[BUILD] 1176LN Rev D DIY

[denov]

The voltages in the schematic are with the unit properly calibrated so you'll see messed up voltages if there is an issue anywhere in the small GR Amp circuit.  Check every component and every solder joint in the GR AMP. Check all the wiring connections to and from it.

Turned out I just needed to re-calibrate it.  I've now got both units calibrated with 1 minor issue.  When I calibrated last I let both units warm up for over an hour.  Everything went smoothly.  In the end both meters where at 0db.  Then after powering them down and racking them up I found that both units now have the meter at +1db after warming up.  Do I need to calibrate again or can/should i use the trim on the front panel to adjust. 

I also notice that getting the correct (down to thousands of a volt) in and out voltages can be a bit tricky as the in and out controls seems to very sensitive.  And getting these voltage spot on seems to be very very import .  I'm correct here?

Beside that these sound great on drums and bass!

 

[mnats]

Hello,

I'm very happy because my 1176 works well, there is compression and levels run ok.

There's just the needle that does not indicate the Gain Reduction  :-\ (part 3 of calibration)
Can you help me locate where the problem may lie?

Thanks,

Probably the gain reduction meter circuit? I know it's not calibrated, but have you checked voltages against the schematic linked in the FAQ which is in turn linked from the first post of this thread?

 

[oskura]

Ive just finished assembling my rev d unit. During calibration, I had no problems with the q-bias or the null adjust, however, at the Reduction Meter Tracking Adjustment I get no drop in dBu on the meter or on the DMM. Toggling the attack knob makes no changes in ether reading. 
I got an answer on another thread that it sounds like its an issue between the ration and meter boards, but after checking my solder joints and components (including pots) on these boards Im not sure where to go from here. Should I be looking for something specific?

Could any other components cause the unit to not compress at calibration? But have no effect on the qbias or null adjustment?

 

[justinheronmusic]

Ive just finished assembling my rev d unit. During calibration, I had no problems with the q-bias or the null adjust, however, at the Reduction Meter Tracking Adjustment I get no drop in dBu on the meter or on the DMM. Toggling the attack knob makes no changes in ether reading. 
I got an answer on another thread that it sounds like its an issue between the ration and meter boards, but after checking my solder joints and components (including pots) on these boards Im not sure where to go from here. Should I be looking for something specific?

Could any other components cause the unit to not compress at calibration? But have no effect on the qbias or null adjustment?

Check your Q Bias Pot and make sure that it is set in the middle before calibrating. I believe these are 12 turn pots. So turn it all the way to the left until you hear it click, then turn it to the right 6 times or so then try recalibrating. You always want to start from a nominal position with every pot - they are not set nominal from the factory - so no matter how many turns it is, try to set it around the middle. If the Q-Bias pot is off, it will trick you into thinking that it's working properly but really it's way off. Not sure if that helps, but it's one thing to rule out!

 

[oskura]

Check your Q Bias Pot and make sure that it is set in the middle before calibrating. I believe these are 12 turn pots. So turn it all the way to the left until you hear it click, then turn it to the right 6 times or so then try recalibrating. You always want to start from a nominal position with every pot - they are not set nominal from the factory - so no matter how many turns it is, try to set it around the middle. If the Q-Bias pot is off, it will trick you into thinking that it's working properly but really it's way off. Not sure if that helps, but it's one thing to rule out!

Hey thank you for the info! I went back and tried it again, resetting the pots and still no change.
We are following Hairballs calibration instructions. We are at step 3: Reduction Meter Tracking Adjustment

"1.  Apply a 1 KHz, 0dBu signal, confirmed with your DMM at IN + and IN - at the input XLR (0.775 VAC). ***Good here
  2.  Move your DMM to OUT + and OUT - at the output XLR.  ***Good here
  3.  Set output control for 0dBu (0.775 VAC) at the output.  ***Good here
  4.  Set attack full CCW (off position). Set input control for +10dBu (2.44 VAC) at your output XLR.  ***Good here
  5.  Turn the attack control ON (Fully CW) and readjust the output level control for "0dBu" if necessary. (<<always necessary)
  6.  Now let's set the meter to display this 10dBu drop.  When the attack is "off" (full CCW) and you see +10dBu at the                  output, set the meter to 0 by using the front panel zero adjust trimmer.  (No increase to +10dBu)
  7.  When the attack control is "on" (full CW) and you see 0dBu at the output, use R44 to set the meter to -10. (No output drop here)
  8.  Repeat 6 & 7 until the output drops 10dBu whenever the attack control is turned ON.  This can be a bit tricky.  You'll want to anticipate how one control will change the other."

We get stuck at step 6 and 7. There is no back and forth on the multimeter between attack on and off. So when we make an adjustment and switch back to the opposite position it reads the same. No adjustment makes any difference. It seems like there is no compression happening.

 

[dbonin]

@Oskura - have you verified, using a DMM  that your unit is actually compressing?  Sorry if this has been asked previously, I'm on my phone and searching is dog slow.

 

[oskura]

@Oskura - have you verified, using a DMM  that your unit is actually compressing?  Sorry if this has been asked previously, I'm on my phone and searching is dog slow.

Thank you for replying,
Could you walk me through checking for this? Im on information overload right now.

 

[midwayfair]

Hook up the compressor to your interface with the compression bypassed.

Put a 1KHz test signal in at the intput, and turn on the compression. Does the output signal level drop when you turn on the compression?

