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Old 21st April 2012, 01:22 PM   #4581
dvv is offline dvv  Serbia
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Quote:
Originally Posted by ThorstenL View Post
... I'll have to decide if I implement signal dependent bias, or not. ...
If I understand this correctly, you are wondering aloud if you should use some form of sliding bias, rather than fixed point bias?

To this day, I have yet to hear an amp with any sliding bias scheme which will sound better because of that scheme. Every time I think I have just heard that, it turns out that the key reason is more likely something else, like an extra pair of output devices, a more powerful power supply, etc.

I have cme to believe that those arrangements are really a waste of time and an unnecessary complication.

On the other hand, 233 mA per output pair seems a bit too much - I could be wrong. I find most do what they do by around 130 mA per output pair, and moving on upwards just makes the sound softer and a little less focused, for lack of a better word. That too can be just as irritating as sharp and sibilant sound.

You really don't want to go the industry way, albeit in the opposite direction. They save by using low bias currents and thus have weedy heat sinks; you might use too much bias current and impose very restricting demands on the constructor regarding heat sinks (and I don't mean me, I also have 0.3 heatsinks).
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Old 21st April 2012, 02:00 PM   #4582
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As an option, there's always Technics SE-A1 and Pioneer Exclusive M5.
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Old 21st April 2012, 02:08 PM   #4583
wahab is offline wahab  Algeria
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Originally Posted by jacco vermeulen View Post
As an option, there's always Technics SE-A1 and Pioneer Exclusive M5.
As well as JVC s Super A amps , among other the awsome AX1/AX7 serie
and AX77..
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Old 21st April 2012, 04:28 PM   #4584
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by ThorstenL View Post
Hi,



I am currently using Spice (still Tina, but with good models now) to play with the effect of Iq on high order distortion.

With +/-60V at modest load and a 0.3K/W heatsink with allowing 30K heatrise in the heatsink I can allow 100W dissipation or 833mA in total (drivers and outputs), so if my drivers are 2SJ162/2SK1056 at 133mA I can run 233mA per output pair.

So far it looks like more bias is more better. Doing this compared to theoretical "optimum" bias appreciably reduces higher order HD. I'll have to decide if I implement signal dependent bias, or not.

Then again, for rated power (150W/8R = 0dBFP) I get 0.12% THD at 50KHz and 0.066% at 1KHz, H2 dominant.

At around 1.5W (-20dBFP) I get 0.04% THD/50KHz with H2 dominant and H3 nearly 16dB down at optimum bias (26mV/120mA).

And at -60dBFP (dB below full power - so 0.15mW) I get 0.008% THD/50KHz H2 dominant.

Using Mosfet output stage with BJT drivers around triples low order HD over Mos Driver and BJT Output BTW, unsurprisingly, with no benefit in high order HD for the same Iq.

Ciao T
What about tube/MOSFET/bgt's ..... Best of all three ....!
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Old 21st April 2012, 04:46 PM   #4585
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by dvv View Post
If I understand this correctly, you are wondering aloud if you should use some form of sliding bias, rather than fixed point bias?
Not sliding, but perhaps 2 or 3 Step, by either manual or automatic selection.

To burn off around 250W or more idle (with all losses in the chain) all the time seems a bit wasteful and anti-ecological (I just did my whole flat with LED Lights and cut the light power consumption massively compared to the dimmed 35/50W Halogen spots I would have used otherwise - strictly to be more green). Even my Tube Amp does not have that kind of idle consumption.

Quote:
Originally Posted by dvv View Post
To this day, I have yet to hear an amp with any sliding bias scheme which will sound better because of that scheme. Every time I think I have just heard that, it turns out that the key reason is more likely something else, like an extra pair of output devices, a more powerful power supply, etc.
Could very well be.

However, I can likely get acceptable performance for every day use (watching movies, my daughter watching her cartoons, listening to music while working etc. which the Amp would be doung 70% of the time it is on, which tends from to be from 8am to well past midnight) at a fairly low bias (e.g. 80mA per pair and thus under 100W dissipation).

Yet I also feel that turning up the bias to the maximum I am willing to put up with thermally (in the interest of reliability) has benefits, something I know you agree with.

