Annoying Hum from Amplifier

[mightymonoped]

Recently had the Alps pot and a service done on my Audio Analogue Puccini SE (non remote version). When checking out the amp before bringing it home, I listened to in an audition room hooked up to a pair of Harbeth monitors and all seemed great.

On getting home, I basically just swapped it over with the emergency backup amp I was using (an even older Rotel RA-903AX), which to be fair had been doing a great job up til that point.
Right from powering on, I noticed a buzzing hum coming from both speakers that got louder when the volume was turned up.

I then went about a series of tests to see what might be causing the issue:-

Tried all of the inputs - hum still there!
Tied unplugging all devices except loudspeakers and power - still there!
Swapped mains cable and socket - still there!
Tried different set of speakers - still there!


Apart from the annoying hum, the amp sounds great, it's just noticeably distracting even when quiet music is playing.
Scratching my head on this one as I don't think it's a ground loop or earthing issue and the other amp works fine?

Going to test it again tonight but wondered if anyone on here has any ideas before I take it back to the guys who serviced it (who, I have to say, seem very competent and helpful)?

[struth]

could also be emi or rf being picked up from other appliances and cables. grounding is another place to look

[RothwellAudio]

Right from powering on, I noticed a buzzing hum coming from both speakers that got louder when the volume was turned up.

I then went about a series of tests to see what might be causing the issue:-

Tried all of the inputs - hum still there!
Tied unplugging all devices except loudspeakers and power - still there!
Swapped mains cable and socket - still there!
Tried different set of speakers - still there!




Humming and buzzing are two very different things - at least to me - and suggest different problems. The fact that it gets louder as the volume is increased rules out a lot of possible problems.

However, there's probably no point going into a lot of detail as what tests to do in what order - it's just been "serviced" and come back with a fault. Get them to fix it.

[sumday]

As above...if the problem remains with all sources disconnected, it must be in the amplifier.

Just for peace of mind though, before contacting the servicer i'd unplug and move the amp to a seperate outlet....as I learnt to my cost recently, WiFi modems and the like can cause some unusual effects with sensitive input stages.....in my case a tube pre.
Oh what fun I had tracking that one down.


Good luck.

[mightymonoped]

As above...if the problem remains with all sources disconnected, it must be in the amplifier.

Just for peace of mind though, before contacting the servicer i'd unplug and move the amp to a seperate outlet....as I learnt to my cost recently, WiFi modems and the like can cause some unusual effects with sensitive input stages.....in my case a tube pre.
Oh what fun I had tracking that one down.


Good luck.

Yep, that's the plan tonight before I take it back. Going to move to a different location and socket away from everything and just check. If still the same, I won't have any niggles when I take it back in.

[hifi_dave]

If it has come back from a service with this problem, I would suggest you return it to whoever did the service.

[mightymonoped]

If it has come back from a service with this problem, I would suggest you return it to whoever did the service.

Will be doing that Dave, just wanted to make sure it wasn't a numpty error on my behalf before I lose the use of it again for a few days.

[hifi_dave]

If you are using it in the same system as previously and you've changed nothing with the wiring etc, it is most likely a fault with the recently serviced amp and should have been fixed.

[mightymonoped]

Just got my amp back and it’s sounding sweet again. Problem was a grounding resistor that had gone open circuit. All sorted and tested with two different sets of speakers. Looking forward to giving the Allo Boss a proper listen now [emoji4]


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