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

Ok, a few things that is good to know:
The below led is supposed to be lit up constantly with no signal.
It means it is operating below threshold, no compression is taking place.
The flickering of both leds means means you hit the threshold, compression is kicking in.
Above led constantly lit means you are above threshold at any time.
The threshold pot works like this: CCW: low threshold = it compress earlier, CW: high threshold.

If I'm unclear, look up the original "instruction manual" on the net.

Good luck!!
//M

I'm about to calibrate this thing, hopefully in the near future.
My only signalgenerator is the one in Pro Tools thru my soundcard.
To get a proper signal I had to measure the output with a DDM.
To get 0 dBu I put my signal generator in RMS mode, and when it showed -16.0 dB
I had 0.775V AC RMS.

Since the 160 is a "new" toy and connected in a bridging way I guess dBu is correct.

Can anybody tell me how much VAC/RMS -60dB is?
One calculation gave me 0.00077459 (0.00219089 V p-p)

Cheers
//M

Dr Gris said:

Can anybody tell me how much VAC/RMS -60dB is?
One calculation gave me 0.00077459 (0.00219089 V p-p)

Click to expand...

I've never went to calculate the exact value for that!
You've measured your computer is outputting 0.775VRMS when you set your fader at -16dbFS. That is 0db.
Now drop your digital fader by -60dbFS from that point - that would be -76dbFS on the fader (or on the output of your signal generator plugin).
You'll notice that it's not that important to hit -60db. It can tolerate -65db or -55db. The important thing is to have a healthy waveform read from the offset pin. Once you see it, just trim R36 for a symmetrical wave shape and you're done. Set and forget!

Dr Gris said:

I'm about to calibrate this thing, hopefully in the near future.
My only signalgenerator is the one in Pro Tools thru my soundcard.
To get a proper signal I had to measure the output with a DDM.
To get 0 dBu I put my signal generator in RMS mode, and when it showed -16.0 dB
I had 0.775V AC RMS.

Since the 160 is a "new" toy and connected in a bridging way I guess dBu is correct.

Click to expand...

So measure AC voltage with your unit under test connected and set the level of your signal generator for a 0dBu=0.775VAC multimeter readout.

Can anybody tell me how much VAC/RMS -60dB is?

Click to expand...

-60dB is a relation of any input voltage * 0.001, same as any input voltage / 1000.
-60dBu (u=0.774597VAC reference) is an RMS voltage of 0.000774597.
-60dBV (V=1.000000VAC reference) is an RMS voltage of 0.001.
-60dBFS is 1/1000 of the max.representable digital full scale level and has no relation to the analogue world without an analogue reference voltage.
If your digital scale ProTools meter would show -16dBFS with the unit connected for a 0dBu input voltage, this digital scale meter would show -76dBFS with the level attenuated by 60dB.
Maybe have a look at http://www.sengpielaudio.com/calculator-db-volt.htm

Harpo said:

Dr Gris said:

I'm about to calibrate this thing, hopefully in the near future.
My only signalgenerator is the one in Pro Tools thru my soundcard.
To get a proper signal I had to measure the output with a DDM.
To get 0 dBu I put my signal generator in RMS mode, and when it showed -16.0 dB
I had 0.775V AC RMS.

Since the 160 is a "new" toy and connected in a bridging way I guess dBu is correct.

Click to expand...

So measure AC voltage with your unit under test connected and set the level of your signal generator for a 0dBu=0.775VAC multimeter readout.

Can anybody tell me how much VAC/RMS -60dB is?

Click to expand...

-60dB is a relation of any input voltage * 0.001, same as any input voltage / 1000.
-60dBu (u=0.774597VAC reference) is an RMS voltage of 0.000774597.
-60dBV (V=1.000000VAC reference) is an RMS voltage of 0.001.
-60dBFS is 1/1000 of the max.representable digital full scale level and has no relation to the analogue world without an analogue reference voltage.
If your digital scale ProTools meter would show -16dBFS with the unit connected for a 0dBu input voltage, this digital scale meter would show -76dBFS with the level attenuated by 60dB.
Maybe have a look at http://www.sengpielaudio.com/calculator-db-volt.htm

Click to expand...

Thanks Harpo,

That link is great, it was the one I used to get my calculation.
When I set the level in my Pro Tools plugin to -75.5 dB I get really close.

