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Old 26th December 2011, 04:00 PM   #171
Pano is offline Pano  United States
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Quote:
Originally Posted by a.wayne View Post
IMHO SS amps suffer from thermal distortion, control this and there is no cold /thin/ sound ..
I've always wondered about this. Could the heat be part of the charm of Class-A transistor amps? Especially those with the driver transistors on the same heatsink as the output devices. Just wondering.
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Old 26th December 2011, 04:01 PM   #172
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Originally Posted by tvrgeek View Post
I would say some as the various methods effect where on the curve the tube runs and all the interrelated effects that argument or cancel each other. Hint: "curve" I have only built a couple of tube amps on a junk Chinese 6P1 chassis and my only textbook is the one from Jones, so I may be missing something.
That has nothing to do with compression. I'm sorry, there's absolutely nothing inherent in tubes that results in compression (or high distortion or low damping or...).
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Old 26th December 2011, 04:03 PM   #173
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Sure, SY. But there might be in typical tube amps.
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Old 26th December 2011, 04:04 PM   #174
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Quote:
Originally Posted by Pano View Post
I've always wondered about this.
You can stop wondering. If it were thermal distortion, you'd see an increase with decreasing frequency. You don't.

Heat may indeed be part of the charm, but it's not due to electrical signals.
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Old 26th December 2011, 04:07 PM   #175
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Originally Posted by Pano View Post
Sure, SY. But there might be in typical tube amps.
If "typical" means those amps that are missing proper cathodes and half their output stage, then compensate by throwing iron at it, then yes, you might be right.
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Old 26th December 2011, 04:08 PM   #176
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Really? Keeping all those active parts at nearly the same temp, no matter the signal, doesn't help?
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Old 26th December 2011, 04:12 PM   #177
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By "typical" I mean common topologies and implementations - including power supplies.
The compression part I'm no so sure about. Soft clipping, maybe.
Yes, I know your opinions of DHT SET amps.
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Old 26th December 2011, 04:12 PM   #178
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Hi,

Quote:
Originally Posted by Pano View Post
Really? Keeping all those active parts at nearly the same temp, no matter the signal, doesn't help?
It may help, or not depending on application, however only for static conditions.

There is so much thermal resistance between the silicone chip and any heatspreader or just the envoironment, by the time a common heatsink can react, the signal is long past. Even having everything on the same die is no guarantee...

Ciao T
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Old 26th December 2011, 05:20 PM   #179
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Pano, you only have 1/2 the story. Class A is not necessarily the most thermally stable operating condition. It can be shown that heavy Class AB-1 is as good or better, if you go back to the root equations. However, thermal stability, both transient and long term is really important, and real designers make sure that the THERMAL CAPACITANCE is very high by close mounting the output devices on good insulators (if necessary) properly torqued down and used with thermal grease on a substantial heatsink . This removes most of the short term gain changes due to temperature.
High input stage operating current, using only a part of the class A portion can also be helpful.
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Old 26th December 2011, 05:28 PM   #180
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Originally Posted by john curl View Post
Coppertop, the REAL answer is to listen for yourself, and to trust your own responses to different amplifier designs. It is true that we audio designers do NOT completely understand what is most important in amplifier design, and I personally have striven to understand it for more than 40 years.
My personal philosophy is to try to cover EVERYTHING that I know is potentially an 'error' in an amplifier's design. So, I will start with the most linear circuit topology that I can think of. Then, I will run it as close to Class A as the heatsinks available will allow. Then, I will make sure that the circuit is fast, at least 100V/us, often faster, and stable with virtually any capacitive load.
Then, (in short form) I will make sure that the amp has lots of peak drive current capability, 30A min, 60A typical.
Finally, I test for the worst case crossover point in the transfer function and monitor the 7th harmonic distortion generated. This is at the transition between Class A and Class AB (about 25W in the JC-1).
Am I completely successful? No, but I do pretty good. There are people of my acquaintance who have owned and sold their JC-1's for another amp. One of the other amps is the AYRE. It is ALWAYS a wake-up call when this happens.
Now what advantages does Charles Hansen of Ayre, have over my Parasound designs?
First, he has COMPLETE control over his design. I am limited to circuit design, getting a proper circuit layout and most of the obvious active and passive parts.
I have little control over internal connectors, housekeeping circuits, protection, RFI proofing the power supply, being stuck with a huge toroid transformer, rather than a super-quality EI or R core transformer. I'm not complaining exactly, I get to control the bulk of the design, but IF I personally made the amp, myself, it would cost at least 3 times as much and sound only a little bit better, on some occasions. In this case, the associated equipment and audio sources would dominate any decision as to an audio difference. But heck, I could pick the exact brand of solder, even, just like I did with the CTC Blowtorch, that just about everybody likes. '-)
I'm sure the difference would be load dependent, well based on the Stereophiles test results, JC1 vs the Ayre.


Quote:
Originally Posted by Pano View Post
I've always wondered about this. Could the heat be part of the charm of Class-A transistor amps? Especially those with the driver transistors on the same heatsink as the output devices. Just wondering.
Yes thermal tracking IMO does cause a change in sound with SS amps.
Class-a sound is more consistent due to the high bias and the heat associated with it. All SS amps sound different and require some warming period for there sweet spot, due to thermal tracking they very rarely stay within this sweet spot during use, unless sweet spot temps are very well controlled.

Class-d suffers very little from this, so once in there operating sweet spot there sonic character changes very little , you either like it or not. Class-a gets similar response , just at the other end of the temperature spectrum.

Ideally the amp should get up to it's sweet spot temp and stay there, this is difficult unless designed for some specific load. Matching and oversized heatsinks pays dividends here, but doesn't erradicate it.

of course your mileage may vary .....

Quote:
Originally Posted by SY View Post
You can stop wondering. If it were thermal distortion, you'd see an increase with decreasing frequency. You don't.

Heat may indeed be part of the charm, but it's not due to electrical signals.
Well not according to the test performed by Atkinson , heat did make a difference to distortion, power and bandwidth.
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