I'd check it on the power supply terminals (pins 4 and 8) of the op-amps that drive the output section. Checking the supply pins of all of the op-amps wouldn't be a waste of time. The voltages need to come up evenly. same rate, same voltage. To ±15v (approximately).
Probed the three op-amps 4562D:
- With speakers attached the voltage comes up to ~7V
- Without speakers attached it will stabilize at 16.5V
Do they both come up to full voltage immediately or is there a bit of a lag with either supply?
Do both channels play to full power cleanly, clipping symetrically top and bottom if the speakers are connected after the amp has powered up?
Will the amp power up with either channel (one channel at a time) connected when you power up?
I think you stated that one channel had positive offset and the other negative offset at startup. What were you using for the reference (black meter probe)?
Do both channels play to full power cleanly, clipping symetrically top and bottom if the speakers are connected after the amp has powered up?
Will the amp power up with either channel (one channel at a time) connected when you power up?
I think you stated that one channel had positive offset and the other negative offset at startup. What were you using for the reference (black meter probe)?
I found the issue. The 5.6 ohm ~2W resistor behind the gain knob went bad (20k ohm).
Now the amp will power up even with the speakers attached 😀
Thank you so much Perry for your support 🙂
I think I will message you via mail about your tutorial.
Now the amp will power up even with the speakers attached 😀
Thank you so much Perry for your support 🙂
I think I will message you via mail about your tutorial.
Yes indeed, I f**ed up the op-amp measurement. I know you said ±15v
But when probed I thought single rail op-amps (only the positive rail was available - neg. one was 0V), and made a false call... sorry 😳
Resistor is looking just fine, I see no sign of overload - so it failed high resistance.
But when probed I thought single rail op-amps (only the positive rail was available - neg. one was 0V), and made a false call... sorry 😳
Resistor is looking just fine, I see no sign of overload - so it failed high resistance.
It's a flameproof so it shows very little evidence of damage. The ceramic coating doesn't burn like the paint coating.
I did just a quick check with a simulated 5R6 resistor, will get a proper one next week. Then I can load test the amp.
Have you had this issue in the past? And should be something checked because of that?
Have you had this issue in the past? And should be something checked because of that?
