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.
Many thanks for any help anyone can give.
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)
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)
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?
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
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
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?
I assume that the single trim pot on each channel is for the bias not the DC offset? Any mileage in fine tuning this?
Hi Rotellian,
I would expect the trim pots to be for bias current. I would expect 50~100mA bias for each output device as a general rule of thumb.
Find some way of measuring the current flow and check the value first. If both channels are close, record the value for future reference and leave it.
-Chris
I would expect the trim pots to be for bias current. I would expect 50~100mA bias for each output device as a general rule of thumb.
Find some way of measuring the current flow and check the value first. If both channels are close, record the value for future reference and leave it.
-Chris
Hi Rotellian,
A DC offset measurement is taken from the speaker output to ground (negative speaker terminal). It is mostly controlled by how well the input transistors are matched, and the DC offset that is designed in (this can be calculated if you have the schematic and know a couple parameters. Tail current and device gain coupled with component values).
Bias current is either measured across a source resistor (0R1 ~ 0R47 commonly) that connects to the output terminals. No load is connected for this measurement.
If you are going to pull any parts to measure them, take a digital picture of the board first.
-Chris
A DC offset measurement is taken from the speaker output to ground (negative speaker terminal). It is mostly controlled by how well the input transistors are matched, and the DC offset that is designed in (this can be calculated if you have the schematic and know a couple parameters. Tail current and device gain coupled with component values).
Bias current is either measured across a source resistor (0R1 ~ 0R47 commonly) that connects to the output terminals. No load is connected for this measurement.
If you are going to pull any parts to measure them, take a digital picture of the board first.
-Chris
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