[BUILD] 1176 Rev A - Back to the beginning...

[pearldrum944]

Okay, here is one that does not seem to be mentioned.  The BOM calls for R76 being 18k, whiile the diagram says 8.2k...any ideas?

 

[mnats]

Okay, here is one that does not seem to be mentioned.  The BOM calls for R76 being 18k, whiile the diagram says 8.2k...any ideas?

Thanks for pointing this out. The value on the BOM and schematic is correct. The screen layer is wrong.

I've corrected the documentation and added it to the errata, but if you notice any other discrepancies you can always refer to the original schematic on the JBL Pro site linked from my Rev A page.

 

[ER]

Hi fellas, a little help would be appreciated. I finished a rev A build and can't get past the Q bias adjustment because I am unable to get signal to the meter to read 0vu when running  .775 volts to the input. My power measures correctly at 30v and -10v. If I leave my input pot wide open I get close to .775 to the input xformer and then it seems to be a step down xformer which brings me down to .45v to the pad of the PCB. Now a couple of things I had wondered about that perhaps I can be set straight on if I did it correctly were:

On the mnats BOM it says r14 & c6 not for 1176. So I left r14 open and I linked C6. However I've seen a few build pics here where it seems that those components were stuffed. Also on mnats board pic at the beginning of this thread he did not stuff R4 but I did because I didn't see documentation otherwise. And lastly the 2k pot trimmers on the board I simply orientated them in the same way as mnats pic as they seemed to be the identical trimmers but I have seen build pics with them reversed, could that be an issue? The only other thing I can think of is if the transistors are orientated correctly on the PCB. I orientated them according the the PCB symbols and used 3708's instead of 3707's. Other than that I'm pretty stumped. Any ideas?

 

[baadc0de]

If I recall correctly, mine didn't work until C6 was stuffed. I got it pre-stuffed with C6 = link.

Cheers,
B.

 

[Stagefright13]

On mine I had to mess with ALL the trimmers to get the meter to rise high. Try playing with the zero adjust also.

The 3708's Do indeed go like the silkscreen.

The trimmers can go in 2 ways I believe. Then you would just adjust it the other way. It IS possible to put them in wrong tho and have a non working unit. Just look at the traces and you will see what I mean.

 

[ER]

If I recall correctly, mine didn't work until C6 was stuffed. I got it pre-stuffed with C6 = link.

Cheers,
B.

Really? Man that seems weird that it wouldn't be documented anywhere...

What about r14, do you stuff it, wire it, or leave it open ended as mnats BOM suggests?

 

[evilcat]

If I recall correctly, mine didn't work until C6 was stuffed. I got it pre-stuffed with C6 = link.

Cheers,
B.

Really? Man that seems weird that it wouldn't be documented anywhere...

What about r14, do you stuff it, wire it, or leave it open ended as mnats BOM suggests?

Wait a minute, are you talking about R14 and C6 in the preamp section ? or Rx14 and Cx6 in the line amp section ?
On my V1.2 boards I only have R14 and C6 in the preamp section and of course, it had to be populated. In the line amp section there is no Rx14 and Cx6 anymore, now that mnats is making the 1108 standalone preamp PCB. Even if the BOM and the V1.2 silkscreen on Mako's pdf are mentionning those Rx and Cx components, they're actually not on the PCB.
Hope I'm clear !!!

Ben

 

[ER]

Yeah 1.2 board here. Too funny, thanks for clearing this up for me!

 

[evilcat]

Cool, I've helped someone ;D (kinda newbie here) !!! Your welcome ER, good luck on your build.

Ben

 

[ER]

Well thar she be, it works, compresses and sounds great. One question I would like to ask as I have no experience with the historic Rev A.

I noticed when I ran some vocals though it (not a very hot signal, perhaps -12DBFS from the DAW) I had to keep the input and output between 9 or 10 o'clock. Otherwise it would really smack down in compression, and the output was providing loads of gain. Usually the knobs of a rev D would be turned higher.

Is that the experience of others around here?

One thing I should note, the calibration video said 0dBu for the q bias, so I fed .775 volts for that step. The meter calibration asked for 0dBm so I ran 1.23 volts for those steps. Was that wrong and should I have also fed  .775 volt for the final calibration steps?

