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In Reply to: RE: 300B PP or SE, serious DIY project posted by Neff on September 09, 2012 at 08:33:05
I have a PP 6C4C amp (like 2a3) and a 300b SET. Input sections for both are 4P1L driver stage. Input stage of the PP amp is 26, and SE amp is another 4P1L stage. For a while the PP amp - which is balanced through all 3 stages - sounded better than the SET. I thought I was done with SE amps at that point - the sound was excellent. Then gradually I worked on the 300b SET and now I wouldn't go back to PP.What I learned in this process was:
1) Only use DHTs, no directly heated tubes anywhere.
2) Only use filament bias for the input stages. That meant choosing between 26 and 4P1L. The 4P1L is slightly better.
3) Use the best interstage transformers you can buy.
4) SE input stages sound better than PP stages if you use filament bias.So I ended up with the schematic shown. Out of all the interstages I tried I liked the LL1660/18mA after the input and the Hammond 126C after the driver. The Lundahl is clearer and has good treble detail, and the Hammond is bifilar and adds a certain warmth and tone. It's better than two LL1660/18mA that way - don't ask me why but it just works.
I haven't built a parallel SET yet - I'm building one as we speak with multiple 4P1Ls in filament bias in the output and O-netics OPTs!!
So at this point I'd say build a parallel PP output stage but use a phase splitting interstage after the driver. Use two stages of 4P1L in filament bias and then a Tango NC16. I haven't used this myself but for the power I think this would be simpler. Stick with the 300b outputs.
I believe the input stages are the heart of the amp and that's where I've put all my development experiments. I avoid larger value cathode resistors and their bypasses like the plague, and I've never found a fixed bias that sounds as good as filament bias, not even battery grid bias. So that's where I am at this point. I absolutely love my amp - voices are just so real they "talk" to you and I listen mainly to vocal music as a result. I never got this with the balanced PP amp - it has all the tone and the detail and is a fraction cleaner on orchestral climaxes. But when I listen to voices it just annoys and irritates me now because that special extra dimension isn't there. Just gotta have my SET fix!! It's really like a drug.
The schematic is substantially correct, though I've played about with some of the values, and also I use glow tubes for voltage regulation of the input and driver stage. I also use choke input DC supplies to the input and driver section filaments, and carefully select the wirewound cathode resistors. I put a lot of work into optimising the first two stages. It's worth it. You may be surprised to see a cheap Russian tube here, but it's kicked out 10Y, 46, 26 and all the other DHTs I've thrown at it! The 4P1L, to give it proper credit, is actually a German Wermacht tube that the Russians copied! Some of those European DHTs were the dog's dangly bits. It is used here with parallel filaments (1+7 and 8) and with pins 2+3+4 connected to the anode. Filament is slightly starved at 1.9v and 600mA. All these details actually matter.
We've been working on all this for a year or more over on DIY Audio on the "One more 4P1L SE" and "26 pre amp" threads. The latter has passed 2,000 posts so you can see how much development has gone into all this kind of stuff (4P1L, filament bias, Rod Coleman regulators etc.).
Andy
Edits: 09/09/12 09/09/12 09/09/12 09/09/12 09/09/12 09/09/12 09/09/12 09/09/12Follow Ups:
Woa... The 300B amp is back on the menu boys!!! There is hope for the 300B amp afterall!!
Did you find ways to make the 300B amp a little more dynamic to close the gap with the PP amp?
Lester
"I absolutely love my amp - voices are just so real they "talk" to you..."
That effect probably indicates you've achieved a near-ultimate level of synergy, including the speakers and environment. I've only heard such realism maybe three or four times in my life. I remember certain ribbons being able to do it (but only at specific locations) as well as a cone/dome two-way system that really surprised me. Vocals through the latter were so lifelike it was scary; I frequently thought someone else was in the house. It's clear to me from many conversations throughout the years that many audiophiles have never heard this. Congratulations!
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Buy Chinese. Bury freedom.
That's EXACTLY what I've been listening to for many years!
My transition was DIY tube SE and PP when I was a kid, stopped DIY through the SS and CD era, little attention to audio through the greater years of marriage, back into audio with stupidly expensive gear starting with SS PP, SS class A, big ultralinear tube PP, then DIY all the way through triode PP, DHT SET and then DHT PSE SET for more power.
