dbx 160vu clone

[damnyankee]

ssltech from another forum recalled this about the dbx 202 vca (the later black can version also found in the 160/161 VU):

"dbx found that the transistors had to be closely matched, and also be extremely well-coupled thermally. Eventually it was decided that monolithic construction was the best way to achieve this... hence the 2151 package type.....there is a large white 'thingie' around some of the transistors. If I recall correctly, it's absolutely crucial to maintaining the stability of the distortion trim. Otherwise you'll find yourself with a unit that just sounds plain old bad [which may explain why the transistors are glued/potted in the "white thingie"].

-please, please please bear in mind that VCAs got a really really bad name because of the distortion artifacts in a time when pleasant tube distortion was a recent -and strong- memory. By all means try to build it, but I hope everyone knows that there are some pretty wierd, voodoo things going on around the blackmer cell, and many competitive "mee-too" VCA manufacturers set up at the same time foundered owing to not being able to make one without some near-catastrophic sonic charateristics...

Try trimming the distortion trim on any that you do build at different gain-settings, and then warm them up with a hair-dryer... then take a distortion reading... you might begin to understand how hard it is!!!"

We need to pay very close attention to this when we start building the 200 VCA...

 

[damnyankee]

AC,

This may help with your footprint issue.  According to dbx, the dbx 2001 VCA has the same pin connections as the 202 black can VCA which should be the same as the original 200 VCA.  For the footprint dimensions of the 2001 VCA:

http://www.vintageproaudio.com/photos/dbx2001doc.jpg

It'll get you in the ballpark anyway.

 

[damnyankee]

right, thats what were getting rid of right? the output mute circuit...
and thanks, i'm trying my best...It will be exciting if it actually works
AC

Just an FYI: if you look over page 10 of the 160 service manual on dbxpro, you'll see the tech calls it the Output Circuit Clamp...and the those part numbers correspond to the part numbers I listed in an earlier post.  Double check...but I'm pretty sure you removed all the components from your Eagle drawing.

 

[damnyankee]

I just need the footprint of the rms and vca modules then I can seriously start the component placement...

AC,

I'm looking at my dbx 119 which has the 200 VCA & 208 RMS cans.  The outer dimensions of the cans are 1-15/16" x 1-1/2" x 3/4" tall.  

Taking the long edge of the can (1-15/16") and measuring inward, the outer edge of the can to the center of the pins is 1/4".

Does that help???

 

[abechap024]

that does help! Any way you could scan it or take a picture of it next to a ruler? and try to make everything as parrallel as possible, so I'll be able to get accurate placement of the pins.
You the man Damnyankee!

Also If I can manage it I'm going to try and cram all the parts needed on the pcb for the VCA and the RMS in the footprint of the PCB that way - you can pop in a a standard rms or vca or just build it peice by peice with the space available on the board.

Also I am seriously considering having a that VCA option. I don't want to loose any good mojo from the 200 vca but at the same time we need to be realistic If I have my way I would build one with the 200 vca and one with a that vca. maybe an onboard option for either.

it looks like the 200 VCA is the most troublesome as far as matching components - building everything in thermal epoxy ETC. and while I'm sure everyone would love to keep it as original as possible, it will be interesting to see if those same people wan to actually sit down and match all those transistors and then find the ???? values for the resistors. There are 5 "select" resistors in the VCA I don't even know were to begin on what to look for when i'm selecting them.

If we could scare up a paper or something on how to build/select resistors for the VCA.

lots of questions that don't have answers till we actually build the unit I guess. I'm planing on adding the footprint/circuit for both RMS and VCA on the PCB then go from there

AC

 

[abechap024]

hey found the footprints,
thanks again for those measurements damnyankee those let me confirm the schematics floating around

 

[damnyankee]

that does help! Any way you could scan it or take a picture of it next to a ruler? and try to make everything as parrallel as possible, so I'll be able to get accurate placement of the pins.
You the man Damnyankee!

Also If I can manage it I'm going to try and cram all the parts needed on the pcb for the VCA and the RMS in the footprint of the PCB that way - you can pop in a a standard rms or vca or just build it peice by peice with the space available on the board.

Also I am seriously considering having a that VCA option. I don't want to loose any good mojo from the 200 vca but at the same time we need to be realistic If I have my way I would build one with the 200 vca and one with a that vca. maybe an onboard option for either.

it looks like the 200 VCA is the most troublesome as far as matching components - building everything in thermal epoxy ETC. and while I'm sure everyone would love to keep it as original as possible, it will be interesting to see if those same people wan to actually sit down and match all those transistors and then find the ???? values for the resistors. There are 5 "select" resistors in the VCA I don't even know were to begin on what to look for when i'm selecting them.

