Dbx Vca Construction

http://www.gyraf.dk/schematics/Dbx202.pdf

I don't want to be lazy, So I'm looking for some good information in how to build this model 200/202 DBX VCA... Mainly why and how to choose the 5 select resistors and how and why to choose the transistors.

Would be nice to be able to build a 202/200 vca for the GSSL and 160vu clones. If we can assemble some sort of information, I'll be happy to try and put it in a nice easy to follow instructions... maybe like some of the literature dbx gave its workers in the 70s ... anyone?? lol

So we have one obvious choice-We need to organize a team to infiltrate the DBX corporations main headquarters here in Utah and find the secret papers on how to build those mystical shiny silver things that are so mysteriously regarded!

:just kidding!. seriously I'll be researching posting anything maybe useful I find.

feel free to chime in.

AC

Hey Abe,

I made some scans of the innards of a black-can 202 if you're interested.... I really can't help in regards to
component choosing though  ;D

cheers,
dave

Sounds great, the more information the better! email them 2 me if you need someone to host it...
Thanks
AC

edit:

I'm considering to make a seperate pcb layout for the vca, so that i could easily swap it with a real dbx if I end up failing....
I would like to be able to compare our diy variant vs the original and even vs the ic version.
Without looking at the pcb, is it possible to make a seperate thatcorp vca board, that could be swapped with a 202?

abechap024 said:

If we can assemble some sort of information, I'll be happy to try and put it in a nice easy to follow instructions... maybe like some of the literature dbx gave its workers in the 70s ... anyone?? lol

Click to expand...

dbx at the time was such an advanced company they had found a way of getting rid of any type of paperwork. Know-how was transmitted by telepathy.    I'm only half-joking here; I visited the company in the early 80's when they were in Massachussets, and a lot of the operation relied on the founding fathers detaining information.

So we have one obvious choice-We need to organize a team to infiltrate the DBX corporations main headquarters here in Utah and find the secret papers on how to build those mystical shiny silver things that are so mysteriously regarded!

Click to expand...

Unfortunately, I don't think there's anything left in Utah. A lot of the archives went missing in the earthquake when the company was bought by AKG and relocated to California.
More seriously, most of the engineers who worked there at the time are out of the radar now, but I think Les Tyler and Gary Hebbert at THAT are definitely the persons to talk to; they have acquired all the intellectual property and have built a vast knowledge base on the subject.
Also David Blackmer may have some insight, but I think he was already somewhat remote from the day-to-day.

I think the biggest issue is going to be matching and thermally coupling the transistors. There is a document floating around which has the selected values written into the schematic. I would be cool to compare a few VCA's to see if there are any differences in the selected resistor values.

I've got a pair of 200 VCA's and a RMS detector from a donor 118 that I plan on using for the 160 build. That should allow us to compare the sound of the original vs the clone vca's down the road.

Mark

hi,



  Any insight David Blackmer might have imparted he won't be doing any time soon, unless you hold a sceance. He is no longer with us.


    Kindest regards


  AndyP

THAT corp sells some transistor arrays that would probably make a decent VCA. Matching and thermal tracking for the IC based transistors  would be quite good.

It's been a long time since I messed with the old school VCAs. I suspect using precision resistors for the low impedance parts, and trimming out distortion will get you most of the way there.

Is this an exercise to replicate the old VCA distortion? The new VCAs are much cleaner. If this exercise is to get the old school grunge, too much matching and trimming may be at cross purposes.

JR

I would look at copying the gold can VCA's.  The black can ones are much more noisy.

strangeandbouncy said:

hi,



   Any insight David Blackmer might have imparted he won't be doing any time soon, unless you hold a sceance. He is no longer with us.


     Kindest regards


  AndyP

Click to expand...

Damn! Why am I always the last informed? 

abbey road d enfer said:

Also David Blackmer may have some insight, but I think he was already somewhat remote from the day-to-day.

Click to expand...

That's one way of putting it, I suppose!

@ JohnRoberts, I think this thread is largely a spin-off from the dbx160 'clone' thread, where the board had layout options for a NOS dbx can, or an ersatz THAT 'emulation' (a la Gyraf SSL clone) or the third parallel option of an individual discrete layout for a 'roll-your-own' experience.

I've done it before using Analog Devices' MAT-04 as the core of the blackmer cell, but I recommend it to nobody.

I understand the pleasure derived from 'self-build' as much as anyone, rather like growing your own tomatoes; NO cheese-and-tomato sandwich can EVER taste as lovely as one using home-grown... (and this coming from somebody who isn't even particularly 'keen' on most tomatoes!) -There's undoubtedly a great satisfaction to be enjoyed from building something which not only works, but works WELL, completely from scratch, and the deeper you go, the deeper the sense of satisfaction can be.

Speaking for myself, I would say that building a VCA is the point at which one crosses the line from 'increased satisfaction' from a more 'home-grown' build, to the point where one has to start making accommodations or excuses for why it's not as good as it could be.

MAT-04's (and the THAT equivalent) are one thing, but trying to do it using individual devices is a LONG way across the line. -You'll ALWAYS be fighting noise and distortion.

