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PMA 6th September 2004 09:23 PM

New error correction amp
 
2 Attachment(s)
Inspired by NP in a "Hawksford" thread, I have developed a new error correction circuit. The schematic of working amp is attached. I have been testing it for more than a month (both measuring and listening) and results seem to be promising.

Upupa Epops 6th September 2004 11:05 PM

Guys, this amp sound very well ;) , you have my recomendation :cool: .

lumanauw 7th September 2004 02:54 AM

I really wanted to understand how an "Error Correction" works. It gives good sound (even we do not listen in Prague).
I havent understand about Hawksford type, then PMA gives another topology.
This topology has no bias adjustment. In the prototype, the swing is limited to opamp's supply?
Which topology has the lowest voltage rail inefficiency? Etalon type has R to ground to set the input impedance.

blu_line 7th September 2004 06:25 AM

please could you explain in more detail.
Already checked your website but found no article :D


grtz

Simon

thanh 7th September 2004 06:43 AM

Quote:

Originally posted by blu_line
please could you explain in more detail.
Already checked your website but found no article :D


grtz

Simon

yes!


:D

Nelson Pass 7th September 2004 04:18 PM

That's a very cool circuit. :cool:

I suppose you could consider dropping diodes 1 - 4.

PMA 7th September 2004 04:54 PM

Quote:

Originally posted by Nelson Pass


I suppose you could consider dropping diodes 1 - 4.

Most probably yes, provided change of resistor values, especially R7. These diodes play interesting role in maintaining thermal stability of the circuit (they are located on PCB, not heatsink).

Anyway - good idea ;) (again ;) ), as I have couple of spare PCB's and it is possible to make direct comparison.

Eva 7th September 2004 05:33 PM

Ummm...

Sorry if this sounds crude but in this schematic I see just an exotic error amplifier with high open loop gain that uses classic feedback to linearize the output transfer characteristic dividing the error by the feedback amount

So using a standard LTP and VAS would do exactly the same job I think, but in a less fashionable way

Any amplifier with global feedback is just an 'error correction' amplifier

Upupa Epops 7th September 2004 06:52 PM

Eva, pleas read little bit more about error correction at Hawksford's pages ;) - maybe after that you will talk different :cool: .

PMA 7th September 2004 07:20 PM

2 Attachment(s)
Quote:

Originally posted by Eva
Ummm...

Sorry if this sounds crude but in this schematic I see just an exotic error amplifier with high open loop gain that uses classic feedback to linearize the output transfer characteristic dividing the error by the feedback amount

So using a standard LTP and VAS would do exactly the same job I think, but in a less fashionable way

Any amplifier with global feedback is just an 'error correction' amplifier

Maybe not exactly. This is a Hawksford-like error correction of the crossover region and it reduces distortion of the output stage by amount of 40dB approx. (without opamp, only the error correction of the output stage). The opamp is used to drive the prototype of the output stage, just for evaluation reason, of course it reduces distortion even more. The AD844 is a high speed CFB opamp (2kV/us) capable to source/sink some 60-80mA. It has to drive the output stage that might be considered as 1.6kOhm//1nF load. Various VFB opamps were tried with unsatisfactory sonic result, leaving trace of the typical opamp sound. The AD844 does not and it also measures in this circuit very well.

The circuit in principle was invented by Nelson and was inspired by Nelson's hand drawn image (see attachement). It is an ingenious mix of negative error-correction feedback (left half) and smoothing positive feedback (right half). The right half is responsible for smooth turn-on and turn-off of the output devices, as can be seen on my web page (measurement well corresponds to simulated image).


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