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Old 18th October 2006, 02:46 PM   #1
prorms is offline prorms  United States
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Default who s got the best schematic?

who has the best schematic to build a 100w to 1000w
iam just wondering wich is the best power amp to build???
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Old 18th October 2006, 02:53 PM   #2
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Best for what? Ease of build? Cheapness? Sound? Measured performance?

One mans best is another mans rubbish.
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Old 18th October 2006, 05:06 PM   #3
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I have one for the accomplished enthusiast. I have taken influences from W. Marshall Leach and G. Randy Slone and would be delighted to elaborate. For the moment; it can be described thus:

Quad-symmetry high dynamic range cascode diff-amp; wide-band cascode push-pull VA stage; Class-A EF buffer with 'transient' feedback; Class AB/B lateral MOSFET output with audio+ feedback; Symmetrical foldback current limiting...

130W->8ohm; <0.03%THD
200W->4ohm; <?THD
300W->2ohm; <?THD

The only way to describe it is that it sounds exactly like what you are listening to (on good speakers). I can't get enough of it. If I am sure a person wishes to build it for his or her own enjoyment, I will gladly provide the schematic via email.

*edit:*
Incidentally, I also have circuit boards and can deliver at cost (via Paypal) of boards plus ups shipping in a couple-week lead time (I don't stock them at present).

*edit#2:*
By the way, I wholesomely challenge the rubbish-sensitive audiophile to give my amplifier a listen along with their favorite music at any time.
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Old 18th October 2006, 05:27 PM   #4
peufeu is offline peufeu  France
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I'm interested
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Old 18th October 2006, 07:15 PM   #5
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Hello Acoustixman,

yes I am interested also.

Have you been able to determine the level of each harmonic component of distortion, even if just from simulation rather than measurement, say for 1kHz 1W output? (I'm just wondering which harmonics are the greatest contributors to the THD figure.)

cheers,
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Old 18th October 2006, 09:11 PM   #6
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What is " audio+ feedback " ? BTW, 0.03 % of distortion is really " amazing " value - with such complicated circuit...
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Old 18th October 2006, 09:40 PM   #7
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Pavel
what's wrong with having 0.03% distortion at 130W?
If it goes down with decreasing power, then it can still sound very good.
Many of amps measuring very low THD at 1kHz at near full power have high distortion at lower powers and higher frequencies.
Single THD number says nothing.
Even your 100W amp will have 10% THD when "forced" to produce 110W.
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Old 18th October 2006, 11:17 PM   #8
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Quote:
Originally posted by cascoder
Hello Acoustixman,

yes I am interested also.

Have you been able to determine the level of each harmonic component of distortion, even if just from simulation rather than measurement, say for 1kHz 1W output? (I'm just wondering which harmonics are the greatest contributors to the THD figure.)

cheers,

Quote:
Originally posted by Upupa Epops
What is " audio+ feedback " ? BTW, 0.03 % of distortion is really " amazing " value - with such complicated circuit...

Quote:
Originally posted by darkfenriz
Pavel
what's wrong with having 0.03% distortion at 130W?
If it goes down with decreasing power, then it can still sound very good.
Many of amps measuring very low THD at 1kHz at near full power have high distortion at lower powers and higher frequencies.
Single THD number says nothing.
Even your 100W amp will have 10% THD when "forced" to produce 110W.

Thank you for the interest. I wonder about posting the design in the open? I feel more comfortable emailing the schematic to those who would build one or two, if anyone would like.

Cascoder: I DIG the handle. I am a fairly faithful cascoder, design wise, ever since I realized what it meant. Surely I'm pleased to make your acquaintance.

Good question regarding distortion. I don't know. The distortion analyzer in use (on borrowed time at local repair shop) was strictly Total HD measurement; I have no actual knowledge of spectra nor individual harmonic coefficients. I apologize. I am a bit of a subjectivist; though not AGAINST or ABOVE objectivism, mostly just under-budgeted. I have access to a 100MHz Tektronix scope with FFT function but the noise/baseline with the function generator was indistinguishable from the amplifier output when lightly loaded, so to be realistic I could only guess the harmonic content.

Upupa Epops: As darkfenriz notes and cascoder alludes, the THD is really not a good benchmark. I was shocked to see that it had any measured distortion AT ALL after having listened to it (makes me think mostly even order). I can't really call it complicated, having reviewed it and improved upon it for months now. I'll admit to 25 transistors and 22 diodes per channel (including protection), a total of 64 pn junctions, 2 N-channels, and 2 P-channels, but they're so dutiful to the cause! It runs extremely cool, and is extremely immune to transient-slewing distortion. It is definitely more like Nirvana than ZEN.

*edit*: forgot to comment on "audio+ feedback". I'm referring to the output being sampled by a low-pass filter for the inverting input (to generate error signal) and the predriver being sampled by a high-pass filter. They have a crossover point at approximately 120kHz, and where audio means 20Hz-20kHz, I'm using audio+ to mean 20Hz-120Hz (actually about 5Hz to 120Hz). The HF feedback beyond this handles square wave artifacts and such and preempts the phase margin at the output. Keeps it stable as a table.
*/edit*

darkfenriz: I agree with my entire heart. Let's just listen happily!

Sounds like some people might like to try this circuit out. I wish there were some way to offer a demonstration, but obviously it needs to be the last powered device in a short component chain to truly appreciate it. I would only ask for credit if you would like to build it, copy it or share it.

...
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Old 18th October 2006, 11:29 PM   #9
suzyj is offline suzyj  Australia-Aboriginal
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Default Re: who s got the best schematic?

Quote:
Originally posted by seanmacss
who has the best schematic to build a 100w to 1000w
iam just wondering wich is the best power amp to build???
The "best" amp for me probably isn't the best one for you. My best amp is David Tilbrook's AEM6000 design, published in Australian Electronics Monthly in 1987. It uses a differential input stage with matched JFET pair and bipolar cascode, and a fully symmetric voltage amp, with Hitachi lateral MOSFETs.

It's a wonderfully complicated, fast amp, with impressive performance. I've built a tweaked variant with a 2 layer 4oz plate-through board, with mainly SMD parts except for the big power stuff, and achieved 0.0013% THD+N at 1KHz and 100W into 8 Ohms.

Click the image to open in full size.

Even better than that, it sounds fantastic. Beautiful clarity. Stay well away if you like your music warm and distorted though.

A writeup can be found at http://www.littlefishbicycles.com/poweramp/index.html . Please bear in mind that it's a (mostly finished) work in progress, and still being updated.

Cheers,

Suzy
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Old 19th October 2006, 12:03 AM   #10
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Suzy:

Nice work! I have yet do do most of this sort of work. I can't break away from my listening room long enough to make this nice of a write-up!

It looks like a good day at the dragstrip... Somebody's going to have to build and hear both of our amps...

*edit:* removed a question that had been answered already.
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