[BUILD] 1176LN Rev D DIY

[audiophreak]

Hi Mike,
          I'm splitting off the OP trans to OP XLR  to X-Y on the meter PCB per wiring instructions and schematic, I have a small powered speaker on the output XLR , and I do hear GR , but haven't actually measured it with DMM .

  I did try a different meter, but got the same result 
In the voltages I posted , there were a few that were a little off , but nothing is jumping out saying " Look  over Here "  at least not to me  :

  I have noticed that after setting the Qbias about 10 times now, that it seems to always be about 18 turns on a 25 turn trimmer , so just guessing the actual value is probably ends up around 500R , I'm kinda lost  :'( 

I;ll also post on my cabling between PCBs


Thanks for taking the time.

 

[audiophreak]

Here is a link to some pix , maybe someone might spot something - I'm gonna check R60 and R35 ... seems relevant


https://picasaweb.google.com/audiophreeek/1176RevDCloseUp?authuser=0&authkey=Gv1sRgCO_r4NvMqp2bXQ&feat=directlink

 

[Bobby Baird]

Looks like you got all the trimmer pots in backwards. Reference page 5 of hairballs build guide for populating the pcb. http://hairballaudio.com/docs/FETGUIDE/Section%20E%20-%20Stuff%20The%20PCB.pdf

 

[audiophreak]

Thanks Bobby Baird !!    I'll try that next  !!

( hadn't seen that guide )

 

[audiophreak]

rotated all five trimmers ( only broke one )  luckily I had some on hand  , verified R60 and R35 ...  but the exact same result  :'(

... also rechecked test voltages , all are as before  :'(

 

[audiophreak]

Board to Board wiring as follows :

pad 4 from Ratio PCB to Meter PCB  - stranded wire
Shielded single conductor cable fro pad 7 and shield/GND to pad 7 ( conductor only ) on Ratio PCB
pads 15,16,17 from main PCB to Ratio PCB  - two conductor shielded cable - Shield as GND
pad 18 from Main PCB to pad 18 on Ratio PCB - stranded wire
pad 19 on Main PCB to pad 19 on Ratio PCB - stranded wire
pad 20 from Main PCB to pad 20 on Ratio PCB - stranded wire
pad 21 from Main PCB to pad 21 on Ratio PCB - stranded wire
out put pot pads to out put pot - two conductor shielded cable
Attack and Release pads from Ratio PCB to Att and Rel pots - stranded wire
X and Y from output trans to Meter PCB - two conductor shielded cable
pads 28 and 29 from Main PCB to Meter PCB - swisted stranded wire
pad 22 and GND from Main PCB to Ratio PCB pad 22 and GND - single conductor Shielded cable
Meter + and - to Meter PCB =+and -

is this right ?? 

  .... I used 2n3707 and had to go through a LOT of them for hFE - If no one see's a gross error - I'm thinking of changing them out with 2n3708 or 5088's


  I'm lost 

 

[Echo North]

You need to measure your actual GR.

The way it stands now the issue could be ANYTHING.  You need to isolate it to a a) meter issue or b) GR amp issue.

Sorry I haven't had time to look at the threads.  Hit the reset on your mind and let's start from square one.

With GR off and the input and output at 12 oclock, feed a 1K 0dB signal into the input.  There maybe some impedance loss, so put your DMM across the XLR input 2 and 3 and adjust your signal generator so you see  0.775 VAC there.

Now move your DMM to output XLR 2 and 3 and see what your AC is.  It's probably more, so roll back on your output till you see 0.775 VAC on the output.  Now you have 0dB at your in and out.  Now measuring the output still click on GR and you should get a big voltage drop at the output with your input at mid way.  Crank it up more and get a huge drop.  What is that voltage?  What is it in dB?  See this chart:

http://www.sowter.co.uk/decibels.php

if it's like 0.06VAC then that's like a 22dB compression, if your meter is showing 5 dB then we no you have a meter driver issue...and so on.

Mike

 

[audiophreak]

Thanks so much Mike !!
   
  resetting my mind as we speak  ;D    will perform this procedure tomorrow and report back.

