DBX Gold Can VCA "Sound"?

[mitsos]

I think the schematic and pics are from a Black can DBX 202 not Gold can DBX 202C, right?  DBX papers say the gold can was an improvement over the black in terms of noise and whatever else. 

I took a black can apart a few weeks ago, thinking to do the same to a gold, then I saw the gold was potted. 

Barclay: Do you remember how you unpotted yours? Just heat, or chemicals too?  I'd love to see the pics for reference at least. I'm sure they're a PITA to trace out though even if I had them in front of me though. 

As for finding some, there are always some on ebay, sometimes cheap sometimes not.  Cheaper than designing your own for sure though! 

 

[barclaycon]

It's a kind of silicone rubber compound that they are potted in.
I think I drilled into the side and pealed back the metal shell - then it comes away as a block allowing you to carefully remove the rubber with a scalpel or single edge razor blade.
Fortunately the rubber compound doesn't sick to any of the components.
It seems to be that the transistors are more modern plastic types rather than the metal can types in the previous version.
The only types I've been able to compare are the ones that were in the Harrison 24 series consoles (200 ?), which were black cans and sounded a bit crunchy. I know we always tried to put plenty of signal through them to get the best performance.
DBX202c gold cans which were in an MCI 600 console and also in the early SSL's,
and the version which was 8 chips in parallel on a PCB ( 202X ?)
That was the cleanest sounding.
But the character of the gold can types always seemed very appealing - particularly for compression.
Subjective, I know - but those are the ones I use.

Now. Let me try to upload a picture (!)

 

[Logic Leopard]

The schematic of dbx 202C gold can

 

[gyraf]

Great to see in it's entirety!

The Hfe marking on Q2 confuses me though, it being a jfet..

/Jakob E.

 

[JohnRoberts]

As someone who lived through the VCA wars, it is worth mentioning that at the time these were designed and used, the engineers made them as linear (clean) as they could. Any pursuit of their legacy failures to deliver linearity seems a bit phoolish.

That corp took advantage of modern IC technology to bring VCA performance up to a much higher level than discrete VCAs ever could.

JR

PS: I have one old VCA patent (US04818951 Roberts) but it was a mid performance class A VCA that avoided factory trims, later at Peavey we used DBX VCAs when they started selling them to all.

 

[Logic Leopard]

Great to see in it's entirety!

The Hfe marking on Q2 confuses me though, it being a jfet..

/Jakob E.

The measurements for Q2 I've got using automatic transistor tester which gave me something like "NPN transistor Hfe 159".
Yes, it may looks kind of weird for JFet.

 

[Michael Tibes]

As soon as you flick every channel of a mix from the VCA equipped large faders to the small old fashioned potentiometer small faders, its like a revelation!
Everything becomes brighter, wider, clearer!

That's pretty much what I remember from older SSLs. Sometimes we used the small faders for mixing if the channel didn't need automation. That's why Ultimation was developed.

I guess the only way to find out would be to build another mixbuzz with gold cans and A/B them?