 

[Stagefright13]

Congrats!!!  ;D

This thread here describes optional components for your build. I didn't do any of the mods many here have. You question is discussed in there. http://www.groupdiy.com/index.php?topic=34502.0

I use my A all the time and love it! Have fun.

 

[evilcat]

I noticed when I ran some vocals though it (not a very hot signal, perhaps -12DBFS from the DAW) I had to keep the input and output between 9 or 10 o'clock. Otherwise it would really smack down in compression, and the output was providing loads of gain.

page 20 of this thread, ilfungo pointed this mod out :
"I added a switch that puts a 100k resistor in series with the link between (22) on the pcb and the 'GR off' switch. This makes the threshold higher and allows more input before gain reduction. In situations like vocal tracking this allows for subtle compression without having to turn the input down and the output up - which adds noise. 100k gives about 4db less gain reduction."

Very easy mod and works well. Me, I put a 220k resistor, that gives me 6dB less in GR on vocals and gtrs and 3dB on drums and other percussive inst. Plus the preamp section is driving harder (more coloured) and the output has to be turned down (much less noise). Just a single SPDT switch and a resistor !

And BTW, -12 dBFS begins to be hot in analog. Depends on the converters but with my Lynx Aurora -16 dBFS on PT equals 0 VU on my analog console, so IMO, at -12 dBFS you're already in the "red zone" ;D. My 2cts...

Ben

 

[ilfungo]

sorry evilcat
maybe a stupid question
I thought if we could insert potentiometer instead of a fixed resistance
could become a threshold control?
thanks

 

[evilcat]

Yeah it could, why not ? That way you could reduce the signal feeding the control amp section. The threshold would be higher only, not lower but it should not be a problem as this 1176 compress a lot quickly...

 

[beaversaber]

hi folks!
Just finished wiring up my first Blue stripe. It passes audio, in/out knobs work....

The unit does not seem to be compressing correctly.  I tried the calibration procedures, and am able to get the FET to attenuate -1db with GR disabled, but then when I switch into GR mode it doesn't attenuate the signal at all.  I have double and triple checked my wiring on the GR disable switch and it seems to be correct (22 and GRN shorted when on, 22 and BLK shorted when off)

my power supply rails seem to be doing what they're supposed to: +29.28v and -9.65v

Any thoughts?  I have also used Mark Burnleys signal probe to trace around, and the GR control section does get signal when I enable GR

 

[evilcat]

It's not quit clear to me : how do you proceed your Bias calibration ? Do you disable the GR by putting pad 22 to ground with the switch in GR position (not in bypass position) ? It's weird that you achieve that calibration step but that your compression doesn't works anyway... ???

Ben

 

[beaversaber]

It's not quit clear to me : how do you proceed your Bias calibration ? Do you disable the GR by putting pad 22 to ground with the switch in GR position (not in bypass position) ? It's weird that you achieve that calibration step but that your compression doesn't works anyway... ???

Ben

No, I use the switch to disable GR.  And ya I don't get it either...

 

[evilcat]

No, I use the switch to disable GR.  And ya I don't get it either...

Ok so, your bias calibration is not well done : you have to stay in GR mode and you're bypassing the gain reduction by putting pad 22 to ground. That way you don't compress but your Vu Meter stay in GR mode. Then you can proceed to the bias calibration. I don't remember it clearly so check the rev D pages videos on Mnats website, it's well explain.
Let us know if it works !
Best,

Ben

 

[beaversaber]

No, I use the switch to disable GR.  And ya I don't get it either...

Ok so, your bias calibration is not well done : you have to stay in GR mode and you're bypassing the gain reduction by putting pad 22 to ground. That way you don't compress but your Vu Meter stay in GR mode. Then you can proceed to the bias calibration. I don't remember it clearly so check the rev D pages videos on Mnats website, it's well explain.
Let us know if it works !
Best,

Ben

In Mnats videos he does the q bias calibration with GR bypassed and the meter in +4 mode, which would make sense because I think this is the first calibration step you're supposed to do (before the meter tracking and everything) meaning GR meter mode wouldn't function properly anyways.

 

[evilcat]

You're right sorry, too old memories... ;D
Still, the bypassing is achieve by putting pad 22 to ground, not by putting the switch in bypass mode. This is what you're doing, right ?