CLX-VU Build Thread (DBX 160VU ) UPDATE: REV 3

[BerndVP]

yes, it's correctly wired.
But I'm reading strange power values if I trace it...

I think I got the 4:1 working, got the 10db change when switching from -30db to -20db
As per the calibration instruction listed here.
Did you check your led's for correct wiring? Take a look at the original schematic they show how they are wired.
Connecting the anode, and cathodes correctly.

 

[Clbraddock]

What is the difference between 207, 208, and 209 RMS units? Are these interchangeable? I've seen all 3 mentioned in various places, but can't find any reference to differences between them.

Edit: Apparently the pinout is different on the 207. Anyone know where I could find the 207 pinout info? Google isn't providing it. Thanks!

 

[Clbraddock]

Does anyone have the rev3 schematic? I have the rev3 build manual, but the manual is really for the THAT vca build and I am plugin a 200 vca into the board. It’s a little unclear what if any components are included/excluded when using an older dbx vca. I’m thinking I’m going to have to compare the schematic to the original 160 schematic which I have. Any help is appreciated!

 

[Clbraddock]

So I might just be talking to myself, but any help would be very much appreciated.
Has anyone used a dbx 207 RMS in place of the 208/209? Supposedly they are interchangeable if you jumper the pin outs to the correct places on the board, but I can’t find much real info other than a service bulletin. Do any other component values need changed? The service bulletin indicates not to connect to the trim hole on the board which seems odd.

 

[Bowie]

Does anyone have the rev3 schematic? I have the rev3 build manual, but the manual is really for the THAT vca build and I am plugin a 200 vca into the board. It’s a little unclear what if any components are included/excluded when using an older dbx vca. I’m thinking I’m going to have to compare the schematic to the original 160 schematic which I have. Any help is appreciated!

I have the original 160VU schematic, which I used for implementing the DBX cans into my rev 3 CLX. If you need that schemo, shoot me your email address. I don't have any schematic specifically pertaining to the rev 3.

 

[EarthTone]

Dude the OP's website is super hacked. Like I can't view any of the manuals, schematics, anything. It all goes to faulty website with questionable content. How do you download the BOM, build instructions, and schematic for this beast?

ET

 

[JMan]

Dude the OP's website is super hacked. Like I can't view any of the manuals, schematics, anything. It all goes to faulty website with questionable content. How do you download the BOM, build instructions, and schematic for this beast?

ET

OP is long gone from here, and his website has been down for years. His exit wasn’t exactly ceremonious, it would seem, and long story short, collective cases now owns and sells a few of his old projects, including this one. That’s where the build manual is housed. As far as I know, there is no published schematic for this project, but some people have referred to the original DBX schematic. No idea if it’s identical or if there are differences, although I’d assume the latter.

 

[Clbraddock]

JMan is correct. I got the boards through collectivecases.com

The documentation is okay if you are going to do a build using modern TI VCAs. The documentation is horrible/non-existent if you want to use vintage VCAs. I may have bit off more than I can chew trying to work an old DBX 200 VCA into this thing, but we will see. I've been comparing to the original 160 schematic and noting any discrepancies. Most of the components are the same, but there are a few places where resistor values are different. There also are a couple places where there is no place on the board for components on the original schematic (from memory CR18 and R96). Im not sure what to do about that yet. Ill post the details when I am a little further along though.

 

[MisterCMRR]

I did a little looking for info on the old David Blackmer modules. Seems to be some good info at dbx 208 / 209 RMS Detector Module for 160, 161 VU, NR Cards Tested, Warranty. on the 207/8/9 modules.
For the 202 VCA, THAT has an application note, AN127, detailing how to use their newer IC VCAs to retrofit (copy attached). I'd think it would be pretty straightforward to adapt a THAT 2252, but even that is now obsolete (see THAT Corporation 2252 RMS-Level Detector ICs).

I'm not familiar with the 200, but I reverse-engineered a Blackmer 202 module back in 1971 for Quad-Eight and designed a copy into each VCA channel for Compumix mixdown automation. Blackmer caught wind of it and sent Quad-Eight a "cease and desist" order - but agreed to sell his modules to us at a good OEM price (bullet dodged!).

Maybe this will help - but maybe you knew all this already.

 

[Clbraddock]

Ok here is what I have figured outs, as far as building this with a 200 VCA and 207/208/209 RMS can. I haven't powered this up yet, and am far from an expert so if you follow any of this and blow yourself up - you've been warned, don't blame me.

On original schematic R1-R19 are part of the power supply, as are C1-C8 and CR1-CR5 and CR15. The original 160 had 24 volts coming off its transformer which is stepped down in the power supply circuit to 15 volts entering the functional portion of the circuit. On the CLX board it is 18 volt coming off the transformer (instead of 24) which is further stepped down to 15 volts entering the circuit. The power supply in the CLX is much simpler/fewer components than the original DBX. As such, the designer reused some of these part numbers in the DIY VCA boxes. Since the voltages are different I used the values printed on the CLX board for part number which would have been part of the original power supply, except that I excluded any such components inside the PCB boxes labeled RMS, VCA, and THAT circuit - since I am using original cans for those roles.

