Hi All,
Working on a DD Audio M3c amp that came in with a blown output section.
Damage included:
Replaced POT (104C), but have audio oscillations when I set the LPF. If I touch the pot shaft I get a 2000 hz audio output at 20V RMS!
Schematic is a good representation of the pre-amp portion of the amp.
If I switch the amp to slave input, it works as expected.
Any advice on how to track this issue down would be appreciated.
Thanks!
Working on a DD Audio M3c amp that came in with a blown output section.
Damage included:
- Inductor to -Rail +12V Regulator
- 1ohm resistors to the output MOSFETS
- TC4452VAT Drivers
- Output MOSFETS (FDA24N40F)
- and a 10ohm resistor between REM and the Remote bass controller (R169)
Replaced POT (104C), but have audio oscillations when I set the LPF. If I touch the pot shaft I get a 2000 hz audio output at 20V RMS!
Schematic is a good representation of the pre-amp portion of the amp.
If I switch the amp to slave input, it works as expected.
Any advice on how to track this issue down would be appreciated.
Thanks!
On IC103, do you see the oscillation on both pins 7 and 8 when you have oscillation at the output?
If I ground my probe on the pre-amp ground, to get better signal integrity and I try to measure IC103 pin 5, the oscillation stops. So the capacitance/resistance of the probe seem to stop the oscillation. Could this be caused by C108?
The capacitors C106, C107, C108 and C109, did not match the schematic. What was strange was that C106 and C108 was not matched and then also C107 and C109. I would have expected those pairs to be matched at least. I replaced the capacitors with the values in the schematic, and the oscillation is gone. Unfortunately the resistors R111, R112, R113 and R114, also do not match the circuit, so now the LPF does not work the way it should.
What if you use the same values as the original?
Or, use all of the values (resistors and capacitors) that are in the DD circuit.
Or, use all of the values (resistors and capacitors) that are in the DD circuit.
I used all of the values in the schematic and am happy to report that the oscillation is gone and it seems to work properly now! Thanks for the help and suggestions Perry!