I'm embarking on building a new tube headphone amp. I guess I've always used tubes that are known for audio. But for this amp I want to build a SE zero feedback spud type with an OPT. The 6EW7 and the 6c45pi would perform really well on paper but they aren't really classic audio tubes. My other option would be to sacrifice some power/gain and use a classic WE417A/5842.
What due you think is more important specs or classic tubes? The reason I ask is because my 6SN7 based head amp sounds 100x better with 1940's RCA's vs new tubes and my 6DJ8 headamp sounds 100x better when I use old Amperex vs newer tubes. So I am leary of the 6EW7 and 6c45pi where there are practically no tube rolling options and audiophile qualities are practically unknown.
What due you think is more important specs or classic tubes? The reason I ask is because my 6SN7 based head amp sounds 100x better with 1940's RCA's vs new tubes and my 6DJ8 headamp sounds 100x better when I use old Amperex vs newer tubes. So I am leary of the 6EW7 and 6c45pi where there are practically no tube rolling options and audiophile qualities are practically unknown.
Neither. Performance in a proposed circuit is #1 for me. "Classic" is fun, no argument, but I want my boxes of gain to PERFORM.
I follow Stuart ... adding that neither 6C45pi nor 417 was originally designed for audio use 🙂
And that 99% of the 6SN7 production spent their live in vertically sweeping spots in B&W TV sets.
Yves.
And that 99% of the 6SN7 production spent their live in vertically sweeping spots in B&W TV sets.
Yves.
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Why is the 6EW7 rarely used, seems the perfect tube to drive anything from headphones to DHTs on paper ?
Mmmh ...
The gain of the small triode is too low to fully drive the large one from an usual audio source.
May be a reason for its desaffection 😕
Yves.
The gain of the small triode is too low to fully drive the large one from an usual audio source.
May be a reason for its desaffection 😕
Yves.
One thing that's cool about DIY is the ability to use a tube that really works well in a design, that might have had nothing to do with audio originally 🙂
Besides, the "non-audiophile" tubes are cheaper, and there are boxes upon boxes of them sitting around for years to come.
Cool design.
This is what I am thinking of building. I want low output impedance and high power. This puts the tube at its lowest Rp. I am on the fence with going parafeed, but I lose a lot of power. The big expensive commercial tube headphone amps all use gobs of power.
Regal, in a conventional circuit, one would AC couple between driver and output stage. This circuit eliminates that, but then AC couples the output stage. So you've removed a small (~100nF) cap from the signal path, and to do that, you then stick a big (50u) cap into the signal path. Which cap is likely to be more ideal?
The power supply caps are always in the signal path (with or without direct coupling).
This ultrapath cap is an attempt at adding a high quality cap so the path through the ground into power supply is eliminated.
Instead of the ground loop passing through all the evil grungy electrolytic caps, it is now passing through the polyprop in oil ASC cap.
So if you move the 50u cap to the power supply, you've eliminated one big ol' cap that the signal passes through (50-100u), and replaced it with a small (100nF), much more ideal, film cap.
Bas,
It is true that the current through the speaker passes through the supply caps. However, the voltage that results over the cap is NOT in any way part of the voltage across the speaker.
So, 'being in the signal path' is technically correct, but it is incorrect to conclude that it has an impact on the output signal.
jd
Well, in theory everything in the universe has influence on the sonics, but it's a matter of how much. The phrase 'it's in the signal path' gives the impression that any changes in this path immediately can be heard, and that is not the case.
For example, the ripple current through the capacitor from the supply causes the ripple voltage across the cap, yet the ripple voltage on the signal is pretty close to zero in a good amp.
jd
Interesting discussion. I do know that single biggest sonic improvement to the amps we've built is swapping out at least the last elco in the power supply (before it hits the amp) with a Solen poly cap.
dave
dave
Sy, I am interested in your opinion as I've learned a lot from you but not following this. Are you suggested parafeed with the 100nf cap?
The idea of the ultrcap is to isolate the PS caps as the other posters suggested. I am not up to speed on parafeed but if I were to parafeed this amp I would move the CCS to the top and require a much higher B+ which adds too much to the cost, unless I give up DC coupling the stages.
This is still a concept with the goal being minimum ouput impendace into low ohm headphones with a lot of power. If you look at the specs on all the multi-thousand dollar head amps they all have gobs of power but haven't been optimized for low output impedance.
Edit: I see you mean, using the 100n for interstage coupling. I think I would still need a big cap on the cathode of the output stage should I do this, so I don't see the gain. All input is appreciated.
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Yes, an interstage cap. There are two ways of getting rid of the big ol' cathode cap- bias through the grid (that requires a small negative supply) or use diode bias (my preferred solution). The nice thing is that you also get rid of the CCS with its complications and performance demerits (in this case, questionable overload and overload recovery characteristics).
It might depend on what type of small cap; there are certainly more options in small caps.
Speaking of overload and recovery, what if (theoretically) the cap interstage scheme was subject to blocking distortion? Would it be better to put the coupling cap in the output where it can't cause blocking? In this case I doubt it's a problem...
edit... I see there could be some DC offset on the output/cathode cap also if there is grid current, but it should be less severe than the coupling cap blocking. Hmmm or maybe not...
Cheers,
Michael
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You have to look at the time constants- that big ol' cap has to discharge itself through the tube's cathode to return to proper bias after overload. That's assuming that clipping hasn't caused a problem with the current sink.
Making an amp overload-proof is not a trivial proposition and is too rarely done, IMO. Moving the cap doesn't help that, it just allows the substitution of a MUCH more ideal cap (sorry, there's not a 50u cap in the world that has the performance of a one dollar 100n polyprop and foil), and saves cost and parts count.
Making an amp overload-proof is not a trivial proposition and is too rarely done, IMO. Moving the cap doesn't help that, it just allows the substitution of a MUCH more ideal cap (sorry, there's not a 50u cap in the world that has the performance of a one dollar 100n polyprop and foil), and saves cost and parts count.
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