Marantz 1250 Phono Hum

[kzeiger]

New to this forum, recently purchased a vintage Marantz 1250. I also have a 1150.

When turning up volume both phono inputs have a slight hum, more noticable around 1/2 volume. Shorting plugs do not make a difference and no turntable is connected. I would like to get my Garrard DD-75 going on this great amp.

I don't want to recap the whole thing but would like to have an idea the 1st place to look that might be the culprit. I do have a service manual.

Thanks for any help.

 

[kholi_pankaj]

Welcome to the forum

 

[skillace]

New to this forum, recently purchased a vintage Marantz 1250. I also have a 1150.

When turning up volume both phono inputs have a slight hum, more noticable around 1/2 volume. Shorting plugs do not make a difference and no turntable is connected. I would like to get my Garrard DD-75 going on this great amp.

I don't want to recap the whole thing but would like to have an idea the 1st place to look that might be the culprit. I do have a service manual.

Thanks for any help.

hi Kzeiger,

I've recently bought a 1250 too. But the previous owner has replaced the original big output filter cap with two 11V 12000uf ones.
Any idea about the spec of the original cap?

 

[pappu]

hi Kzeiger,

I've recently bought a 1250 too. But the previous owner has replaced the original big output filter cap with two 11V 12000uf ones.
Any idea about the spec of the original cap?

If power supply circuit is not altered then there will be two filter capacitors of 1000mfd/70 volt in series. I don't know how the capacitor of 11 volt is installed in power supply as filter capacitor. check the voltage there. this circuit is not drived by 9 volt or 12 volt.

 

[skillace]

Pappu, you are right.
The caps have been replaced by previous owner with two 12000mf 71V chemicon caps.
Anyway, I've changed them with two 15000mf 71V nichicon caps. Those are the only one I found close to original specs.