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

[redmojosteve]

Hi Abe
Thanks for the quick reply.  It is puzzling me as the power supply section is straightforward, even for me to understand! I have got two boards and one transformer so it would suggest that the transformer side of things is the problem as both boards are similarly affected. I am checking the voltages against the ground point on the power rails pads (marked "G") but I am wondering if I could have a ground problem. I have only grounded the boards via the screen on the input jack connection.  From the schematic it shows the centre tap(CT) as being grounded but when I check between the "G" on the power rail pads and the CT point there is no continuity. I am wondering if I have missed something. Thanks for your patience!
Cheers
Steve

 

[abechap024]

Hi Abe
Thanks for the quick reply.  It is puzzling me as the power supply section is straightforward, even for me to understand! I have got two boards and one transformer so it would suggest that the transformer side of things is the problem as both boards are similarly affected. I am checking the voltages against the ground point on the power rails pads (marked "G") but I am wondering if I could have a ground problem. I have only grounded the boards via the screen on the input jack connection.  From the schematic it shows the centre tap(CT) as being grounded but when I check between the "G" on the power rail pads and the CT point there is no continuity. I am wondering if I have missed something. Thanks for your patience!
Cheers
Steve

Hmmm, yes center-tap is ground. there should be continuity. I would double check your transformer wiring again. The problem has to be there I would bet. Sounds like you are measuring it fine.

Good Luck! You will get it!

 

[redmojosteve]

Hi Abe
It's a bit embarassing but the problem turned out to be a dry joint on the CT terminal. However rather than beat myself up too much, the reason was simple. The large Molex connectors for the AC provide a substantial heat sink. As I soldered the pins from the underside of the board, as there isn't any other way, there was insufficient heat to fuse the solder with the ground trace, which is on the top side of the board of course. It is now sorted out and I am getting +-15V and +-29V. It's a bit more than the 24V so I hope this is OK. Looking at some earlier comments it seems this is not so unusual.
Anyway, now for the setting up...
Thanks for your help

Steve

 

[warpie]

I'm getting around +/-28V on these rails too, so I think you're OK.
I think there're' only smoothed and not regulated anyway.

 

[redmojosteve]

OK the story so far...
I have the Rev 3 boards, PSU OK now, gain, threshold pots work (plenty of gain!); Ratio-sort of; above and below leds OK; switches don't seem to be working (triple checked to ensure the wiring is correct), strangely the VU meter on one channel moves up one step on the scale (R109 still disconnected of course), R36 doesn't seem effective, passes audio but no discernable compression. It feels as if I have left something out! Time to really start looking

Regards

Steve

 

[Mirouf]

Hi!

So I finish my unit with original DBX RMS 208 (which is a discrete version, not the same as the one which is on the board (Rev2)) and DBX 200.

And I can't calibrate it... it's working, compressing, everything is ok, but I dont see the same thing on the offset pin when i try to adjust R36, if I put the input signal to -60db, I've got a blured triangle waveform (even if there is not input signal), and if I rise the level, I see something like a square waveform coming through the other one, but if I adjust R36, nothing happen, except at one end, everything go flat and a big hum appears.

I double and triple check everything, try all the trimmers, the original calibration setup, but I can't figure it out... And if I try to continue, I can't have the -11mV a the R79 pins, meter works, but has the level calibrartion isn't ok I can't get all the "0"

Other strange things:

- with the RMS unit on the board, I can't have the below led to work (above seems OK), and without the RMS unit, the below LED works fine
- I can't get ride of a hum (even if the RMS unit is off the board), with low noise mod or not, it seems there is a lot of ripple in the +/-24V rails, is that OK? I change the 1000uF to 2200uF, and it seems to be better but not as expected
- i don't seems to have unity gain when not compressing, something like -10db is lost. But as I can't calibrate it, I'm not sure...

So my question is:

Do you think it's not possible to use DBX RMS 208 and 200 VCA? Do you see anything i can do?

I'm thinking the 208 i've got is an older version than the one you can build on board, maybe it the problem...

I made 2 boards the same, and the 2 are behaving the same, I don't think the RMS or the VCA is dead, cause the unit is working.

Anyone do the same with success?

Abe, any idea?

 

[abechap024]

Hi!

