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

[0dbfs]

I managed to buy the wrong attack pot with a dpst switch instead of a spdt, meaning I can just break the pad 22 to ratio board circuit without grounding it. So for testing I just soldered in a separate toggle switch for taking pad 22 to ground. Now I find that for all practical purposes this switch does nothing. What side effects would leaving the side chain input floating instead of grounded have.

I'm more of a sound person so excuse my patchy understanding of electronics.

Cheers,
Tomas

This would probably make the side chain susceptible to noise and therefore inadvertent triggers when the intent is to bypass. It must be fairly sensitive because the signal line is shielded.

Best,
JoBu

 

[0dbfs]

Allright. Looks like I had the wrong resistor in the GR control amp that was causing distortion due to malformed CV. For R37 I had a 470R instead of 470K. Oops!

I'll attempt to calibrate later today once I give her a good chance to get a bit warmed up. My initial tests of running audio through was much more clean than previously. I also dropped the level going in so I'll have to play with that a bit. Maybe a fixed pad going into the pre-amp section or something... Have to think about that and see if it needs it once I get it acting mre like it's supposed to.

Cheers,
JoBu

 

[JoeMorris]

Built one of these (with fellow board denizen snipsnip) via hairball kit and mnats board over the weekend. Sounds great. Thanks fellas!

 

[MicDaddy]

Sometime ago I had an issue using either Rev A as an insert on my Dynacord analog mixer....

I had originally wired the Y cable TRS to XLRF/XLRM  pin 3 cold/shield and pin 2 hot/signal on either XLR. 

I had neglected to tie pins 1 and 3 as the insert point is unbalanced.  Soldered a small component leg between pins 1 and 3 on both XLRF/XLRM and tada..

Hum eliminated.   

Now I can properly smash my awful drum playing via the main inserts.

I have 2RU for another 1176, do I go for a 2-1176 and which Revisions?  I'm thinking F or D, any suggestions?

Also, for those of you with a 2-1176 or 'dual' 1176 build, how often do you use it in LINK and why? 

 

[dtrax]

I'm getting close to finish wiring up my stereo 1176, and R-OPT1 has got me thinking. Just the other day I was using my mono 1176 and wished the internal threshold was just a bit higher, to get a touch more saturation. Much to my surprise and joy, Mnats already thought of that!

However, there isn't much info regarding the actual value of the trimmer pot. Looking at the schematic, the resistors preceding R-OPT1 are as follows:
R21 = 56k (4:1)
R20 = 56k (8:1)
R19 = 68k (12:1)
R78 = 47k (20:1)

My assumption is each ratio has a slightly different threshold to compensate for increase/decrease in GR according to the ratio selected. So, can I just find a trimmer that's above the highest resistance? In this case, 68k. In other words, would a 100k trimmer work? Or am I going about this all wrong?

(Side note, I'm surprised there isn't more information on the matter. This, IMO, is a great mod. It definitely increases the versatility and opens up many more tonal options.)

 

[evilcat]

There's another way to modified threshold : 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 !

Ben

 

[0dbfs]

Awesome. I think I have a 250k pot and a drill laying around.

Will test first!

-jb

 

[dtrax]

Thanks for the info evilcat! When I get home tonight I'll give this a shot.

 

[evilcat]

Happy to help guys, have a nice mod !

 

[kevriv]

Ok, so I built my kit. and it powered up just fine there was a little issue with the last calibration step and getting it perfect, but it was close enough. Sound passed through just fine and it sounded awesome. Then I took it over to a buddy's place, plugged it up and blew a fuse. Opened her up thought i Found a short got rid of it then it powered up again, but it sounded awful really noisy and quiet Kind of like something making a partial connection with ground. Took it back to my place to check it out some more and blew the fuse again. went through did some more cleaning and I blew another fuse. Any ideas? If I'm blowing fuses does that mean it is a short for sure?

Kevin

 

[kazper]

Deleted since it's not a issue in the revision A.

 

[mnats]

http://www.groupdiy.com/index.php?topic=44909.0

Recently I was asked to debug and calibrate several DIY 1176LN's with the mnats PCB, and discovered what I think is a fairly significant error. In the preamp section, R12 is specified as 920 ohms. I suggest that people use 1.8K instead.

The original UREI Rev D and E schematics show 910 ohms for R12, but many examples actually use 1.8K, and all Rev F  units use 1.8K. Basically, I think the 910 ohm value was a mistake that crept into certain D's and E's. (Some of them do use 1.8K, which makes me think that UREI had a service bulletin or upgrade procedure that addressed this.) All UREI Rev F units use 1.8K, as do the UA 1176LN reissues.

If you use 910 or 920 ohms instead of 1.8K, DC bias in the Q3 / Q14 section will be incorrect, and you'll lose about 8 dB of headroom in the input section. Besides the headroom loss, you'll also have 8 dB less limiting available. (Since Q3 / Q14 precede the sidechain circuit, having less gain before clipping at this point forces you to run the input pot lower, reducing the amount of possible limiting before onset of distortion.)

The error in the value of R12 is understandable, since 910 ohms is shown on the old schematics. But these units will work and sound much better with 1.8K. I can't imagine any benefit to using 910 but if you disagree, please speak up.