 

[dbonin]

This has been posted a bunch, but here it is again:

Testing if your unit is compressing by measuring the AC voltage drop at the output XLR pins 2 & 3

1.) Apply a 1 KHz, 0dBu signal  [ confirmed with your DMM at pin 2 and 3 of the input XLR (0.775 VAC) ].
2.) Move your DMM to pin 2 and 3 of the output XLR.
3.) Turn your output knob until  0dBu (0.775 VAC) is measured at the output.     
4.) Set attack full CCW (off position) set release to 7 or full CW for fast release. Set the Meter to GR mode.
5.) Turn your input knob until  +10dBu (2.44 VAC) is measured at your output XLR.        <---------------- NOTE THAT NOW THE ATTACK IS OFF!! (My input sits now at the dot between 24 & 18, and my ouput knob sits between 48 & 36) (Measuring 2.44VAC on my DMM on the output xlr, pins 2/3)

6.) Turn the attack control ON (full CW) and observe the voltage drop at each of the ratio settings

For each of the ratios, on a rev D, you should be seeing something close to this, shown with attack on:
Ratio:
20 (Att On .788VAC)
12 (Att On .679VAC
8 (Att On .642VAC)
4 (Att on .585VAC)

 

[lalalaetc]

Hello, All!

I have been over my schematic and work a few times, but I'm totally stumped. I just finished an old style Rev-D with Hairball kit, and I'm not getting anything to the input terminals of the PCB.
I can trace signal up to the primary of the input transformer, and on one leg of the secondary (louder than the primary side), but not the other. I should note that this is when bypassing the t-pad (my t-pad has some noticeable grit in it, and I wanted to make sure that the issue didn't lie there).
When I don't bypass the t-pad, I get nothing from the secondary.

Any thoughts would be deeply appreciated.

Thanks!
Wyatt

 

[mnats]

I have been over my schematic and work a few times, but I'm totally stumped. I just finished an old style Rev-D with Hairball kit, and I'm not getting anything to the input terminals of the PCB.
I can trace signal up to the primary of the input transformer, and on one leg of the secondary (louder than the primary side), but not the other. I should note that this is when bypassing the t-pad (my t-pad has some noticeable grit in it, and I wanted to make sure that the issue didn't lie there).
When I don't bypass the t-pad, I get nothing from the secondary.

When you write "one leg of the secondary" what are you measuring in relation to? Where is your input being applied specifically? A transformer provides galvanic isolation so if your answer to either question has the word "ground" in it you'll have a problem.

 

[lalalaetc]

Bugger! Yes, I was measuring relative to ground. I was figuring (incorrectly) that since the Tx secondary is connected to the chassis along with the audio input ground, that this would still be valid

 

[frederickalonso]

Is it sounding like the real unit?

 

[lalalaetc]

So, I'm still having trouble with what I suspect to be my input transformer. After re-reading a good deal of this thread, I notice that Mike suggests to another participant tracing voltage from the input on. This is what I was doing previously, and my signal (and voltage) still dies at the transformer. There is no signal getting to my PCB. Everything is fine at the primary of the input Tx, but I have nothing at the secondary. I'm about to order a replacement Tx from Hairball, but want to make sure I'm not missing something first.

Thanks!
Wyatt

 

[mnats]

So, I'm still having trouble with what I suspect to be my input transformer. After re-reading a good deal of this thread, I notice that Mike suggests to another participant tracing voltage from the input on. This is what I was doing previously, and my signal (and voltage) still dies at the transformer. There is no signal getting to my PCB. Everything is fine at the primary of the input Tx, but I have nothing at the secondary. I'm about to order a replacement Tx from Hairball, but want to make sure I'm not missing something first.

Have you removed the input transformer PCB from the circuit, then measured the primary and secondary windings? Like most electronic parts, audio transformers are seldom faulty when new. Though I think there was a rare instance when the windings were brought out to the wrong pins...

 

[audiophreak]

What input transformer are you using ?

 

[lalalaetc]

Im using the Altran C-3837-1, as provided by Hairball.

I pulled the Transformer board for testing, and here is what I'm getting:

Primary (+ to -): 51.5R
Secondary (+ to -): 14.3R
Pri and Sec to Gnd: Inf

 

[mnats]

I pulled the Transformer board for testing, and here is what I'm getting:

Primary (+ to -): 51.5R
Secondary (+ to -): 14.3R
Pri and Sec to Gnd: Inf

That looks normal, so it's a mystery why a signal fed into the primary isn't making it to the secondary. Maybe try testing it in isolation to verify but I'm pretty sure your issue is elsewhere. Let us know when you find it and what it was.

 

[lalalaetc]

Thanks for your reply!

I reinstalled the Transformer board, and started tracing again. This time, I get no output from my t-pad. I knew this had been an issue in the past, as I could feel loose material churning inside as I turned its post. Only, I was testing output on it previously... Odd

Well, I'm not any longer. When I bypass the t-pad, all seems fine now. I'll attempt the calibration process with the t-pad out of line for now, while I await a new one to arrive.

Thanks again! Ill post updates.

 

[mnats]

I reinstalled the Transformer board, and started tracing again. This time, I get no output from my t-pad. I knew this had been an issue in the past, as I could feel loose material churning inside as I turned its post. Only, I was testing output on it previously... Odd

Well, I'm not any longer. When I bypass the t-pad, all seems fine now. I'll attempt the calibration process with the t-pad out of line for now, while I await a new one to arrive.

Given the apparent intermittent nature of your fault(s) I would suspect poor solder joints or mis-wiring rather than outright faulty parts. While you could calibrate without a T-pad it's hardly an ideal way to do it...

Just a suggestion - try measuring the T-pad to see which of the three ganged pots is causing the problem. I hope that the subtext is getting through not just to one but to all having issues: measure rather than assume.