BA6110 VCA - Clear some CV questions up for me please?

rlorentz · Joined: Aug 13, 2008 Posts: 16 Location: Washington, DC

Ok,

I've got a load of BA6110 chips and I'm trying to make a bunch of (simple) VCA's based from these. We're talking synth use here, so let's not wander to the realm of hi-fi (or I wouldn't be using these chips anyhow).

There's not a whole lot to the circuit except for an Offset Adjustment and a variable voltage.

#1 Vr (Offset Voltage): This looks like it will bias the signal above or below 0v. Should this just be a trimpot and I calibrate it to keep dc bias out of my amplified signal? Or does it need to be a pot to change bias of different signals?

#2 Variable Voltage between -15v, going to Pin 7 as Icontrol through a 30k resistor. To me it looks like I would hook up a *0 to 15v* voltage source ground to the BA6110's -15, and the hot of the voltage source to the 30k? OR, should I be feeding in a *0 to -15v* inverted CV there?

My source for the VCA CV is a 555 based ADSR that is not inverted. If one needs an inverted cv (I see this mentioned a lot), how do you do it? I know how to set up an opamp as an inverting amplifier, but the minimum gain looks like it is 1 + [resistor ratio, 1 at lowest]... so there must be another way to do this without changing (maybe clipping) the signal...

Thanks for any advice, trying to breadboard this today and I've been chewing on the problem all week in my head...

Robert

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BA6110 App Note for use as VCA

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211 · Joined: Jul 18, 2006 Posts: 50 Location: Marseille - France

Tony algood (Oakley modular) made some years ago a triple vca unit using Ba6110. Lately he replaced the 6110 with LM13700. There are all the answers you ask in his vca design.

I made his 6110 vca, and it works great. I'd like tell to you more about his circuit, but these schematics are copyrighted by tony, he's still selling them for only 2-3 €.

I strongly suggest you to contact him.

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

There's also the roland dual-VCA that Curetronic has a 6110-version of.
It is linked from this very forum, or more directly: http://www.curetronic.com/curetrbau/neubau/130m.htm

This original schematic uses the BA662, but Curetronic uses 6110's.

rlorentz · Joined: Aug 13, 2008 Posts: 16 Location: Washington, DC

To directly answer my question for any others curious on the matter,

The CV that controls the BA6110 is NOT INVERTED, which becomes obvious looking at the schematics held in the rest of the datasheet.

What you do is hook your CV "ground" up to -15 and have it go up to 15V as it's peak amplitude. (Maybe can go higher, you're controlling via current not voltage, I haven't analyzed the max because it's not important to me right now)

Thanks for the responses and hopefully this helps somebody! I got clued in on this answer thanks to the friendly faces on the SDIY list.