So either a "low/high" switch or a system that cranks up the bias when it gets loud may very well have merit outside strict audiophile concerns.

Note, the Amplifier is not meant as a general project for others, it is strictly a one off for my personal use, according to my personal ideas and concepts.

I am merely sharing the concepts and Ideas as they may benefit others even if they run counter to their views, as it allows us all to sharpen our wit in seeking good arguments to promote our own views and concepts in opposition, while others may find the ideas and concepts agreeable and benefit from them too, or may even like the whole design once done enough to replicate it wholesale.

Ciao T
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Old 21st April 2012, 04:51 PM   #4586
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Hi,

Quote:
Originally Posted by a.wayne View Post
What about tube/MOSFET/bgt's ..... Best of all three ....!
I think if we where to do that we would have to add a SIT somewhere and use laser biasing...

Don't get me wrong, I like hybrids as concepts, but if I am going to put up with tubes and all that implies, personally, I might as well use a tube amp.

My question is more to what degree the things I have learned with tube gear bear transplanting to solid state, with the aim of "good sound".

I'm perfectly prepared to fail, after all, I have a tube amp that works well and plays mostly loud enough...

The next after that may be to see if we can apply the same concepts to Class D...

Ciao T

Last edited by ThorstenL; 21st April 2012 at 04:57 PM.
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Old 21st April 2012, 05:24 PM   #4587
a.wayne is offline a.wayne  United States
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Yes , agree one can get good sound out of a total tube build and even thou they seem to add some kind of harmonic richness to the music there is a kind of drive delivered by SS amps that sound more like the source to me ......


Interesting to see your project of course I would like to scale up ...
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Old 21st April 2012, 06:30 PM   #4588
dvv is offline dvv  Serbia
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Thorsten, let's talk some statistics.

About 99% of the current class AB amplifiers use less than 80 mA per output pair. Most are of no interest to people like they congregate here, we all want something better than average, average doesn't cut it for us.

Yes, I absolutely do agree that more bias, moving the output stage more towards class A, is beneficial to the sound we hear.

The bias switch scheme you mentioned is used in some form in my Marantz amps. In fact, at a point, you can barely discern a very low level "click" as it shifts into higher bias mode. All done with NTC devices. But, ...

No automatic system is foolproof. There will always be situations when the system misreacts, for whatever reason or set of cirumstances. While this may not be dangerous to anyone or the electronics, it never fails to **** me off. I just can't stand "ifs", "buts" and "maybes", not if I can help it. Less variables by default means better reliability.

Thus, having played with this effect, admittedly in all cases with factory made units, I have come to the conslusion that about 130 mA per output pair is the highest point at which I can actually HEAR the difference. And that's the point at which I call it a day. In aid of your concept, most gave up by about 100 mA, only the HK 680, the one with just 12 dB of global feedback, went on to 130 mA; at 140 mA, I could not hear any differences at all. So I reduced it back to 130 mA and left it there. Not because I had to, it has a massive heat sink which could ride out more, but because I heard no additional benefit.

True, it's a factory made unit, so it would probably require some modification do fare better at higher levels, because as was done, I really shifted the work points of the predriver, drivers and output transistors - NOT a terribly good idea, but far easier than modifying the whole thing. In other words, if you design straight off for it, obviously you will have better results, no doubt there.

You will of course do as you please, but I would advise you keep it on a constant level, even if it is elevated in comparison with the average. Keep it simple and ellegant, is what I say.

Use the minimum you have to use to achieve your goals, but no less. And no more.
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Old 21st April 2012, 06:31 PM   #4589
dvv is offline dvv  Serbia
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Quote:
Originally Posted by a.wayne View Post
Yes , agree one can get good sound out of a total tube build and even thou they seem to add some kind of harmonic richness to the music there is a kind of drive delivered by SS amps that sound more like the source to me ......


Interesting to see your project of course I would like to scale up ...
Natch!

I mean, without 1 kW of power per side, it ain't HiFi.
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Old 21st April 2012, 06:41 PM   #4590
a.wayne is offline a.wayne  United States
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HiFi no , life like realism ......True dat ..........
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