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Old 19th September 2009, 07:35 PM   #1
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Default Duncan's amp Mosfet Regulator

I can't find a post that references this design on the forums. For those that don't know it it's here: http://www.duncanamps.com/technical/mosfet.html . Is it largely thought that this design is outdated? Do people generally use the Maida type design now?

I'm planning to use these in a guitar amp, a variable one for the power amp, and a fixed one for the pre amp, if that makes any difference.

Any help is appreciated.
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Old 19th September 2009, 08:25 PM   #2
SY is offline SY  United States
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It's a good design (though I wonder about the stability and noise without an output cap). It's unlikely to be significantly better than a Maida, and a Maida is simpler and cheaper. The Maida isn't the be-all and end-all, but it's good performance for something that simple, and for stages with reasonable PSR, it's "good enough." As is the simple diff-amp regulator like Duncan's.
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Old 10th November 2014, 07:27 PM   #3
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I looked at the design with the thought of tweaking it up a bit. Replaced the CCS with DMOS. The improvement in PSRR under simulation is pretty interesting:
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Old 10th November 2014, 07:29 PM   #4
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Here's the modified circuit -- should look familiar. I set the current to 10mA on the CCS:
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Old 10th November 2014, 08:01 PM   #5
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Here's a comparison of the modifiedDuncan (green), Maida Regulator (magenta), the regulator which SY used in "His Majesty's Noise" (yellow), "Last Pass" (red) and the modified Duncan. The grey dotted line is the filtered output of the half-wave rectifier. Load was 17mA.
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Old 11th November 2014, 04:41 PM   #6
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Quote:
Originally Posted by jackinnj View Post
Here's the modified circuit -- should look familiar. I set the current to 10mA on the CCS:
Q5 is up side down...
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Old 12th November 2014, 01:55 AM   #7
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Quote:
Originally Posted by aparatusonitus View Post
Q5 is up side down...
You're right -- it is, however, wired correctly for the tests.
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Old 12th November 2014, 02:08 PM   #8
Ketje is offline Ketje  Belgium
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Originally Posted by jackinnj View Post
You're right -- it is, however, wired correctly for the tests.
Possible, but there is still something rotten in (forgotten where ) and also in this schematic .
Mona
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Old 15th November 2014, 03:14 AM   #9
PRR is offline PRR  United States
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> thought that this design is outdated?

For a guitar amp??

It is "too new". And as Duncan himself asks, it is "over the top".

The best (and most-copied) guitar amps were designed 60 years ago and use crude un-regulated supplies.
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Old 15th November 2014, 02:03 PM   #10
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Quote:
Originally Posted by Ketje View Post
Possible, but there is still something rotten in (forgotten where ) and also in this schematic .
Mona
Q5 is flipped.

Quote:
Originally Posted by PRR View Post
For a guitar amp??

It is "too new". And as Duncan himself asks, it is "over the top".

The best (and most-copied) guitar amps were designed 60 years ago and use crude un-regulated supplies.
Not necessarily for a guitar amp --

The point of the exercise is to compare with other regulators for phono-preamps such as the Maida, Last-PAS, Audio Research, HPHV etc.

When Duncan wrote his web-piece DN2540's probably weren't around. See Walt Jung's "Sources 101: Audio Current Regulator Tests for High Performance, Part 1" AX 2007 and archived on his website.

Last edited by jackinnj; 15th November 2014 at 02:07 PM.
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