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Old 10th November 2008, 07:15 AM   #41
Mooly is offline Mooly  United Kingdom
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Hi Nico,
I can see your getting some stick over all this but you can't leave us all dangling.
The figures do sound almost to good to be true -- do you have a zobel network on the output.
To slew that kind of voltage across even a few nano farads will cause huge currents, even the on resistance of laterals if they could be switched instantaneously would be a limiting factor.
Where in the amp are you making this measurement ?
Maybe you have developed something a bit radical, a different topology but you can't just leave it like this.
Even a slew rate of 1/10 your figure is pretty amazing.

A few clues maybe
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Old 10th November 2008, 09:00 AM   #42
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Quote:
Originally posted by Mooly
Even a slew rate of 1/10 your figure is pretty amazing.
Now you are being funny, the rise time of 30W at 580V/uS is funnier though.
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Old 10th November 2008, 09:04 AM   #43
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Default Re: Fast Class A Amp

Quote:
Originally posted by Nico Ras
I HAVE FOUND THAT A FAST AMP PERFORMS BETTER THAN A SLOW AMP.

THIS LITTLE 30 WATT CLASS A THAT I AM DESIGNING FOR SOMEONE HAS A SLEW RATE OF 580V/uS AND THERE IS NO RINGING OR OVERSHOOT, JUST A NICE SMOOTH-OVER.

THE FREQUENCY SELECTED WAS 250kHZ. THE AMPLIFIER BAND WIDTH IS CURRENTLY LIMITED 0.1 HZ TO 7.4 MHZ.(-1dB)

SOUND IS CRISP AND VERY CLEAR WITH INCREDIBLE DETAIL. THD AT FULL POWER AND 100Khz IS BELOW THE PROVERBIAL 0.0008%. THE THD AT 1 MHZ 0.003%. AND AT 10 HZ 0.0002%. aT 1 KHZ IT IS 0.000012%

TWO TONES 19KHZ AND 20 KHZ GIVES INTERMODULATION PEAKING AT -134 AND -138 DBC, JUST BELOW THE NOISE.

I AM USING FOUR PAIRS OF 2SK1058 AND 2SJ162

I WAS TASKED TO MAKE THE ULTIMATE AMPLIFIER, IT Makes my toenails curl when listening to Diana Kral.

ISTHERE MORE ISSUES THAT I SHOULD CONSIDER. BESIDES GROUP DELAY, WHICH IS JUST ABOUT 0.138 DEGREES OVER THE 0 - 200 KHZ RANGE.
COMMENT WELCOME.
Nico,

I can think of a few things, but they are more related to how the
amp will perform in a real world environment.

- Ability to drive difficult loads, say 1 or 2 ohms, but obviously within
the OP stages current capability.

- Composure when driving capacitive loads. The usual square wave
into 1uF / 8ohm load.

- Ability to preserve linearity when driven from a higher source
impedance, say 10 or 12k representative of a passive pre amp
for example. A lot of designs will perform significantly worse
when driven from source Z's much higher than a few hundred ohms
due to IP stage CM distortion and capacitance modulation.

I'm assuming from your ultra low 1MHz distortion that it should
do well in the latter, but it's worth checking.

Good luck with the venture.

Terry
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Old 10th November 2008, 09:43 AM   #44
syn08 is offline syn08  Canada
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Quote:
Originally posted by fab
"Into 4 ohms I was able to get about 250 watts from a single channel!..."
...at best, for a couple of minutes. Unless you are using some sort of special cooling that would help dissipate 50-60W average power per device. Not realistic for 2SK1058/2SJ162 plastic case, you would need to keep the case temperature to max 60-70 degrees. Very large heatsink, and probably forced cooling, certainly way more expensive than throwing another 1-2 pairs of output devices.

And that's before any SOA considerations under reactive loads.

And that's before any considerations regarding the claimed performance (0.005% IMD) in a Miller compensated single pole design.
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Old 10th November 2008, 11:03 AM   #45
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Quote:
Originally posted by darkfenriz
a genius or a clown.
D Martin ?
(i just love puzzles)
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Old 10th November 2008, 11:10 AM   #46
Mooly is offline Mooly  United Kingdom
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Quote:
Originally posted by jacco vermeulen


Now you are being funny, the rise time of 30W at 580V/uS is funnier though.
I don't know who's worse you or Lumba
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Old 10th November 2008, 11:35 AM   #47
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Mooly,
actually, I forgot about Jacco. He should be considered worse with a safe margin.
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Old 10th November 2008, 06:54 PM   #48
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Default Re: Re: Fast Class A Amp

Quote:
Originally posted by Terry Demol


Nico,

I can think of a few things, but they are more related to how the
amp will perform in a real world environment.

- Ability to drive difficult loads, say 1 or 2 ohms, but obviously within
the OP stages current capability.

- Composure when driving capacitive loads. The usual square wave
into 1uF / 8ohm load.

- Ability to preserve linearity when driven from a higher source
impedance, say 10 or 12k representative of a passive pre amp
for example. A lot of designs will perform significantly worse
when driven from source Z's much higher than a few hundred ohms
due to IP stage CM distortion and capacitance modulation.

I'm assuming from your ultra low 1MHz distortion that it should
do well in the latter, but it's worth checking.

Good luck with the venture.

Terry
Thank you for your comments I will check your advice. The input impedance of the amp is low (2k Ohm) as it is driven from a known source.
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Old 10th November 2008, 07:03 PM   #49
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Quote:
Originally posted by syn08


...at best, for a couple of minutes. Unless you are using some sort of special cooling that would help dissipate 50-60W average power per device. Not realistic for 2SK1058/2SJ162 plastic case, you would need to keep the case temperature to max 60-70 degrees. Very large heatsink, and probably forced cooling, certainly way more expensive than throwing another 1-2 pairs of output devices.

And that's before any SOA considerations under reactive loads.

And that's before any considerations regarding the claimed performance (0.005% IMD) in a Miller compensated single pole design.
Hi syn08, it is not uncommon to measure high power under instantaneous conditions, few listen to sine wave for a continuous period. Square wave is even worse. Few class AB amps are designed to operate under 100% conditions continually.

However, as you rightly state SOA considerations are very important.
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Old 10th November 2008, 07:06 PM   #50
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Quote:
Originally posted by jacco vermeulen


D Martin ?
(i just love puzzles)
Hi Jacco,

I am guessing - a golf cart motor controller?

Nico
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