So I finish my unit with original DBX RMS 208 (which is a discrete version, not the same as the one which is on the board (Rev2)) and DBX 200.

And I can't calibrate it... it's working, compressing, everything is ok, but I dont see the same thing on the offset pin when i try to adjust R36, if I put the input signal to -60db, I've got a blured triangle waveform (even if there is not input signal), and if I rise the level, I see something like a square waveform coming through the other one, but if I adjust R36, nothing happen, except at one end, everything go flat and a big hum appears.

I double and triple check everything, try all the trimmers, the original calibration setup, but I can't figure it out... And if I try to continue, I can't have the -11mV a the R79 pins, meter works, but has the level calibrartion isn't ok I can't get all the "0"

Other strange things:

- with the RMS unit on the board, I can't have the below led to work (above seems OK), and without the RMS unit, the below LED works fine
- I can't get ride of a hum (even if the RMS unit is off the board), with low noise mod or not, it seems there is a lot of ripple in the +/-24V rails, is that OK? I change the 1000uF to 2200uF, and it seems to be better but not as expected
- i don't seems to have unity gain when not compressing, something like -10db is lost. But as I can't calibrate it, I'm not sure...

So my question is:

Do you think it's not possible to use DBX RMS 208 and 200 VCA? Do you see anything i can do?

I'm thinking the 208 i've got is an older version than the one you can build on board, maybe it the problem...

I made 2 boards the same, and the 2 are behaving the same, I don't think the RMS or the VCA is dead, cause the unit is working.

Anyone do the same with success?

Abe, any idea?

Hi, hmm interesting, did you make sure to use the correct resistors/parts for the discrete VCA?
Also what do you mean by "with" and "without" the RMS unit?
Do you have your LEDS wired correctly?
You need to choose one of the transistors next to the VCA with the VCA so maybe that is your problem, I don't know.
How much hum do you have?

 

[Mirouf]

Hi, hmm interesting, did you make sure to use the correct resistors/parts for the discrete VCA?
Also what do you mean by "with" and "without" the RMS unit?
Do you have your LEDS wired correctly?
You need to choose one of the transistors next to the VCA with the VCA so maybe that is your problem, I don't know.
How much hum do you have?

Hello,

Yes I'm sure about the parts, I double check for that.
So, "With" means with the RMS unit solder on board, "Whitout" with it desolder of the board (yes I can do that with this version ;-). When I remove it, the unit doesn't compress anymore and act like a pre (it seems ok to me)
The Led is wired OK, I redo it to be sure.
I put a random BC550C, maybe it's part of the problem, but I don't have problem with the VCA, it's the RMS I can't figure to calibrate, so I think this is different.

For the hum it's a quite audible one, but with my scope I see a pretty high riiple on the 24V rails (triangle waveform), I put some 2200uF instead of the 1000uF, but it's still there. Maybe it's a different issue, but I think the hum is not linked to the RMS thing...

So I believe i've got mutliple problems, making it hard to find which cause what...

 

[redmojosteve]

Hi Abe
I reckon it's all now working nicely. Good on acoustic guitars and superb on heavy rhythm guitar. I haven't tried it on drums yet but I will do soon. I have two 2-channel G1176s so it will make for an interesting comparison.
Regards
Steve

 

[abechap024]

Hi Abe
I reckon it's all now working nicely. Good on acoustic guitars and superb on heavy rhythm guitar. I haven't tried it on drums yet but I will do soon. I have two 2-channel G1176s so it will make for an interesting comparison.
Regards
Steve

Hi Steve,
Just saw your earlier post today, Glad you got it all figured. I'ts good on kick

Best of luck recording!

 

[abechap024]

Hi, hmm interesting, did you make sure to use the correct resistors/parts for the discrete VCA?
Also what do you mean by "with" and "without" the RMS unit?
Do you have your LEDS wired correctly?
You need to choose one of the transistors next to the VCA with the VCA so maybe that is your problem, I don't know.
How much hum do you have?

Hello,

Yes I'm sure about the parts, I double check for that.
So, "With" means with the RMS unit solder on board, "Whitout" with it desolder of the board (yes I can do that with this version ;-). When I remove it, the unit doesn't compress anymore and act like a pre (it seems ok to me)
The Led is wired OK, I redo it to be sure.
I put a random BC550C, maybe it's part of the problem, but I don't have problem with the VCA, it's the RMS I can't figure to calibrate, so I think this is different.