(I wasn't sure whether I should start a new thread or post on the main 1176LN Rev D DIY thread, but decided on a new thread because the topic seemed deserving of attention.)

Note that the Rev A has a completely different preamp design so you will have a hard time trying to find the right resistor if you attempt to apply this correction.

 

[kevriv]

I was able to get my build to turn on without blowing the fuse today and this is what I found....

First the unit looked to be working fine I did the q-bias calibration and it was looking good. I then moved jumper to take r44 out of the circuit to perform the next callibration step. I realized that I had done the q-bias looking with the meter on +8 instead of plus 4 and went back to start over which is when the meter pinned hard to the right even with the input knob all the way down.

When I turned down the output knob it went down. I then ran 0dbu 1K signal through it to listen and found that the output knob would cause the unit to distort when it was above 1/2 of the way up with the input knob set really low.

with the input knob all of the way down the noise floor on the output knob was ridiculous when it was turned up to about 3/4 of the way up

When I put my hand over the unit the noise characteristic changed.

When I touched any of the large caps in the power section the noise went away

when I touched c3 I was picking up radio

Moving the attack knob caused a frequency sweep

At a loss,
Kevin

 

[0dbfs]

Kev, Check your grounding. I had similar issues with spurious noises and the output knob pegging the meter until I went through and tidied up the grounding. Pin 1 of the XLR's, CT of the transformer, and IEC-Earth all to a chassis star-point....

I spent a bit of time staring at the schematic, and testing various grounding configs while listening to the output.

Hope that helps!

Cheers,
jb

 

[kevriv]

Thanks JB,

I discovered transformer ct was grounded wrong. I got it right all my ground points are testing out now, but I'm back to blowing fuses. I am so lost.

K

 

[MicDaddy]

Thanks JB,

I discovered transformer ct was grounded wrong. I got it right all my ground points are testing out now, but I'm back to blowing fuses. I am so lost.

K

Are the fuses you are blowing 250mA time delay/slow blow or fast acting?

There's quite a few people having documented the 250mA failing either because they are not mechanically very robust, or the inrush of on-current is popping them.  Use your own discretion, IME bumping up to a T500mA (slow blow) cured the issue.

How did you have the ct grounded, and how did you correct it?  I'm only curious, thanks.

 

[kmozart]

Hi Everybody! My First Post here, but reader for a long time....
I LOVE REV A of 1176!!!
I built one with the stock BOM from Hairball, and the Hairball kit with blue stripe. It was working great on the first try, after the build!!! No Noise or whatsoever...
I calibrated it RIGHT after the build, and I was able to go thru all 3 steps without any problem. Then I let it burn for a day and a half.
Now I'm trying to recalibrate it, Bias calibration goes Good, then Null calibration is OK, but I'm having trouble calibrate the discrete meter circuit.

I'm applying 1K,  0.775V on the input, attack knob OFF, Meter Switch on +4, and I align the signal with out knob to read 0. when I turn the attack knob on, meter goes below -10 and even with the input on full clock wise, I can't get it to go to -10, so I can not set the knobs for -10 db compression. Any idea why is that? also when i go to GR mode and try the trimmers, seems like R44 is also not able to get the level up to -10? Did anything burned in the "burn in" period of a day and a half? I was able to align it before,...

Any help appreciated,...

THANKS!

 

[0dbfs]

Maybe turn the output knob up or down to get it to read -10 at output with GR enabled... Then bypass GR and re-adjust input knob to read 0... Rinse/repeat until you don't have to make any more I/O adjustments between GR ON/OFF. Try the opposite if needed.

Best,
j

 

[MicDaddy]

from nimbleswitch-

Step 3: Adjust Gain Reduction Meter Tracking

Ok. .775v coming in.

    * In GRmode, Input control at 12 o'clock, and adjust output control
      to give .775v coming out of the unit.
    * Now, switch to bypass, and adjust the input control(the t-pad)till
      your output of the 1176 reads 10db(2.4495).
    * Then switch back into GRmode and again readjust the output
      control(of the unit) to read .775v at the unit's output.
    * Then switch to bypass yet again, and readjust the input
      control(t-pad) till the unit's output reads 10db(2.4495).
    * This goes back and forth a few times till the 10db swing
      holds...i.e, in bypass mode you have 2.4495v coming out, and then
      switching into GRmode, you have .775v coming out. Thus the 10db
      swing...10db of gain reduction.
    * Immediately insert R44 with input signal still present and adjust
      it till your internal VU meter rests at -10dB. You'll probably be
      quite close to this setting without adjustment.


It's been my experience easier to 'see' what's going on with the DMM than watching the VU

 

[StudioChris37]

Hey Guys
Ive scoured this thread and im either not reading something right or im doing something completely wrong. Got my REV a built, and fired up but im smoking r32. As a few others seemed to be earlier on in this thread. The thing is ive got the new 1.2.5, The output transformer is wired correctly according to the silkscreen on the PCB and im still fryin' em like hotcakes.

If i remove Q6, they dont fry, if i unhook the output trransformer, they dont fry. Im lost and unless im completely misreading all this info, something is wrong.

any input would be greatly appriciated guys.

thanks!

Chris