-I hear time and time again -frequently via Private Messaging- from people who are looking for gold-can or black-can VCAs "in order to have some sonic alternatives" and I have to say that I cannot fathom that approach. -I love different distortion 'character' from -for example- different guitar amplifier designs, just as uch as the next man... but black-can VCAs? -they were the very threshold of acceptability to me. -They represented the first level at which VCAs crossed the line from 'unpleasant'.

I rationalize it by telling myself that not everybody has had the same experiences as I have, and that there's an understandable wish to 'explore', but anyone who's ever wandered into a minefield tends to have the sort of experience that puts them off going back to re-explore... That's my personal experience with VCAs.

Having played with them casually, I now have such a high regard for THAT corp. and its product, that I would never DREAM of trying to build another VCA...  In simplest terms, it's just working harder, to make an inferior sounding result.

Keith

SSLtech said:

I've done it before using Analog Devices' MAT-04 as the core of the blackmer cell, but I recommend it to nobody.

MAT-04's (and the THAT equivalent) are one thing, but trying to do it using individual devices is a LONG way across the line. -You'll ALWAYS be fighting noise and distortion.

-I hear time and time again from people who are looking for gold-can or black-can VCAs "in order to have some sonic alternatives" and I have to say that I cannot fathom that approach.

I rationalize it by telling myself that not everybody has had the same experiences as I have, and that there's an understandable wish to 'explore', but anyone who's ever wandered into a minefield tends to have the sort of experience that puts them off going back to re-explore...

Having played with them casually, I now have such a high regard for THAT corp. and its product, that I would never DREAM of trying to build another VCA...  In simplest terms, it's just working harder, to make an inferior sounding result.

Click to expand...

Amen.  Here in the age of wide-eyed DIY, there will always be an army of people who think they know better.  There will be a few people obsessive enough to build it as well as, and that will give the rest a sense of irrational exuberance that cannot be argued with.  Many will build it, and having listened to too many 'distortion as point of life' records, or never used any real quality factory supplied equipment, will decide it sounds just fine, and call it an exciting new tool.  If they are happy, I will be too.  But yes, it's really easier to buy the part from the experts, and try to move on to bigger and better life goals.  Part of this is the false premise that we are now more advanced, and that it trickles down; some things don't.  I still don't build my own engines with a mill and a drill press; it can be done, but why?  I like building things too, but when it comes to cloning, I don't see the point in many cases.  If I want that one thing badly enough, I will expect to need to buy the real thing.  Obsessing over a recreation seems like a tailspin to me.  YMMV.

I don't understand the nostalgia for old stuff just because it is old. There is a thread elsewhere singing praises for old opamps (ugh).

The newest generation THAT corp VCA is actually a much different animal than those old crusty early VCAs. No amount of selecting and trimming can beat the results of several generations of IC development. 

Dynamics processors will be colored enough by the side chain gain manipulations, why add more baseline noise and distortion if you don't have to?

But I repeat, what is the intent of the OP..? if he wants to get the exact "sound" of the old school VCA, make one the old way... but be careful about what you wish for... they weren't very good.

JR

Or to restate my rambling, buy the real thing if you must have the exact sound.

If it's all about fun on the test bench, with no huge letdown if failing, party on.  Just not for me or my time. 

Wow, wholly discouraging ramblings batman!  ???

It's not Geerslt***tz is it?

Come on guys, there's something to be said for trying to obtain a goal. Maybe it's a waste of time, maybe it isn't, that's really not for anyone to judge. I'm sure someone said the same thing to Blackmer at some point.

Anyway, dbx 1** series are ripe for picking of 200 VCA's and RMS modules and can
be had cheaply enough. I've got a donor here that I've got exactly $30 into.

160's definitely have a flavor, largely because of the type of technology involved. We're not talking 202's here guys, at least not for the 160 clone. If it's your cup of tea is a topic for another discussion, perhaps in Studio A.

I wouldn't trade my 202C based GSSL for anything; it's another extremly useful crayon in the box, that's all.

Mark

I'm clearly a curmudgeon.  I just don't see the point of cutting the grass with my teeth, when the lawnmower works so well.   I don't need to milk a cow; even after mastering all the bits around it, I could never need that much milk.  

You are free to ignore me, but I wouldn't ignore SSLtech or JohnRoberts.  

I have trouble watching people delude themselves.  I may be wrong.  I don't think so.  

People on GS generally don't know what they're talking about; that's a difference.  

I want to stick my hand in this fan blade."  

"No man, don't do it!"  

"I dunno, maybe he should."  

I had great results when I stuck my hand in one, he definitely should."

Some people take these conversations seriously.  

It's easier to save the time, and buy the 160VU.  They're not worth a fortune.    Those are facts in my world.   They clearly aren't in others worlds.    

Buy real dbx 200 series modules, and stick them in the clones.  Amen, sounds reasonable.  

Make a priority list for your own DIY, and then ask yourself where replicating this particular aspect of a part fits in the hierarchy; is it worth the time?    