 

[audiophreak]

O.K.    now I'm seeing something  ;D    not sure what to do next though 

    Signal Generator sending 1k @ 0db (  0.783vac )  measured at end of XLR from Sig Gen - when plugged into input XLR of unit it Drops to ( 0.512vac ) on the back side of the input XLR !!!    with input at 12:00

  with DMM on input XLR input pot full CCW ( off  ) I get ( 0.595vac @ 12:00 position ( 0.512vac ) and at full CW ( up ) - ( 0.629vac) 
    These measurements  are the same with unit  off or powered

  I say input pot - but its the T-Pad Attenuator

  I have it wired / cabled as in mnats instructions ?? 

 

[audiophreak]

... so following that weirdness , I had to set my Sig. Gen to +4 to get 0.811vac at the input XLR (  Sig.Gen. disconnected from unit I get +1.240vac fro Sig.Gen. )    adjusted output pot to match vac at input/output XLR's , with input control at 12:00 position and engaged GR , nothing changed at output XLR and no GR indicated on meter.
  Increased input control 3/4 up ( 3:00 position )  in GR , meter reads -7db  , output XLR reads  +0.379vac =  almost -7db 

  again, not sure where to go from here , but meter seems to be reading correctly , but it looks like to input signal drops significantly before it even gets in to the compressor .

  any thoughts ??? 


EDIT :  I also noticed that with +4 from Sig.Gen. and unit in GR mode , when I put it " SLAM : ratio the meter pegs as did my Rev.J's  , but as I increase the input control  past half way up ,the meter actually comes down and  goes below 0  ???

maybe a problem with the Ratio PCB  ????

 

[Echo North]

O.K.    now I'm seeing something  ;D    not sure what to do next though 

    Signal Generator sending 1k @ 0db (  0.783vac )  measured at end of XLR from Sig Gen - when plugged into input XLR of unit it Drops to ( 0.512vac ) on the back side of the input XLR !!!    with input at 12:00

Normal.  Just impedance loss.  Increase the signal generator until you see 0.775 at the input.  You may have to go as high as 1-2VAC depending on the sig output impedance.

  with DMM on input XLR input pot full CCW ( off  ) I get ( 0.595vac @ 12:00 position ( 0.512vac ) and at full CW ( up ) - ( 0.629vac) 
    These measurements  are the same with unit  off or powered

Again impedance loss.  The T-pad varies a litte depending on the position.  All normal.

 

[Echo North]

... so following that weirdness , I had to set my Sig. Gen to +4 to get 0.811vac at the input XLR (  Sig.Gen. disconnected from unit I get +1.240vac fro Sig.Gen. )    adjusted output pot to match vac at input/output XLR's , with input control at 12:00 position and engaged GR , nothing changed at output XLR and no GR indicated on meter.
  Increased input control 3/4 up ( 3:00 position )  in GR , meter reads -7db  , output XLR reads  +0.379vac =  almost -7db 

  again, not sure where to go from here , but meter seems to be reading correctly , but it looks like to input signal drops significantly before it even gets in to the compressor .

  any thoughts ??? 

Impedance loss 

Have I mentioned this is normal?  ;D

The lack of GR is concerning though and does point to the fact that you seem to have a circuit and not a meter problem.

Check you ratio PCB R values and wiring.

I'll try to go through it more tomorrow....checking threshold...

 

[Echo North]

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

 

[audiophreak]

well ... Job is keeping me from this now , but should be able to spend a few hours on it this afternoon.

  I was able to read those exchanges and will check and test those points and components.

  Mike , Thanks so very much for taking the time , its greatly appreciated

 

[Echo North]

well ... Job is keeping me from this now , but should be able to spend a few hours on it this afternoon.

  I was able to read those exchanges and will check and test those points and components.

  Mike , Thanks so very much for taking the time , its greatly appreciated

No worries, We'll get you up and running.

