Hi all.
I built this and have triple checked it with the schematics.
I first tested it with a sinewave and monitored it on my scope and got good wave forms on input and output . So I tried connecting it to my Philips ag9016 which it double insulated and with the vol on pre down no problems.
As soon as I turn up vol I get hum .
On inputs I used the shielded cable that is connected to input ground on the sockets that are isolated from chassis . The ground shield is not connected at the points the cables go to the 4 way selector.
The ground on shielded cable that go to output are grounded.
Any ideas
Thanks
I built this and have triple checked it with the schematics.
I first tested it with a sinewave and monitored it on my scope and got good wave forms on input and output . So I tried connecting it to my Philips ag9016 which it double insulated and with the vol on pre down no problems.
As soon as I turn up vol I get hum .
On inputs I used the shielded cable that is connected to input ground on the sockets that are isolated from chassis . The ground shield is not connected at the points the cables go to the 4 way selector.
The ground on shielded cable that go to output are grounded.
Any ideas
Thanks
Attachments
Try these two things first, if the hum seems to be 100/120Hz.
Move the audio circuit ground wire from the star ground to the negative terminal of the second 330uF capacitor,
(the one closest to the rectifier tube).
The pin 4 on the rectifier socket is being used as a tie point. Remove the two connections to that tie point,
and relocate the tie point closer to the audio circuit, and farther from the rectifier tube.
It is possible that all the common grounds of the L+R inputs and audio circuits are causing the hum, if it is 50/60Hz
instead of 100/120Hz. In that case, use a separate ground bus for each audio channel (including the inputs), and
connect each audio ground bus to the star ground separately. You would then need to use separate decoupling
capacitors for each channel (two 10uF and two 22uF) to keep the grounds separate.
Move the audio circuit ground wire from the star ground to the negative terminal of the second 330uF capacitor,
(the one closest to the rectifier tube).
The pin 4 on the rectifier socket is being used as a tie point. Remove the two connections to that tie point,
and relocate the tie point closer to the audio circuit, and farther from the rectifier tube.
It is possible that all the common grounds of the L+R inputs and audio circuits are causing the hum, if it is 50/60Hz
instead of 100/120Hz. In that case, use a separate ground bus for each audio channel (including the inputs), and
connect each audio ground bus to the star ground separately. You would then need to use separate decoupling
capacitors for each channel (two 10uF and two 22uF) to keep the grounds separate.
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