Pioneer GM-X622 low output - diyAudio
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Old 13th February 2012, 12:31 PM   #1
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Default Pioneer GM-X622 low output

Hi!

So I have here a Pioneer GM-X622 which looks all okay and powers up fine but the output seems to be low. When the amp gain is turned down all is normal. Then at some point when turning the gain up it stops producing output. Like for 2 seconds its all quiet and then it makes a loud pop and then again silence. Reducing the gain fixes again the problem and the amp plays normally but quietly. Looked the output signal with a scope and with a 4R dummy load (1kHz sine) and it looks normal, but the output signal level is always very low, the gain doesnt effect it at all. Voltages on the output transistors are normal and nothing seems to be burnt or anything.

Any ideas?
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Old 13th February 2012, 01:36 PM   #2
timwebb is offline timwebb  United States
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U check for DC on the RCA shield? It could be the DC off set in the amp
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Old 13th February 2012, 06:46 PM   #3
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I had a problem like that and it was the gain pot.The owener tried turning the pot pass it limit.I was also getting DC on the speaker outputs when it pop.
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Old 13th February 2012, 07:02 PM   #4
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What do you mean with this DC offset? How to check it?

Yeah, I also thought it might be the pot itself, so I cleaned it and oiled it and turned it many times but still the same effect. And when reducing the signal level before the amp input, it lets dial the amp gain a notch up before silence so its not likely the pot.
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Old 13th February 2012, 07:10 PM   #5
timwebb is offline timwebb  United States
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How much current is it pulling
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Old 13th February 2012, 07:43 PM   #6
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Without input signal (RCA-s disconnected) 0.56A so in idle its 0.56A

With a signal (1kHz sinewave) I can crank it up to about 11-12 amps (4R dummy load), then it falls somewhere in the idle consumption. Amp has gain fully on, bass boost on and passing the full range (no hpf/lpf). Changing the volume from my soundcard.

However i think it didnt do 12 amps before, because it didnt get that hot so quickly. May the DMM between power supply(a small resistance) mean anything relating to that?
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Old 13th February 2012, 08:57 PM   #7
timwebb is offline timwebb  United States
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There is much not much to see.what is your voltage on the RCA shield? Black probe on negative. Redone the RCA shield?
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Old 13th February 2012, 11:58 PM   #8
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What's the resistance between the RCA shield on the signal lines feeding the amp and the ground terminal on the power supply feeding the amp?

Does it do it in high-pass mode?
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Old 14th February 2012, 09:30 AM   #9
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Resistance between amp ground and RCA shield is 18kOhms. Amp RCA shield and the RCA cables other end (shield), between that its a normal 0.1 Ohms.

Voltage measured between amp ground and amp RCA shield is about 0.007 VDC

Yes, it does it in low pass, high pass and with the filters turned off.
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Old 15th February 2012, 10:25 AM   #10
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I'll try it another way. If you're driving signal from your computer into the amp and you unplug the RCAs from the amp, what is the resistance from the amp ground to the RCA shields coming from your computer?

Laptop or desktop?
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