DBX V8 VCA module teardown
« on: December 17, 2018, 10:57:04 AM »
I have found on evilbay a DBX 160S stereo compressor in need of repair

This unit uses the V8 vca modules which are notoriously prone to failure

Indeed it turned out one of the two channels had a bad vca module

These modules are entirely potted in resin, so that complicates things a bit.

Is this really to increase temperature stability or it is pure hatred for the entire repair technicians species ?

I asked for a replacement to the UK dealer for DBX spare parts and they price these at 180 GBP + VAT !!!

At this price I felt extremely motivated to get out the heath gun and razor blade and invest some time in getting the circuit board out and attempt reverse engineering it.

I did read somewhere the V8 module is in fact quad vca ics in parallel, with a driver opamp and I was expecting to find some THAT-series vcas but in fact it turned out dbx used a proprietary part which looks exactly like the THAT ics but is labeled DBX V2.

I was wondering if someone has had any experience with these ics and if they are actually re-labeled THAT parts ?


Re: DBX V8 VCA module teardown
« Reply #1 on: December 17, 2018, 10:59:10 AM »
Some photos of the hacking process

Re: DBX V8 VCA module teardown
« Reply #2 on: December 17, 2018, 10:59:44 AM »
Some photos of the hacking process

Re: DBX V8 VCA module teardown
« Reply #3 on: December 17, 2018, 11:05:19 AM »
The circuit board removed of all components and cleaned, ready to be traced

Re: DBX V8 VCA module teardown
« Reply #4 on: December 17, 2018, 11:08:25 AM »
Here you can see the point of failure, one of the traces going to the regulators had completely melted down

Re: DBX V8 VCA module teardown
« Reply #5 on: December 17, 2018, 11:37:02 AM »
Preliminary schematic

JohnRoberts

Re: DBX V8 VCA module teardown
« Reply #6 on: December 17, 2018, 11:44:41 AM »
I have found on evilbay a DBX 160S stereo compressor in need of repair

This unit uses the V8 vca modules which are notoriously prone to failure

Indeed it turned out one of the two channels had a bad vca module

These modules are entirely potted in resin, so that complicates things a bit.

Is this really to increase temperature stability or it is pure hatred for the entire repair technicians species ?
perhaps some of both...  holding junctions of discrete devices constant is useful. Making things harder to copy is another.
Quote
I asked for a replacement to the UK dealer for DBX spare parts and they price these at 180 GBP + VAT !!!

At this price I felt extremely motivated to get out the heath gun and razor blade and invest some time in getting the circuit board out and attempt reverse engineering it.

I did read somewhere the V8 module is in fact quad vca ics in parallel, with a driver opamp and I was expecting to find some THAT-series vcas but in fact it turned out dbx used a proprietary part which looks exactly like the THAT ics but is labeled DBX V2.

I was wondering if someone has had any experience with these ics and if they are actually re-labeled THAT parts ?
There were some early IC VCAs made by a Japanese company using DBX licensed design.

Do any of the THAT corp white papers describe upgrading to use modern VCAs in the old configuration?

JR
It's nice to be nice....

Re: DBX V8 VCA module teardown
« Reply #7 on: December 17, 2018, 01:29:12 PM »
Here is a preliminary drawing of the pcb

I am gonna try re using the original pcb but hopefully this will be usable in the future for somebody who wants to save 200 quid for a new vca

Re: DBX V8 VCA module teardown
« Reply #8 on: December 17, 2018, 01:36:10 PM »
There were some early IC VCAs made by a Japanese company using DBX licensed design.

Do any of the THAT corp white papers describe upgrading to use modern VCAs in the old configuration?

JR

There is a THAT design note about replacing the older modules like the ones used in SSL consoles 202C, 202XT, etc.

http://www.thatcorp.com/datashts/dn127.pdf

But let's keep in mind the V8 module is much more recent. The DBX 160S and 160SL who used these were manufactured I believe sometime in the 2000s, definitely after Harman acquired DBX.

I didn't expect that DBX was still making their own ics, I assumed I would have found THAT ics inside the V8 module.

But maybe the DBX V2 ics are just custom labeled THAT parts ?

squarewave

Re: DBX V8 VCA module teardown
« Reply #9 on: December 17, 2018, 03:41:20 PM »
I very seriously doubt DBX (or Harman) would use THAT parts. All of the old and modern (and THAT) VCAs are based on the Blackmer circuit which originally came from DBX so I see no reason why they would change that.

