
I listen mostly to simply recorded acoustic classical music.
The spheres I was using for a long time are an easy load and sensitive enough to go quite LOUD in the room. So they are efficient as well. 91db/w 35-13k IE a bandwidth product of ~400,000 which is subjectively ideal. The shape produces very little waveform distortion. Very revealing of engineering in recordings. I bought them instead of a fairly new pair of black QUAD 57s.
I have heard them with two different SE amps for more than two weeks in each case:-
one was a DIY Pass Zen FET amp. Nice but not as good or as loud as the bi-amped Once-Were LEAK Stereo 20s.
second were a SE UL pair of monos using 13E1 (regulator tube) valves. 18WPc and 20 to 20Khz. Again nice enough.
In neither case were they any more 'inner glow' than the bi-amped LEAKs, and didn't play nearly as loud, not enough jump or SLAM, either!
And, they both drew more power.
One LEAK was in pentode mode 20wpc - effectively active drive as no LP on the bass-mid driver. Amps 2 in triode 6?watts, driving a passive 3rd xover/Fs trap/Eq @ 3.5 kHz into a big soft dome.
VR's? when we were doing the rebuild/mods - 1990s - there were only a few good NoS Mullard GZ34s available here in Aussie and they were too expensive. Used ones not much cheaper either and back then the Asian made varieties were not up to spec. And had interestingly colourful ways of failing.
I've never heard any evidence of the effects of down-shifted EMI/RFI from the SS diodes, so often mooted in these and other fora.
I am / should be known for my quite profound skepticism about the hard line DB testing viewpoint - because I understand the maths of stats. Just search on objectivity with my moniker.
But, I am also deeply skeptical about audio subjectivity, and expectation bias - especially among DIYers in particular. And I have always had a tight budget. A very good discipline I find.
e.g. I would rather double the wattage of signal path resistors from 1/4W to a 1/2W and so on, as this will audibly reduce noise in audio circuits, and I use a mixture of MF brands.
For signal path capacitors in these NFB (less than as OEM'd) amps I've found that Wima MKPs and a few MKS are just fine. Teflon caps are a good idea in the NFB circuits, along with Holco Rs or better. The cathode Rs are low-L packaged 20W glassy dark-blue things whose brand and catalogue numbers I forget.
LBNLeast? The job of a [properly designed] power amp's PSU is to provide an overbuilt / hopefully inexhaustible supply of DC current, which you can only hear if it's gone unstable. Audible FR ripple is way less than HJL's specs.
The amps are at least as 'quiet' as any SS PP AB1 amp I've used.
3d, nuance, wonderful timbre.
The amps and their mods are described here in Reviews at AA.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 04/13/16
My personal audio path has convinced me that tube rectifiers are the way to go and on my SET I don't lack SLAM or SPEED, compared to many SS amplifiers I've listened to, if, of course, the SET satisfies the output power needed by the speaker.
Of course I am using a choke input filter after the rectifier and the whole PSU has very good passive regulation qualities. Currently I'm using Telefunken EY83 and AZ11 of the same brand. The Telefunkens for now are the best brand I've heard. I'm in love with the sound this rectifier gives.
From experience, I think a lack of SLAM or speed can come from many other points, like a resistor's sound signature, capacitor (especially in the cathode). It's not fair to directly blame the rectifier or Rdc of PSU components.
Hello,
You end with these words :
"It's not fair to directly blame the rectifier or Rdc of PSU components."
From the schematics of your amp builds you posted, I see you use high-storage chokes, with high DC resistances. I would have to conclude you have never built of heard a L1/C1/L2/C2 filter chain using low storage and low DCR components.
Had you had this experience, you would not write about "Rdc of a power supply" as you do now in 2016 !
I have built amps BOTH ways, and I know all Ls to the Final's filter chokes need to be 20 Ohms or less ( I use 10 Ohms or less ) and all Cs 50 uF or less, and all HY's about 2 HY., or less. Above those values, audio performance, dynamic contrasting, and timing of the amp on music playback suffers in "my" DIY amp listening - 34 years worth.
We should discuss this privately. Contact me through Forum eMail please. Regards and best wishes,
Jeff Medwin
~!
The Mind has No Firewall~ U.S. Army War College.
aknaydenov ,Great posting, yes everything is audible IF one listens.
"Illigitum Tatum Non Carborundum."
Have fun, I do !Jeff Medwin
Edits: 04/09/16 04/09/16
x
!
The Mind has No Firewall~ U.S. Army War College.
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