[BUILD] 1176LN Rev D DIY

[college101]

If your using a 2k trimmer, its only a few turns to move the needle...I forget what I actually measured but it was close to 2K...

I would venture a geuss and say that something is shorting out your trimmer...maybee solder bridge on the pads between wider and ground....

I agree, you can use a voltmeter to set the reduction level, but the point your missing about the third calibration step, is you have to be able to get the 76 meter to accurately show that change in level...you can adjust all day long, if the needle doesnt show what your doing to the signal, you dont have any idea of the actual compression being applied...

 

[imo]

To use the voltmeter, you would put it on the output XLR and measure there. I would suggest downloading the real 1176 manual for details on how they calibrate, or at least the Purple audio. It does sound though that there maybe something wrong in the trimmer section if you can adjust from one side to another and have no change. Just for peace of mind try the voltmeter to make sure. Start with a '0' db, .775v signal at your input XLR. output all the way up and input down. Raise your input pot until you have around .87v. that is a 1db increase in your output. Turn your trimmer clockwise until this goes back down to .775. That is a 1 db fall and will work even if your meter is not working properly.

 

[college101]

imo..The problem I am having with my meter is in the third step of calibration.. My q bias calibration worked correctly

I also complted the second step of the calibration....

In terms of the third step! I have had problems...

I am able to complete Part A of the third step in VU mode(+4) but once I change to GR mode to complete Part B, I can not adjust R44 to show any reduction...

I stalled DIP sockets to physically remove R44 from the circuit, once I place it back into the circuit, my needle drops to minus 20 and no amount of adjustment to R44 causes the needle to move...

Overall, seems to me that R44 is shorting out, but, with R44 in circuit, I can do Continuity checks- there would be four points to check, and all of them pass the continuity test...

1-wiper side of R44 to collector= Passed
2-wiper side of r44 to R68 1.5K= Passed
3-TP1 connection to Q13 collector= Passed
4-TP1 connection to R69 1.5k= Passed

 

[cybergolio]

have you seen R'45 is at the wrong place on the mnats shems ?

 

[college101]

Ok...where does it go cybergolio?

 

[cybergolio]

in parallele whith the +20DB switch& not the +4DB

http://www.purpleaudio.com/product/PurpleMC76.pdf

(the purpple & urei are sames )

 

[college101]

I geuss I assumed that was the +20 switch on the mnats schematic!

So I need to pull R45 and solder it in the ratio connector parrallel to R63 but switch side of the trace?

 

[cybergolio]

i'm not sure it's really important in your case & it wasn't on rev D but appears on E.

in the rev after (F,G,H) it change his place but the others R changes too !

We have always in the other side of the GR the famous unknown "t&c".
Hope it's could help you.

 

[college101]

Since mine is a Rev D, I think it may be different...

Hopefully, my tech calls me soon to come over and get this on his bench!

 

[cybergolio]

"Revision E was essentially the same as revision D. Revision E added 220 Volt operation as well as a 10MΩ resistor across the ratio switch to avoid ‘pops’ while changing between compression ratios."

source : UA LN1176 manual

 

[college101]

OK..I think I have figured it out...I have over solder'd the pads for R44 and need to cut out the middle terminal pad now..  I tested for Continuity and realized that I must have a solder bridge on the TP1 connection and the wiper...which has to be the problem

 

[edanderson]

check again.  look at r86, it should be a 100 ohm trim pot.  all the rest are fine as 2k, including r44.  in some cases you may even want to substitute a 5k for r44, but usually a 2k will work -- in my experience the value is usually between 800 and 1500 ohms. 

if you look at how r44 is connected you can see that it is as a variable resistor, with the wiper tied to one end.  that means that a 2k trim can do everything that a 1k can do (be set to any value from 0 to 1000 ohms) but has a wider range.

ed

edit: my post was in response to someone who posted saying that they thought they should use 2k for all the trim pots, and why did their mouser order using the hairball BOM include a 100 ohm trim pot.  i guess they deleted their post b/c now it is gone.

 

[college101]

Thanks ED- I have a 5K in for R75..  My R44 reading was around 1.5K when I had no input signal and was able to adjust it to -10(but I had no input signal- so this doesnt really count in my book)

So I am still stuck...

First I decided to try and dig out the solder bridge...which I did, but it still seems to complete the continuity test on meter...Atleast on my board...seems like the wiper connection IS connected to the ground side of the trim pot...SO to rule this out..  I THEN went bread board style...

took some lead trimmings and put one in the knobside dip socket and one on the ground side of the dip socket... nothing in the middle wiper socket...  Connected with some breadboard jumper connectors(wiper and trimmer to one clip that connected to the top side, and then a second connector to the bottom dip socket to the ground side of the trimmer) BINGO...In GR mode I can adjust R44 and move the needle!!! Im excited at this point!!!

