John Curl's Blowtorch preamplifier

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hitsware

hitsware

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Joined 2002
miller-music.one/
>It has already 2 negative feedbacks:

>parallel by voltage through 1M resistor)

Yes but not much.

>and serial by current (1K in source).

I don't consider degenerative feedback to be negative.
The 1 K makes the circuit Av predictable and because of
the resultant *10 open loop Av makes the 1M have little
affect (AC wise)

>I would suggest one more:
>positive feedback by voltage.
>Disconnect 470 uF capacitor from
>ground and connect it to output.

Thank you Mr. Bootstrap :)

>10 uF is odd, big green LED's dynamic resistance is smaller >anyway.

Better safe than sorry.



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Hybrid amplifiers are amplifiers that combine errors of current amplification by transistors with errors of voltage amplification by tubes
Anatoliy Lisovskiy
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Wavebourn@yahoo.com
http://Wavebourn.com


Last edited by Wavebourn on 09-27-2008 at 04:52 AM
IP: 76.239.177.xxx
Today, at 04:48 AM Quote:
 
Wavebourn

Wavebourn

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Joined 2006
wavebourn.com
hitsware said:

I don't consider degenerative feedback to be negative.
The 1 K makes the circuit Av predictable and because of
the resultant *10 open loop Av makes the 1M have little
affect (AC wise)
Click to expand...


Don't matter how your call it: generative, or degenerative, or regenerative, I would prefer to shunt it by cap, but to add one resistor in series with input: feedback and input will go to the same point. An audiophile's sweet dream...
 
EUVL

EUVL

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Joined 2003
xen-audio.com
Please, please gentlemen, don't do it here and read my post carefully -- no global feedback, I wrote . I knew it was going to happen and phrased it deliberately, and did not use the word negative (or positive, degenerative, .... , and whatever else).

Please find one of those old threads to discuss the definition. I am sure everyone knows what I was intending to say.


Many thanks for your corporation,
Patrick
 
EUVL

EUVL

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Joined 2003
xen-audio.com
John,

> I have never made one of those. It would be interesting.

If you were to make one of these, would you still use your beloved complementary, folded-cascode, JFET frontend as in the Blowtorch, or would you think that it might (not) give enough swing which retaining low enough distortion ?

Or would you "copy" Charles and use MOSFETs in the diff pair instead ?


Regards,
Patrick
 
john curl

john curl

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Joined 2003
Mosfets or jfets, they both work. jfets are better, however, for input stages.
The design put forth, while probably OK sounding is not what I had in mind. My first independent design, from 40 years ago, was more sophisticated than that design. Full complementary balance is a must, for me, and has been since 1967.
 
EUVL

EUVL

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Joined 2003
xen-audio.com
Assume at least 100W rms output on 8 ohm, that means at least 40V output across the speakers, or +/-20V balanced.

Unless the load resistor of a "blowtorch" frontend is increased substantially from 1k to say 10k, I was worried that the JFETs would be struggling to deliver the current with the folded cascode.

And if we were to use 10k load resistor for the frontend, we might be compromising bandwidth for the follower ??


Patrick
 
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