Other discrepancies between original 160 and THAT BOM - On original DBX 160VU the following values are used:


R25 22
R26 100k
R27 50K
R28 300k
R29 470
R30 200
R31 29.9K
R32 100K
R48 200
R96 10K (no place on board for this)
R100 15M.
R101 3.3M

C12 .33uf 250v
C13 22uf

Q7 BC560C

Other Things
R96, R97, and CR18 are missing from PCB - they go to a series or transistors Q10, Q11, Q12, Q13 which are also not on the PCB. Anyone know what these components were doing? Are they part of the meter or led circuits which have been redone?

R106, R017, and R109 are part of the meter emulation so I used the values on the PCB

R100 and R101 are way way different values than the DBX schematic. Anyone know what these do? Are they part of the meter or led emulation?

Anyways that's more or less what Ive figured out so far. Please feel free to add on or correct.

Edit: R100 and R101 trim the DC voltage to the power rails. Use the values on the PCB/BOM.

 

[Clbraddock]

Question on grounding.

It looks like the IEC ground plug is only connected to the case and nowhere to the transformer or board. Is this correct? The board gets its ground reference from the center tap off the power transformer only? Looking at the DBX 160 schematic I dont see any other connections to ground. Just want to be sure.

Thanks!
Chris

 

[JMan]

It looks like the IEC ground plug is only connected to the case and nowhere to the transformer or board. Is this correct?

Correct, the IEC ground plug should connect to the chassis, as close to the IEC as possible.

Don’t connect any of the toroidal transformer wires to chassis ground, no.

The PSU/main board should also have a chassis ground connection, but I don’t remember where that is on this board — I’d bet it’s a pad for a Molex connector somewhere toward the end of the power supply section, but I couldn’t say for sure.

 

[Clbraddock]

Thanks Jman!

Are you sure about the main board though? Where the AC enters the board there are pads for AC CT AC. This would be coming off the toroidal. I dont see anywhere else where there is a pad to connect ground. See pic.

Edit: Looking at the manual again, I guess pin 1 on the input and output xlr is tied to chassis ground. Maybe thats what you mean.

 

[JMan]

Thanks Jman!

Are you sure about the main board though? Where the AC enters the board there are pads for AC CT AC. This would be coming off the toroidal. I dont see anywhere else where there is a pad to connect ground. See pic.

Edit: Looking at the manual again, I guess pin 1 on the input and output xlr is tied to chassis ground. Maybe thats what you mean.

Yes, the main board will need to be grounded as well. At the very least, if it isn’t, the power supply won’t function correctly.

However, you are correct that it is not grounded from the “AC in” pads. Glancing at the picture, perhaps it is the pad with the big “G” where the silkscreen says “power rails” along the bottom edge of the board?

Since the power supply and audio circuit are on the same board, I would expect that there is only the one connection to chassis ground that is shared by everything on the board.

Also yes, you want to tie your pin 1 of your xlrs to chassis as well, although this is independent of the main board ground connection.

 

[Clbraddock]

Hmm darn. Maybe someone who has built this thing can chime in if they know the answer. I'd hate to connect the wrong pad to the chassis. I've been looking at pics of completed units (see post 567) and still cant figure it out.

Anyways, still really appreciate your help Jman!

 

[JMan]

Hmm darn. Maybe someone who has built this thing can chime in if they know the answer. I'd hate to connect the wrong pad to the chassis. I've been looking at pics of completed units (see post 567) and still cant figure it out.

Anyways, still really appreciate your help Jman!

No worries. An easy way to tell for yourself would be to take you multimeter in continuity mode and see if that “G” pad in the “power rails” is connected to other signal ground pads around the board. If so, it’s a good chance that’s your chassis connection.

 

[Clbraddock]

So you might be on to something. I did continuity testing between the G pad and some of the places on the below diagram indicated as ground and I got continuity. The schematic is vers 2 and my board is vers 3 so not every ground on the schematic had continuity but most did and most other places on the board did not have continuity to the g pad.

Edit: higher res pic at:
http://juggernautmusic.com/media/2018/CLX-VU/Circuit1.jpg

 

[EarthTone]

OP is long gone from here, and his website has been down for years. His exit wasn’t exactly ceremonious, it would seem, and long story short, collective cases now owns and sells a few of his old projects, including this one. That’s where the build manual is housed. As far as I know, there is no published schematic for this project, but some people have referred to the original DBX schematic. No idea if it’s identical or if there are differences, although I’d assume the latter.

Thank you for your helpful response! Sorry I just saw this message, several weeks later. I know the owner of Collective Cases and so I'm sure he'll be able to supply the build guide, thanks!

ET

 

[Clbraddock]

Hi Earthtone, I can send you the ver 3 build guide if you need it. Its not the most complete guide on earth, but its better than nothing. Let me know if you need it.

Edit: Unrelated, but my meter and switch came from hairball today, so Im going to try and power this thing up. Fingers crossed.

 

[JMan]

Good luck! Looking forward to hearing how it goes!