T
[email protected]
- Jan 1, 1970
- 0
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374
(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:
http://home.comcast.net/~garyworld/site/?/photos/
[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374
(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:
http://home.comcast.net/~garyworld/site/?/photos/
[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee