THis amp needed ALL aluminum caps replaced. Some board corrosion caused by the 470uF caps in the audio section. I also replaced all 5x NE5532 opamps as they were quite corroded as well and there was bad DC on many of the legs and speaker terminals. I now have some decent audio at speaker terminals, but only with the muting jfets removed. When the jfets were in circuit I could get some audio, but the lower waveform was clipping on one channel badly, and the other channel had barely any audio. With them removed, audio is cracking very badly. I replaced the gain control and also cleaned and checked the Mono and EQ buttons for operation.
Whats most likely to cause crackling at terminals? I see fluctuating signal even on RCA center with my scope.
Second, why is the amp half in mute?
Whats most likely to cause crackling at terminals? I see fluctuating signal even on RCA center with my scope.
Second, why is the amp half in mute?
What's the DC voltage on the gate of the jfets?
The crackling sounds like electrolyte contamination.
The crackling sounds like electrolyte contamination.
I've solved the crackling problem - there was massive corrosion under the balance port. Removed and cleaned well. Amp sounds clean now.
Gates of muting jfets have -3 and -3.6vDC on them referencing either ground or secondary ground.
Gates of muting jfets have -3 and -3.6vDC on them referencing either ground or secondary ground.
You'll have to find the negative supply that drives the gates of the jfets. It should be similar to what's shown on the Orion page. Is the negative voltage being produced? If so, is the optocoupler working as it should.
On the Optocoupler which has leg5 leading award the gates of the jFets;
1. 1.244
2. 0.037
3. 0
4. -3.73
5. -3.71
6. -3.1
1. 1.244
2. 0.037
3. 0
4. -3.73
5. -3.71
6. -3.1
It doesn't look like it's building the negative voltage. There could be leakage between pads for the electrolytic cap that filters the negative voltage.