[BUILD] 1176LN Rev D DIY

Those values are actually good.  All of your side chain numbers look great.

About unit gain that is not true.  At 12 and 12 o'clock you will get a huge boost.  Also keep in mind the input pot curve on the Bourns T-Pads is a little different that the originals so it will seem hotter.

Typically when we use the the input is around 9 o'clock and the output near 12 o'clock.

Noise is still an issue however.  Kinda stumped.

Mike

Hairball Audio said:

Those values are actually good.  All of your side chain numbers look great.

About unit gain that is not true.  At 12 and 12 o'clock you will get a huge boost.  Also keep in mind the input pot curve on the Bourns T-Pads is a little different that the originals so it will seem hotter.

Typically when we use the the input is around 9 o'clock and the output near 12 o'clock.

Noise is still an issue however.  Kinda stumped.

Mike

Click to expand...

Hello Mike:

Well, the 12 o'clock thing comes from the official 1176 original manual, where it says that having the input and output at that position you have unity gain. But maybe when this input pot, as you said, it's different, I don't know. But I find it strange that when I need to crank the input to aprox 12 o'clock way to start compressing a signal then I have to put the output almost at minimum so I don't have a huge boost. Is that normal? When I see videos of other 1176s DIY they usually have a symmetrical position of input and output!

And about the noise the truth is that it's the biggest issue in order to record... I attached 2 audio files so you can hear it. I connected the 1176 directly to the input of my interface with no input signal, input knob full CCW, OFF position:

The first one is with the output knob at 12 o'clock and the second one is with the output full CW.

The interface's channel itself is almost perfectly clean.

http://www.filedropper.com/inputatlowestoutputathalf

http://www.filedropper.com/inputatlowestoutputatfull

The original Allen and Bradley inputs had a unique curve that you don't usually see.

Hiss with the out full CW is normal.  That's just noise floor being amplified by 40-45dB.

Under normal operation we have our input at 9 or 10 o'clock (7-10dB of gain) and out output at about 12 o'clock.

Kind of stumped.  What is your signal chain again?

Mike

Yes but that "noise floor" is all from the unit! I mean if connect the preamp (WA TB12) directly to the interface almost all that hiss is gone... I don't know, I'll investigate which elements are susceptible to introduce that type of noise so I can change them and see if it's reduced!

About the gain, honestly I'm pretty sure it's something wrong in there, because my "normal operation" is input at 9 or 10 o'clock to have 7-10dB of GR but the output at 7 o'clock!

If you don't really know what can cause that issue now don't worry, hopefully I find the problem someday!

Thanks.

patxiplg said:

Yes but that "noise floor" is all from the unit! I mean if connect the preamp (WA TB12) directly to the interface almost all that hiss is gone... I don't know, I'll investigate which elements are susceptible to introduce that type of noise so I can change them and see if it's reduced!

About the gain, honestly I'm pretty sure it's something wrong in there, because my "normal operation" is input at 9 or 10 o'clock to have 7-10dB of GR but the output at 7 o'clock!

If you don't really know what can cause that issue now don't worry, hopefully I find the problem someday!

Thanks.

Click to expand...

Hard to to know without having my hands on it.

That output is fishy.  We have a repair service on the site if that interests you.  Otherwise keep looking and post if you find anything fishy.  Sounds like you have way too much gain somewhere which could be caused by many things.

Mike

I know but I'm not in the states so it would be very expensive and take so long...

I'll try to research and find out why it's happening.

Thanks!

I have just finished 2  X 1176 Rev D Mnats builds. I sourced all the parts from my local electronics store. The only thing I couldn't source locally was the 2K Bourns trim pots. I used a blue 202 trimpot. They look cheap but I am sure they could work. Only problem is - they don't. I am trying to calibrate the Q bias and am not having any success . I am feeding the input XLR  @ 2.75  from my interface. As I measure the output on pins 2 and 3 with all the knobs and buttons as per hairballs directions I am only reading  .09 vac and the trim pot doesn't affect anything. Perhaps I have something else askew..yet they both do exactly the same thing. I have checked all the wires - resistors etc all is correct. Could this just be a trim pot issue, or are can anyone offer an idea to check .

Click to expand...

Those trimmers are fine.  Are you sure you're using the right footprint for them though?  Look at the traces.

What is your DC at pad 18? Does it change when you adjust the Qbias?

Hey Mike:

I think I'm going to replace all the transistors and see if that solves the problem of the huge gain and noise. Could you tell me which ones have no relation with audio signal so I don't change those?

Thanks!

Hairball Audio said:

I have just finished 2  X 1176 Rev D Mnats builds. I sourced all the parts from my local electronics store. The only thing I couldn't source locally was the 2K Bourns trim pots. I used a blue 202 trimpot. They look cheap but I am sure they could work. Only problem is - they don't. I am trying to calibrate the Q bias and am not having any success . I am feeding the input XLR  @ 2.75  from my interface. As I measure the output on pins 2 and 3 with all the knobs and buttons as per hairballs directions I am only reading  .09 vac and the trim pot doesn't affect anything. Perhaps I have something else askew..yet they both do exactly the same thing. I have checked all the wires - resistors etc all is correct. Could this just be a trim pot issue, or are can anyone offer an idea to check .

Click to expand...

Those trimmers are fine.  Are you sure you're using the right footprint for them though?  Look at the traces.

What is your DC at pad 18? Does it change when you adjust the Qbias?

Click to expand...

Hello There,

I've gone throughout all the thread and still have some problems. Friend of mine built it.