I think it's worth mentioning because a lots of people can't get the correct V reading at R79.
The first time I calibrated a device using software and soundcard I was off because
I thought 0dBu was -18dBFS on my system insted of -16dBFS.
It wasn't until I put my DDM measuring Vrms on pin 2 & 3 I knew I was off.
I'm not implying people are doing it wrong, just a thing to consider.

It's my feeling this forum has an increaslingly crowd of newbies like me building kits
and it can be easy to overlook things like this, well it was for me ;D

Regards
//M

Dr Gris said:

Ok, a few things that is good to know:
The below led is supposed to be lit up constantly with no signal.
It means it is operating below threshold, no compression is taking place.
The flickering of both leds means means you hit the threshold, compression is kicking in.
Above led constantly lit means you are above threshold at any time.
The threshold pot works like this: CCW: low threshold = it compress earlier, CW: high threshold.

If I'm unclear, look up the original "instruction manual" on the net.

Good luck!!
//M

Click to expand...

Thanks, that confirms what I was thinking based on having used a vintage one a while back.  What puzzles me is what causes the Above led to be lit constantly.  Is the led behavior a direct byproduct of compression and is there a component that calibrates the activation of the leds?  I can hear when the compression kicks in, releases, etc and it's all functioning normally.  As is the meter, even though I haven't calibrated yet.  Right now I'm just trying to understand exactly what triggers the LEDs.  Looking at the original schemo, are they fed off R62 or is that something else?

For clarity, my Below light was lit before I installed the DBX black can, so they both physically function, but with the VCA installed my Above is lit regardless of threshold, input, etc.
Thanks.

hi all,

patience is starting to wear thin with this project as have spent 3 days faulting finding this. The documentation is pretty confusing as it isn't exactly clear which components should and should not be involved. would be much better to have a definitive BOM and revise instructions.

Anyways my unit still wont setup correctly, R43, R56, R59, R34 and R63 don't seem to do anything.
The meter on the left channel seems to setup correctly but the other one doesn't?

I put a sine wave into the input and get my scope on pin 1 and offest pin (not offset as silk screen is wrong) i get a nice sine wave which i can see on the scope.
when i adjust R36 there is a very small point where the wave appears, the shape of the sine only seems to get wider than the actual shape change?

rms symmetry i have no idea how to do?

level calibration doesnt seem to work?

threshold knob adjustment doesnt seem to work as threshold knob does nothing?

1:4 ratio calibration doesnt seem to work either?

is the thing im missing here that R109 should be disconnected before trying any of these?

as this sees to be the next step.

regards

Spence.

Spencerleehorton said:

I put a sine wave into the input and get my scope on pin 1 and offest pin (not offset as silk screen is wrong) i get a nice sine wave which i can see on the scope.

when i adjust R36 there is a very small point where the wave appears, the shape of the sine only seems to get wider than the actual shape change?

Click to expand...

I don't get it! Do you have rev3 board or older?
I used custom made probe (made out of old sharp screwdriver with 470uf cap in series) and insert it into Offset pin (hole with ring around it in the detector section).
It should be very straightforward to see wave on the oscilloscope (I used cubase's built in plugin "multiscope"), and wave should look like the picture Abe put in his CLX Manual rev3.
If you don't get this waveform shown right, I'd guess that is where your problems are. As a first take in troubleshooting, I'd swap all the ICs in the detector section. As a matter of fact, when I did mine, I noticed that out of 10 LM301 ICs one was faulty! So try to swap those - maybe you have a faulty one.

Spencerleehorton said:

rms symmetry i have no idea how to do?

Click to expand...

I found that this is super-confusing.
What I did - I took a different software to do it!
I couldn't get anything ot of RMAA software. So I took Smaart 7 and set it into FFT mode. When I sent sine wave into the unit I monitored output in Smaart. Distortion is very visible. Now the most important step is to set compression to 20db. I send -10dbFS signal from my computer, set ratio to none (CCW) and treshold to CW, and just adjust output to have -10dbFS on the input of my computer. That is unity gain without compression. Than as a next step I set treshold and/or ratio pots just to get -30dbFS on my input into computer. As the compression kicks in, distortion is more noticable on the FFT analyzer. And than it's time to tweak R34 to get the second harmonic at the lowest point.
I had a lot of problems here since whenever I tweaked R34 the level of the sine would go up and down. So it was unclear if I was reducing the second harmonic or just going up/down with the output level. In the end, I found a compromise with lowest second harmonic compared to third harmonic, without going too much off with the output level.
At some point I was like "damn, I don't care!"! That's when I stopped and decided that RMS is calibrated!

