pre amp hum

[karma67]

ive got a hum from the pre amp only through the right speaker,i removed the earth's from the amp,turntable and pre amp to see if it was a loop,this reduced it but its still there,i then got paranoid about getting electrocuted and put them back :)
whats the logical way off tracing/removing the hum?

[struth]

Have you changed anything, or moved anything ??

[karma67]

i didnt get it with the denon dl-160 but since upgrading to the mp500 its there,i also didnt have it when i tried the firebottle.

[struth]

I guess I would initially disconnect all cables from the tt including the mains and see if it is still there.. if it isnt then we are looking at tt and associated cabling Jamie

[struth]

You could have a little dc getting onto the right channel speaker as well, which would be likely to be a leaky capacitor, probably in the main amp

[struth]

ah you've changed a post lol. try rerouting the cabling and see if you get any change. could have a bad connection into the right rca phono, maybe inside the pre. Could just be a mismatch gain wise between amps or a capacitor on right side of phono is leaky.

[karma67]

well on futher inspection ive plugged the tt back into the amp and its still there so we can rule out the nak,i have also noticed that removing the tonearm earth lead from the amp doesn't do anything,does this point to a dodgy earth lead?

[karma67]

ive just tried the tt in different sockets around the flat and with some the hum is louder,the hum is there regardless of whether the socket is switched on or off too?????

[Ali Tait]

Disconnect the interconnects between the preamp and the amp. This will tell you whether the hum is from a source or pre or from your amp.

[karma67]

ok done that and ive dropped the left channel.no sound through the speaker at all,plugged the pre back in to the amp through AUX and both speakers are working??
that tells me somethings wrong with the phono stage in the amp,yes?

[walpurgis]

Check the headshell cartridge tags, make sure they're secure onto the cartridge pins and not touching each other.

Also, some older phono plugs can have middle positive pins that don't contact inside phono sockets too well. That can cause hum.

It's also possible that the pre-amp input sockets have opened up a bit inside and are not making good contact with the plug. If you know what you're doing, you can take the cover off the pre-amp and check and if necessary squeeze the centre tubular contact slightly to mate better against the plug pin (not while it's plugged in obviously).

All of these are problems I've come across in the past.

[Ali Tait]

Not quite sure what you mean. If you have the pre disconnected from the amp, then there are no sources connected to the amp. If you still have hum, that means the amp is the problem.

[karma67]

Check the headshell cartridge tags, make sure they're secure onto the cartridge pins and not touching each other.

Also, some older phono plugs can have middle positive pins that don't contact inside phono sockets too well. That can cause hum.

It's also possible that the pre-amp input sockets have opened up a bit inside and are not making good contact with the plug. If you know what you're doing, you can take the cover off the pre-amp and check and if necessary squeeze the centre tubular contact slightly to mate better against the plug pin (not while it's plugged in obviously).

All of these are problems I've come across in the past.

cheers geoff, i'll take a look.cartridge tags are new as are the interconnects.


Not quite sure what you mean. If you have the pre disconnected from the amp, then there are no sources connected to the amp. If you still have hum, that means the amp is the problem.

what i mean is,i've unplugged the pre from the amp and tried the tt in the phono input of the amp.
perhaps im not explaining it very well?
with everything connected as normal and on and tt switched off at the mains there's hum, ,infact you dont have to fully plug the tt in just hold the plug at an angle so only the earth pin goes in and its even hums thern as well! unplug the tt and the hum goes.

[Ali Tait]

Ah, ok alles claar.

[karma67]

ah switching the phono leads round puts the hum now through the left speaker

[struth]

then its coming from the tt and associated cables.

[Ali Tait]

Indeed.

[karma67]

i think geoff was right on the money,ive just plugged the tt back into the amp only and pushed and wiggled the phono plugs and now ive got both channels working :) happy days are here again! thanks guys for all the input.

[walpurgis]

Indeed.

Indeed twice! :D

[Ali Tait]

:D.

Nice one Jamie, looks like you're sorted.

[walpurgis]

:exactly: :thumbsup: :piano: :lol:

[struth]

The rca's on the tt may need some attention :)

[walpurgis]

The rca's on the tt may need some attention :)

Yes. Sometimes, if they are a bit of a tight fit it's quite easy to not push them in far enough to make proper contact (I hate overtight plugs).

[Canetoad]

Ah, ok alles claar.

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