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Old 2nd January 2016, 11:48 PM   #11
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Originally Posted by AKSA View Post
Hi Ivo,

Happy New Year to you!

I use much bigger, 480W mosfets for the Maya, and yes, they have much higher transconductance and parasitic capacitances. The NAKSA 125 uses 280W devices.

I could fill a page on this; it's my stock in trade for the last twenty years. Firstly, higher transconductance means there is very little change in Vgs on these devices over the full waveform, and the Cgs is bootstrapped by a common source. These devices have transconductance around 25S plus, where bipolars are markedly less (typically 12S for a C5200), so the waveform compression of mosfets is superior to equivalent bipolars. A single pair of very large mosfets are superior to multiple pairs of bipolars; more resolution and easier to drive. It is much easier to drive large mosfets than most expect, and in fact I found using drivers increased phase shift and gave no subjective improvement in sound. We are working with audio, not radio frequencies, and up to 20KHz a high driver current is more than sufficient drive.

There are some dark secrets in using mosfets in this way. They are skittish devices, inclined to self-oscillate. Robert Cordell helped me from a 1984 white paper on these fascinating devices. These days I would not use anything else, and we can think SS traction technology for this; hybrid electronics use them in VFD modules.

Thanks Steve, absolutely, different devices, and we think, you and I, that the bigger mosfets sound as good and even a bit better.....

Hugh
Yes, and in my prototype experiments I've used some even larger N channel mosfets with good results.
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Old 12th January 2016, 08:14 AM   #12
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Sorry Ive been on business travel past week in Tokyo but Skiing this weekend in Nozawa in Kanazawa in Japan.
Hugh's new Amp sounds better every day I guess that the Caps are running in.

Colin was right I had 7B ST mono blocks but they sound very dry and not engaging.
I spent a lot on money on these and regret it to be honest.
Sold them on gumtree with a big loss
So far pretty dam happy with Hugh's beasties sound nice very musical and can drive my bloody difficult Dynaudio Contors5.4's
On 0419803286 OZ number if someone wants me
Cheers,
Garry
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Old 13th January 2016, 12:35 AM   #13
andyr is offline andyr  Australia
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Originally Posted by wombats777 View Post

I had 7B ST mono blocks but they sound very dry and not engaging.

Cheers,
Garry
But that's the Bryston "house sound", surely - so how come you were persuaded to buy them?


Regards,

Andy
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Old 13th January 2016, 12:40 AM   #14
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Default Too True

Hi Andy ,
You are right I made a mistake.
I thought it was a good idea at the time but time proves otherwise.
Cheers,
Garry
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Old 16th January 2016, 06:42 AM   #15
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Hi Garry,


Thanks for the clarification, Brystons may measure well but don't sound all that well IMHO. That may be sacrilege considering they are Canadian as well as myself but the ultimate truth is not solely in measurement, or we wouldn't be holding tubes so close to our chest . The Bryston amps contain a loop within the gnfb loop, that darn op stage, complex and measures well, but just sounds simply not that alive!.


Colin
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Old 16th January 2016, 07:15 AM   #16
AKSA is offline AKSA  Australia
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Ah yeah Colin, you and I have been down this road together, haven't we?

You are the zero global feedback guy, I'm a bit half in and half out, as you know. The Maya (series II for you!) has about 26dB of global feedback but lots of nested feedback.

I admire the build quality and warranty for Bryston. It's the best in the business, and it is true the specs are very, very good. People need to figure out if this is their cup of tea; I'm strongly influenced by subjective listening, and this is very difficult to justify in the absence of hard measurements. I honestly believe that the ear is far more sensitivity than many accurate instruments in this comprehensive field.

Thank you Garry, great praise!

Cheers,

Hugh
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Old 16th January 2016, 08:50 AM   #17
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Hugh,

Of course, it's almost the agree to disagree scenario . A figuratively pick your poison. If audio weren't so subjective it would have been nailed during the slew rate and thd wars of the late 70's early 80's.


Colin
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Old 1st February 2016, 02:20 AM   #18
Bigun is offline Bigun  Canada
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....lots of nested feedback.
Did my TGM8 finally tempt you into using CFP
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Old 1st February 2016, 02:46 AM   #19
AKSA is offline AKSA  Australia
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Hi Gareth,

I use a CFP on the GK2, and on my Glass Harmony both in 1994 and the recent version I'm working on now. I like the CFP, generally, but not at the output stage. I love it in the Class A mode.

Your TGM8 is dang good, no question........

Cheers,

Hugh
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Old 17th February 2016, 08:49 PM   #20
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I'm really enjoying my new Maya. I think its sound is so pure and transparent.

Thanks Hugh
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