But if you're just trying to get the thing running, I would find a THAT based module or make one if the V8 pinout or control or behavior is different. The THAT VCA is going to be hard to beat so if the ins and outs are the same, I would definitely just use THAT.


EmRR

Re: DBX V8 VCA module teardown
« Reply #10 on: December 17, 2018, 03:56:13 PM »
I very seriously doubt DBX (or Harman) would use THAT parts.

Quote
[THAT was] Originally formed through a management buyout of the dbx OEM (Original Equipment Manufacturer) division

which usually happens because the parent wants to offload ownership of a piece while still using them as primary supplier....but no telling now. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

JohnRoberts

Re: DBX V8 VCA module teardown
« Reply #11 on: December 17, 2018, 05:42:17 PM »
That corp was founded by several former DBX engineers to exploit that IP and make it easier to sell VCAs, etc to former competitors.

Dave Blackmer hasn't been around for a while  (RIP 2002), but he left DBX well before that.

JR
It's nice to be nice....

abbey road d enfer

Re: DBX V8 VCA module teardown
« Reply #12 on: December 18, 2018, 02:16:59 AM »
I did read somewhere the V8 module is in fact quad vca ics in parallel, with a driver opamp and I was expecting to find some THAT-series vcas but in fact it turned out dbx used a proprietary part which looks exactly like the THAT ics but is labeled DBX V2.

I was wondering if someone has had any experience with these ics and if they are actually re-labeled THAT parts ?
Having spoken with Gary Hebert and Les Tyler at the time, I know for certain they are re-labelled THAT parts. The prototype version used 8 VCA's (hence the name); the idea was that it was not necessary to use the highly selected parts (2181).
I don't know what they decided when they chose to scale down to 4.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

JohnRoberts

Re: DBX V8 VCA module teardown
« Reply #13 on: December 18, 2018, 10:16:07 AM »
Having spoken with Gary Hebert and Les Tyler at the time, I know for certain they are re-labelled THAT parts. The prototype version used 8 VCA's (hence the name); the idea was that it was not necessary to use the highly selected parts (2181).
I don't know what they decided when they chose to scale down to 4.
Perhaps they put it on the bench and determined that 8 was not better than 4.... certainly not 2x.

JR
It's nice to be nice....

squarewave

Re: DBX V8 VCA module teardown
« Reply #14 on: December 18, 2018, 10:29:57 AM »
Perhaps they put it on the bench and determined that 8 was not better than 4.... certainly not 2x.

JR
That THAT design note says that the newer process improved performance enough that 8 wasn't necessary.

JohnRoberts

Re: DBX V8 VCA module teardown
« Reply #15 on: December 18, 2018, 10:41:12 AM »
That THAT design note says that the newer process improved performance enough that 8 wasn't necessary.
Gary Hebert wrote an AES paper describing the new generation VCA platform (when it was new), not surprising. The new stuff really is better.

JR

PS: Now for TMI Gary Hebert owns/plays an old Ludwig drum kit.
It's nice to be nice....

abbey road d enfer

Re: DBX V8 VCA module teardown
« Reply #16 on: December 18, 2018, 11:15:54 AM »
Perhaps they put it on the bench and determined that 8 was not better than 4.... certainly not 2x.

JR
What I meant is I don't know if they chose to opt for the better parts or continued to use the vanilla types in the V8. Indeed the 2155 with the new process is better than the former selected 2151.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

squarewave

Re: DBX V8 VCA module teardown
« Reply #17 on: December 18, 2018, 11:25:01 AM »
Indeed the 2155 with the new process is better than the former selected 2151.
You  mean 2181? 2155 is old.

abbey road d enfer

Re: DBX V8 VCA module teardown
« Reply #18 on: December 18, 2018, 11:50:05 AM »
You  mean 2181? 2155 is old.
Sorry, I meant the 2180, the non-trimmable version.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

squarewave

Re: DBX V8 VCA module teardown
« Reply #19 on: December 18, 2018, 12:04:02 PM »
Sorry, I meant the 2180, the non-trimmable version.
Just so that I'm clear, is the 2181A is the absolute best performing VCA available?


 

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