Noticeable hum through speakers

[FennerMachine]

Thought I would start a new thread for this one!

I got my Quad 44 pre amp back last week after being serviced. I now have a strange problem.

With the Quad 44 connected to the Cyrus Smart Power’s with a 4-pin DIN to RCA connector I get a very noticeable hum through the speakers. I have also had this once using the RCA output from the Quad. No sources are connected.

From some research I’ve done it sounds like an earth loop problem. I have also contacted Quad and they gave me a few suggestions to try to eliminate the problem.

If I turn off the Quad the hum is still audible which is strange as that should kill the power from the Quad. I have to turn off the Cyrus amps from their rear switch.

I’m going to try a few things tomorrow such as using a different wall socket, trying the RCA outputs from the Quad again and seeing if I still get a hum by disconnecting the 4-pin DIN while it’s humming.

Anyone got any ideas as to what could be the cause and what else I can try to fix it?

 

[Andrew Everard]

If it's a ground loop problem, I'm not in the least surprised that it continues even with the Quad turned off, as the preamp will still be connected to the mains and thus still earthed.

Of course if the hum continues with the cable disconnected bewteen the two, but still attached to your power amplifiication, then the problem is either in the cable or the power amps, and of the two the cable is the more likely suspect.

If the hum's sttill there when the cable is removed completely, I'll be very surprised!

Of course, it could be 'leakage' – in the form of RFI – from the preamp's transformer being picked up on the interconnect cable rather than a ground loop, but the eventual solution, unless Quad can solve the problem, might be to try a different interconnect cable, or consider a ground-loop busting device between the preamp and power amplification, although this last measure really should be a last resort.

Good luck – from bitter experience, hums such as these can be tricky to track down, and even tougher to resolve.

 

[FennerMachine]

Did some experimenting today, I think the problem is now solved!

When the 4-pin cable is pulled out of the Quad the hum stops so narrowed down to the Quad or cable.

I received my new cable, converting the 4-pin to 2 RCA plugs and used some Chord interconnects.

I got the same hum but the 1.6v output seemed OK.

I then changed the wall socket that the Isotek Cleanline is plugged into back to the one I was using before I got the Quad serviced.

So far I have played about 30 minutes of music with no hint of a hum, buzz, click, pop, nothing! Must be a faulty wall socket, the fridge & freezer in my room interfering or an earth loop from using different sockets.

So far the overall sound is better than what I can remember but early days yet. Prefer it to the Cyrus aCA7.5 anyway!