John Curl's Blowtorch preamplifier part II - Page 2433 - diyAudio
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Old 9th July 2012, 11:59 PM   #24321
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Try with 100dB gain.
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Old 10th July 2012, 12:00 AM   #24322
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Everything that looks like aside looks sexy, if don't understand how it works.
No free cheese in this world exist, except in a mouse trap. All decisions have to be carefully weighted. I use servos in dynamic load of tubes on gyrators, but I don't add more of gain in the servo loop than is needed to stabilize working point. If additional amplifiers are used in servos, you have to remember that this amplifiers have own properties, like noises and distortions, and this noises and distortions are added to the amp that you stabilize using servo. Each and every particular case have to be weighted, what it brings more: harm, or goodness.

And of course the amp with even matched JFETs like in John's favorite topology would benefit from a servo that uses good opamp, but it does not mean that any amp would benefit equally.
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Last edited by Wavebourn; 10th July 2012 at 12:02 AM.
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Old 10th July 2012, 02:03 AM   #24323
RNMarsh is offline RNMarsh  United States
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When a servo does replace even a high quality capacitor, the sound often improves becuase of the low freq extention --- but not because of freqs but because of lowered group delay..... the audible group delay effect builds with multiple roll offs from various connected equipment if they all used coupling caps..... so go all direct coupled from source to speaker.
The little (Marsh) headphone amp talked about here (DIYAudio) and published in Linear Audio does not use a DC servo and is rock solid dc stable on the output vs temp and drift and has thd below -100db into 30 Ohms. No IC's used. I dont see why any other low gain line level stage shouldnt be able to do as well without servo. High dc gain circuits is another matter. -RNM

Last edited by RNMarsh; 10th July 2012 at 02:08 AM.
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Old 10th July 2012, 02:10 AM   #24324
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Go for it, everyone. To heck with servos. '-)
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Old 10th July 2012, 03:14 AM   #24325
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Quote:
Originally Posted by john curl View Post
Go for it, everyone. To heck with servos. '-)
Right !
Back to best capacitor / application
rated by :
DC voltage accross
AC voltage accross
AC current through
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Old 10th July 2012, 06:17 AM   #24326
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John, do you know how 2sk363 is noise wise, no details are supplied in datasheet. Ive found a supplier and looking to purchase large number for future edeavors, only line level and amps use.
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Old 10th July 2012, 06:42 AM   #24327
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Originally Posted by homemodder View Post
John, do you know how 2sk363 is noise wise, no details are supplied in datasheet. Ive found a supplier and looking to purchase large number for future edeavors, only line level and amps use.
Same chip as in the long-gone 2SK147. Make sure you buy enough for everyone

Very low noise. 700pV/rt Hz at 10mA, typical.
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Old 10th July 2012, 06:54 AM   #24328
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Thanks, I wasnt sure about this part on the flicker noise. Ive had agent look for them for the past year and a half and he has finally had some luck ,what should be enough till my retirement age.
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Old 10th July 2012, 06:59 AM   #24329
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Could be good, could be bad on flicker noise. That may be WHY they don't spec. it very well. I had a bad batch of 2SK147's about 20 years ago, had to send them back to the distributor. I would be careful.
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Old 10th July 2012, 07:23 AM   #24330
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Thats what Im afraid of, toshiba didnt specify noise on these for some reason if they are the same chip as 147. I hope they will ok for intended use, I just cant find reasonably prices Jfets with high gm anywhere else.
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