Hawksford output error correction circuit?

Jorge

Member
2001-04-30 7:32 pm
Brazil
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.
 
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.
 

Attachments

  • cordell.zip
    2.9 KB · Views: 909

Jorge

Member
2001-04-30 7:32 pm
Brazil
Hello, Andy

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...

:D
 

Attachments

  • hawksford basic.zip
    1.5 KB · Views: 823

Jorge

Member
2001-04-30 7:32 pm
Brazil
aparatusonitus

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/audio_lab/malcolmspubdocs/J3 Distortion correction PA.pdf
 
Hi Jorge,

I am familiar with Steven EC amp (as you can see from complementary diff. pair CCS), but Steven is quite exlicit about Etalon using EC output stage (not sure about Suplifier, tought). And Steven is for sure one of EE giant around here...Wish I could say same thing for myself one day, I've just started:D

boraomega,

You can uploud whatever you want at LTspice, just put model in spice directive card (press upper right botton .op and place a model in it, then OK, model will appear at working sheet)
 

Jorge

Member
2001-04-30 7:32 pm
Brazil
boraomega said:
Hello people!
Where did you find models-definitions for 2SC3281/2SA1302 or any other Japanese semi?! They are not coming with LTspiceSwitcher CAD III installation!

Here tou have it (from another post):

.MODEL 2SC3281 NPN( IS=10.000E-15 BF=155.65 VAF=100 IKF=9.2028 XTB=1.5 ISE=54.325E-15 NE=1.3056 BR=10.787 VAR=100 IKR=1.8561 ISC=106.69E-15 NC=1.6728 NK=.55624 RC=26.745E-3 CJE=2.0000E-12 CJC=534.41E-12 MJC=.33333 TF=8.0821E-9 XTF=3.1968 VTF=21.461E-3 ITF=169.59 TR=187.91E-9)

.MODEL 2SA1302 PNP( IS=21.479E-12 BF=136.48 VAF=100 IKF=19.980 ISE=21.504E-12 NE=1.3784 BR=329.48 VAR=100 IKR=19.980 ISC=4.3670E-9 NC=1.4264 NK=.72845 RC=93.301E-3 CJE=755.31E-12 MJE=.33333 CJC=1.1417E-9 MJC=.33333 TF=1.2802E-9 XTF=10 VTF=10 ITF=1 TR=10.000E-9)
 

Jorge

Member
2001-04-30 7:32 pm
Brazil
aparatusonitus

I did not say the Etalon doesn't have any form of EC - I've said it doesn't have a Hawksford one (the output transistors are not in the EC loop).

AFAIK the Hawksford EC is the better circuit around, some people even wonder why it wasn't patented.

It's perfectly possible to modify the Etalon for an Hawksford EC topology.
 
Re: aparatusonitus

Jorge said:
I did not say the Etalon doesn't have any form of EC - I've said it doesn't have a Hawksford one (the output transistors are not in the EC loop).

Oh, I see now, sorry about that.

Jorge [/i]AFAIK the Hawksford EC is the better circuit around said:
It's perfectly possible to modify the Etalon for an Hawksford EC topology. [/B]

I'll try ( or anyone of you guys, I won't mind) and report back.

OT- Tonight at Split (my hometown) are playing Brasil vs Croatia soccer team, yammi.
 
Jorge,

I think te etalon has an error correction loop. The two 560 ohm resistors are connected to the output at the same spot as the dc loop.

What is different is that there is no R1 ( numbering from the Hawksford paper) and indeed no emitter follower at all. My guess is that the 6k8 restor defining the impediance at the vas collector serves the same function. The tandberg amp has a similar output circuit.