Buzz on Audio Pot Travel Denon PMA-520

A simple way to confirm/eliminate is temporarily solder say a 50K between wiper and one end , for each pot, and see if the problem spot moves.

Rang a bell symptomwise and this repair brief off my files, off URL below

Cambridge Audiolab 8000C preamp 1994 Both channels function ok but with no or low signal there is a low level mains hum. Hum for only about a third of full range of vol control,when present it is constant volume regardless of vol setting. When hum is present the setting of the tone controls makes no difference to the amplitude of hum. The mains transformer was 30v-0-30v with 120 deg C thermal fuse. This unit is double insulated with phono connector returns commoned but not to ground. With the earth point disconnected there was significant voltage on the chassis.

138 V ac one of the secondaries to ground and about 110V ac chassis to ground. With 3.3M connected between chassis and ground there was 60V ac so 20 microamp of leakage between primary and secondary. Although 500 V megger insulation test showed >200M between primary and secondary. On changing the transformer noticed one of the chassis screws was far too long in the area of the mains switch. With time the end of the screw had pushed into and deformed the insulation around the mains line at that position. It had not punctured through but is obviously undesirable so replaced with a screw only 1/3 the length of the original. So SAFETY NOTE NOTICE for all Audiolab amplifiers check the clearance of the chassis screw that protrudes into the area of the mains switch wiring and REPLACE with shorter screw. This errant screw was the cause of the hum, removing it and the hum went but the leakage ac remained so had to replace the mains transformer. Whether the leakage and screw problems were related i've no idea. Replaced with 25-0-25V torroid and half wave rectified DC on main cap of 35V innstead of 42V but seemed to work OK. There is little power used in a pre-amp so I assume it is only there to give weight - the customer requires some mass for his money as well as functionality.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I've had just a few pots that did not respond to normal cleaning, but finally did, with more aggressive cleaning technique.

In my case, I used an air compressor aimed at the carbon element, used more De-Oxit and Caig D-100L, worked it some more, hit it with the compressor again, etc. After several tries the pots finally responded to the treatment. Maybe there was some crud physically adhered to the carbon element - who knows?

Mark Z.

If still the same area of pot after R addition and no track problem then this amp also had similar problem if the buzz was mains bourne triac noise. Ground and faux ground with the wiper getting too close to the pot casing

Ashdown ABM500 bass amp, 1997 on my repair brief file

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I'm only getting this buzz (more of a buzz than a hum) on the left channel. On other portions of the sweep, it is dead quiet. On the right side, I get some very minor white noise once I turn up the amp way up, much more than one would do with speakers connected (I'm using headphones). The buzz and white noise are actually quite low and not really bothersome, but they are there.

What pot supplier did Denon use during this period, 1994 or so I'm guessing? Does the model number give some indication of the manufacturer? I've contacted tritonics to see what they say about availability, but would rather fork over a couple of bux.

The pot has two sets of four pins. The resistor being spoken of would attach between which pins?

OK, got an estimate on the part from Tritonics:

The part number for location VR401 is 2110524005 - Special Order -

$11.34 plus shipping and handling and sales tax, if applicable.

Tritronics, Inc. Parts

For that money, it's worth just 'going for it', if for no other reason than to prove it one way or the other. I am dubious that it is going to be the cause of the trouble, though ...

Arfa