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Humming Carver PM-1.5

Longaevus

Longaevus

Active Member
In order to properly feed a pair of JBL's Ti-3000 I recently traded, I purchased the aforementioned Carver power amp only to find out two strange behaviors:

A) buzzing speakers - the speakers have a permanent buzzing sound that increases when both/either left and right gain controls of the amp are used. As I have investigated this is probably due to a ground loop somewhere. I have tried to connect the amp directly into several different wall outlets in the house to no avail. Not that it hampers the ability to listen to music but with quieter genres it is audible and of course, annoying, as it shouldn't.
My only guess right now is that the XLR»RCA adapters somehow are bad quality ones and a ground loop is occurring, as far as I know XLR cables/connections are balanced and properly ground isolated contrary to the more common RCA. Could this be fixed by returning the adapters and getting proper XLR»RCA cables?...

B) humming amp - after trying to solve the buzzing speakers problem with no luck I noticed something that feels a bit more troublesome. Upon powering it, the amp hums quite a bit, it can be heard from a few feet away, louder than the cooling fan for example. My bet is that it is transformer related but I am ignorant to electronics and have no idea how to diagnose or fix this.

I know the amp is old but it should be a competent one if in good working order, my fear is that I have been sold a faulty amp which repair will require a large investment that does not make sense financially.

Any help would be DEEPLY appreciated guys :bye:
 
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Does it hum/buzz the same with no cables connected to the amp inputs?

As far as XLR, no, it cannot be assumed the grounding is properly isolated. In my HT system I had a bit of ground loop hum. I eliminated it by disconnecting the cable shields at the ends of all the XLR cables going to the amps.
 
whoaru99 said:
Does it hum/buzz the same with no cables connected to the amp inputs?

As far as XLR, no, it cannot be assumed the grounding is properly isolated. In my HT system I had a bit of ground loop hum. I eliminated it by disconnecting the cable shields at the ends of all the XLR cables going to the amps.
Click to expand...

Right now I am making another test which is to check if the noise is only when cold. It's been on top of my living room table for some minutes now and the hum does not go away, the only thing connected is the power cord.
 
Check on "TheCarverSite" for info, there is a handfull of tech's that know Carvers inside and out plus they have manuals. That should be a very solid performer when you get it figured out.

BillWojo
 
You are in Portugal and your ac is 230vac at 50hz. Your home maybe 'noisy' as Euro 50z transformer or p.s. hum so try other outlets and maybe take it to another house or shop to test it. Transformer coils and possible transformer wires losing stability. Possible AC plug is old and rubber like. does the unit have a earth ground lug? Is transformer hot or vibrating?

lots of tests with no meter.
 
Binkman said:
You are in Portugal and your ac is 230vac at 50hz. Your home maybe 'noisy' as Euro 50z transformer or p.s. hum so try other outlets and maybe take it to another house or shop to test it. Transformer coils and possible transformer wires losing stability. Possible AC plug is old and rubber like. does the unit have a earth ground lug? Is transformer hot or vibrating?

lots of tests with no meter.
Click to expand...

I've read about the possibility of DC current is reaching the amp and provoking the noise but I guess if my home is vulnerable to this then most homes where I live will probably too but nevertheless I will try to power it on my folks house just to be sure.

Regarding the ground lug, there is one and it reads something like "remove jumpers to isolate inputs from chassis", something like that, also just to be sure I have tried it both with a jumper and without to no avail, same hum/buzz.

I am just worried this is not normal because in case it is I'll just pump the volume up! :rolleyes:
 
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