I'll stop with the projected and expected realism.   Enthusiasm is great, but it should be tempered with realism.  

Consider this document again.  Particularly the last paragraph of the first page.   Consider that tempco effects will be different once mounted in a particular box (the thermal coupling and potting box helped this), unless you can make your test jig mimic the exact end environment.  

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

Make note of the number of people having difficulty matching FET's for stereo 1176's; this is far more involved. 

Matching replacement transistors for gain characteristics in 40 year old devices is no walk in the park sometimes either.  If you have Langevin AM16's or Altec 9470A's with bad outputs, it can be a long and frustrating trial and error process to simply achieve flat frequency response on the bottom end.  You really need a hacked module with transistor sockets fitted to get a match, and the gain of modern 'identical' parts is always so much higher than you get oscillations.  You have to source original parts, or alternates, or the lowest quality of the moderns. 

I'd almost rather try to make my own tubes. 

I know, I'm no fun at all sometimes.  

JohnRoberts said:

I don't understand the nostalgia for old stuff just because it is old. There is a thread elsewhere singing praises for old opamps (ugh).

Click to expand...

Our mutual acquaintance Mr. Katz used to have a lovely signature:

"There are two kinds of fool in this world: one who says 'This is old and therefore good' and one who says 'this is new and therefore better'!"

Biasrocks said:

Wow, wholly discouraging ramblings batman!  ???

Click to expand...

Do not confuse realism with discouragement.

Biasrocks said:

Maybe it's a waste of time, maybe it isn't, that's really not for anyone to judge. I'm sure someone said the same thing to Blackmer at some point.

Click to expand...

The POINT of this is to that there may be people -lots of people- who would say "I built this because I thought it would be decent... for pity's sake, if you KNEW it was going to be significant effort for an inferior result, why didn't you TELL anyone?"

I think that it's not helpful to suggest that people shouldn't post their own experiences if they're not 'sunny' or optimistic.

I can think of several dozen things I've undertaken where I really WISH people would have told me I was wasting my time... (although I might not have listened anyhow!)

As I mentioned elsewhere, by all means build it, and if your aim is to learn and study why some things don't work as well as others, this can even be a fine thing to study. -However, if your primary aim is nice sound, you'll never get anywhere NEAR what you can achieve with a THAT component.

Keith

SSLtech said:

Do not confuse realism with discouragement.

Click to expand...

Hell no, I'm a realist.

I'm the guy using the VCA's out of a 118.

Biasrocks said:

Maybe it's a waste of time, maybe it isn't, that's really not for anyone to judge. I'm sure someone said the same thing to Blackmer at some point.

Click to expand...

The POINT of this is to that there may be people -lots of people- who would say "I built this because I thought it would be decent... for pity's sake, if you KNEW it was going to be significant effort for an inferior result, why didn't you TELL anyone?"

I think that it's not helpful to suggest that people shouldn't post their own experiences if they're not 'sunny' or optimistic.

I can think of several dozen things I've undertaken where I really WISH people would have told me I was wasting my time... (although I might not have listened anyhow!)

Click to expand...

My intention is not to discourage anyone from posting their experiences. Hell, that's what makes this place what it is and I'm certainly in no place to even entertain asking people not to post.  8)

I reacted to a series posts that were all "why would you do it???" Perhaps someone underestimated the time and effort it would take to get a satisfactory result, but we all learn from the experience and that can't be a bad thing.

As I mentioned elsewhere, by all means build it, and if your aim is to learn and study why some things don't work as well as others, this can even be a fine thing to study. -However, if your primary aim is nice sound, you'll never get anywhere NEAR what you can achieve with a THAT component.

Click to expand...

I have to disagree, I find the 160vu to be a very pleasant and useful sound in my productions. There's a reason why these things are sought after to this day.

Mark

hmmm....The only reasons, I would even care to want to try to build my own VCA are:

1) Main Reason for me is SOUND - I haven't had the chance to discrimintely listen to a THAT chip vs. a Discrete VCA. I have much to learn and the experience of the people on this forum is priceless. If it is  wasted effort, as it sounds it could be sonically (if the discrete just sounds BAD) then it might be  a waste of time

2)  second is just to learn. This is an end in itself

Thanks
AC

Hi,

  Abechap, imho, you have to discriminate between two issues here.

  I would summarise as follows.

1) Discrete (original vca, = highly desirable. ( i can only vouch for 202c, and 2001(classA), not the 200, or 202.).
2) Building your own that performs like an original = highly improbable.

  I have several G-SSL variants. I will list them in order of most frequent usage.

2001's - every day, mixbus, other bus duties( i have 2 of these)
202c's - every day, drumbus
2151's - sometimes, drumbus
2181's - hardly ever.


  I sold my 202XT's. They sounded just like 2151 to me. They are probably a tad quieter, though.


  draw your own conclusions. Just don't let anyone tell you that there is any comparison between the discrete versions and the monolithic ones that follow. They are all great, but some are greater than others. This is not snakeoil, just the benefit of my experience.


  I would just save my pennies, and buy some originals if I were you.


  Kindest regards,


  AndyP