AND THEN I realize...Oh I have no input signal...turn on the 1k tone...

I go back and zero the meter in +4, and as I am turning up R71...I run out of turns to adjust it to 0... I can only get it to -5 and then it is stuck....

What do you guys think now?

 

[college101]

Re-read your post again Ed... The wiper of R44 is connected with the main trimmer side to the Q12-E side

The ground is connceted to the TP 1 side

Still cant get it to work correctly

 

[edanderson]

the point of r44 is to set a resistor value from q12-e to q13-e.  those points are already connected by r68 and r69, so r44 is in parallel with them.

the wiper and one end of the trim pot should both be connected to q12-e, and the other end of the pot should be connected to q13-e, via the jumper installed at tp1.  note that the wiper could be connected to the other end of the trim pot instead and it would still work, you'd just have to turn the trim the other way.  as long as the two ends of the trim pot are not shorted (test the trimmer and the pads with the trimmer taken out), that part should work.

when you went back to zero the meter in VU mode, and applied the test signal, did you take r44 back out of the circuit?

ed

 

[college101]

I left R44 in circuit when I went to zero the meter...

My understanding of the calibration was- after the q-bias step 2, you re-insert R44 into the circuit for step 3 in the calibration...before performing part A

Ed- I noticed what you were saying about being in parralell... I am going to try again tonight once I get home and report back...

I am hoping, if I turn it the other way, everything starts working as it supposed to!

***One more question though!****
The only difference from MNATS web site schematic and picture display is that I have an additional audio ground coming from the output transformer wiring to the chassis ground connected(other then that- my wiring and parts/layout match exactly)**(mnats site does not show this)**  And the turning the R44 trimmer the opposite way...

 

[Hyder]

Could someone please confirm for me that the FIRST step in the calibration is setting the Q bias, and is R44 in or out via the 3 pin header???

Thanks,
Hyder

 

[college101]

Yes HYDER..Thats how I performed my Q bias calibration ( have you watched MNATS calibration videos on youtube?)

In other news...I still cant get my R44 to work correctly...The connection that is close to Q13E basically makes my needle drop to -20 when connected... After following the traces and studying the trace layout...the TP1 connection point connects between Q12 and Q13...BUT if I have signal coming in, via the 1k tone...out of circuit, the meter reads -7 exactly...as soon as I connect R44.. The circuit acts like it is going to ground and the needle drops to -20....no amount of adjusting the ohms to it does anything...I swept it from a value of 2k all the way down to 100 ohms...Nothing..

Im still stuck guys

 

[Hyder]

Yes HYDER..Thats how I performed my Q bias calibration ( have you watched MNATS calibration videos on youtube?)

In other news...I still cant get my R44 to work correctly...The connection that is close to Q13E basically makes my needle drop to -20 when connected... After following the traces and studying the trace layout...the TP1 connection point connects between Q12 and Q13...BUT if I have signal coming in, via the 1k tone...out of circuit, the meter reads -7 exactly...as soon as I connect R44.. The circuit acts like it is going to ground and the needle drops to -20....no amount of adjusting the ohms to it does anything...I swept it from a value of 2k all the way down to 100 ohms...Nothing..

Im still stuck guys

Thanks, yes I  have watched the vids. I'm unclear if the jumper for r44 should be in or out, or off?

My unit is a hairball push button REV D and it passes audio, the VU meter shows gain reduction as well as input level.
It looks pretty accurate too, and sounds very good.

Just when I try to do the Q bias, No drop at all. Trimmers are good, I checked them with my DMM. They go from 2k all the way down to 10 ohms. solder joints are clean.Values are correct, Matched all my hfe on the transistors.

STUMPED!

 

[edanderson]

***One more question though!****
The only difference from MNATS web site schematic and picture display is that I have an additional audio ground coming from the output transformer wiring to the chassis ground connected(other then that- my wiring and parts/layout match exactly)**(mnats site does not show this)**

do you mean the bare wire that is soldered to the frame of the hairball 5002 type transformer?  the purpose of that wire is to ground the frame of the transformer to the chassis.  if you measure continuity between the frame of the transformer and your chassis, then you don't need to use that wire for that purpose.  if there is no connection, you can scrape away a little of the paint around one of the screw holes to ensure electrical continuity.

you could use it to accomplish the connection shown in the last photo on this page:

http://mnats.net/1176_reva-d_hairball_wiring_meter_circuit.html

if you ran the ground wire already and you have continuity from the transformer frame to the chassis, you can ignore the bare wire.

ed