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

[insideout]

Hi folks, assuming sufficient va, is there any reason I can't put my clx-vu in the same chassis and share the 25-0-25 transformer being used for an mnats 1176 as pictured (hoping my picture appears...):
thx, Mike

 

[insideout]

For some reason I can't find this diagram for using a rotary switch - can anyone point me to it?
appreciated,
Mike

Just an update on my diagram above. Just finished building it (the thing in the drawing). Works perfectly!!  CCW is INPUT. CENTER is GR.  CW is OUTPUT.

Awesome, and good diagram in case anyone else wants to use a rotary switch.

 

[sr1200]

Sorry forgot that was on my server.

 

[horizonsound]

Hi Abe (and everyone).

Recently completed the assembly of two units, and true to form I rushed and did not read the manual, powered it up and blew the TL071 chips to pieces. Really, they both shattered. My rail voltages were -8/+27. After adjusting and replacing the TL071's, I'm having problems calibrating the RMS section. There is only a very feint waveform at the test point, which is not affected by the signal put onto the input of the unit.

I suspect that all other chips are damaged as well, so have put in an order to replace them all.
Only issue is, that the CA3083 chips are near impossible to find. Everywhere appears to be out of stock or discontinued. Help! Abe, where did you source yours from???

Cheers,
Anthony.

 

[berkleystudios]

Hi Abe (and everyone).

Recently completed the assembly of two units, and true to form I rushed and did not read the manual, powered it up and blew the TL071 chips to pieces. Really, they both shattered. My rail voltages were -8/+27. After adjusting and replacing the TL071's, I'm having problems calibrating the RMS section. There is only a very feint waveform at the test point, which is not affected by the signal put onto the input of the unit.

I suspect that all other chips are damaged as well, so have put in an order to replace them all.
Only issue is, that the CA3083 chips are near impossible to find. Everywhere appears to be out of stock or discontinued. Help! Abe, where did you source yours from???

Cheers,
Anthony.

you'll have to get the CA3083 on ebay. thats where I got mine

 

[horizonsound]

Of course. How silly of me.
Too easy.

Cheers,
Anthony.

 

[abechap024]

Of course. How silly of me.
Too easy.

Cheers,
Anthony.

Yea I've done that before and it sucks. I need to get a stash of them!

 

[horizonsound]

Yea I've done that before and it sucks. I need to get a stash of them!

Picked up a few from a seller in the UK. Now just waiting....

Could you confirm a few things with the RMS calibration for me, just to make sure?
-60dB level signal, is equivalent to about 0.002Vp-p? My signal generator only gives Vp-p
The signal is then applied to pins 1 (ground) and 2 (hot) of the input connector.

At this point, I get an almost sawtooth wave out at the Offset Pin, which can be slightly adjusted by R36. Adjusting the signal generator - even turning it off - make no change to this.

Still have to replace the CA3083 chips, and THAT chips, which might be the cause of this issue.

Cheers,
Anthony.

 

[abechap024]

Yea I've done that before and it sucks. I need to get a stash of them!

Picked up a few from a seller in the UK. Now just waiting....

Could you confirm a few things with the RMS calibration for me, just to make sure?
-60dB level signal, is equivalent to about 0.002Vp-p? My signal generator only gives Vp-p
The signal is then applied to pins 1 (ground) and 2 (hot) of the input connector.

At this point, I get an almost sawtooth wave out at the Offset Pin, which can be slightly adjusted by R36. Adjusting the signal generator - even turning it off - make no change to this.

Still have to replace the CA3083 chips, and THAT chips, which might be the cause of this issue.

Cheers,
Anthony.

Yea my guess is some of the chips are blown. The square wave should completely disappear and actually there is only a small window it should appear. Something is probably blown so its showing full signal all the time maybe? Speculation. Good luck.

 

[horizonsound]

Yea I've done that before and it sucks. I need to get a stash of them!

Also helps if I install C11....

Abe, in the parts kit you sent all the .33uF film capacitors as "185K", which implies 1.8uF. Is this ok to use?

Other than that, calibration is going smoothly.

Cheers,
Anthony.

 

[horizonsound]

Hello again,

I've managed to get through most of the calibration process. It's compressing audio well.
Now to set the meter.

I have a question regarding the step of adjusting R124 and connecting R109. Should there be any signal on the input, and what are the meter switches and controls supposed to be set on?

Cheers,
Anthony

 

[abechap024]

Yea I've done that before and it sucks. I need to get a stash of them!

Also helps if I install C11....

Abe, in the parts kit you sent all the .33uF film capacitors as "185K", which implies 1.8uF. Is this ok to use?

Other than that, calibration is going smoothly.

Cheers,
Anthony.

Yes, 1.8uf because the impedance is lower with the That chips

And with regard to the meter calibration, once you lift one side of R109, it doesn't "see" anything but the voltage that sets the "0" so to answer your question, it doesn't matter, it wouldn't change it one way or the other.
Happy compressing

 

[horizonsound]

Done! In the end it was a pretty easy build, though the calibration procedure is one of the most difficult ever.
It definitely has that signature DBX sound, and can be quite savage at high gain reduction. Sounds fantastic when put lightly over a drum mix.