If we could scare up a paper or something on how to build/select resistors for the VCA.

lots of questions that don't have answers till we actually build the unit I guess. I'm planing on adding the footprint/circuit for both RMS and VCA on the PCB then go from there

AC

I have been agonizing over the 200 VCA: how to thermally match the transistors, how are we to engineer the cans, etc etc etc.

Here's what Jim Williams posted on another board regarding the 160VU:

"When I do the mod on them the VCA is replaced with a that 2180A, the opamp is changed to a National LM6172, the trim circuits are removed from the vca, the electrolytic coupling cap is replaced with a Wima 4.7 uf mks-2, bypassed with a MIT .01 PPMFX. Power supply cans are replaced and enlarged [we know with 35V 4700uf FMs] and some phase compensation and power supply bypass caps are added. Bandwidth is raise up one octave. Slew rate is increased. Distortion is lowered. Fog is removed. All is well."

So I'm OK with pulling the 200 VCA for the THAT 2180A; I don't know if the surrounding components will need to be changed or not.  I've read others who have done the mod - they state they didn't notice much of a sonic difference after the swap.

However, isn't component quality much better today than in 1967?  If so, I have to believe we could find modern upgrades to those old transistors that behave similarly.

 

[abechap024]

NICE
thats is good. If you could find out how exactly he installs the 2180 we would be set. otherwise we could probably figure it out.

but right now i've been working on the RMS unit. I made a RMS package component in DIPTRACE so the footprint and pin spacing is good to go (hopefully!) But the circuit is an issue...

I copied the circuit from the GS page (fro mthe link earlier in the post) and the given schematic doesn't have any diodes in it, which worries me because isn't the RMS unit supposed to convert the AC to DC?
Also queefbag posted a hand drawn schematic that is hard to make out, and also I don't know if it has been tested...
I'm going to google search but if anyone has a known WORKING schematic that would be great.
smeghead moment, Mark has a link to the info
I'm getting excited as the PCB is actually going to happen, just got to find these last details.

and Damn Yankee I think we should just shoot straight for the 2180 - much easier to source and for all intents and purposes sonically superior. If anyone wants a complete original 160VU they can buy one !
But if someone really sees a valid reason to NOT use the 2180 vca (besides its just not what the original used) than i would be interested to knowmaybe i'm just getting lazy - lets shooot for original VCA THEN the that replacement

But from what I've read, some old DBX 160s can just sound plain old bad. So I think were betting on the safe side of the fence
AC

 

[abechap024]

wait! holy smokes are they using the ca3083 transistors as Diodes!? Brilliant.

the bc341/bc361 are hard to find could I just substitute the BD435/6 ? Seem close enough?

Thanks
aC

 

[matthias]

I also wanted to build an 160 clone some time ago, but I have the orignal unit and I'm happy with it..
I collected some information about the vca and rms modules of the dbx 160

dbx model200 vca module.pdf

dbx160 208-209 rms module.pdf


to build a clone of the dbx 160 is not so hard to do, but i would make a new pcb layout with more options...
like....

- use original circuit for the rms module
- leave out the mute cirucit
- leave out the complete metering ciruit and add a simple gr metering instead
- make option for 200vca / that 218x vca (the characteristic is 6mV/db for the 200vca and 6,1mV /db for a modern that vca)
- maybe a switch for (old/new) signal path
- that 1200 line receiver / that 1646 line driver at input/output
- a switch for different release times

 

[damnyankee]

Matthias,

I have been waiting for you to chime in here.  I think you're the one a few years ago to tip us off that the VCA is *not* the 202, but the 200 (and thank you for posting those vca & rms pdfs).  It would be nice to have a pic of the 160VU pcb for reference (all I had was a 161VU and it was off another board).

We're going to need your help here.  We have several issues we need to resolve.

1.  Building the VCAs:
a.  the thermal issue with the transistors (do they need to be thermally matched and isolated?)
b.  finding replacement transistors for the BC109's & BC179/263's.
C.  finding/building the cans (or if we use modern transistor replacements can we leave the VCA pcbs out in the open and perpendicularly mounted to the pcb like the dbx 118???)

2.  Meters: as you know, the originals are long obsoleted.  We need an alternative.  I contacted David Kulka (as you may know, he's highly respected and a great guy).  He had some reproductions made as his company is a dbx repair center but he said they were extremely expensive to get made (his cost: $275 and his reply to me yesterday is he still has some left and he'll let them go for that.).

3.  What kind of iron would you recommend?

4.  In response to your recommendations on the new board:

- use original circuit for the rms module?  Already done; according to many (including an old dbx tech), that RMS circuit is what greatly contributes to the mojo.  Also, I see you have both the 208 and 209 RMS...I think the subtle differences is in a cap or two, correct?  It's great you have the pcbs ready for etching!  Thank you!

