Hello, I need to replace power caps on my old Marantz PM78 becuase I began to hear in my headphone at zero volume level a little continuous 50 hz hum, so I've thought to try to replace power caps.
Since I don't want to dismantle my amplifier before to be sure to have found the right components, please, anyone who has known these gears, original 12000 uF 63 V caps have two, three or four legs eachs?
How much might it be difficult in your opinion mounting Mundorf M-Lytic, which are two legs type? I'm going to buy 15000 uF 63 V but I'd want to be sure before..
Thanks in advance!
Since I don't want to dismantle my amplifier before to be sure to have found the right components, please, anyone who has known these gears, original 12000 uF 63 V caps have two, three or four legs eachs?
How much might it be difficult in your opinion mounting Mundorf M-Lytic, which are two legs type? I'm going to buy 15000 uF 63 V but I'd want to be sure before..
Thanks in advance!
you are going to waste your money since i don't think that this is the cause of the problem ...Yes capacitors might be a bit off specs due to age and temp but still these are not the cause of the problem...
Ground loop might be one of the causes coming from any of the peripherals , but also hardware like ground connections inside the amplifier ...
Ground loop might be one of the causes coming from any of the peripherals , but also hardware like ground connections inside the amplifier ...
Thank you for your opinion. Just yesterday I discovered that hum disappears completely if I put amplifier in class "A" with the front switch: does this confirm your hypothesis?
If the main smoothing capacitors were not within specification, I would expect 100hZ hum as it is after the bridge recrifier thast acts as a frequency doubler and placing it in class A would make it worse.
Check the leads and mains lead for good continuity. Look for an earth loop.
Check the leads and mains lead for good continuity. Look for an earth loop.
John you have been writing this before and its partially wrong
In the PSU when a capacitor is out of range IE from 12.000 fallen to 6.000 for example or has for some reason increased esr you will notice nothing unless you call for power Then distortion and or other problems of balance might appear .
In low listening level you will probably notice nothing ..
Then if a capacitor is totally blown expect mains noise but then the amplifier will not play anyway
So out of specs and totally gone is two different things ....
Kind regards
Sakis
In the PSU when a capacitor is out of range IE from 12.000 fallen to 6.000 for example or has for some reason increased esr you will notice nothing unless you call for power Then distortion and or other problems of balance might appear .
In low listening level you will probably notice nothing ..
Then if a capacitor is totally blown expect mains noise but then the amplifier will not play anyway
So out of specs and totally gone is two different things ....
Kind regards
Sakis
If the hum goes away in Class A operation, it can't be the caps - after all, you would expect higher ripple on the supplies then, not less. Not sure what the actual problem would be though. Some contact issue maybe?
Thank you very much, the strangeness of muting hum in class A in effect makes think to other issues. Then I'll try some different wirings in next days, I'll let you know.
However any ideas about tweaking this beautiful amp..?!
However any ideas about tweaking this beautiful amp..?!
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