phase splitter into LM13700 VCA to fix unwanted offset?

[Boner]

So I've been playing around with VCAs using the LM13700 OTA and the whole issue with unwanted offset has been driving me crazy for days now

In multisim I went ahead and tried running a signal into a phase splitter beforethe VCA and the output was about a million percent better in terms of offset. What do you guys think of this in theory? Good idea? Bad iead? Good results just a mirage?

I havent tried breadboarding it just yet, still playing around in multisim.

[slacker]

Assuming you mean DC offset can't you just run the output through a capacitor to remove it, or are you talking about something else?
In the real world you'll probably find you need a trimmer pot in there to balance the split signals enough to give the improvement shown in the sim. For example you could replace R17 and R46, centre lug to vref and the outer lugs to either side.

[Boner]

I think I meant bleedthrough

When you adjust the gain of the VCA via the potentiometer, the output of the VCA swings. Using a cap to filter out DC doesnt seem to filter it out

[ElectricDruid]

Interesting idea. I'll have to give it a try sometime on the breadboard.

The usual solution is to have a trimmer set up as a voltage divider feeding the OTA input that you're not using for audio. So you just feed in some DC to trim out the offset.

Using a cap after the chip would only work if you didn't change the OTA's gain. As soon as you start modulating the gain, the DC offset gets modulated and you get control feedthrough. If the control input has any audio frequency content (like a square wave LFO, for example, or a fast envelope) that'll produce audible thumps and clicks in the output even with no input signal. That can't be removed with just a cap - the only way is to try and get rid of the DC offset itself to prevent the problem occurring.

HTH,
Tom