Hello. I'm having this problem with the amplifier. It's in perfect condition, but it hasn't been used for some time. It has typical noise faults in potentiometers, switches, etc. After fixing the above, everything behaves fine, except when it reaches clipping. I've attached a video. I'm using 10 kHz, without load for safety reasons (with load the behavior is the same). It starts clipping in the positive half-cycle, not the negative, and the effect worsens when increasing the volume until the protection relay is triggered. There's an offset shift (I think). I don't know how to explain it, but the clipping doesn't occur continuously, but in parts, as if it were a ripple in the power supply. However, that's not the case. Towards the end of the video, you can see it by doing a quick oscilloscope scan. The strange thing is that the exact same thing happens on both channels. The power supply is fine, the input signal is fine. The positive and negative rail feeds of the input section and through R345 and R346 are OK. I replaced C229, 230, 231, 232, 311, 312, 319, and 320 with no changes. I disconnected D301, 303, 305, and 307 on one channel, as well as the collectors of Q325 and 327, but nothing changes. I'm starting to think this may be by design and not a real problem. No one in their right mind would use the amp at that extreme, but I can't be sure.Any comments?Thanks, everyone.
The clipping occurs for both channels, so that hints for a commen error.
Are the supply voltages equal (within some %'s)?
Are ground lines/tracks/points still on zero volt (ref to the chassis ground) everywhere?
Check R345/346, as they reduce the supply voltages for the first stage for both channels! If one is failing, things are becoming unbalanced.
I don't think it's in the safety circuit (Q325/327).
Are the supply voltages equal (within some %'s)?
Are ground lines/tracks/points still on zero volt (ref to the chassis ground) everywhere?
Check R345/346, as they reduce the supply voltages for the first stage for both channels! If one is failing, things are becoming unbalanced.
I don't think it's in the safety circuit (Q325/327).
Yes.
It´s ok
The earth is consistent, there is no disconnection anywhere.
It¨s ok, 100 ohms approximately 1 volt drop.
Yes, no changes.
When clipping begins, the 2.4V between the driver bases shifts toward the negative side of the supply with respect to the audio power output, junction of R of .22 ohms, the Vbe voltage of Q304 and Q306 is around 0.14V, but when it reaches the clip, the Vbe of Q306 increases to 1V, then the protection circuit activates. The same thing happens on both channels. Now I also replace C302 assuming some leakage, but everything remains the same.