 

[audiophreak]

OK , got to spend some time back with this , but picked up a couple more shows , will be on the road till Tuesday, so this is what I had time for:

  Ratio      CR2,3          Pad 21      Pad 20 reads -7.19vdc on all ratio's except Slam its -3.9vdc
  20:1 =  -7.09vdc      -7.12vdc
  12:1 =  -4.13vdc      -4.15vdc
  8:1  =  -3.01vdc      -3.o3vdc
  4:1  =  -2.08vdc      -2.09vdc

0db input 12:00GR on :
  Ratio      Pad 22               
  20:1 =  0.226vac     
  12:1 =  0.190vac     
  8:1  =  0.183vac     
  4:1  =  0.177vac

got -10.09vdc on one side of R64 and -7.12 on the other side for a -2.97vdc drop

unfortunately forgot to check current through R64 , that will have to what till next week.

I was able to verify all parts and connections on Ratio and Meter PCBs and R52/53

  if I'm reading those pages correctly , the -2.97 drop across R64 doesn't seem enough making the threshold too high ??


recap :  the unit passes audio cleanly, was able to do            Q Bias  and Discrete Meter circuit adjustments no problem ( or at least went according to mnats videos )  Gain Reduction meter tracking , I can hear GR but cant seem to get to -10db GR only 4-5db GR with input control almost all the way up.

 
       
   

 

[Echo North]

OK , got to spend some time back with this , but picked up a couple more shows , will be on the road till Tuesday, so this is what I had time for:

  Ratio      CR2,3          Pad 21      Pad 20 reads -7.19vdc on all ratio's except Slam its -3.9vdc
  20:1 =  -7.09vdc      -7.12vdc
  12:1 =  -4.13vdc      -4.15vdc
  8:1  =  -3.01vdc      -3.o3vdc
  4:1  =  -2.08vdc      -2.09vdc

0db input 12:00GR on :
  Ratio      Pad 22               
  20:1 =  0.226vac     
  12:1 =  0.190vac     
  8:1  =  0.183vac     
  4:1  =  0.177vac

got -10.09vdc on one side of R64 and -7.12 on the other side for a -2.97vdc drop

unfortunately forgot to check current through R64 , that will have to what till next week.

I was able to verify all parts and connections on Ratio and Meter PCBs and R52/53

  if I'm reading those pages correctly , the -2.97 drop across R64 doesn't seem enough making the threshold too high ??


recap :  the unit passes audio cleanly, was able to do            Q Bias  and Discrete Meter circuit adjustments no problem ( or at least went according to mnats videos )  Gain Reduction meter tracking , I can hear GR but cant seem to get to -10db GR only 4-5db GR with input control almost all the way up.

 
       
 

I'll have to look closer when I have a bit more time, but I don't see anything concerning. 

Maybe your qbias is set wrong? Did you feel good about your qbias adjustment?

 

[audiophreak]

Yes , I've done QBias adjustment multiple times now , all the same and it goes pretty much like the video :  input control full CCW , output control at 3/4 up , VU mode with pad 22 shorted to ground, 0db 1k input , turn up input control till meter reads +1 , turn QBias trimmer till 1db drop and meter reads 0db ... it all seems to go as described.

    The only thing Ive noticed is that on a 25 turn trimmer  , it takes about 18 turns for meter to start dropping , I measured from wiper to ground after calibration and its about 586ohms.

 

[Echo North]

Yes , I've done QBias adjustment multiple times now , all the same and it goes pretty much like the video :  input control full CCW , output control at 3/4 up , VU mode with pad 22 shorted to ground, 0db 1k input , turn up input control till meter reads +1 , turn QBias trimmer till 1db drop and meter reads 0db ... it all seems to go as described.

    The only thing Ive noticed is that on a 25 turn trimmer  , it takes about 18 turns for meter to start dropping , I measured from wiper to ground after calibration and its about 586ohms.

I'll try and take some measurements tomorrow.  Something is off.  Maybe the sidechain amp or something.  You used 3707's? or 3708's?

 

[audiophreak]

I used 3707's , bought about 60 of them , went through them for hFE , my Fluke meter doesn't check hFE , I got a cheep meter that does from eBay - maybe its not accurate