Modular VCA's

Hi guys,

I have not spent the hours it would take to read through all of the info regarding VCA's on this forum, so I'm not sure if anyone here will be interested in this. I have designed a PCB for a modular VCA utilizing four THAT 2181LB VCA's and the associated parts to glue it all together. Since I really enjoy this forum I thought I would offer them for sale here if anyone is interested (before I offer them elsewhere). I may be posting this in the wrong section. Anyway, I'm thinking the price would be less than $100 each- give or take depending on how much I have to assemble/test. There is some setup required for best distortion performance. I don't have hundreds of these to sell, at least at this point, therefore since I feel that this is a really good deal I can't sell more than a handful to any one person (I know that some of you have built more than one GSSL). I will have a photo to post later today.

Anyone interested?

Tim

Do I understand right?

$100 for a single VCA module?

:grin:

Hello, this is interesting, but what's the difference in sonic quality / noise and distortion specs in your modular VCA in comparison with a (trimmed) off the shelf THAT 2181LA? Any specs or example sound files?

I do a decent amount of repairs on DBX comp/lims. I see a fair number of bad modular VCA's, and it seems that there are very few sources for these things. So, I decided to make some for my own use because everyone else seems to want approx $200. Maybe I have missed the boat somewhere, if my projected price is way off mark please show me where I could have bought them for less! I am not talking about a single VCA that sells for $4.50-ish, I'm talking about a PCB that will fit the old dbx type footprint as used dbx 165's, SSL compressors, etc. The old dbx stuff has discrete transistors in their "gain cell" that were matched for temp stability,etc. Definitely not an easy DIY project - I have been warned off of that by those who would know.

I am still in the process of ironing out the fine details of setting them up, gathering proper input and output resistors, etc. I do not have any sound files to share as of yet, but the benefits are lower noise and distortion - but you can still mess it up with the SYM pot if you want. This is where I'm not sure if anyone here will be interested in these or not. If you like the higher distortion, etc., of a single SIP VCA, then these things are probably not worth the $ or effort to install.

Tim

I think you'd need to get price at around $60. 202C's can be found in this price range...they are fairly plentiful in console automation systems. I got mine from Randy Blevins of Blevins Audio Exchage, came from an MCI 500 series console fader unit.

For a 4X parallel SIP VCA arrangement....
Cost is primarily:
4X VCA's ($6 ea, $24)
1X Buffer IC ($7 or so for an AD797)
2X Pots for 'magic' low level and high level distortion adjust ($2 ea)
1X PCB ($10)
2X filter caps ($1 ea)
10X resistors ($.1 ea)
6X pins ($.1ea)

Total cost should be under $40-$50 depending on quanity purchased...

Just my stab at it....

Cheers,

Kris

If you cut out (or copy/paste) the area around the VCA's on the SSL-Clone compressor PCB and mount the related components, you have a decent 202-replica. I lifted it from a 202XT, I think.

Modern-day 2181's - even in singles - are way better than the old glorious modules..

Jakob E.

I bought 2 THATs 2002T (I think) on the Black Market, 4 x 2181LA, for $65 each.

Can you offer any impressions of the 2002T vs a single 2181 VCA?

$65 is a good deal, I would think, for any modular VCA that works. Considering parts cost, it would not be worth the time it takes to assemble and test one of these things for $65. This reminds me of trying to make some BA440 op amps for a 1081 - I did the PCB layout and then found out that I could buy used ones for WAY less than I could make them for (and I was looking at quantites of 50 or so), especially counting the time it would take to assemble those crazy things.

[quote author="q2audio"]Can you offer any impressions of the 2002T vs a single 2181 VCA?[/quote]
Not yet, but soon ...

... and look at the forums Black Market:
DBX 202 VCA Modules for sale. $50 each.

q2audio, instead of trying to come up with a fabricated modular IC, which may be hard to sell owing to the other VCAs available why not just sell the PCB? That way, you get a price break for buying in quantity. I'd be interested in buying some PCB's to make my own modular VCA's. Then I could put 2181LAs in, and choose the buffer IC, etc.

Just a thought.....since I'd planned on doing something similar myself.

Cheers,

Kris

Actually, I think that selling PCB's would be the best solution for anyone interested. Populting them with pre-trimmed VCA's would eliminate a few parts from the PCB as well as the pain of adjusting them. Would $10 each (+ acutual shipping cost) be fair? They have one problem, and that is a pad that somehow was moved by .050" at some point while I was laying out the board and I did not catch it until it was too late. This is no big deal since it is easy to put a bend in the pin and it lines up with the original footprint. At the $10 ea. price I would install gold pins and make the necessary bend.

There is one IC buffer "on board" and it only buffers the control voltage, the audio comes in directly to a SIP resistor bank and goes out directly - no caps or IC buffers. I suppose someone could change this from the 5532 that I use to something more expensive, but the important thing is to drive the Ec port with a quiet, low-Z source.

Tim

EDIT: I have a photo of a VCA but nowhere to post it. Anyone interested in a photo send me your email address and I'll forward it to you.

EDIT: added photo