John Curl's Blowtorch preamplifier part II - Page 2821 - diyAudio
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Old 16th October 2012, 09:12 PM   #28201
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Back in 1975-6, I designed circuits for him. We went to Paris together from Montreux, Suisse to Paris in his Porsche 356. (Hard on the ears and the body!) to work at a studio.
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Old 16th October 2012, 09:24 PM   #28202
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Quote:
Originally Posted by PMA View Post
Very fast bipolar CFA designed for high PSRR at high frequencies may sound great, I agree. Tough competition to JFET miracles
on the pit lane with very fast (HEX/MOS)FET CFA designed for high PSRR at high frequencies...

Ultra compact and nice resuming, PMA.
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Old 17th October 2012, 02:08 AM   #28203
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Thumbs up CFA

CFA
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Old 17th October 2012, 07:49 AM   #28204
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My dilemma with servos are what caps to use in them? Are they contributing as much colouration as a series DC blocking cap? I often use 220n - 2u2 PP caps for my servos but to make these caps a "super" cap, cost a small fortune and takes up huse amounts of PCB space....


/S

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Originally Posted by john curl View Post
If you want the 'hand carved by virgins' sound, I should think that you must go to the Mundorf or similar cap. In fact, in a project that I am associated with, the first cap, a typical mylar, was changed to Rel, with great subjective improvement, then 'Mundorf with even a further subjective improvement. I recommended a SERVO to remove the cap completely.
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Old 17th October 2012, 02:09 PM   #28205
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Originally Posted by staccatiss View Post
My dilemma with servos are what caps to use in them? Are they contributing as much colouration as a series DC blocking cap? I often use 220n - 2u2 PP caps for my servos but to make these caps a "super" cap, cost a small fortune and takes up huse amounts of PCB space....
If you use a Fet Op. Amp, the inverting input impedance is so high that you really don"t care about any inductance or resistance of the cap.

The cap can have only an influence at frequencies lower than the cutting frequency of the low pass filter.
Means far away from the audio range, as you can set this frequency very low.
Because the high impedance, you can use any polypro film cap, and concentrate on the quality of the op amp: Low noise, low drift and offset; unity gain stable.
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Old 17th October 2012, 02:17 PM   #28206
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Not to mention that, with a good design, paired and thermally coupled parts, you can design an amp with a drift and offset low enough that you can forget about-it.
And a clever protection circuit can protect-it against DC in the input, as well he can protect your speaker from amp failure.
I do not have any serial cap in all my home system.
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Old 17th October 2012, 02:34 PM   #28207
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Are you going to share your circuit 'secrets' with us, Esperado? '-)
On my part, I usually use a quality mylar cap for the servo, BUT I do make sure that the servo is operating well below the audio bandwidth. Servos become subjectively problematic if care is not taken to decouple them and to keep the bandwidth very low. Still, I am often reminded that better caps make better servos. It is most likely true.
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Old 17th October 2012, 03:40 PM   #28208
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Has anyone tried thermal feedback?
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Old 17th October 2012, 04:15 PM   #28209
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Quote:
Originally Posted by john curl View Post
Are you going to share your circuit 'secrets' with us, Esperado? '-)
On my part, I usually use a quality mylar cap for the servo, BUT I do make sure that the servo is operating well below the audio bandwidth. Servos become subjectively problematic if care is not taken to decouple them and to keep the bandwidth very low. Still, I am often reminded that better caps make better servos. It is most likely true.
Hi John,

See Section 8.4 on page 167 in my book for a description of using the DC servo integrator output for detecting DC offset for protection. See also page 335 under Loudspeaker Protection Circuits.

Cheers,
Bob
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Old 17th October 2012, 04:16 PM   #28210
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Good idea, Scott. Why don't you show us an example of how to do it?
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