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Old 27th April 2006, 04:16 PM   #1
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Default Amplifier Output Distorted

I have just acquired an amplifier that has a distorted output on one channel. Is this most likely to be one or more of the output devices? (possibly 2 x 2sk414 2 x 2sj119, although i will check when i remove the lid tonight). Or would there be no output at all if one or more had gone?

Many thanks for any help anyone can give.
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Old 28th April 2006, 12:06 AM   #2
infinia is offline infinia  United States
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Hi
You have the schematics? Good to compare the bad channel to the good one to get some headway into touble shooting your amp.
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Old 28th April 2006, 01:49 AM   #3
anatech is offline anatech  Canada
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Hi Rotellian,
Bad outputs usually sound like silence, fuses are blown.

Make and model will help. Do not swap parts from channel to channel. No gerfingerpoken unless you know exactly what you are doing!

An exact description to the best of your ability of what you are hearing.

-Chris
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Old 29th April 2006, 10:33 AM   #4
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Hi thanks for the replies.

Can confirm it does use 2 x 2sk414 2 x 2sj119. Its an Inca Tech Dirk a smaller version of the Claymore they made. On checking one of the output fuses has apparently blown - yet sounds were still coming from the output? Ive never had that before so am bit confused. Guess ill try replacing the fuse and see what happens (guess it may well blow again)
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Old 29th April 2006, 01:32 PM   #5
anatech is offline anatech  Canada
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Hi Rotellian,
Measure the DC voltage on each side of the fuse holder before replacing the fuse. If it's in the mV range, got ahead and install another fuse. If now, post your results.

-Chris
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Old 9th May 2006, 05:53 PM   #6
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I will measure the dc hopefully tomorrow. Meanwhile i replaced the fuses in both outputs and hooked up to some old speakers. Both channels appear to play without distortion but one channel (the affected channel) is definitely quieter than the other one. Could it still be the output device/s on that channel?
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Old 9th May 2006, 05:59 PM   #7
anatech is offline anatech  Canada
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Hi Rotellian,
Quote:
Bad outputs usually sound like silence, fuses are blown.
From above.
Measure the gate resistors and gate voltages with respect to the output terminal.

An open gate resistor usually will cause excessive current and more blown fuses.

-Chris
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Old 9th May 2006, 07:23 PM   #8
latala is offline latala  United Kingdom
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Iwould replace both supply fuses with a 5watt 100 ohm fuse. Do not connect a spk at this time! Switch on the power and measure the dc offset at the output terminals it should be near 0v.
If so then measure the volt drop acrooss each resistor expect around 10 volt
If this is the case fit the new fuses
if you have a large dc outut voltage or voltage drop on the resistors you have a problem
If the resistors overheat you then have a faulty output device/devices.
Regards Trev
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Old 10th May 2006, 09:02 AM   #9
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OK measured the dc offset (without fuse in holder)

On the left channel:

24mv
7.5mv (output side)

right channel:

-0.2
-6mv ? (output side)


It is the right channel that is sounding down compared to the left. It was the left that blew a fuse.
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Old 10th May 2006, 01:27 PM   #10
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From what little i know, this would seem to indicate that the dc offset isnt too bad considering its quite old (unless i measured it incorrectly). I guess the volume pot could be to blame. (although i tried it using a lower input to enable using more of the volume control range and the channel imbalance is still there, although better).

I assume that the single trim pot on each channel is for the bias not the DC offset? Any mileage in fine tuning this?
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