I used the Hairball Lola knobs. They look pretty cool.

Cheers, and thanks for the help.

Anthony

 

[hotel valkenburg]

got one of those 200 series VCAs off evilbay curious about the pin configuration, all the pins align correctly to the board, except there is no COMPR pin or that is to say it is cut short and soldered to the VCA's can.  is this ok? or should i pop her free and hook it up? seems like it should be the ground pin thats connected to the can.

 

[abechap024]

got one of those 200 series VCAs off evilbay curious about the pin configuration, all the pins align correctly to the board, except there is no COMPR pin or that is to say it is cut short and soldered to the VCA's can.  is this ok? or should i pop her free and hook it up? seems like it should be the ground pin thats connected to the can.

Yes, its quiet strange the pins they sometimes have/don't have. I actually have never seen a 200 vca with all the pins (not that I've seen THAT many) but all those pins are spec'd in the engineering sheet. It should be just fine

I'm working on a simple discrete 200 vca using THAT corp transistor array that can pop into peoples PCBs....discrete is very fun...

 

[late]

Hi Abe

Never have plans about to add attack/release pots like 165a have? Or is it too hard?

 

[Baltazar]

Hello!
A few years after i ordered I finally had the time to start working on these rev2 boards!
First unit is assembled first i tried it without any ICs, no smoke, adjusted voltage to +15 and -15v.
With IC's in, +15 is fine but i cant get the negative side to go above -11,45v. R100 is out of range...

I also notice that the two LEDs illuminates a little all the time and the VU is pegging "downwards" so to say.

Remove one IC at the time until voltage bumps up or what is you suggestions?

Best

 

[abechap024]

Hello!
A few years after i ordered I finally had the time to start working on these rev2 boards!
First unit is assembled first i tried it without any ICs, no smoke, adjusted voltage to +15 and -15v.
With IC's in, +15 is fine but i cant get the negative side to go above -11,45v. R100 is out of range...

I also notice that the two LEDs illuminates a little all the time and the VU is pegging "downwards" so to say.

Remove one IC at the time until voltage bumps up or what is you suggestions?

Best

Yes I would remove the ics. Check make sure the regulator is getting enough voltage, and you have correct resistors around that area.

 

[shot]

I came back to this build after a month or so of waiting for some TLC...

I'm still struggling with calibration and I think I have one problem.
First of all, calibration..
- When I try to tweak R34 overall level just goes up and down. Second, third (and higher) harmonics stay always in same relation with first harmonic (100hz test tone). Their relation doesn't change for better or worse. I suppose this is not normal?

- Level calibration is out of range. When I first started on this project I wired Lorlin rotary switch and I was getting lots of strange readings from R79 voltage. I now replaced it with pushbutton switches and it is far more better. When the meter is in input or output position my readings don't respond anymore to panel pot's position. I get constant reading from R79 resistor's leg. But this reading is too high! When the unit is fed with 1.228VRMS signal (measuring between input connector's pins 1 and 2, ground and hot), lowest reading on R79 I can get is -0.105 VDC. Should I change R63 trimmer from 50K to 100K to go lower on targeted -0.011 V DC? I believe this is the crucial point to get targeted -0.011 since my next calibrations can't get where I want them!

- 1:4 calibration... I can't do it! Compression is very hard and it wont let signal raise by 10db when I raise up the input signal. Since I'm using my audio interface, I can't raise the input signal to +10db - my output converter won't let me. I tried with first signal -40db and raised it to 0db. On the output of the compressor there's merely 2db raise when it should be 10db. I'm guessing it has to do with the previous step of the calibration - I probably have to hot signal into the sidechain (R79), right?

- vu meter calibration. No problems with setting zero position on the input and GR. Input level is showing correctly. But GR level on vu meter is always showing less than it actually is. When I compare my input on the computer's analyzer (Smaart7), actual GR is let's say 20db but my vu meter is showing aprox 11db. I found out that if I tweak R56 I can get the needle to drop a bit to almost 16db of GR but not more. And this is still off from the actual 20db's! I tried rotating R59 and nothing happens. What are R56 and R59 for? They are before TL082 opamp connected to the vu meter compensation circuit. What do they do? (not mentioned in manual rev3). Will I get better readings when I successfully adjust R79's voltage?

And lastly, I have a problem with negative (pin3) output! It is dead! When looking at the schematic I can't understand it. I get a signal of about -20db on the input leg of R92 and after that signal is almost lost. Since R93 is 200R to the ground I guess the signal is draining to the ground. I didn't try it, but I guess if I pull out R93 there would probably still be low signal, definitely way too different than the positive (pin2) signal. I've checked component values if I maybe put a wrong one but they're all okay. Interesting thing is when I adjust output voltage between ground and positive pin2 to 1.228V my vu meter is reading -5.5db. I don't know if this has anything to do with it. Should I just put an 1:1 output transformer and feed the output to transformer and have the signal balanced that way?

I've listed a lot of my problems but other than that this unit is sounding very good! Ok, maybe to hard compressing but compression sounds great!

 

[Dr Gris]

For level calibration you need 1.228V RMS between pin 2 and 3, not between pin 1 and 2
if I'm not mistaken....

Best
//M