Just few measures :

DC @ pad 21 :
4:1: -1,47VDC
8:1: -2,43VDC
12:1:-3,58VDC
20:1:-6,64VDC

AC, with calib sine @ pad 22 :
4:1: 0.004VAC
8:1: 0.004VAC
12:1: 0.004VAC
20:1: 0.004VAC

NO VDC Change at pad 18 when trimming the Null adj. but VDC is -1.16V

Any infos or help?

Best regards.

llo everyone,

I am looking for advice on my builds. I have built 2 1176 Rev D. I have checked the voltages against the schematic, continuity and double checked values.  R 59 does not show movement on the meter at output.  All the voltages are correct for Q4 Q5 Q6.

I decided to go with 2n5088 instead of the 2n3707/3708 Transistors.

Voltage @ output XLR is .041

Q11 G - 2.774
            S - 2.158
            D - 2.481

Q 12 C - 2.935
            B - 3.591
            E - 2.913

Q 13 C - 3.799
            B - 0.925
            E - 2.675

These values are very low with reference to the schematic except for Q13 Base.

I am presuming it could be a bad transistor in Q11?

Ok, founded !

R37 was 470 instead of 470k.  8)

Thanks.

patxiplg said:

Hey Mike:

I think I'm going to replace all the transistors and see if that solves the problem of the huge gain and noise. Could you tell me which ones have no relation with audio signal so I don't change those?

Thanks!

Click to expand...

I'd probably just start with Q6.  You could do all the transistors in the boxes labeled "signal" and "Line" amp.  Possibly one of those is weird.  Make sure you don't have any 470Ω, 47K, 470K resistors swapped.

bxershrts said:

llo everyone,

I am looking for advice on my builds. I have built 2 1176 Rev D. I have checked the voltages against the schematic, continuity and double checked values.  R 59 does not show movement on the meter at output.  All the voltages are correct for Q4 Q5 Q6.

I decided to go with 2n5088 instead of the 2n3707/3708 Transistors.

Voltage @ output XLR is .041

Q11 G - 2.774
            S - 2.158
            D - 2.481

Q 12 C - 2.935
            B - 3.591
            E - 2.913

Q 13 C - 3.799
            B - 0.925
            E - 2.675

These values are very low with reference to the schematic except for Q13 Base.

I am presuming it could be a bad transistor in Q11?

Click to expand...

Did you insert the 2n5088's into the alternative footprints correctly?

i have a general question, what is the average "warm-up"-time of your 1176 until it reaches the normal condition? mine takes about 30 minutes until my meter reaches 0dB if calibrated properly. is this okay?

weiss said:

i have a general question, what is the average "warm-up"-time of your 1176 until it reaches the normal condition? mine takes about 30 minutes until my meter reaches 0dB if calibrated properly. is this okay?

Click to expand...

I would not be concerned - warm up time can be 15 to 20 minutes depending on ambient temperature.

Cheers!

Thanks for your reply Mike. Yes the 2n5088 transistors are in the other footprint on the board. I built 2 of the 1176 with parts from you. AS I test the working one against the non functioning one I have posted here - all the values are correct except at Q11. I have reflowed the solder points for Q11 and the voltages there are still not as per the schematic. I will take the ones out from my functioning 1176 build and sub them in to see if the problem is fixed.

bxershrts said:

Thanks for your reply Mike. Yes the 2n5088 transistors are in the other footprint on the board. I built 2 of the 1176 with parts from you. AS I test the working one against the non functioning one I have posted here - all the values are correct except at Q11. I have reflowed the solder points for Q11 and the voltages there are still not as per the schematic. I will take the ones out from my functioning 1176 build and sub them in to see if the problem is fixed.

Click to expand...

Be sure to check all the wiring that goes over there too.  Pad 7/29/28.

bxershrts said:

I am looking for advice on my builds. I have built 2 1176 Rev D. I have checked the voltages against the schematic, continuity and double checked values.  R 59 does not show movement on the meter at output.  All the voltages are correct for Q4 Q5 Q6.

Click to expand...

Are both units behaving identically or is one working?

bxershrts said:

Q11 G - 2.774
            S - 2.158
            D - 2.481

Q 12 C - 2.935
            B - 3.591
            E - 2.913

Q 13 C - 3.799
            B - 0.925
            E - 2.675

Click to expand...

A dash before a voltage measurement indicates a negative voltage. Are all of the measurements negative with respect to ground? What is the measured value of R79?

Also the two voltages I've marked in blue are connected together and should be identical. What is the reason why they are not in your unit?

Good morning Mnats. Thanks for your reply.  Australia.... what part do you hail from? Gotta go Freo Dockers!

My apologies for adding the separating dash in my response. These are all positive voltages.  The voltages on each side of R79 are 3.66 and 28.85 vdc. There is no negative voltage as per Base and emitter on Q12 or Source on Q11

The voltage differences at the base of Q12 and the source of Q11 are what led me to think a bad transistor.

The one unit works brilliantly. I did sub a 5k pot to have more swing on the Qbias.

I first checked all voltages as per your schematic. I have stopped at the GR Meter Driver. This morning I moved on  As I then fed a 1k signal to the input , I checked the output to look through the rest of the circuit and I only see ( .5 volts) at the output xlr - even with the output pot all the way up. SO looks like I will have to see whats going on there too. Perhaps my first issue affects my low voltage at the output?

Thanks for your advice Mike and Mnats

I have just checked the voltages at Q11S and Q12B and they are both identical at 3.843 volts dc. Not a negative voltage of -.09 as on the schematic.