VCF/VCA schem (link)

[Paul Perry (Frostwave)]

Interesting LM13700 based VCF and VCA from the British Oscar synth, redrawn by the legendary Sam Hoshuyama.
http://houshu.at.webry.info/200803/article_1.html
Interesting because it is +-5V - I'm sure it would work on +-4.5, so that's 9V!

[R.G.]

Thanks, Paul. I very much like OTA SVFs!

[9 volts]

This is off the topic, I bought at a garage sale this thing called a vca 110 (looks like an oscilloscope plugin or something). I got it for the components but now wonder if I could use it somehow (eg vca?).  Anyone used or know anything about this thing?
ps thanks for the link

[Paul Perry (Frostwave)]

I can't say anything without at least a description of what it looks like - is this it? http://www.jaguareletrica.com.br/imagens/weg_img49.jpg

Maybe you have part of a modular synth! if so, I'm sure you could sell it for much more than the worth of the parts. Any manufacturer name on it??

[StephenGiles]

Many thanks. This could no doubt be driven by an EH Space Drum sweep generator, modified for LM13600 and .......who knows what else.......but judging by the pathetic amount of interest in the Royal Filter................ 

[slacker]

Looks interesting. I like the fact that it's got 2 filters, I bet there's some great sounds to be had by feeding them different CVs, like an envelope follower into one and and LFO into the other. Time to order some LM3700s me thinks 

Out of interest what is U4 (bottom left) doing? Looks like some sort of bias voltage?

who knows what else.......but judging by the pathetic amount of interest in the Royal Filter................ 

I don't know about anyone else but I'm interested in the Royal Filter I just can't really add anything to the discusion because I don't have the skills to figure it out without breadboarding it and I haven't got any time to do that 

[StephenGiles]

Thanks Slacker , I might have some time daylight time over Easter to try and crack that sweep generator that I keep barking on about. But this VCF will join my flight reading folder!

[Paul Perry (Frostwave)]

Out of interest what is U4 (bottom left) doing? Looks like some sort of bias voltage?

That would be my guess as well. Looks a strange way to do it, but if there was a spare 1/2 of a LM13700 left over..
One really has to give credit to the OSC stuff, like Korg, they are very original.

[9 volts]

Thanks Paul, it has ave written on the front panel and has an input and output. Two controls gain and eq both look like trims accessible from holes in the front panel. It's rear slts into something. It would be cool if it's part of a modular synth as I've always wanted to build one at some stage (eg when the skills  are up to it)

[Paul Perry (Frostwave)]

9 volts, does it look like part of this: http://www.broadcaststore.com/store/model_detail.cfm?id=11558

because, there is a voltage controlled amplifier module called an "AVE VCA" that forms part of some high-end broadcasting mixers.
the idea is, you can use the voltage controlled amplifiers to fade a bunch of independent signals up & down simultaneously, by tying the control voltage inputs together.

[9 volts]

It has that slot in look about it, but the output fits my oscilloscope probe (not sure what that plug ids called. I noticed one side panel has acces to adjustable trims also. These are HF-comp. opt-1, opt dc,ipt-comp and ipt dc. I'd love to try and find out what it is. Maybe I'll take some photo's of the board etc. It has an older possible kit look about it eg screwed together alloy, but all the writing is atched so it's not hand made. Thanks again

[Paul Perry (Frostwave)]

maybe it is a CRO plugin after all, the HF-comp might stand for "HF compensation", like where you have a small trimmer cap that compensates for lead capacitance.
Whatever it is, they obviously have more interesting garage sales in your neighbourhood!

[9 volts]

Ha, thanks Paul. At any rate, I think I'll hold out on gutting it until I work out whether I can use it somehow. ps on topic- those oscars have a great sound.

[Paul Perry (Frostwave)]

yeah, the Oscar has it moments, when they work.
The main problems were low quality sockets that tarnish... and also they kept rewriting the operating system code, so no two behave exactly the same.
it's very quirky, which is an advantage, in that what's the point of the same synth made by a dozen different companies?

[slacker]

If anyone's interested I threw one of the filter sections together on breadboard this afternoon. It works fine on 9volts, I just used a voltage divider to give a 4.5volt vref and connected all the points marked ground to that and connected the -5v points to ground. Apart from that I built it as per the schematic except I used lm13700s instead of lm13600s because they were what I could get hold of.
For the resonance and cutoff CVs I just used 100k pots as voltage dividers across the supply and connected the wipers to the control pins through 20k resistors.
It sounds very nice in both LP and HP modes, it's very clean and quiet across the whole frequency range. It self oscillates if you crank the resonance up but it does so it a pleasant way and you can get that nice ringing effect if you get it just on the edge of oscillation.
It's definitely worth having a look at if you like filters.

[Paul Perry (Frostwave)]

Thanks Ian, it really helps when someone actually verify circuit!
I must say, I was hoping when I gave the link, that someone would do the hard yards. Sweet!

[slacker]

Here's a couple of quick samples of the filter in action. These are still just one stage, I haven't had time to build a second one yet.

http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/album170/oscar.mp3.html Guitar with envelope follower

http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/album170/oscardrums.mp3.html Drum loop with knob twiddling

Enjoy