Spencerleehorton said:

level calibration doesnt seem to work?

Click to expand...

As I've said in previous post, all of my problems with level calibration were directly due to the wrong meter switch. I had lorlin rotary and it was impossible to get a good reading on R79. But when I got pushbuttons to replace rotary it was all good.

Spencerleehorton said:

threshold knob adjustment doesnt seem to work as threshold knob does nothing?

1:4 ratio calibration doesnt seem to work either?

Click to expand...

You won't get this part of the calibration if previous steps are not done properly! When you get them right, this will be a breeze...

Spencerleehorton said:

is the thing im missing here that R109 should be disconnected before trying any of these?
as this sees to be the next step.

Click to expand...

Yes! Keep it disconnected!



Luka

hi,

i have 4 gang switches btw so these should be fine right?, i have double checked and treble checked the wiring is good and they do seem to switch between it all ok.

it does seem now i have disconnected R109 thats the RMS unit wave form sets up better now on the first stage of the setup

RMS symmetry i will try your way.

once these are set hopefully i can then move on through the setup, now i know that R109 has t be disconnected through out this.

I have twiddled everything in every which way but still cant get over LED to change or goto Under LED?

ratio when turned CW cuts all audio out at about 11 o'clock starting from about 7 o'clock, it does reduce the audio level in this range.

hopefully something positive will happen soon!!!

regards

Spence.

hi,

when i get back in the workshop tonight i'll take a picture of the scope wave form to see what you think.

regards

Spence.

Hi,

Here my picture of my scope.

Regards

Spence.

I'd say your input level into the detector is too high so you get this kind of waveform.
Maybe go and check all solder points from input to detector for a cold joint. Also check ICs in detector. Are you using CA3083 or NTE929?

I'm on my holidays now, away from home and studio (finally!!) so I can't measure the voltages on IC legs on my unit. That would be helpful perhaps.
Can someone who has working unit help Spence and measure voltages on all IC legs with -60db signal on input? That would maybe narrow down the problem.

I'm an IDIOT!!!!
Checked voltages without chips then with chips. Then when putting it all together I managed to put
the Molex connector for the pots in a mirrored way....NOT GOOD!!!
It was quite a show. I managed to pull the mains quick but one of the pots caught on fire for a short while  ;D
Changed the Molex back to the right position and turned it on again.
The Ratio pot on one channel is not working and the Threshold on the other channel is not working.
Both gain pots are working.

I still managed to do some calibration to it, like RMS trim, RMS symmetry and level calibration.

I guess it's time for pot shopping....

Just wanted you to know you're not the only one struggling with this one  8)

Keep it up!!
//M

Regarding the scope pic, like I've said before, I don't know anything about anything...but what I did was:
Making sure I had -60dB at input using a DDM measuring Vrms at input pin 2 & 3.
( In my case that meant setting my Pro Tools signal generator plugin to -75.5 dB in RMS mode)
When probing ( I also have an old Tek scope) I simply went for symmetry.
Switching V/div and Time/div so I could see the wave two times in the screen.

When trimming for lowest distortion I didn't notice much difference.
I could clearly see the 2:nd and 3:d harmonic but no big changes, if any to be honest...
I used a software plugin recommended by Mike at Serpent called Blue Cat FreqAnalyst.

A wild guess about your Ratio problem: check R41,42,45,46,48,78 for correct values and no cold solderjoints. Don't know how to check myself but I would also look at IC: 4558
I'm just looking at the original schematic and at the components close to the Ratio pot.

I wish I could be of more help!

Best
//M

Dr Gris said:

I'm an IDIOT!!!!
Checked voltages without chips then with chips. Then when putting it all together I managed to put
the Molex connector for the pots in a mirrored way....NOT GOOD!!!
It was quite a show. I managed to pull the mains quick but one of the pots caught on fire for a short while  ;D
Changed the Molex back to the right position and turned it on again.
The Ratio pot on one channel is not working and the Threshold on the other channel is not working.
Both gain pots are working.

