John Curl's Blowtorch preamplifier part II - Page 2214 - diyAudio
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Old 9th April 2012, 02:12 AM   #22131
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The Symmetry Crossover was well known in the USA, and founded by Noel Lee, of all people. He gave it up to do Monster, after a few years. I do not specifically know this manufacturer, unless they are associated with HK in some way, who I worked with at the time.
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Old 9th April 2012, 06:24 AM   #22132
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Quote:
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I do not specifically know this manufacturer...
John,

It's a SONY !
That gain module is from their top of the line crossovers TA-D88 and TA-D900.

Sony TA-D88B on thevintageknob.org
Sony TA-D900 on thevintageknob.org

I studied a lot of Japanese amp and preamp designs in the early '80's. We used to have "Musen to Jikken" and "Denpakagaku"(?) magazines going back to 1977 or so in our library at the company I was working for. Those mags published many schematics of comercial offerings, including exotic ones. Some of them used interesting, not seen before topologies. I always wondered who were the designers of these and thought that there must be some very good engineering potential and some very clever guys over there whose names we probably will never know.
Fast forward 30 years. Thanks to the internet and the amount of information available, I'm beginning to think otherwise. The picture becomes clearer now and small pieces of puzzle one by one snap into their places. I can certainly see now where one or the other manufacturer "got inspired" in the process of creating their own products. Hmm...
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Old 9th April 2012, 08:30 AM   #22133
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Sony also reportedly borrowed the Dayton Wright bootstrapped cascode input design. i wonder if anything of Nelson's made it into their product range as well.
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Old 9th April 2012, 01:49 PM   #22134
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It is difficult to say where each design came from. I was somewhat surprised on the similarity of the Sony schematic to my own, but we may have derived it from the same place, which was the Levinson JC-2 phono stage 1973-76, published in 'The Audio Amateur' by me, in 1977, once my royalties were arbitrarily cut off. However, it could have been completely independently developed as well. It is a rather trivial execution of a fundamental design 'subcircuit' that has been used by many sources, both professional and amateur.
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Old 9th April 2012, 02:08 PM   #22135
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The Levinson JC-2 modules for reference. Please note the polarity mistake in the line amp, before emulating.
Attached Images
File Type: jpg levinson JC-2.jpg (203.0 KB, 371 views)
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Old 9th April 2012, 05:22 PM   #22136
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What I am trying to get across here is WHY I develop circuitry with this approach. I am fundamentally trying make circuits that 'sound good' not necessarily circuits that 'measure' good, even though I get both, most of the time. Yet, I am NOT trying to make a circuit 'sound' a particular way, but basically to NOT have a sound. If you can get the electronics 'out of the way' so to speak, then with 'luck' and a good musical source, you can sometimes achieve moments where 'you are there' at a performance that may have actually happened 50 years ago, for example. This is my goal.
To do this, an audio stage has to be extremely linear at working levels, reasonably to very quiet, depending on its location in the chain, fast, have an extended low and high frequency bandwidth, and virtually very low, or no easily measurable higher order harmonics. Some secondary considerations are more subtle, like high open loop bandwidth, and open loop DC stability, due to inherent symmetry of the circuit operation. These cannot yet be easily 'proved' but you can't argue me to ignore them.
I may have left something out, but that is pretty much all there is to it. The rest is just technology, parts quality and availability, construction and shielding, etc.
To me it is 'obvious' from years of experience that this is the way to go with solid state design. Yet, many here will disagree. Why they disagree is debatable. Some will accuse me of 'fooling myself' and others into believing that there are actual sonic differences in any 'reasonably well designed' circuit that measures well, and will attempt to force me into double-blind testing, that will invariably give null results, due to factors not well understood. Well, to each, his own.
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Old 9th April 2012, 08:32 PM   #22137
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Quote:
Originally Posted by john curl View Post
What I am trying to get across here is WHY I develop circuitry with this approach. I am fundamentally trying make circuits that 'sound good' not necessarily circuits that 'measure' good, even though I get both, most of the time. Yet, I am NOT trying to make a circuit 'sound' a particular way, but basically to NOT have a sound. If you can get the electronics 'out of the way' so to speak, then with 'luck' and a good musical source, you can sometimes achieve moments where 'you are there' at a performance that may have actually happened 50 years ago, for example. This is my goal.
To do this, an audio stage has to be extremely linear at working levels, reasonably to very quiet, depending on its location in the chain, fast, have an extended low and high frequency bandwidth, and virtually very low, or no easily measurable higher order harmonics. Some secondary considerations are more subtle, like high open loop bandwidth, and open loop DC stability, due to inherent symmetry of the circuit operation. These cannot yet be easily 'proved' but you can't argue me to ignore them.
I may have left something out, but that is pretty much all there is to it. The rest is just technology, parts quality and availability, construction and shielding, etc.

Hi John,

Thank you for the concise summary of your design philosophy.
I, for one, view your approach with high regard. Though being a self-educated electronics technician I have no design skills, my limited background in electronics and my limited experience with "High End" audio systems lead me to appreciate your approach and philosophy as being commendable.

You seem to omitted in the above description "shortest possible signal path" and "no capacitors in the signal path, as long as it's possible".

Quote:
Originally Posted by john curl View Post
To me it is 'obvious' from years of experience that this is the way to go with solid state design.
It looks to me that most of the above, save symmetry and perhaps extended low frequency bandwidth, applies also to tubes design.
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Old 10th April 2012, 12:24 AM   #22138
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What I am trying to get across here is WHY I develop circuitry with this approach.
John, you can do pictures now you are unstopable.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
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Old 10th April 2012, 01:55 AM   #22139
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About time.
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Old 10th April 2012, 06:12 PM   #22140
KBK is offline KBK  Canada
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About time.
Well, might be a good idea, with Scott saying that the time is running out. We're all gonna die! But...that's always been true. meh!

As for shortest signal path, I like the idea of components sticking out both sides of the board, if indeed a board is used (vertically mounted or distanced from the chassis proper).

Some of those older 'holdover' designs were quite decent sounding, due to such execution. Although few ventured into the dual siding of through-hole components, which is probably the last bastion of perfection, outside of no boards at all.

remember solder's original use, it was stated that way for a reason: solder is glue, it is not an electrical contact or flow point/system.

Only metal to metal is.

It really is that simple.... But complex and time consuming to execute correctly.

Last edited by KBK; 10th April 2012 at 06:23 PM.
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