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Dynaco-Doctor Forum Welcome! Need support, you got it. Or share your ideas and experiences. |
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Dynaco-Doctor Forum Welcome! Need support, you got it. Or share your ideas and experiences. |
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In Reply to: RE: "Individual cathode bias resistors is a plus" posted by xaudiomanx on December 23, 2018 at 16:29:49:
I agree with you that measurements come second to sound quality. If measurements were all that was important, we'd all be using 1970s solid-state amps instead of tube amps, since they measure better. But I'm not willing to say that there is NO correlation between measurement and sound quality.
That is my dilemma. Since, like you, I don't build enough to invest in scopes, signal generators, etc. Also like you, I find a few guys more knowledgeable than me, and try and at least follow some of their guidelines.
If it sounded like I was saying that the EFB is better because it measures better, that wasn't my sole intent. I believe it makes the amp sound better, to my ears, and the measurements seem to back that up. Extended tube life is simply a bonus.
Regarding your friend Da Hong's lesson regarding power transformers, that's a good one, and there are others who feel the same way. Remember all the hate Jeff (Dr lo mu) took for saying the same thing? Although I will agree that it was not so much what he said, but how he said it that was the issue. But your listening tests have proved to you that a "larger than necessary" power transformer sounds better, and no measurement can back that up... Or can it?
Below is a bit from a Stereophile interview with Paul McGowan, the "P" in PS Audio, where he said that his then partner, Stan Warren discovered that an amplifier sized transformer made their preamp sound better, but they couldn't explain why at the time. Only later did they figure out that it was the larger transformer's lower secondary impedance (a measurement!) which made the difference. Here's the quote:
"Way back when Stan and I were partners" I was the "P" of PS Audio; the "S" was Stan Warren, who's off doing his own thing in Eugene, Oregon, I experienced a classic case of the value of listening to things as opposed to just trying to pencil everything out. We were just making preamps and phono stages, I don't think we were making a power amp at the time, and Stan called me into the listening room saying, "You've gotta hear this."
He sat me down and played me an LP.
I said, "Yes, that sounds fine."
Then he did a classic A/B and it was one of the biggest jaw-droppers I've ever heard.
"What the heck did you do?" I asked. We were listening to a phono stage, and I figured he'd done something to the circuit, because each one of us was playing around with circuits at the time.
"I changed the transformer!" he said. "I couldn't find the appropriate small little weeny preamp transformer we would normally hook up, but I found this large power-amp transformer that happened to be exactly the same voltage. I hooked it up and you heard the difference."
The only thing he did was change the transformer. We went from a 100mA transformer to a 10A transformer, exactly the same voltage, the circuit was drawing no more current, and the difference was just staggering. To this day it's one of the biggest differences I've ever heard.
We scratched our heads, we asked everybody we could, but neither of us had a clue why we could hear such a big improvement from the bigger transformer. We couldn't measure any difference, but we said, "What the heck, it works." So we began producing what we called the "High Current" power supply, an add-on box. We built 'em for years, actually, before we finally figured out what was happening. Which was the large transformer's very low secondary impedance, maybe under an ohm, whereas it's of the order of 35-50 ohms for a small transformer with the same voltage."
End quote.
The only problem with that is, especially with Dynaco equipment, there's precious little room for even larger capacitors, much less a huge power transformer. You can put everything into a larger chassis, but as you've often said, "It's better, but it's not a Dynaco anymore". Although I'm not really interested in having a museum quality Dynaco amp.
Regarding transformers, I'm facing that issue now with a PAS. I'd like to try a separate (and higher current) filament transformer, as I've had more than a few people tell me it will make a nice improvement. The problem is, where do I put it? There's no room on the PAS chassis, and I already have the power transformer mounted on the outside back of the chassis, an idea I got after seeing a Van Alstine modded PAS, as shown below.
The preamp was modded by me years ago to David Vorhis' The Last PAS circuit, so I'm not "defiling" a stock PAS by further modding it. Maybe I should run a free "wanted" in the Asylum Trader, asking if anyone has an old, beat-up PAS chassis they'd like to sell. I could build an external power supply, connected via umbilicals for B+ and filaments, and have more room to work.
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Follow Ups
- RE: "A measurement!!!!!!" - 1973shovel 09:57:37 12/24/18 (0)
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