[BUILD] 1176LN Rev D DIY

[allfreak]

Thanks for the warning. I took cover, but nothing happened. I checked a few voltages and everything looks fine.
The first to calibration steps where no problem and worked perfectly.
I put R44 back in the circuit and switched off the attack knob. Ratio 20:1 meter to +4.
With the 1 kHz signal I adjusted the output so that the meter shows 0.
After switching the attack knob back on... nothing happens. In fact lowering the input lowers the Vu needle - same as output control...
I guess I screwed up. If I am correct, increasing the Input should push the signal into the threshold and cause a larger gain reduction on the VU.
Already searched my **s of in the web to get clues. I'm frustrated.

 

[sr1200]

The meter in +4 shows OUTPUT signal not GR.  (mistyped)

 

[allfreak]

Hmm. So is the meter setting of +4 wrong for this step? I watched the mnats calibration video and he is on VU not GR.
I have the pushbutton version not the one with rotary switch. ???

 

[allfreak]

Am I doing it wrong or is it a problem with my unit?

 

[jplebre]

you need to switch back between both. The idea is that the 0vu signal you see get's reduced by 10db, and you see the -10db in GR mode, and also a decrease of 10db in 0vu

 

[jplebre]

sorry, allfreak, just re-read your post and may have confused the callibration procedure you are doing.
Are you doing QBias (step one), null adjust/meter callibration or meter tracking?

 

[allfreak]

I'm doing the gain reduction meter tracking. The last of the three videos on mnats website.

What I understand is that you can adjust that 10db drop using the Input and ouput controls. With the attack knob in off and the meter set to +4 I adjusted the output knob for 0 on the VU Meter. Turning the attack knob back on should result in a drop which is adjusted with the Input control to -10.
repeat that until both conditions are met without further adjustment.

My Unit however has no drop at all. In fact I can switch back and forth with no difference in the VU meter. And raising the input should drop the needle more. The opposite is the case.

The switching to th GR Mode of the meter is supposed to happen after input and output are set so that  the variable resistors can be adjustted in this mode to get the right reedings on the VU.

The unit seems to work. It passes audio an compresses. Even the all Button mode cruches the audio as it should. So either I've got something backwards in the calibration procedure or there is a problem with the unit.

Can anybody tell?

 

[jplebre]

if you can hear compression but "And raising the input should drop the needle more. The opposite is the case. "
Does the meter track GR correctly?

And:
were you able to do calibration step 1 correctly (Q Bias), or was it showing the opposite behaviour as well?

 

[allfreak]

Well, as far as I can compare it to the UAD version of the 1176 it does exactly the same. It shows the gain reduction from 0 downwards. In +4 it shows signal from around -20 upwards.

However as far as I know I can't switch the UAD plugin attack control to off (although its in the graphic).

No problems with the first two calibration steps. I think that it has to be some kind of brainfart on my side "translating" the calibration of the rotary switch version to my pushbutton version...

What bugs me is that I can't figure out where I'm wrong.

 

[Tweekhead]

Hello everyone!

I've taken some time off from attempting major builds, and made a butt load of guitar pedals, Radioshack electronics learning lab stuff, etc...

This unit has been sitting in a corner for quite some time now, and I was wondering if anyone could spot any issues from my iPhone pics, "sorry no camera for higher res", or had any insight into what might be the problem. Seeing how I had very little experience with higher voltages, I had a friend who has been into ham radio wire up the units power supply and meter. He also added an external power switch to the front of the unit.

Anyways, the unit passes audio just fine, and works fine as a mic pre, but nothing as far as gain reduction. Followed all the instructions during calibration, and if I remember correctly all went well till the induction part? forgive me if I'm wrong with that part, I'm posting these pics now, and going to watch the vids again tonight after holiday stuff with family.

 

[Echo North]

I always feel the "passing signal but no GR" is a pretty simple one to fix.

Read the 2-3 pages of this Steve_H exchange. Check the pad 22/21 stuff.

http://www.groupdiy.com/index.php?topic=29981.msg614820#msg614820

Start there.  You need AC @ pad 22 and -DC @ 21 as a starting point.

 

[Tweekhead]

Echo, thanks so much for the reply! I'll check it out now!

 

[frazzman]

I'm doing the gain reduction meter tracking. The last of the three videos on mnats website.

