Volume dropping and amp vibrating

[ScepticSchizo]

Hello good people of ASR.

I have been reading quite some rather interesting reviews and posts on the website for some years now, and I feel confident that some of you will be able to help me out with an issue I am having.

I've been lucky enough to purchase a Marantz PM Pearl for a bargain. It works all as should, apart from the left channel dropping in volume when played at very low level. When I turn up the volume it levels up with the right channel again. It doesn't happen often, only playing at low volume and after a fair amount of time.

The other odd thing is that when I lightly touch it it seems to vibrate. The whole chassis sorta feels like a current is flowing through it if that makes sense. When I put a little more pressure on my fingers touching it I don't feel it.

I run it as a power amp. I have inspected all the cables, ran it as a main amp etcetera but it did not make a difference.

Any suggestion of to what could be causing either of the issues?

 

[DoubleWoofers]

On the volume, it sounds like a bad volume pot. I believe that had an analog volume control.

Vibrating? .... could just be the transformer if it is slight. When you put more pressure on it, you damp the vibrations. It may just not be sitting flat.

 

[Chrispy]

How can you say an amp is working correctly when it obviously isn't? Being old doesn[t make up for poor performance, even if you want to call it "vintage"....

 

[restorer-john]

The 'vibrating' feel is common with metal cased, no earthed chassis modern products. They are supposedly double insulated, but inductive/capacitive coupling/eddy currents etc cause that 'buzz' you feel. Put your DMM hot on the chassis- you'll likely read an unloaded voltage of 100V or more.

 

[restorer-john]

How can you say an amp is working correctly when it obviously isn't? Being old doesn[t make up for poor performance, even if you want to call it "vintage"....

It's probably just a dirty set of contacts in the speaker relay. Nothing 'poor' about it in real terms and every amplifier with speaker relays will suffer the same issue sooner or later.

 

[Chrispy]

It's probably just a dirty set of contacts in the speaker relay. Nothing 'poor' about it in real terms and every amplifier with speaker relays will suffer the same issue sooner or later.

Well after service perhaps that will be borne out....but doesn't make it working correctly now in any case.

 

[DVDdoug]

apart from the left channel dropping in volume when played at very low level. When I turn up the volume it levels up with the right channel again. It doesn't happen often, only playing at low volume and after a fair amount of time.

As John says, it could be a slightly corroded relay contact or maybe a slightly corroded connector. You can get resistance in the contacts/connection and when you turn-up the volume the slightly-higher voltage "breaks through" the corrosion and then it's OK for awhile.

You can try opening it up and wiggling the connections/connectors (while it's running) to see if you can track it down. Just be careful in the power supply section! Or with it off, you can unplug & re-plug all of the internal connectors. Usually that's enough to "fix it" just from the normal wiping when they are plugged-in and unplugged.

The other odd thing is that when I lightly touch it it seems to vibrate.

There was a thread awhile back about DC (combined with the AC) on the AC line (or an asymmetrical AC voltage). ...And that would be the power transformer vibrating.

I think I had that problem once. When my TV was on my amplifier would vibrate enough that I could hear it. I has assumed it was some kind of noise on the power line. There was no unusual noise buzz coming from the speakers and the amp is still working, although I have a different TV and it doesn't happen anymore.

I've been lucky enough to purchase a for a bargain.

Or maybe not...

 

[sam_adams]

The other odd thing is that when I lightly touch it it seems to vibrate.

Is there an audible 60 Hz hum from the device—not the speakers? If there is, you may have some DC on your AC mains supply.

 

[ScepticSchizo]

How can you say an amp is working correctly when it obviously isn't? Being old doesn[t make up for poor performance, even if you want to call it "vintage"....

Apologies. Very rude of me to miss out the word 'almost' and cause such chaos and confusion.

 

[ScepticSchizo]

The 'vibrating' feel is common with metal cased, no earthed chassis modern products. They are supposedly double insulated, but inductive/capacitive coupling/eddy currents etc cause that 'buzz' you feel. Put your DMM hot on the chassis- you'll likely read an unloaded voltage of 100V or more.

Anything I can, or should do about it or isn't it of any issue really?

 

[ScepticSchizo]

You can try opening it up and wiggling the connections/connectors (while it's running) to see if you can track it down. Just be careful in the power supply section! Or with it off, you can unplug & re-plug all of the internal connectors. Usually that's enough to "fix it" just from the normal wiping when they are plugged-in and unplugged.


Or maybe not...

I'll open it up this weekend and wiggle about some connections. I'm not very experienced with electronics but I am always happy to learn new things. And yes, I'll make sure I'll try the unplugged option first as I am rather good at electrocuting myself.

It is still the best sounding amplifier I have, so I still consider it a bargain at £350

 

[ScepticSchizo]

Is there an audible 60 Hz hum from the device—not the speakers? If there is, you may have some DC on your AC mains supply.

I can't hear any hum coming from it. And if it where to be some DC on the AC means would I notice it with other amplifiers as well?

 

[sam_adams]

I can't hear any hum coming from it. And if it where to be some DC on the AC means would I notice it with other amplifiers as well?

Yes you would. It might also manifest only during certain times of the day as local load changes, also.

 

[wwenze]

Anything I can, or should do about it or isn't it of any issue really?

No issue. The moment you touch it, the voltage drops to a low voltage like <3V