If you wondered how Halcro amps have such low distortion

[bcarso]

Ran across this while looking for something else:

http://www.patentstorm.us/patents/6600367-description.html

 

[JohnRoberts]

I think I recall a Cordell article in Audio Magazine (IIRC) describing a linearized mosfet output stage and Hawksford published lots of interesting stuff in AES Journal.

JR

 

[moamps]

I had wondered about the Cordell error correction circuit for quite a while until I decided to build it myself. :wink:

I used the Cordell circuit (see Bob Cordell's site for more info) for the output stage and then added my own tube/transformer input stage. Both the measurements and the listening tests I've done so far (as shown on my site) confirm that BC's error correction concept is a good and workable idea indeed. Moreover, I honestly think my concoction is definitely the best-sounding SS output amplifier I have built and heard so far. Disclaimer: I have no affiliation with Cordell Audio. Just a curious bugger. :grin:

Regards,
Milan

 

[JohnRoberts]

Thanks for the links.. Cordell's THD analyser was a nice piece of work too.

JR

 

[Guest]

[quote author="JohnRoberts"]I think I recall a Cordell article in Audio Magazine (IIRC) describing a linearized mosfet output stage and Hawksford published lots of interesting stuff in AES Journal.

JR[/quote]

Bob uses feedback tricks in his plain and straightforward opamp-type designs, while Williamson's and other's designs described in the article contain combination of a precision class A amplifier and a more powerful one feeding this one by a power. Indeed, it helps to reduce power consumption by class A amplifier, or make class D amplifier to sound better if to look from the different side, but it is not the best way to skin the cat. I've found a combination of A+C to be still effective while sounding better, if approximation of the resulting transfer function is made properly.
Here is the sample I made in mid 70'th:

 

[Guest]

Here was an improved design (3-step approximation, BJTs work up to 3A, FETS take the rest evapoirizing binding posts and an oscilloscope tip):

 

[JohnRoberts]

[quote author="Wavebourn"][quote author="JohnRoberts"]I think I recall a Cordell article in Audio Magazine (IIRC) describing a linearized mosfet output stage and Hawksford published lots of interesting stuff in AES Journal.

JR[/quote]

Bob uses feedback tricks in his plain and straightforward opamp-type designs, while Williamson's and other's designs described in the article contain combination of a precision class A amplifier and a more powerful one feeding this one by a power. Indeed, it helps to reduce power consumption by class A amplifier, or make class D amplifier to sound better if to look from the different side, but it is not the best way to skin the cat. I've found a combination of A+C to be still effective while sounding better, if approximation of the resulting transfer function is made properly.
Here is the sample I made in mid 70'th:

[/quote]

HUH?

The schematic you posted looks like it might be a crude quasi-complimentary output stage if you make the three lower power device into PNPs. However still not remotely like the Cordell MOSFET output stage's error correction/linearization topology (which was also class AB IIRC).

JR

 

[Guest]

[quote author="JohnRoberts"]

HUH?

The schematic you posted looks like it might be a crude quasi-complimentary output stage if you make the three lower power device into PNPs. However still not remotely like the Cordell MOSFET output stage's error correction/linearization topology (which was also class AB IIRC).
[/quote]

1. Bob Cordell's design has nothing to do with A+D approach described in the patent.
2. What I've posted, is the similar approach, but instead of supplying floating power for class A, class C works on the load directly (class A works on the load through R1). It is simplier, but sounds better.
And indeed, bottom transistors are PNP. It is class C complementary voltage follower. I have to stress that it has to work in class C, not in class B! It sounds better when a diode between bases is removed, but consumes more power. The idea is, crossover points must be on higher possible output power. No crossover point close to zero power must be allowed for the audio amplifier!!!

Here is my "Tango" pair I used for a later 3-step approximation:

Walker used similar approach in his "Current Dumping Audio Amplifier". It used 2-step approximation, like my first Swinik.

And in conclusion, all this means dances around old good class A amp trying to breed it with something else in order to save some electricity and to patent everything that is not covered yet by asphalt...

 

[Samuel Groner]

Just for the records all (as far as I know) power amplifier patents by Bruce Halcro Candy:
* US 5-892-398
* US 6-052-027
* US 6-600-367 B2
* US 6-798-285 B2

Many interesting ideas and worth a read if you like excentric (but high-performance) design!

Samuel

 

[JohnRoberts]

That last one still hurts my head...

JR