Static like hissing sound eminating from power amp. - diyAudio
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Old 23rd September 2008, 08:35 AM   #1
Brit01 is offline Brit01  United Kingdom
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Default Static like hissing sound eminating from power amp.

I have a Carver power amp TFM-55 and pre CT-3.

I have been suffering from a significant audible hissing sound through my speakers when I turn up the line level control on the power amp past 65%.

I connected a cd player directly to the power amp to see if it was my pre-amp but I still get the annoying hissing sound through the tweeters. It's like a static hissing sound.

If I disconnect all sources from the power amp and turn up the line level control it is almost dead silent.

I've cleaned all pots, changed interconnects, re-wired and isolated power cables, removed tv's in close proximity etc.

Any ideas what could be causing this? A grounding problem has been mentioned.

Please help.
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Old 23rd September 2008, 10:34 AM   #2
poynton is offline poynton  United Kingdom
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Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)
with no input connected - silence

with an input - hissing


is the input lead acting as an antenna??



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Old 23rd September 2008, 11:13 AM   #3
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see, if you could trace it back to the CDP.
Shorted RCA plugs work as noiseless, blameless sources and help greatly in troubleshooting.
If the CDP is guilty, it may have a defective mute circuit.
Regards
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Old 23rd September 2008, 12:41 PM   #4
Brit01 is offline Brit01  United Kingdom
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Quote:
is the input lead acting as an antenna??

I bought a new interconnect but not that good. Maybe I need to try with a more expensive one with very good shielding??

The amp has 380 watts per channel so this is going to pick up every little detail. Also Klipsch speakers with high sensitivity, 93db.



Quote:
Shorted RCA plugs work as noiseless, blameless sources
I tried with one pair of shorted plugs, swapping them from each input. Didn.t make any difference. Maybe a pair in every input??
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Old 23rd September 2008, 01:05 PM   #5
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Quote:
Originally posted by Brit01
I tried with one pair of shorted plugs, swapping them from each input. Didn.t make any difference. Maybe a pair in every input?? [/B]
so the noise persists, if the CDP is replaced by shorting plugs?
regards
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Old 23rd September 2008, 01:50 PM   #6
Brit01 is offline Brit01  United Kingdom
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Quote:
so the noise persists, if the CDP is replaced by shorting plugs?
Not sure what you mean here.

Are you referring to the line input for the cdp on the pre-amp?
I have tried shorting plugs on all line inputs on the pre.

If I connect the cdp directly to the power amp and turn up the line level control on the power amp to max then I get the significant hissing.

Also with just the pre-amp connected to the power amp with no cdp connected I still get the hissing when the power is turned up to a high level.
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Old 23rd September 2008, 02:24 PM   #7
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Quote:
Not sure what you mean here.
first test would be:
-connect the shorting plugs to the power amp and listen
second:
-connect the preamp, use shorting plugs on the CD input, select it and listen
third:
-connect the CDP to the CD input and listen for noise
regards
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Old 23rd September 2008, 02:35 PM   #8
Brit01 is offline Brit01  United Kingdom
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Quote:
first test would be:
-connect the shorting plugs to the power amp and listen
second:
-connect the preamp, use shorting plugs on the CD input, select it and listen
third:
-connect the CDP to the CD input and listen for noise
Hi,

Last 2 tests I have tried and noise is present.

First test I have not tried: i was not sure if that was advisable with the power amp.
I did listen to the power without anything attached and the noise was hardly audible (90% improvement). In other words just a very faint sound when I put my ear to the tweeter but this can be normal and does not affect anything.

You recommend to attach the shorting plugs to the inputs of the power?
I can try this when I get back home later.
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Old 23rd September 2008, 03:18 PM   #9
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Hi,
Quote:
You recommend to attach the shorting plugs to the inputs of the power?
don't do it, if you are uncertain.
I have once killed a pair of woofers, because of plugging something to the amplifier while it was on.
What about tuning the power amp to a low setting?
You still have the preamp for gain control.
regards
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Old 23rd September 2008, 03:41 PM   #10
Brit01 is offline Brit01  United Kingdom
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Quote:
What about tuning the power amp to a low setting?
Hi,

Yes that's what I am doing now but I notice the sound does improve when I use the full power of the Carver but at the expense of the audible hissing noise.

So I'm keeping the line input control at about 65%. Still loads of power as it has 380 watts at 8 ohms but I really want to find out what is causing this noise and to eliminate it if possible.

i'm a member of the Carver club but haven't solved anything with them yet. They mentioned a possible grounding problem but I have no idea how to solve this if this is the case.
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