I still managed to do some calibration to it, like RMS trim, RMS symmetry and level calibration.

I guess it's time for pot shopping....

Just wanted you to know you're not the only one struggling with this one  8)

Keep it up!!
//M

Click to expand...

hi Dr Gris if you have burn your pots and after change,  your treshold  control not work (as a gain) and your Ratio control not work you can change the CA3083 !

A had the same problem !


For My CLX i have a Small problem about the LED : BELOW & ABOVE :

When i have no sound in input the BELOW is ON fully ! but when i have a 0db sound in input the BELOW shutdown (TH and ratio 0)

After when i use the thresold pot with a ration the Below Led Switch ON

it's normal ?

Thanks for the tip.
It worked after I changed the pots and now it's calibrated!!!!!
Everything seems ok except the meter tracking isn't very accurate.
The trimmer R56 is for setting the meter to track more accurate over the whole scale,
but after some trimming back and forth I decided to not give a.....

Insted I opened a session and patched it in on a kick and snare track and BAM!!!!
I built this for two reasons mostly, kick and electric bass, and on kick it was exactly like the originals
are famous for. A fat SMACK!!!!
It was also very good on the snare, will be a tough fight between this and the 1176....

EMB1:
No sound, below led should be fully on= constant light
Don' t understand what you mean about Threshold and Ratio...
Where do you have 0dB? On the CLX meter scale feeding it with a 100Hz +4dB (1.228Vrms) sinus wave?
Have you calibrated it?

Start with a +4dB signal on input. Rotate Threshold all the way to the right(CW) where it says 3V.
Ratio pot set to 1.
Meter should read 0 in all meterswitch positions (IN/GR/OUT) and below LED should light constantly.
If you now rotate Threshold to the left (CCW) slowly below LED goes out, and above LED is also dark,
thats the spot where your indicator on the Threshold knob should point at " a little bit more" then 1.
When turning Threshold more to the left, the above LED lights up. The meter still shows 0 because
Ratio is still fully to the left (CCW) at 1.
If you now turn Ratio to the right(CW) the meter still shows 0 on input but when you switch to GR or OUT
the meter shows a lower value and the above LED is lit.
With a +4dB signal and Threshold fully CW the Ratio should not make the above LED light up at any position.

For anyone in doubt, I think it's easier to think of the Threshold pot as a Voltage trimmer to set where the compression kicks in.
With a +4dB signal and Threshold at 3V no compression should take place because +4dB is 1.228V, and that's less than 3V.
And the LEDs indicate where the signal is in relationship to the Threshold

Oh boy, my longest post ever on any forum, I'm tired but I hope I made some sence....

Best regards
//Magnus

Hi guys,

Have figured my problem, r35 and r72 were 900R rather than 900k!!
Unit calibrates now, headache over! Time for some kick drum and bass!

Regards

Spence.

Since I think the case is just a little bit to narrow I tried a different approach.
Yes, there's more hum in left channel but I think it will work under the circumstances I will use this.
Gonna try it in "real world" scenario.

Here's a pic. Will try to tidy up the wiring a bit and secure the LED's.

Dr Gris said:

Since I think the case is just a little bit to narrow I tried a different approach.
Yes, there's more hum in left channel but I think it will work under the circumstances I will use this.
Gonna try it in "real world" scenario.

Here's a pic. Will try to tidy up the wiring a bit and secure the LED's.

Click to expand...

Hell, if it works, go for it.  I tried numerous ways to position it with the 25-25 Antec but the only way to eliminate hum was vertical mounting in one particular spot.  Unfortunately, that's 1/8" taller than the case.  Certain horizontal positions were acceptable but I decided to be neurotic and go for zero hum.  Did a little grinding and bent a small arc in the lid directly above the torroid.  I wouldn't sell one like that but I'm keeping this particular piece so it's not an issue.

Hi,

I would like to ask a question. I am testing at 100Hz as instructed. When I look at the O/P of the RMS unit I am getting a DC level dependent on the input signal level and on top of it is added an AC signal, at 100Hz which looks like full wave rectified signal input. Is this added AC supposed to be there or should I be expecting just a DC level?

This added AC is causing bad distortion on the final O/P of the unit.

Any ideas anyone?

Regards

Spence.