Higher Voltage Rails on DBX118

[a soBer Newt]

Got a DBX 118 on the bench that had been perviously modified and never worked right. Poking around I found that if I used a bench supply at +/-15V it started behaving its self vs the +/-12V. My question is how would you adjust the setup of the current regulator to get from +/-12 to +/-15.

 

[chilidawg]

have you tried adjusting the 50K trim pot marked as 12V cal. on the schematic, while probing the supply output?

 

[abbey road d enfer]

I would start with trying to understand why it doesn't behave. What changes significantly when you up the voltage? If you gave a description of how it doesn't behave, that would be one step in the right direction.

 

[a soBer Newt]

Major changes that someone did were: OA2 changed to NE5532 OA3 changed to LME49720NA OA4 changed to NE5532, most of the Rs in the audio path were changed to metal film on the main board but not on the VCA cards, caps in the audio path were changed to film style.

R45 gives voltage trim of +/-10V to +/-12.3V

Test setup APSYS2 -5dBu Unbal - GND output.
Front panel controls: switch in the out position threshold just changed from yellow to red, Compression 1.0 See first scope capture.

If I remove the right channels VCA the signal cleans up. Second scope capture.

Bench supply actually seems to be causing a HF oscillation 80kHz

Also weird one both VCA boards are in, driving left channel and put scope probe on R32 where it connects with P3 pin 3 signal cleans up.

 

[abbey road d enfer]

Also weird one both VCA boards are in, driving left channel and put scope probe on R32 where it connects with P3 pin 3 signal cleans up.

Looks like an oscillation. Maybe return OA3 to TL082.