Hi all, I am having a problem with my Arp 2600 Ring Modulator which I am really hoping someone can help me with as I’d rather avoid a hefty repair bill.
According to the service manual, there should be no (< 10mv) output from the ring modulator when the VCO1 slider is down and the VCO2 slider is up, however the output is very loud. Raising the VCO1 slider while the VCO2 slider is up does cause some ring modulation but it’s only a very slight change to the VCO2 tone. It’s like the balance between VCO1 and VCO2 is wrong - VCO1 is too quiet and VCO2 is too loud.
The problem is present regardless of the DC/Audio switch position. I have tried adjusting the trimmers as described in the service manual but they do not fix the issue. R33 doesn’t appear to make any difference to the levels. I have checked the circuit boards and can’t find any obviously broken/burnt out components/bad connections/etc.
Does anyone have any idea what might be causing this? Any ideas would be greatly appreciated!
I am no electronics expert but I have a digital multimeter and an oscilloscope and I am reasonably comfortable with taking measurements, replacing components etc so I’m hoping that with a little bit of help I can fix this myself.