it's only audible when you turn the pot, if you let it rest it goes away.
I just put a ad843 duo in ic207 and a opa2132 in ic208 and the the issue is completely gone.
I just put a ad843 duo in ic207 and a opa2132 in ic208 and the the issue is completely gone.
so stay with FET-opamps otherwise refit of C279/C280 may help
btw what opamps were originally inside the preamp?
regards
btw what opamps were originally inside the preamp?
regards
maybe it has to do with C279/C280.
Originally there were jrc2043 (low noise jrc4558) opamps in this preamp
Originally there were jrc2043 (low noise jrc4558) opamps in this preamp
its related to the opamps bias current, the cap would stop it flowing through the pot
fet opamps have significant lower bias currents
4558 are evil...
fet opamps have significant lower bias currents
4558 are evil...
It is a german phrase telling you I accept my error and changed my mind.
I am convinced the crackling comes from dc and perhaps the blocking cap may help with that.
But I am not sure blaming the bias current anymore.
regards
I am convinced the crackling comes from dc and perhaps the blocking cap may help with that.
But I am not sure blaming the bias current anymore.
regards
I put C279/C280 back in, problem stays the same with the ad843's in ic208 position. Crackling in the first part of the wiper (near zero volume).
ok, I'm curious about this..
If you don't mind measuring dc across the caps and the pot?
Perhabs there is a difference between the AD and the OPA.
If you don't mind measuring dc across the caps and the pot?
Perhabs there is a difference between the AD and the OPA.
with 4 ad843's in the circuit I also have the issue, so it it is not the difeerence between the ad and opa. Hence if I iuse the ad843(ic207) and the OPA2132(ic208) I don't have the issue.
It happens only with AD843 in IC208.
It happens only with AD843 in IC208.
my mods:
IC201, 207, 208, 209 -> OPA2134
C261, 262, 217, 265, 279, 218, 280, 266, 215, 216, 281, 282 -> short
Jumper W112, 113, 110, 109 -> small choke
C617, 618 -> OSCON 68u/20V
C221~224 -> 0.47u
C607, 608 -> 470u/35v + .1u
C613 add .47u
BD601 -> 4 fast diodes
C601~604 -> 1000P
D602~603 -> ZD15V
here is photo:
http://picasaweb.google.com.tw/alphatec002/NAD1300
IC201, 207, 208, 209 -> OPA2134
C261, 262, 217, 265, 279, 218, 280, 266, 215, 216, 281, 282 -> short
Jumper W112, 113, 110, 109 -> small choke
C617, 618 -> OSCON 68u/20V
C221~224 -> 0.47u
C607, 608 -> 470u/35v + .1u
C613 add .47u
BD601 -> 4 fast diodes
C601~604 -> 1000P
D602~603 -> ZD15V
here is photo:
http://picasaweb.google.com.tw/alphatec002/NAD1300
http://www.diyaudio.com/forums/showthread.php?threadid=77540&highlight=
I followed sletol (see thread above) his mods, by using only ic207 and replaced the volume pot by a dact ct2 attenuator.
I followed sletol (see thread above) his mods, by using only ic207 and replaced the volume pot by a dact ct2 attenuator.
An externally hosted image should be here but it was not working when we last tested it.
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