- leave out the mute cirucit Already done (per Jim Williams' recommendation); infact, AC has removed it from his Eagle pcb build (he posted it a day or two ago so would you please double check it to ensure we removed all those components?).  As an FYI, he's building a faithful reproduction of the pcb exactly to the 160Vu schemo [http://www.dbxpro.com/product_downloads/Service_Manuals/160-161-162%20Service%20Manual.pdf] and we're hoping the schemo is correct.  If you could double check the output mute clamp circuit to ensure we have all the components removed, it's located on the lower right hand corner of the schemo.

- leave out the complete metering circuit and add a simple gr metering instead  WE'LL NEED YOUR EXPERTISE.

- make option for 200vca / that 218x vca (the characteristic is 6mV/db for the 200vca and 6,1mV /db for a modern that vca)  AC IS BUILDING THIS IN; HE MAY NEED YOUR EXPERTISE.  HOW WOULD YOU DO THIS?

- maybe a switch for (old/new) signal path  WE'LL NEED YOUR EXPERTISE.

- that 1200 line receiver / that 1646 line driver at input/output  WE'LL NEED YOUR EXPERTISE.

- a switch for different release times  WE'LL NEED YOUR EXPERTISE.

5.  One thing I want to do is put in 35v 4,700 FMs on the mains caps to silence power supply noise.  That was a huge help on my dbx 118 & 119s (different circuits I know, but Jim Williams does this on his 160VUs too).

Anything you can do to help us get the PCBs finished up so we all can start generating component lists/where to buy would be great!  Then we have to look at how to rack 'em (mono - 1.2 rack? side by side in 19" rack? recreate the original box?

Much obliged, Mathias!

DY

 

[damnyankee]

Hi AC:

Here's the scoop on the 2150 THAT & the 2180 THAT VCA circuit: http://www.thatcorp.com/datashts/dn137.pdf

Keep in mind the the boards for the 200 VCAs and the 208/209 RMS's are already been done and ready to etch - so you don't have to worry about those.

Again my question is, can we find modern replacements for the BC-xxx transistors which don't require the thermal issues we're concerned about?  Matthias, can you weigh in on this???

Thanks for all you have done, AC!

DY  

 

[damnyankee]

A quick question:  should we be thinking about contacting Tat Purusha at some point soon to see if he would interested in doing/selling front panels/racks?  

 

[matthias]

hi

It would be nice to have a pic of the 160VU pcb for reference (all I had was a 161VU and it was off another board).

I will upload a bunch of detailed pics later this day...

We're going to need your help here.  We have several issues we need to resolve.

1.  Building the VCAs:
a.  the thermal issue with the transistors (do they need to be thermally matched and isolated?)
b.  finding replacement transistors for the BC109's & BC179/263's.
C.  finding/building the cans (or if we use modern transistor replacements can we leave the VCA pcbs out in the open and perpendicularly mounted to the pcb like the dbx 118???)

that could be very difficult
a. I think the transistors need to be matched in any way to get a good performance out of the vca. thermal matching is the second thing..

b. the bc109 is still available... don't know about the BC179/263


c.  I think you don't need the cans.
-> most of the modules are not filled with epoxy (afaik only early dbx160/161 and dbx117 modules) maybe this was just something to protect the design...
-> the modules doesn't get hot or even warm
if this was a critical point all modules would have been potted with epoxy.

2.  Meters: as you know, the originals are long obsoleted.  We need an alternative.  I contacted David Kulka (as you may know, he's highly respected and a great guy).  He had some reproductions made as his company is a dbx repair center but he said they were extremely expensive to get made (his cost: $275 and his reply to me yesterday is he still has some left and he'll let them go for that.).

I had a broken meter in one of my units and ordered an original replacement meter from musiciansservice.com I think I paid 150$. the meters are very fast but also very sensitive.
btw: A friend of mine also has a dead meter on his dbx 162.

I think it's unpossible to find another meter with the same characteristic.
maybe a fast ma-meter would work, but the needle would have to stuck in the middle if you want to get all modes (in/out/gr) work properly... without modifying the circuit.

for the 160 clone I would omit a real meter and use good led meter instead. maybe add a second led bar for input/output (like in the dbx 160x )

3.  What kind of iron would you recommend?

nothing. there's no output transformer in the dbx 160.
A neve ba283-output stage would be cool, but I think it's not necessary.