For the hum it's a quite audible one, but with my scope I see a pretty high riiple on the 24V rails (triangle waveform), I put some 2200uF instead of the 1000uF, but it's still there. Maybe it's a different issue, but I think the hum is not linked to the RMS thing...

So I believe i've got mutliple problems, making it hard to find which cause what...

For the Hum,
You could get some perf board and wire some rectifiers off board with some 1000+uf caps and then wire the output of that into the board. The idea is to get that noisey 60hz, 120hz off of the main board.

Best,

Abe

 

[Mirouf]

I was planning to do something like that to get the hum go away!

I'm wondering if the discrete RMS and the discrete VCA make a a big difference in the consomption of the circuit, inducing the hum.

I'm planning to build a RMS on the board to see if everything work find with it, and try to figure out with this isn't working with my discretes ones.

 

[abechap024]

I was planning to do something like that to get the hum go away!

I'm wondering if the discrete RMS and the discrete VCA make a a big difference in the consomption of the circuit, inducing the hum.

Thats interesting, very well could be!

I'm planning to build a RMS on the board to see if everything work find with it, and try to figure out with this isn't working with my discretes ones.

Good luck, I finally got my hands on a set of discrete RMS/VCAs from some old DBX sound reduction stuff so I'm getting around to making a pair, and then hopefully I'll make a pdf on how to do it to help other people too, so this is good stuff!

Best,
Abe

 

[Mirouf]

So,

I finally get my unit to work:

I remove the original RMS 208, and build the on-board RMS, it make the unit behave the right way to calibrate. I don't know why my discrete version isn't working (in fact it is working, the unit is compressing but I can't find a way to calibrate)

I add an external power supply, it a bridge rectifier and a pi filter with 2*2200uf, 12ohm 1W resistor and 4*1000uF after the resistor, and the in the 2 boards. It kills all the ripple, no they are dead quiet.

It's working great, I can keep the discretes VCAs which are working great without too much concern.

I still can't reach one point in calibration: the -0.011VDC at the leg of R79, no way I can have it. So I do this a little as I feel looking at the above/belaw Led and trying to do the same on the 2 units, and everything sound fine to my ears! So the unit find is way to the studio and I already use it on a mix. I must says it was great and I don't regret the time I spent making it working!

Thanks Abe!

 

[abechap024]

So,

I finally get my unit to work:

I remove the original RMS 208, and build the on-board RMS, it make the unit behave the right way to calibrate. I don't know why my discrete version isn't working (in fact it is working, the unit is compressing but I can't find a way to calibrate)

I add an external power supply, it a bridge rectifier and a pi filter with 2*2200uf, 12ohm 1W resistor and 4*1000uF after the resistor, and the in the 2 boards. It kills all the ripple, no they are dead quiet.

It's working great, I can keep the discretes VCAs which are working great without too much concern.

I still can't reach one point in calibration: the -0.011VDC at the leg of R79, no way I can have it. So I do this a little as I feel looking at the above/belaw Led and trying to do the same on the 2 units, and everything sound fine to my ears! So the unit find is way to the studio and I already use it on a mix. I must says it was great and I don't regret the time I spent making it working!

Thanks Abe!

Nice! Thanks good news. So what did you use for Q7 (the transistor that goes with the VCA) did you just use a standard bc560c?

Thanks!

 

[Mirouf]

Yes, I just pick one and it's working great!

 

[supiarmando]

Does anyone have some pcbs? I am interested in buying 2 pcbs!!! Any help is very appreciated!!!

 

[abechap024]

Does anyone have some pcbs? I am interested in buying 2 pcbs!!! Any help is very appreciated!!!

Email Sent. Have 2 left ordering more very soon. Thanks

 

[supiarmando]

Maybe stupid question, but is there a wiring for "how-to stereo link". I read the pages but did not find. Any help would be great. Thanks

 

[abechap024]

Maybe stupid question, but is there a wiring for "how-to stereo link". I read the pages but did not find. Any help would be great. Thanks

You want to connect the 2 timing caps together to have the units behave in stereo. You still want to match the controls as close as you can to get it tighter, but no different than 2 x 1176s