Hawksford output error correction circuit?

[Jorge]

Hello,

I've been simulating his Distortion Correction in Audio PowerAmplifiers circuit as presented in fig. 5 of the paper.

Well, it simply won't reduce distortion! (but does lower output impedance).

Any clues?

BTW, I believe the circuit is wrong - the collector of T2 should be connected to the base of T4 and not to -Vc as drawn.

Thanks for any clues.

[andy_c]

Hi Jorge,

You are right. Looks like there is an error in his schematic. T2 should be a PNP with collector connected to the base of T4, and there should also be some emitter degeneration in T2 and T1. I've attached an LTSpice sim of Cordell's version of the Hawksford error correction from his AES article. Looks like I was playing around with the supply voltages, so they don't match up. If you need this article, just shoot me an email at my ISP.

[Jorge]

Thanks for Cordell's circuit!

After my posting I went back to LTS and found what was wrong - too much distortion in the follower pair driving the output devices!

Went to a CFP and now it works; made some changes so I could change just one resistor when running sims.
I tested with driving source impedance from 1K to 10k; the balance equation does not hold for high driving impedance (probably due to the input impedance of the following stages affecting it).

I was able to reduce distortin by some 20dB.
Not bad at all...

[aparatusonitus]

Hi,

I've also been simulating two circuit with EC output stage, an Etalon Integra and Ultimate Suplifier (well, half of it). No matter what I do, I could't find a solution for severe distortion at output stage. Maybe you guys could take a look and suggest something?

[aparatusonitus]

...and Ultimate Suplifier

[Jorge]

Looking at the circuits you've posted, there's no error correction circuit as it's done by the Hawksford topology.

See my posting above - Hawksford basic - in which the bias pair gets signals both from the driver pair AND the output stage.
So it's an error correction comparing the driver signal with the output stage signal to generate the correction.
None of the circuits you've posted do that.

Get Hawksford paper here:

http://www.essex.ac.uk/ese/research/...ction%20PA.pdf

[thanh]

Hi Jorge ! I can't view file .asc . Can you post your schematic in jpg type ?

[aparatusonitus]

Hi Jorge,

Please, take a look here http://www.diyaudio.com/forums/showt...470#post380470

and here http://www.suplifier.nl/ Ad C) #7

Thanh,

To be able to wie acs. file, please download LTSwitcherCad simulation program, it's free!

http://www.linear.com/designtools/so...gistration.jsp

[Jorge]

I've looked at your links.

This one has a Hawksford based EC circuit:

http://www.diyaudio.com/forums/showt...446#post330446

(many broken links - for instance Pavel's)

But Etalon and Suplifier doesn't have it.

And when the VAS has low distortion Hawlsford'st do makes wonders!

[Jorge]

Yes, get LTSpice - the best free SPICE on the NET!

If you still can't open it, pls let me know and I will post a .JPG image.