The magic started with triode PP and peaked at SET. I haven't touched my PSE845s for years (other than tube rolling) but every little improvement I make on my source (exclusively vinyl), I hear!
Funny that others should mention the surround sound thing because that's the way a few friends, new to audio have described what they've heard.
The sound stage is deep and wide with sound extending well beyond the speakers, vocals are to die for and articulate but full bodied instruments placed with pin point accuracy across the sound stage.
Naz
I have & had amps like that. I would be doing something else in another room & all of a sudden a radio announcer would say something and I thought a stranger was in the house.
I used to get that kind of effect a lot. In fact, that was my goal with SE triode amps when first got started.
This is what I call "magic mushroom" or "psychedelic sound" for you rabid objectivists. i don't think they know about this yet at Harman! ;op
The wildest was with a SE 71A with globe tubes. I could hear stuff behind me. The sound went way behind the back wall. There was no sense of speakers whatsoever.
Vocals has crazy inner detail and I could really hear breath modulation and small glottal and fricative articulations.
It was a good amp with 71A STs but the globe tubes were really insane.
I couldn't play big loud program with 700mW but on "Tuck and Patti" type stuff, WATCH OUT.
I also found that paper cone speakers help with this tripped-out effect, especially 755As. Not sure why. Never got anything close with compression drivers. That was a different problem set entirely.
I also found that good oil caps and AB resistors helped a lot, which is why I went around talking them up. There are probably other recipes, but that is the one I knew in 1988.
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Free your mind and your ass will follow -- Parliament/Funkadelic
I had a DIY PP 6V6 triode amp with soundstage so wide I would place dummy rear speakers & everyone thought the speakers were connected. Another is a song when the signer whispers and the location changes from in front to a whisper next to my right ear. Any closer & the female singer would have left a wet spot. Freaky.
Vocals through the latter were so lifelike it was scary; I frequently thought someone else was in the house..."Well, my point wasn't about being literally scary, though it actually is pretty lifelike. What I mean is that the vocals go beyond mere words - like they talk TO you. You pick up the inflections, the breathing, whatever makes language come alive. It's subtle but it's more than subtle because it actually makes a big difference. I've no idea if I'm making the point clear here. If I A-B the SE and PP amps the difference in emotional impact is obvious, though in other respects the sound is quite close. It's the difference between words and meaning. Once you hear it it's like a drug - it's addictive.
Also backing vocals just float in the air. I listen to voices when I go to bed - the hifi is in my writing room/bedroom - and I fall asleep to voices. I listen to a lot of modern Gospel - Kim Burrell, Dorinda Clark-Cole, Committed etc. I'm not religious as such though my grandfather was a preacher. I just dig the voices. I'm a jazz musician (bass and piano) and used to do a lot of gigs with singers. I listen to a lot of jazz singers as well, plus a lot of opera, Bach Cantatas etc.
I'm sure other guys hear this because I've often seen posts about uncanny voices with 300b SETs. My speakers are full range single unit Mark Audio Alpair 10s. So no crossover at all. I'd use ribbons if I had more space - I used to use Apogee Caliper Sigs. until one day I decided I'd like to see out the window.
Andy
Edits: 09/09/12
Whoa...you posted while I was writing a post saying the same thing. Dead on about the vocal articulations. I know EXACTLY what you mean.
You can sometimes get that effect with bells and triangles too, where they sound SO real it scares you.
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Free your mind and your ass will follow -- Parliament/Funkadelic
You can sometimes get that effect with bells and triangles too, where they sound SO real it scares you......"
YES!! That's exactly it. The triangle at the start of Steely Dan "Babylon sisters". And the start of Ravel's piano concerto. And Feria from Ravel's Rhapsodie Espagnol, where the tambourine and the xylophone are pretty scary too.
If you want some scary music try Ravel's L'Enfant Et Les Sortilèges in the Maazel recording. At the start where the voice comes in with "J'Ai Pas Envie De Faire Ma Page" you almost jump out of your chair. In fact the whole recording is magic (in the original 2 disc version with Rimsky, not the later remastered version). If you speak both English and French, "How's your mug" and "Keng-Ca-Fou, Mah-Jong" are entrancing. I mean, "I punch, I knock you out you stupid chose....."
Andy
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