Hi Ian,
the power resistor theoretically should never carry more than about a volt.
But ,during a failure mode the diodes may survive long enough with kA through them to develop a lot more than 1V, could we be approaching 10Vpk? that would be 10Wpk.
A wire wound can survive a much higher short term peak than any of the film types. It is survivabilty in the very short term that matters and even then only once for that fuse blowing incident.
I suppose you could deliberately set up a test with mains direct to audio ground (no PSU or amplifier inside) and close the case up. Stand back and switch on.
Tell us what happens and which parts survive the test and which are burnt out/test abnormally.
the power resistor theoretically should never carry more than about a volt.
But ,during a failure mode the diodes may survive long enough with kA through them to develop a lot more than 1V, could we be approaching 10Vpk? that would be 10Wpk.
A wire wound can survive a much higher short term peak than any of the film types. It is survivabilty in the very short term that matters and even then only once for that fuse blowing incident.
I suppose you could deliberately set up a test with mains direct to audio ground (no PSU or amplifier inside) and close the case up. Stand back and switch on.
Tell us what happens and which parts survive the test and which are burnt out/test abnormally.
I have seen it burn out even 1W carbon types... I only use flameproof wirewounds for that now...
Some progress!
First up I have now sucessfully moved over to a two transformer set up, so I have a transformer per channel now, i.e. true dual mono. This setup has resulted in no hum, as did the setup using one rectifier board to supply the two channels when using a single trasnformer. I feel pleased that I have proved a theory and hope that others can use this advice when they design their amps or find it useful in solving an exisiting issue.
I have also had a chance to install a disconnecting network as discussed above and, whilst this had no bearing on the hum issue, what it has done is surpressed noise (such as pops and cracks) from other electrical equipment in my household, i.e. the fridge, boiler and light switches.
All in all it has been an interesting learning experience and no doubt I'll get some more knowledge when I upgrade my pre-amp to include a buffer stage.
Thanks to all who have contributed to this thread. 😀
First up I have now sucessfully moved over to a two transformer set up, so I have a transformer per channel now, i.e. true dual mono. This setup has resulted in no hum, as did the setup using one rectifier board to supply the two channels when using a single trasnformer. I feel pleased that I have proved a theory and hope that others can use this advice when they design their amps or find it useful in solving an exisiting issue.
I have also had a chance to install a disconnecting network as discussed above and, whilst this had no bearing on the hum issue, what it has done is surpressed noise (such as pops and cracks) from other electrical equipment in my household, i.e. the fridge, boiler and light switches.
All in all it has been an interesting learning experience and no doubt I'll get some more knowledge when I upgrade my pre-amp to include a buffer stage.
Thanks to all who have contributed to this thread. 😀
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