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Old 1st November 2007, 09:35 AM   #1
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Default Would a Williamson sound better with a CCS tail in the driver?

I would like to ask if anyone has tried adding a negative rail and a CCS in the tail of the differential driver of a Williamson-style amp and, if so, whether it make any appreciable improvement to the sound.
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Old 1st November 2007, 11:05 AM   #2
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I've used a Solid State current source in this position, there are enough volts dropped across the cathode resistor for this so no negative rail is required. Listening showed an opening up of detail and an improvement in dynamics.

HTH

Chris
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Old 1st November 2007, 11:15 AM   #3
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Default Re: Would a Williamson sound better with a CCS tail in the driver?

Hi Ray_moth,

Quote:
Originally posted by ray_moth
I would like to ask if anyone has tried adding a negative rail and a CCS in the tail of the differential driver of a Williamson-style amp and, if so, whether it make any appreciable improvement to the sound.
It simply cannot make much of a (noticable) difference changing the driver stage more towards a differential amp operation by "lenghtening" the tail, because AC symmetry is excellent already due to the preceeding concertina stage.

There are several small tweaks possible on the Williamson that gain much more and better improvement (both measurable and soundwise) than giving the driver stage a CC sink at the cathodes.

Everbody eager to improve on the original Williamson first should carefully read and digest the arcticle "Improving the Williamson Amplifier" by Talbot M. Wright, Electronics World, 1961.

You can find scans of that article here.

Regards,

Tom

P.S.: In that article, don´t miss the additional small cap labeled C11 and think closely about its function - and what this in turn means regarding your question
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Old 1st November 2007, 03:59 PM   #4
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"No system made of optimal subsystems will be optimal".

The most of asymmetry is caused by output transformer.
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Old 2nd November 2007, 10:16 AM   #5
316a is offline 316a  England
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Quote:
Originally posted by Wavebourn
The most of asymmetry is caused by output transformer.
...not if the output transformer is specified as per the design . Split bobbin=good balance , the Partridge WWFB used in the design is excellent , almost faultless in fact

cheers

316a
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Old 2nd November 2007, 10:21 AM   #6
316a is offline 316a  England
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Default Re: Would a Williamson sound better with a CCS tail in the driver?

Quote:
Originally posted by ray_moth
I would like to ask if anyone has tried adding a negative rail and a CCS in the tail of the differential driver of a Williamson-style amp and, if so, whether it make any appreciable improvement to the sound.
It should do , to date I have never found a diff stage not benefitting from a high impedence tail . I have had very good results with 6SN7/6J5/7N7 with CCS loads for both the anode and the tail . For the top loads connect a high value resistor (2.2M etc) across the CCS and for the tail , use a cascode , adjust this in circuit for slightly higher current than that of the combined top loads

cheers

316a
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Old 2nd November 2007, 08:30 PM   #7
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Thanks for the responses. My thinking was that if the triodes in the 6SN7 are well-matched, there's no obvious reason why a CCS should help.
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Old 3rd November 2007, 07:06 AM   #8
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Quote:
Originally posted by ray_moth
My thinking was that if the triodes in the 6SN7 are well-matched, there's no obvious reason why a CCS should help.
Did you read the article I pointed at? Among other things, it shows that even matching/selecting of the 6SN7 voltage amp (driver) sections becomes uncritical when you rebias that stage as outlined in that article.

Regards,

Tom
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Old 3rd November 2007, 12:58 PM   #9
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Quote:
Did you read the article I pointed at?
Yes, I did read it and I didn't see anything about the balance of the driver stage becoming uncritical. I think I agree with his points about the various stages being under-biased, but even that seems to be controversial - I've asked about it before and received a mixture of opinions.

Two schools of thought seem to exist, namely, that
- a CCS is unnecessary in a differential stage with balanced inputs; or
- that a CCS improves the stage, giving better balance.

Either the problem is insoluble and both parties are guessing; or one of the parties is plain wrong; or, as I suspect, a CCS does help to overcome any imbalance in the gain.
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Old 3rd November 2007, 01:05 PM   #10
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Default Re: Re: Would a Williamson sound better with a CCS tail in the driver?

Quote:
Originally posted by 316a


It should do , to date I have never found a diff stage not benefitting from a high impedence tail . I have had very good results with 6SN7/6J5/7N7 with CCS loads for both the anode and the tail . For the top loads connect a high value resistor (2.2M etc) across the CCS and for the tail , use a cascode , adjust this in circuit for slightly higher current than that of the combined top loads

cheers

316a
I don't think that this can work properly. A diffamp with a CCS in the common cathode tail needs to have a changing current in the anodes. A CCS in the anodes cannot work IMHO. Thats against the principle of such a stage.

Regards, Simon
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