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Old 22nd October 2007, 10:46 AM   #1
noge is offline noge  New Zealand
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Default Carver buzz at idle

I have friend with a Carver M-500t which puts out what sounds like a dimmer buzz at idle.

After reading the Carver postings here, I've come to the conclusion that it's probably noise from the triac in the Magnetic Field PSU. This can apparently misfire under light load conditions.

Does this cause a buzz at the outputs?

Does anyone know how to fix this?
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Old 13th December 2007, 11:40 AM   #2
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Hi, Yes the buzz sounds like dimmer noise because the main transformer is basically on a dimmer.

there are filters built into the amp, but i'm guessing they're optimised for US mains, or they're just crap.

i have a coulpe of racks of PM1.5's , same problem, although varies from amp to amp!

the usual solution is to fit a good filter Externally in the power cable to each amp.

when i say filter, i don't mean one of those 'power conditioning plugs'
I use some nice filters made my Roxburgh (RS), they come in a aluminium can about 50mm dia. by 75mm tall with a mounting stud on the top. (similar to the ones you find inside washing machines).

These contain a pair of big chokes, 2 Class-X caps and a Class-Y cap.
techninally, you should swap the LOAD and LINE connections round because you are trying to stop interference coming OUT of the amp, not giong in.

I use this 20A one in each of my PM1.5's....

hmm - cant find it.. but here's somethin similar

http://rswww.com/cgi-bin/bv/rswww/se...eID=uknetscape
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Old 11th March 2008, 06:31 PM   #3
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Hi to all,

I also have nearly the same problem with my PM 1.5.
Buzz at idle (on the left channel a little bit louder)
I tried several filters but none of them worked.
Also the Link to RS components doesn't work anymore.
Can anyone give me a hint which filter to use?

Greetz David
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Old 14th March 2008, 12:45 PM   #4
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Hi viddipaldi,
I will have a look for the filter i use when i get the new farnell catalogue (they promised last week).

I should clarify: the filters we use are to reduce switching spikes caused by the carver which travel back down the mains cable to more sensitive parts of a touring system, for example PA mixers and the multicore (which in a touring system is 50 - 100M long with the mains feed taped along side it).

We found the buzz worst when using multiple amps in racks.
Although fitting filters to the start of the multicore power feed might would have been effective, the buzz would still pick up in all sorts of places (most annoyingly in the guitars and amps of the bands we were working with).

Buzzes were different with different combinations of carvers in use.

bearing all this in mind....

does the buzz still happen if you use the amp on its own with no input, input pots turned down, away from any other sources of interference (i.e. at home) ?

If this is the case then you probably have a problem with the amp's power supply - possibly dried out caps, leaky rectifier diodes, incorrectly set idle pot or damaged snubbers around the triac.
If you acn be bothered, you should get the amp to a service guy who knows these amps well.

On the other hand, if the buzz is the result of the carver(s) causing interference elsewhere in your system then you should consider using filters - either on every other mains feed from your distro, or as me and most of my colleagus prefer, one large filter per amp.

I hope this helps - i'll have a look for a suitable filter - remind me if i havent posted in 2 weeks

jonathan
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Old 15th March 2008, 09:58 AM   #5
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Hello Jonathan,

thank you very much for your description. It helped me a lot to understand.
The buzz is also with no inputs, the pots turned down and no other equipment around.
So there are no filters which would help me. I have also tried with a filter from a washing machine, but no change.

If I turn the left pot up the buzz is getting louder and in maximum position it decreases to that noise it is when the pot is turned down.
The right channel is the same but not that much, the buzz is a bit quiter.
I can record a sound sample of it, maybe it can be helpful for diagnostics.
If we play with the band the buzz doesn't matter, you won't hear it anyway, but I think if I am able to find the problem it would be good for the amp itself.
Can you give me any other hint wich components I should try to replace first? Maybe I can isolate the problem swapping several components from left to right channel to hear which components caused more of the buzz in the left channel?

Once more thanks a lot for your time and help, guys
David

Btw. I do have the schematics of the amp, the changes described have been made to my PM 1.5 from the owner before.
I am not the expert but in our company we have two specialists for electronics who are on hand.
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Old 19th March 2008, 11:50 AM   #6
djk is offline djk
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A typical filter will not work properly with a Carver, try this:

Click the image to open in full size.
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Old 19th March 2008, 01:01 PM   #7
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Interesting, where did you get that ?

jonathan
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Old 21st March 2008, 03:35 AM   #8
djk is offline djk
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GE SCR Handbook, 6th edition.
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Old 21st March 2008, 12:28 PM   #9
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Excellent :-)
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Old 21st March 2008, 02:06 PM   #10
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Where can I purchase such a type of filter?
Maybe any infos for the components to use would also help :-)
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