What I understand is that you can adjust that 10db drop using the Input and ouput controls. With the attack knob in off and the meter set to +4 I adjusted the output knob for 0 on the VU Meter. Turning the attack knob back on should result in a drop which is adjusted with the Input control to -10.
repeat that until both conditions are met without further adjustment.

My Unit however has no drop at all. In fact I can switch back and forth with no difference in the VU meter. And raising the input should drop the needle more. The opposite is the case.

The switching to th GR Mode of the meter is supposed to happen after input and output are set so that  the variable resistors can be adjustted in this mode to get the right reedings on the VU.

The unit seems to work. It passes audio an compresses. Even the all Button mode cruches the audio as it should. So either I've got something backwards in the calibration procedure or there is a problem with the unit.

Can anybody tell?

Hi allfreak,
I have through exact same problem as you on my rev f. Can't complete this calibration step as switching GR on via attack switch does not result in the expected drop - same as you. I realised last night I had the transistors in my GR circuit in the wrong way which resulted in no compression. After correcting this the unit appears to function ok but can't complete this adjustment. Let me know how you progress and I will do the same.

 

[allfreak]

I'm still working on that and I'm not satisfied with what I've got so far. I really only did some guitar effects up until starting the 1176 and I have nothing to do with electronics other than that. So I'm doing the nooby dance here...

3rd calibration step:
Very confusing was that there seam to be settings where the needle doesn't drop at all switching the attack pot on and off. 

I've managed to get the drop of 10db although the input knob does not "work" in a consistent manner. The signal was to weak at the beginning. I was shooting for -18dBfs from Pro Tools (Apollo interface) via the built in signal generator. After checking with my DMM at pins 2 and 3 of the input xlr I noticed that the signal was way too low. Around 0.22VAC. I had to crank the signal up to -6dBfs to get 0.775VAC. Maybe because the Apollo sends the signal to putput 3 and 4 simultaneously while I was only using output 3.

It seams that the input control is lowering and raising the needle when I lower or raise the input. After watching the calibration video, I was expecting the opposite response. It is not linear though. Turning it all the way to the left had the needle follow all the way to the left. Turning the input up lets the needle follow up to a certain amount and then it barely moves at all. That was around -13. I was then fiddling around a bit and got to a point where the 0 and -10 conditions where met. I was ignoring the needle response when setting the input knob and made only very little adjustments. Switched back and forth a lot to get it to the 0 and -10.

I don't know if any of this is normal. If someone with a clue could clarify the 3rd step and the behavior of the input this would probably help beginners a lot.

One other thing: Is it normal that the VAC at the input xlr is reacting to the input knob to some amount?

 

[frazzman]

I'm still working on that and I'm not satisfied with what I've got so far. I really only did some guitar effects up until starting the 1176 and I have nothing to do with electronics other than that. So I'm doing the nooby dance here...

3rd calibration step:
Very confusing was that there seam to be settings where the needle doesn't drop at all switching the attack pot on and off. 

I've managed to get the drop of 10db although the input knob does not "work" in a consistent manner. The signal was to weak at the beginning. I was shooting for -18dBfs from Pro Tools (Apollo interface) via the built in signal generator. After checking with my DMM at pins 2 and 3 of the input xlr I noticed that the signal was way too low. Around 0.22VAC. I had to crank the signal up to -6dBfs to get 0.775VAC. Maybe because the Apollo sends the signal to putput 3 and 4 simultaneously while I was only using output 3.

It seams that the input control is lowering and raising the needle when I lower or raise the input. After watching the calibration video, I was expecting the opposite response. It is not linear though. Turning it all the way to the left had the needle follow all the way to the left. Turning the input up lets the needle follow up to a certain amount and then it barely moves at all. That was around -13. I was then fiddling around a bit and got to a point where the 0 and -10 conditions where met. I was ignoring the needle response when setting the input knob and made only very little adjustments. Switched back and forth a lot to get it to the 0 and -10.

I don't know if any of this is normal. If someone with a clue could clarify the 3rd step and the behavior of the input this would probably help beginners a lot.

One other thing: Is it normal that the VAC at the input xlr is reacting to the input knob to some amount?

