Denon PMA-520 Integrated Amp "Buzz"

[DreadPirate]

As I turn the volume control on this integrated amp, I get a slight buzz sound, but only on portions of the travel. For example, dead quiet between 1-15, buzzy between 15-20, dead quiet again after 20. Could this be more than just the volume pot?

[Piercarlo]

Originally posted by DreadPirate
As I turn the volume control on this integrated amp, I get a slight buzz sound, but only on portions of the travel. For example, dead quiet between 1-15, buzzy between 15-20, dead quiet again after 20. Could this be more than just the volume pot?

If there not poor wipe contact (audibile when playing with volume in the suspect positions), then the cause is a latent unstability of the preamplifier that follow volume pot. A problem not new with Denon what not ever care properly ground routings (or lack in screening internal signal cabling, a negligence that I've meet often in commercial amplifiers, Denon and others).

Hi
Piercarlo

[anatech]

Hi DreadPirate,
Odd problem. Order a control from Denon.

Hi Piercarlo,
I did warranty on these. They were not built like Threshold or other high end brands, but then again they were put together better than many others. You can't knock them for that! They were good value for the money.

A problem not new with Denon what not ever care properly ground routings (or lack in screening internal signal cabling, a negligence that I've meet often in commercial amplifiers, Denon and others).

Now, why would you say that? This was not a problem we've encountered.

Denon was manufactured to a level a bit higher than the price tag. You can not fault them for not being as well built as top end products. There were very few troubles with Denon (over here at least).

-Chris

[Piercarlo]

Originally posted by anatech
Hi Piercarlo,
I did warranty on these. They were not built like Threshold or other high end brands, but then again they were put together better than many others. You can't knock them for that! They were good value for the money.

Nothing to say. But the defect still remain defect.

Now, why would you say that? This was not a problem we've encountered.

I've meet that problem a couple of time. With this of Dread Pirate, is the third chance I get of hear of that...

Denon was manufactured to a level a bit higher than the price tag. You can not fault them for not being as well built as top end products. There were very few troubles with Denon (over here at least).

Nothing to say but, as yet said before, a defect still remain a defect. Not general or ill-fated pherhaps but just a defect (not owned only by Denon of course: every consumer products has some "black highlights" to hide - It's not strange, just normal: full workout of defects of design and production and reasonable or cheap prices are plainly incompatible between them).

Hi
Piercarlo

[anatech]

Hi Piercarlo,
Well, I am just interested if you actually did troubleshoot the actual cause in any of the two you saw. What I do have a problem with are the following comments you made ....

then the cause is a latent unstability of the preamplifier that follow volume pot.

and ...

A problem not new with Denon what not ever care properly ground routings

I would have seen this for sure!

If the source goes open, you can expect to pick up noise in any design. Often companies run signals through flat cables alternating ground and signal. I don't like the practice, but it does seem to work inside a shielded case. Even very high end manufacturers may do this from time to time. If every signal was carried inside a shielded conductor, you could expect some capacitance that then has to be driven. I guess these are real tradeoffs.

-Chris

[DreadPirate]

This actually could be a common, yet undetected problem. I only pick it up on headphones while doing a very critical evaluation. I like the sound of this unit, will probably spring for an ALPS pot, I'll report back if that did the trick, can't say when I'll get around to it, unit is fully functional otherwise.

The volume control was quite noisy before I cleaned it.

[anatech]

Hi Dread,

This actually could be a common, yet undetected problem. I only pick it up on headphones while doing a very critical evaluation.

That's entirely possible. The substitution of the alps pot for the original would be interesting.

-Chris

[Piercarlo]

Hi Piercarlo,
Well, I am just interested if you actually did troubleshoot the actual cause in any of the two you saw. What I do have a problem with are the following comments you made

"then the cause is a latent unstability of the preamplifier that follow volume pot".

and

"A problem not new with Denon what not ever care properly ground routings"

I would have seen this for sure!

Well. I've buy used, some years ago, an old PM 502 (or so) which exhibits the same defect (plus others) described by DreadPirate about its 520.
Instabilities were due to a subsequent volume circuits which were designed in order to behave as a "tube-like" circuits (especially from the NFB viewpoint), with tone network embedded in the NFB network of main preamplifier stage instead of being implemented in an active dedicated circuit as usual.

Internal cabling was just of unscreened kind but with a little "trick" that masked the problem: input sockets have an internal spring that short input to ground when no cable is inserted: i don't perceived the problem til a day I've left inserted a CDP (a Philips CD104 with an unusual grounding scheme that, when off, is floating and heavily humming). Chasing for the cause of huge humming I've neared my hands to the bunch of cables (that believe shielded although not thick) and hum raise heavily.... and so the truth come out: no internal screen of any kind, neither for the phono MM stage, was used.

"I don't like the practice, but it does seem to work inside a shielded case. Even very high end manufacturers may do this from time to time. If every signal was carried inside a shielded conductor, you could expect some capacitance that then has to be driven. I guess these are real tradeoffs".

May be... However this practice I've meet for some three-four times in the years and in every case hum was slightly heavier than usual. Another problem I've noticed in this case was a markedly, audible higher diaphony than the usual. In uone situation (Leak 1800) this practice appear to have somewhat compromised high frequency stability (not at the top however...) because the amplifiers sounded sensibly more or less harsh as I moved the internal cables (wrapped toghether with plastic ribbons).

Hi
Piercarlo

[anatech]

Hi Piercarlo,

with tone network embedded in the NFB network of main preamplifier stage instead of being implemented in an active dedicated circuit as usual.

Ah! Not a volume thing. I intensely hate that practice. Almost everyone did or does this to this day. Even some Nakamichi units do this. That subject has been covered elsewhere in this forum. Some amplifiers are unstable once their inputs are open circuited. This would be more of a problem with integrated amps and receivers since the input is assumed to always have an impedance to ground. That is something you can not fault the designer / manufacturer for.

"A problem not new with Denon what not ever care properly ground routings"

I would have seen this for sure!

I'd have to see one. There was never any service note on this, but there have been for other brands.

a Philips CD104 with an unusual grounding scheme that, when off, is floating and heavily humming

Can't blame Denon. Everyone leaves the input open. Marantz used to short the unused inputs to ground in the selector switch on the 22xx, 23xx and 2500 / 2600 receivers.

-Chris