non-Pass amps youv'e built/heard


Paid Member
2002-03-29 5:19 am
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.


2002-03-12 7:46 am
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.

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.

Best sounding amps

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.



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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...


Paid Member
2002-03-29 5:19 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 (?)
aksa info

pmkap said:
The best kit amps I've heard is Hugh Dean's AKSA.
Does anybody else have more theory/objective/subjective opinions of this kit amplifier, and tweaks, or any other suitable types ......... Anybody ? ....... Please ! .........

Anyway Hello All, especially Harry, Bernhard, Sonny, Eric von Deutche, and the other intelligent, knowledgeable. and other fellow experienced contributors that I missed - I'm looking for some considered technical and subjective advice.

I'm looking for a MUSICALLY DECENT SOUNDING (for loud, good old rock and modern youngsters stuff) reasonably simple amplifier module design that is economical, quick, easy, reliable, sonic performance consistent and idiot proof for the application of a/several SERIOUS active multi-way, multi-driver, multi-cabinet loudspeaker system/s for hireable Function Room, Hall and Home Party DJ and maybe some Live stage PA usage. Phew.

I figure on reproducing the modern recently re-invented Line-Array way, only downsized a bit so that multiple cabinets can fit into standard motor vehicles.
I envisage each multi-active cabinet to deliver several hundred watts total into multiple paralelled drivers clean, so 4 ohm (or 2.6 ohm or even 2 ohm) loaded sonic performance is important. Likely 200W or so into 3 or 4 paralleled bass drivers for lows. Probably all drivers will be impedence compensated - I think this is mandatory and the cost is not too great.

Stacking (or hanging) multiple LA cabinets improves their cylindrical directional characteristic and their overall efficiency, and because they will be active and modular, total system max power can be easily definable.
My desired commercial angle is the bigger budget the hirer has, the more cabinets and the bigger, better and NICELY louder system they can get = The whole point of this eventually costlyish exercise is to result in a much wanted hireable REALLY good sounding replay rig, that on every old, or new, top 40 tracks gets the whole crowd up dancing and enjoying it.

I have spent a lot of time around a lot of gear from DJ to live pub/club to seriously big international touring shows.
Usually the first two sounds suck. The big unlimited budget pro tour stuff is GOOD, damm good - for example an AC/DC show stage system/pa system afternoon sound check can be quite interestingly educational ! .....ditto .... U2.... EJ/BJ.... MJ.... ND.... MC.... GE.... Kiss.... &etc &etc....
I also fix a lot of this pro stuff in my usually quieter repairs shop.

I'm also looking for any relevant pointers and opinions and experience and advice regarding sort of cost no object (within limits) longish line send and recieve stages, and LL crossovers / filters / eq / tone / dynamic range / limiting / enhancement etc.

I'm all ears ! Please feel free to giveyour advice freely.

Regards and thanks in advance, Eric.

I wish! My local dealer wasn't happy about me photographing the amp while he was on vacation and I was helping to mind the store! I believe it is a Toshiba Jfet diffamp front end with cascode and a Hitachi Mosfet gain stage. Maybe the mysterious Mr. S. N. in North Corolina would know. When it comes to amp design, he knows everything and I know the rest. Mr. S.N. are you reading this. I actually don't like to rip off commercial designs since it is the result of insane amounts of labor on the designers part to design it in the first place. I do pay close attention to part selection though! There are plenty of excellent DIY, amatuer, Pass, and Borbely designs to base a "guilt free" design on. An amazing amount of commercial designs are based on the work of Mr. P and Mr. B. The hard work and generousity of these two is unmatched in the audio world.