Sounds like you're on the right track, I've built many other diy compressor and eq projects but left the 1176 to the end as I knew it would be tricky with all its off board wiring and calibration procedure . I'm using a testtone generator in cubase , and had time make simular tweaks until I got close to .775 vac. If I follow the tracking calibration exactly as mnats video, switching GR back on via attack not doesn't give me the 10 db drop. Seems odd, I'll need to investigate more

 

[sr1200]

You put the jumper back on for part 3 of the calibration yes?

Also, did you have the signal generator OFF when you zeroed your meter (IN GR MODE)

Afte the meter is 0'd in GR mode with no signal present.  Then go to +4 mode.  Turn your sig gen on with the input at about 50% and output at 50%.  Chances are when you turn the sig gen on your needle will pin to the right.  Adjust output to get the meter to read 0. 

Last tip, when you start, make sure your attack is at its quickest (fully clockwise) and after you turn it off,  when you turn the Attack knob back on, make sure you turn the knob fully clockwise.  Otherwise the needle might sit for  a LOOOOONG time.

 

[allfreak]

I followed everything to the letter. Good tip with the attack though. I waited quite a bit until the needle settled.

Spent the day testing the unit and it sounds great. As far as I can tell it does what it is supposed to do. Did a vocal track and a parallel drum compression crush track. Then I compared it with a UAD 1176 LN and it is pretty close. Think my crushed drum track sounds a tid rounder, it's great.

Thanks to everyone, especially to Mako for the PCBs and Mike for the Kit. Both their stuff has outstanding quality and makes it rather easy to build. Of couse it is a lot of fun, too.

 

[Echo North]

I'm still working on that and I'm not satisfied with what I've got so far. I really only did some guitar effects up until starting the 1176 and I have nothing to do with electronics other than that. So I'm doing the nooby dance here...

3rd calibration step:
Very confusing was that there seam to be settings where the needle doesn't drop at all switching the attack pot on and off. 

I've managed to get the drop of 10db although the input knob does not "work" in a consistent manner. The signal was to weak at the beginning. I was shooting for -18dBfs from Pro Tools (Apollo interface) via the built in signal generator. After checking with my DMM at pins 2 and 3 of the input xlr I noticed that the signal was way too low. Around 0.22VAC. I had to crank the signal up to -6dBfs to get 0.775VAC. Maybe because the Apollo sends the signal to putput 3 and 4 simultaneously while I was only using output 3.

Could be an impedance issue.  The 1176 input impedance is 600Ω  if your output impedance is similar you're going to get a fair bit of loss.  I know on my 600Ω output sig gen, I have to output about 2.1VAC to get 0.775 at the input.  For small signal audio you want to bridge impedance for max voltage transfer.  You want your signal generator output around 50Ω ideally for less loss.

One other thing: Is it normal that the VAC at the input xlr is reacting to the input knob to some amount?

Yes because the T-Pad does not maintain a constant impedance.  In a perfect world it would, but in electronics things are never perfect.  The impedance can very 100Ω.

Mike

 

[frazzman]

I followed everything to the letter. Good tip with the attack though. I waited quite a bit until the needle settled.

Spent the day testing the unit and it sounds great. As far as I can tell it does what it is supposed to do. Did a vocal track and a parallel drum compression crush track. Then I compared it with a UAD 1176 LN and it is pretty close. Think my crushed drum track sounds a tid rounder, it's great.

Thanks to everyone, especially to Mako for the PCBs and Mike for the Kit. Both their stuff has outstanding quality and makes it rather easy to build. Of couse it is a lot of fun, too.

Still no luck unfortunately! I tried the tip of making sure the attack pot is turned fully when enabling GR again with the attack pot. Basically for the meter tracking calibration, I zero meter when in GR mode with no signal going through. Then change to +4 , input 1khz sin wav,  turn attack pot ffully ccw to disable GR, alter input and output pots until 0db achieved, then enable attack again by turning ffully cw.  I see a tiny shift in the meter but nothing major

 

[sr1200]

Lets try this.
Go back and re-do the first two calibration steps.  (pay close attention to when/where the jumper is on / off)
Then, on step 3, after you 0 the meter, turn the input up to like 75-80% instead of 50% then see if there's a bigger drop.

It could be that your adjustment pot is turned all the way one way, in which case you might not see a drop. 
If the needle DOES infact move, (albeit a tiny bit) I dont think you're far off.