Duncan's amp Mosfet Regulator

[josh777]

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 Is it largely thought that this design is outdated?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.

 

[SY]

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.

 

[jackinnj]

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:

 

[jackinnj]

Here's the modified circuit -- should look familiar. I set the current to 10mA on the CCS:

 

[jackinnj]

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.

 

[aparatusonitus]

Here's the modified circuit -- should look familiar. I set the current to 10mA on the CCS:

Q5 is up side down...

 

[jackinnj]

Q5 is up side down...

You're right -- it is, however, wired correctly for the tests.

 

[Ketje]

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

 

[PRR]

> thought that this design is outdated?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.

 

[jackinnj]

Possible, but there is still something rotten in (forgotten where ) and also in this schematic .
Mona

Q5 is flipped.

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.

 

[Ketje]

Q5 is flipped.

Look again, the current household doesn't add up
Mona