4.  In response to your recommendations on the new board:

- make option for 200vca / that 218x vca (the characteristic is 6mV/db for the 200vca and 6,1mV /db for a modern that vca)  AC IS BUILDING THIS IN; HE MAY NEED YOUR EXPERTISE.  HOW WOULD YOU DO THIS?
- maybe a switch for (old/new) signal path  WE'LL NEED YOUR EXPERTISE.
- that 1200 line receiver / that 1646 line driver at input/output  WE'LL NEED YOUR EXPERTISE.
- a switch for different release times  WE'LL NEED YOUR EXPERTISE.

I think I'll draw a schematic for you...

5.  One thing I want to do is put in 35v 4,700 FMs on the mains caps to silence power supply noise.  That was a huge help on my dbx 118 & 119s (different circuits I know, but Jim Williams does this on his 160VUs too).

that sounds good. I'd also change he power supply for something modern (lm317/lm337)

Anything you can do to help us get the PCBs finished up so we all can start generating component lists/where to buy would be great!  Then we have to look at how to rack 'em (mono - 1.2 rack? side by side in 19" rack? recreate the original box?

I'd do a mono pcb and a pcb behind the frontpanel with led metering and pots/switches (similar to the ssl clone) for each channel. this would fit in a single unit rack enclosure .

and for two channels you also need a switch to link the control voltages.

Keep in mind the the boards for the 200 VCAs and the 208/209 RMS's are already been done and ready to etch - so you don't have to worry about those.

ah, ok..  didn't know that..  do you have any info about matching the transistors?
something I couldn't find out is the number on the vca modules, sometimes there's written
"7.2" "7.5" "7.7" on it... maybe it has to something with matching values of the transistors.

 

[damnyankee]

Thanks, Matthias - I knew you'd have some great alternatives to consider.

As I said, the VCA & RMS boards are done ready to etch (in fact, I think the RMS file you uploaded contains both the 208 & 209 boards).  

The transistors are going to be the bugger.  That's why I was hoping we could find a modern alternative.  Isn't materials/quality control much better today vs 1967?  If so, we could try to group buy a bunch in an attempt to get the same manufacturing lot.

As far as the 200 VCA labelling (7.2, 7.5, 7.7 - my dbx 119's have 7.6, 7.8, and 8.0): I've read they are the same, just a component was changed - meaning, one of the BC transistors wasn't available so a cross reference to it was installed in it's place.  Now whether this is true or not, I can't say for sure...but it makes sense.  

I've also read there were no differences between the 200 VCAs: what was installed in the dbx 117 & 119 were installed in the dbx 160VU.  Again, I can't say for sure but it makes sense to me considering the old dbx 117 cut sheet lists the price of the 117 at $159 new...that was a chunk of change around 1970.

 

[matthias]

watch out for a dbx 154 noise reduction unit. that contains 4 vca and 4 rms modules.

I also compared my dbx 160vu with a lot of other dbx comps (163, 162, 160xt,160x, 903) and there's not so much difference...
searching and matching parts for the 200vca  is a waste of time in my opinion.... take a that2181 vca at first and then try to get some 200-vca modules...
I'm pretty sure if you will hear the (small) difference you'll will be very happy with the that-substitutes

 

[abechap024]

You guys rock! great info.
On the PCB I'm able to put the footprint for the RMS unit and put the parts inside the footprint, that way people don't need to buy/build/etch a different pcb for the 208 unit. Kinda like what was done with the gyraf SSL units' 202 VCAS.

I want to do the same for the VCA. But it seems we have more options for the VCA so maybe we can have the 200VCA footprint and inside that the holes to build a discrete VCA and then to the side a place for a that 2081 VCA.

I need to re read the post again, but first I'm going to go through and look for any mistakes on my PCB, while I'm fresh.
Thanks you guys!
AC

 

[matthias]

I've found two hires pics of my 160-vu

dbx160.JPG
dbx160-2.JPG


please tell me if you need some more...

 

[abechap024]

About the meter....
I like what you are saying about just having a GR meter. That is all I personally really look at in a compressor. It would be *nice* maybe to once in  while see how hard you were hitting it, but that can all be learned from experince.

So for the sake of keeping costs down and keeping the circuit as simple as possible.

Meter Circuit MOD!


Also Matthias how do you feel about changing the power supply? There are a lot of hard to source transistors in there and also looks like a real PITA.
My gut tells me, that changing the power supply to a modern supply *should* hardly effect the sound. what are your thoughts

Also if you've worked out how to implement the That VCA that would really save some time

Thanks again

AC  

 

[damnyankee]

Thank you for the images, Matthias - I see the 161VUs are missing more than a few components than your 160VUs.

Would it be too much trouble to shoot a pic of the solder side and give the dimensions of the board?  It's for my dbx files more than anything else.

Thanks!

DY