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BrianL 30th March 2002 05:15 PM

non-Pass amps youv'e built/heard
As a newcomer, I see lots of discussions regarding Nelson Pass'
designs, but frankly room heaters just won't do it for me when my long-term goal is to triamp an Ambisonic "surround" setup.
Might have been OK back in Seattle but I'd have to double my air conditioning here in the desert to be able to listen 8 months/year.

For years I've been curious if anyone has built and/or listened to the following amps:

1. Robert R. Cordell's design presented in an AES paper and IR app-note. Used Hawksford's error-correcting output stage.

2. Mark Alexander's current-feedback amp, either IGBT or MOSFET version.

3. "Clone" of the incredibly expensive/complicated Halcro amp

4. Any of Doug Self's designs -- the ultimate "objectivist" himself.

I'm looking for comments based on actual experiences.

mrfeedback 2nd April 2002 05:37 PM

Me too.


FBJ 2nd April 2002 07:01 PM

I have built 3 Borbely 60watt and 2 servo 100watt mosfet amps (class AB output stages) from past TAA issuses and I still use them (not all at once). The sounds is great and I really enjoy them but I brought a newer amp kit of Mr. Borbely, the Mini-Servo amp (class A) from Welbrone Labs, haven't put it in the kind of chassis I want yet but I have listened to it and yes I think it is better than his older designs.

capslock 2nd April 2002 09:26 PM


do you have a reference or link for Cordell's paper? Older AES papers have turned out to be hard to get here...

The ultimate objectivist has a couple of "unclean" explanations in his webpages. Also, while I find his op amp measurements intriguing and sometimes astonishing, I thing he could at least state the feedback resistor values he was using. If they are too great, they can significantly degrade distortion performance, particulaly with FETs.


sonnya 2nd April 2002 10:04 PM

He also compare opamps in noninverting mode even when manufactures say they perfom a lot better(OP275 from AD) in inverting or with a balanced low resistance (<2k) feedback network.
I think he have maybe used the same feedback network for them all?
When a inverting test was done you would probobly see another result?


HarryHaller 2nd April 2002 10:48 PM

Best sounding amps
2 Attachment(s)
Easily one of the best I have heard is the McCormack DNA-225.
Steve McCormack has been designing forever and is one of the most under rated designers out there. Toshiba C3281/A1302 outputs, Toshiba jfets, Hitachi mosfets, Caddock resistors, and excellent layout and power supply decoupling. Amazing without insane pricing of some of the competition. I could live with it and couldn't think of too much to hotrod in it.


HarryHaller 2nd April 2002 10:52 PM

More DNA225
2 Attachment(s)
Another picture and website m/index1.html

pmkap 2nd April 2002 11:47 PM

The best kit amps I've heard is Hugh Dean's AKSA. Its sorta like Doug Self's objectivist designs, extended beta output bipolars (like Steve McCormack's), speedup caps... meets the curmudgeonly Hugh Dean, no current mirrors, current sources, for objective preferences.
I took my Llanno monoblocs over for a 'shootout' and was blown away. No contest. They reminded me (given my poor auditory memory) of the Bel 1001s. I ordered the AKSA kitsets...

PassFan 3rd April 2002 02:42 AM

Harry, the last link you gave is skrewed up. You know how lazy people are.:D

BrianL 3rd April 2002 04:10 AM


The Cordell reference is:

Cordell, Robert R.
A MOSFET Power Amplifier with Error Correction
Journal of the Audio Engineering Society
Vol 32, No 1/2; 1984 January/February

The same design appeared with a slightly different text
in an application not in an old International Rectifier databook,
circa mid to late 80s (?)

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