I have Come into possession of a OAS-24 (24 channel automation system) from B&B/Aphex Audio. How do I best rejuvenate this?

[richeyrub]

I was clearing out a loft in a studio and i found this.

At first glance it seemed to be a power supply and IO module for a tape machine, But for what i wasnt sure. this studio used to have a bunch of MCI stuff (consoles, tape) so I assumed maybe that but nothing I looked up from MCI remotely resembled this.

Not helped by the rear of it looking like this which i felt looked alot like some of the mci interconnects. But there was 0 branding on this thing, and that didn't sit right with me.


And for a while my looking up "OAS VCA" and "B&B Audio" didnt really bring up anything useable until I quite literally put 2 and 2 together and googled them together which led me to finding out that this was actually a 24 channel automation system Based around 1537a VCAs, which where found in early SSls from what i understand.

Unfortunately, I have no remote/CPU for this thing, and i haven't found it. (Yet). Either way, if i do find it i expect there to be issues (I mean its been dormant since the late 80s from what I can tell), and potentially outdated, and not really easily worked into modern systems. I do have a analog sound craft series 4 that ive been rebuilding and think it would be fun to incorporate this into that. From an analog signal line, that's not the hard part.

From what i understand these VCAs just need a voltage level to operate on pin 8. If i hijacked this with something like an Arduino just outputting a constant voltage (that i can adjust as needed) would that be enough to get this to work and have the vca respond? It seems the entirety of the circuitry is on these cards, with the exception of the cpu. Id love to experiment with making a detection circuit and making a gate/compressor out of this, or even building my own midi controlled automation computer. I know these VCAS individually are worth a decent amount, as well as the transformers. but this thing seems to cool to part out for cash, and would be hard to sell as a whole without any remote. ( I am supposed to sell this on behalf of the studio, but that deal was made before we knew what it was, and thought it was some extra tape machine IO, and the owners of the studio seem interested in what could come of this)

The reality is i very Noobish when it comes to this stuff, and I don't know if Y'all cant tell, but I'm most definitely not from the era this machine is from. (Its about twice my age)


Hopefully someone would have some information or experience with this thing!
-RR

 

[radardoug]

I would say you dont have the ability to do much with it, and you dont have all of it, and you probably have next to zero documentation, so sell it, give it away, or dump it.

 

[Monte McGuire]

On the other hand, you've got a cute Jensen output transformer there as part of a complete signal path with a B+B VCA, so it seems like some sort of compressor hacking could be easy to do. People held the 1537A in high regard back in the day. All you need is a detector circuit, which could be a lot of fun to experiment with. Nobody wants a VCA mix automation system anymore, unless it's a well known quantity with a decent computer, so I'd consider your 'find' to be a pile of VCAs waiting to be hacked into dynamics units. The annoying parts (signal path, chassis and PSU) are already done - all that's left is the detector circuit... the fun part! You have 24 channels too, so you could fit one dynamics processor for each channel, just like an SSL. Don't throw it out please

 

[plimousse]

Please look page 3, High performance system. It's the heart a OAS-24...
You need only control voltage to drive your VCA
Cheers,
P.

 

[SIXTYNINER]

Please look page 3, High performance system. It's the heart a OAS-24...
You need only control voltage to drive your VCA
Cheers,
P.

Cool .... ,
on the paper seems to have nice performances ,
also applications type are interesting....,

very worthy of a working test , and more important how it sound ,
before give it away ,

 

[richeyrub]

I know it’s been a minute but I figured I’d give an update. Unfortunately I haven’t gotten around to much, funds are pretty low personally so I can’t go out willy-nilly buying things to test and build for this.

in fact I only got around to actually turning it on yesterday, and despite this fan on the psu being from the 80s, it’s one of the quietest, fans I’ve ever felt, or heard. And it’s no slouch when it comes to pushing air either.

I started it up and tried to check for voltage from the PSU but I can only get a couple millivolts, which didn’t seem right to me, but I still decide to put one card in and see what would happen if I ran audio through it.
It was really noisy and crappy. But I decided to try another card, and the noise floor was significantly less, but still there (albeit expected) this card actually passed audio despite no voltage. I don’t have any way to send a controlled amount of voltage to the card, so grab the battery that had about 2v in it and wired it up. Positive to the control pin input, negative to ground. And it reduced the volume. My next step is to buy an Arduino and some dacs I think, and/or probably a proper test bench if I’m actually going to take this seriously.

 

[JohnRoberts]

IIRC back in the day, the Aphex VCATT (cut only voltage controlled attenuator) made a serious run at the larger VCA business.

I don't know about availability of obscure single sourced ICs.

It will surely be a learning experience

JR

 

[mjrippe]

I have a couple Aphex VCA cards with B&B chips in the Black Market.
https://groupdiy.com/threads/fs-rca...limiters-transformers-etc.80349/#post-1032320

 

[richeyrub]

IIRC back in the day, the Aphex VCATT (cut only voltage controlled attenuator) made a serious run at the larger VCA business.

I don't know about availability of obscure single sourced ICs.

It will surely be a learning experience

JR

Well it certainly has! i havnt had to much time but currently the only way i can control this vca with my limited tools is using the natural resistance from the point of my finger to my arm. turns out 15volts is to much for the 10v fader i had so i had to improvise.

the whole thing runs on 15v from what i can tell, and by grabbing from the +15v source and bridging to the control pin on the card i get on/off control. by bridging through a fader thats built for 10v, i get fire. by using my body, i get level control! Im currently investing in tools and equipment, but im not sure what my next step is from here.

On the other hand, you've got a cute Jensen output transformer there as part of a complete signal path with a B+B VCA, so it seems like some sort of compressor hacking could be easy to do. People held the 1537A in high regard back in the day. All you need is a detector circuit, which could be a lot of fun to experiment with. Nobody wants a VCA mix automation system anymore, unless it's a well known quantity with a decent computer, so I'd consider your 'find' to be a pile of VCAs waiting to be hacked into dynamics units. The annoying parts (signal path, chassis and PSU) are already done - all that's left is the detector circuit... the fun part! You have 24 channels too, so you could fit one dynamics processor for each channel, just like an SSL. Don't throw it out please

I think my next step is attempting to make a compressor with it! is there a detector in a chip ic? wishful thinking. Currently i reading through THAT corps documentation. something like this circuit might work out just fine, but since the cards are only set up with a control in, im not sure how the "symmetry" side of the circuit would be incorporated. maybe im reading that wrong. they have simpler circuits online maybee i should start with that, but its so tempting to go all out first try!. I have a dbx 166 (original vca version) that im going to take a look at and see if i can ctrl+c ctrl V parts of that circuit.

I would say you dont have the ability to do much with it, and you dont have all of it, and you probably have next to zero documentation, so sell it, give it away, or dump it.

unfortunately thats just too much effort.