https://www.valvewizard.co.uk/paraphase.html
https://caryaudio.com/wp-content/uploads/2013/06/Sweet-807.pdf
That red resistors is shown as a 50K pot - an open loop version of the paraphase. Could have no phase inversion all the way to rather to much. This will control the 2nd harmonic null or your syrupy pot.
The second amp I think the op-amps are just bias monitoring to allow you to set the bias with the LED's on the op-amps.
https://caryaudio.com/wp-content/uploads/2013/06/Sweet-807.pdf
That red resistors is shown as a 50K pot - an open loop version of the paraphase. Could have no phase inversion all the way to rather to much. This will control the 2nd harmonic null or your syrupy pot.
The second amp I think the op-amps are just bias monitoring to allow you to set the bias with the LED's on the op-amps.
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Actually, it’s a push pull SLA-70. They used EL34’s, 6L6’s. Also, as I remember, there was a pot as baudouin0 says. The round black looking things are the trim pots over the driver/phase splitter tubes.
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That is a floating paraphase (?) phase splitter, used quite a bit before the days of LTP's and Cathodyne converters. Incidentally, it is a similar circuit as used in the Leben CS 300 amp, which is renowned for its lush and rich sound. (Tells you sweet little lies as one reviewer put it) Without that red resistor, it won't work.
I think its a pentode output from the layout, the data sheet says only a modest amount of NFB (4dB). The black pot is the phase amplitude balance (red resistor) I think. So its going to have poor slew rate, poor speaker damping and a variable amount of 2nd harmonic - all the right ingredients for a valve sound - lush, rich and syrupy. A long way from blameless/transparent/clinical/analytical.
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It wouldn't be a Cary if it didn't have that. ;-) Don't get me wrong, I've always liked their stuff, and I simultaneously fell in love with ProAcs and 300B amps when I heard the combo at a dealer 30 years ago. But "clinical" (or even "accurate') are not terms that I would apply to Cary amps. ;-)
I agree its what you like that matters. I thought the first kit I built (K4040) was great until I put a 10KHz sinewave in and got a 10KHz triangle out. Then it got modified to a LTP driver and the valve sound went. However since building quite a few amps, I prefer the amp to be transparent and produce the music accurately. They can still look beautiful even if they sound the same as a modern transistor.
I'm not referencing Cary as being clinical. I also agree that they are "not" the most accurate amps; however, this was about trying to understand what makes an amp have a warm (I call it syrupy) sound and the SLA-70 was an amp that offered that, in my opinion.
BTW, those SLA-70's were not the best built amps around (I know because I built many, in the beginning); however, I did like the way they sounded...
I was replying to baudoin0's comment.
I assume what makes the Cary "syrupy" is a relatively soft driver/phase splitter, a very low amount of global feedback, lack of regulation, output transfromer specs, and a number of other design choices. If you go to the other extreme, ARC amps are generally highly regulated and employ stiffer designs. They are considered "neutral" and sometimes "analytical." They certainly will measure better than a Cary and, properly maintained, can be just as musical.
Many later Cary amplifiers are based on earlier Cary amplifiers, such as the 807 pp.
Yes, there are small or medium circuit changes along the way, and/or tubes changes along the way, etc.
Then larger changes come along.
Reminds me of the purposely slow progression of phono cartridges in the early 60s to early 70s.
Don't do all the improvements at once, or you will reduce your total sales.
I find many things that cause different sound characteristics is:
Amplifier damping factor
Speaker impedance versus frequency
Mechanical/Acoustic damping of the speaker drivers
Room size
Room treatments, reflective, absorbive
And . . .
The LPs and CDs that are being played, on various turntables/cartridges and CD players.
Sound characteristics are according to the Total System, not a single component.
Back to Double Blindfold Testing.
It is a Mean thing to say that Karl Friedrich Gauss was just an Average man at the Peak of his career, and at the Center of the Gaussian Curve.
Yes, there are small or medium circuit changes along the way, and/or tubes changes along the way, etc.
Then larger changes come along.
Reminds me of the purposely slow progression of phono cartridges in the early 60s to early 70s.
Don't do all the improvements at once, or you will reduce your total sales.
I find many things that cause different sound characteristics is:
Amplifier damping factor
Speaker impedance versus frequency
Mechanical/Acoustic damping of the speaker drivers
Room size
Room treatments, reflective, absorbive
And . . .
The LPs and CDs that are being played, on various turntables/cartridges and CD players.
Sound characteristics are according to the Total System, not a single component.
Back to Double Blindfold Testing.
It is a Mean thing to say that Karl Friedrich Gauss was just an Average man at the Peak of his career, and at the Center of the Gaussian Curve.
And most importantly, one’s personal taste…. Being that I play the drums (well, I did a lot some years ago), I have yet to hear any system reproduce the attack of a drum. Add in, how it’s recorded, where it’s recorded, how it’s mixed and mastered… I think it’s almost impossible to recreate a live performance; so, I like to tailor the sound to my likings…
in other words, what I find enjoyable…
I really don’t know. I’m not an engineer, nor, do I have a full understanding of this stuff…. So, some of the things being talked about, in this thread, is way over my head.
OK, well your pic of the SLA-70 appears not to have any regulation circuits.
Regulation enforces operation within a desired parameter somewhere in the circuit - usually voltage or current.
If you happen to have built a kit tube circuit with resistor plate load and then "upgraded" it to a constant current source you would have heard a difference.
There are many kinds of regulation that can influence the sound by their application but in addition their use is indicative of an approach to the design itself that cannot be considered inconsequential.
Regulation enforces operation within a desired parameter somewhere in the circuit - usually voltage or current.
If you happen to have built a kit tube circuit with resistor plate load and then "upgraded" it to a constant current source you would have heard a difference.
There are many kinds of regulation that can influence the sound by their application but in addition their use is indicative of an approach to the design itself that cannot be considered inconsequential.
Since you do drums kmr audio have an tube affects box which adds distortion. They have some sound snippets which shows what happens.
https://kmraudio.com/blogs/blog/adding-harmonic-content-how-can-it-work-for-you
https://kmraudio.com/blogs/blog/adding-harmonic-content-how-can-it-work-for-you
Basically you're going to hear fewer colorations from the amp itself, and therefore a more faithful representation of the source material.
Its quite common to add distortion (or other effects) to individual instruments and then mix them together in a linear way. However adding distortion to an amp can have the effect of mudelling the sound. Typically bass notes can intermod with vocals. There are spectral band compressors which are used extensively in transmitters etc. which do this rather better.
I prefer a transparent amp.
Those sound snippets show you what can be done on drums etc.
I prefer a transparent amp.
Those sound snippets show you what can be done on drums etc.
If you still have an SLA-70 on the shelf I could suggest listening to it for a month and then switching out the 220K plate load resistors on the 6SL7's for some CCS loads. Cascode Mosfet current sources are easy, reliable and not too expensive.
I would quibble with Grover's pat answer. So I suggest trying stuff for yourself. You might not think of yourself as having a technical enough mind for such things , but if you know because you've "built many, in the beginning", I'd argue you are plenty technical enough to do it and get experiential understanding of the results.