Bipolar caps in Juno 6

I'm restoring a Juno 6 and it has some 1uf and 10uf bipolar caps in the oscillator / filter. I'm wondering why the VCF needs to be isolated with the caps on either side? And could these could be omitted and replaced with jumpers? I don't see why the whole thing wouldn't be sitting at ground and they would be unneccessary. Perhaps to protect the VCF chip?

The IR3109 is a custom chip with four variable transcunductance amplifiers for the voltage controlled filter (VCF)

That schematic does not show me enough to determine voltages but the chip is likely single supply. Since that schematic uses two ground like symbols I will ASSume one is actually ground and other is a + or - DC supply rail.

You can probably substitute regular polar electrolytic caps once you determine the static DC biases around the chip.

JR

Here is the full CPU board schematic

OK a bunch of old school CMOS so single supply rail is likely +V .  I see a LS42 logic chip on same rail and that is 5V digital logic.

I suspect you can use polar caps with the + end facing toward the 3109, but if you have a working unit, easy enough to confirm with a VOM.

JR

Voltage key. It is a dual rail +15 / -15
There also is a +5v with a un-filled up arrow

I guess the offset control on VR5 would create a DC voltage that needs blocking, but it could be + or - against the cap

Roland would have put polarized caps in if possible because they only have a few NP throughout the circuit

dmp said:

Voltage key. It is a dual rail +15 / -15
There also is a +5v with a un-filled up arrow

I guess the offset control on VR5 would create a DC voltage that needs blocking, but it could be + or - against the cap

Roland would have put polarized caps in if possible because they only have a few NP throughout the circuit

Click to expand...

I try not to speculate about what other engineers would do... I have rarely (like never) found bipolar caps the best solution.

Do whatever you want... as I suspect you will...  over and out.

JR

JohnRoberts said:

I try not to speculate about what other engineers would do... I have rarely (like never) found bipolar caps the best solution.

Click to expand...

Thanks for the help - I'm not excited about having bipolar caps in there either. Not sure what to do other than some good film caps if they would physically fit