John Curl's Blowtorch preamplifier part II - Page 2433

john curl · 9th July 2012, 11:59 PM

Try with 100dB gain.

Wavebourn · 12:02 AM

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.

RNMarsh · 02:08 AM

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

john curl · 10th July 2012, 02:10 AM

Go for it, everyone. To heck with servos. '-)

hitsware · 10th July 2012, 03:14 AM

Quote:

Originally Posted by john curl

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

homemodder · 10th July 2012, 06:17 AM

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.

bcarso · 10th July 2012, 06:42 AM

Quote:

Originally Posted by homemodder

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.

homemodder · 10th July 2012, 06:54 AM

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.

john curl · 10th July 2012, 06:59 AM

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.

homemodder · 10th July 2012, 07:23 AM

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.

10th July 2012, 12:00 AM	#24322
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	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. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative. Last edited by Wavebourn; 10th July 2012 at 12:02 AM.

10th July 2012, 02:03 AM	#24323
RNMarsh diyAudio Member Join Date: May 2012 Location: 2457 Cascade Trail; Cool, CA. 95614	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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9th July 2012, 11:59 PM	#24321
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Try with 100dB gain.

10th July 2012, 02:10 AM	#24324
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Go for it, everyone. To heck with servos. '-)

10th July 2012, 06:17 AM	#24326
homemodder Account disabled at member's request Join Date: May 2006	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.

10th July 2012, 06:54 AM	#24328
homemodder Account disabled at member's request Join Date: May 2006	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.

10th July 2012, 06:59 AM	#24329
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	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.

10th July 2012, 07:23 AM	#24330
homemodder Account disabled at member's request Join Date: May 2006	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.