All things G1176 - the new "repost" thread.

[adrian]

hello!
i've just "finished" my 1176 unit (mnat version J), and it doesn't work as i expected... :-\

my problem is that if I put input and output pots at 12o'clock in bypass mod i've 22db of gain!
then when i turn on it seemed to compress ...

and when i'm in GR mod the VU (SIFAM AL19) goes to the right (i don't know how to explain, it indicate full full full!) even if there is nothing in input! i tried to use the bias trimpot but nothings happen, ???

I use the mnat external power supply that deliver correct voltages,
I just use a oep tranformer on the output,

i checked transistor voltage and value that i'm not shure to be good are:

Q4 -- 12,03 -- 29,02 -- 11,43
Q13 -- 14,78 -- 29,3 -- 14,17
Q15 -- 17,08 -- 29,3 -- 16,55

instead of: (http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=57%3A1176lnproblems&option=com_content&Itemid=62)

B C E
Q4 -- 11.8 -- 30 -- 11.2
Q13 -- 15.1 -- 30 -- 14.5
Q15 -- 16.6 -- 30 -- 16.0

i did a search on this thread but i didn't found a similar problem, maybe it's 2 different problem?

 

[gswan]

These voltages look roughly OK so far. What about the other transistors?
The 1176 unit has a total of approximately 36dB gain through the various stages. So 22dB is not unexpected. Where this occurs on your pots will depend on the type of pot used (you did use log pots for the input and output controls, right?). You can check each stage for gain separately. The first stage should be about 26dB and the second stage about 10dB.

Did you perform the calibration correctly?

 

[adrian]

thanks for your answer!
yes i use log pots 10K on input and 100K on output,
when i'm turning the GR meter Zero trimpot nothing happens...
the others transistor value are like they should i've checked it,

I gonna try to find a oscilloscope to check amplifier stage as shown here http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=57%3A1176lnproblems&option=com_content&Itemid=62

nobody had this problem before?

 

[gswan]

But have you performed the calibration of the compressor correctly first?

 

[adrian]

are you talking about the qBias trim ?
i tried to use it as descibe on gyraf website but nothing happened....
i gonna check solders on it...

 

[gswan]

Yes. This is the most important of the calibration settings. Unless you get this right nothing else will calibrate correctly.

 

[adrian]

ok, thank you i gonna try to find what's wrong with this trimmer.....

 

[gswan]

Check the orientation of your FETs.

You should see a swing from 0V to a few volts -ve on the centre leg of the trimmer when it is wound from one extreme to the other.

 

[Biasrocks]

and when i'm in GR mod the VU (SIFAM AL19) goes to the right (i don't know how to explain, it indicate full full full!) even if there is nothing in input! i tried to use the bias trimpot but nothings happen, ???

I had the same problem with my meter. There are two pads provided for the meter on the main pcb board. I moved the wire to the other pad provided and I was able to calibrate the meter correctly. Try it and see if that solves the metering problem.

Mark

 

[gswan]

Geoff,
have checked R21, it is 7.5 k, and the voltages read 1.5 and 1.5.

The R16 trim does not effect the readings on Q4...

What is up stream from the Q4?

Ben

Ben,

Did you fix this one? I git sidetracked and didn't get back to it until now. I had a module on the bench here that exhibited the same DC bias readings in the first stage (all else was OK). I tracked it down to a faulty capacitor C8. Try replacing this if you are still stuck.

 

[stitch-o]

Hey kats,
I'm building a Rev A.
Before I get too married to the wiring scheme, I thought I'd double check I'm working from the correct document.
This the right scheme (with the blue from the 5002 OT on XLR+ and the red on XLR-)?

 

[Echo North]

If you look at the original schematic it seems so indicate blue + and red -.

Although, I think we've determined this may not be phase dependent.

Mike

 

[stitch-o]

If you look at the original schematic it seems so indicate blue + and red -.

Although, I think we've determined this may not be phase dependent.

Mike

Hey Mike,
Thanks for helping answer my stoopid questions before I aired them in public  ;D

I'm def looking to make sure this is the right overall correct scheme as well confirming the +/- on the XLR out, as I had read some opinions that the skylar RevD .pdf is the right way, but it is a fair bit different than this one I posted.

 

[s2udio]

Hey kats,
I'm building a Rev A.
Before I get too married to the wiring scheme, I thought I'd double check I'm working from the correct document.
This the right scheme (with the blue from the 5002 OT on XLR+ and the red on XLR-)?

Why the mains live to the meter pcb !?

 

[stitch-o]

Hey kats,
I'm building a Rev A.
Before I get too married to the wiring scheme, I thought I'd double check I'm working from the correct document.
This the right scheme (with the blue from the 5002 OT on XLR+ and the red on XLR-)?

Why the mains live to the meter pcb !?

The bottom button on the meter push-button array is a power switch.

 

[gswan]

FYI, I've added a new PSU design here:
http://www.axtsystems.com/index.php?view=article&catid=35%3Apsu&id=84%3Apsu8&option=com_content&Itemid=64

This works well with a dual 1176. There's a new incarnation of such a beast on the site as well, using Flashstar meters:
http://www.axtsystems.com/index.php?option=com_content&view=category&id=34&Itemid=62

 

[s2udio]

Ahh thanks for the update...........looked a little odd from the layout.

 

[stitch-o]

..........looked a little odd from the layout.

That's how all 1176's work and have worked, I believe.

 

[JoleFIN]

Right, doesn't the OFF position simply disable the meter?

Mark you were right, it disables the meter too so I can't use both GR + OFF buttons at the same time for the calibration. Gotta redo this..

The levels are what concerns me, when I have ie. 20:1 ratio selected and input+output at full 0 (CW), I get the output to peak around -6dB at max. It equals around to having the gain reduction off and output volume in the half-way. Is this normal? Does this make any sense :
20:1 and input+output volume at full CW = GR OFF & input full CW and output volume at (-)24 (straight upwards / middle position).

Here's a shot of a vocal track, upper is raw and lower is 20:1 limited (falsely named the file as 4:1). The limited has the input and output volume knobs at full, so I cannot get it any louder.
http://www.joelkalsi.com/diy/1176/20_to_1.png

 

[user 37518]

I have my G1176 working very nicely for the last months, but yesterday suddenly something happened when i tried to use it, the compressor works, but it has very low output gain, im guessing that the output stage amplification is the problem because the input seems to drive the compressor in the same way as before, i just have low output. Even on bypass i have a very low output signal, a transistor may got busted due to heat? im guessing the bd140 or 139 may be the problem, i sometimes leave the thing turned On for the entire session and i know that the psu regulator, the 1 watt resistor, and the bd140 and 139 can produce a fair amount of heat, so what do you guys think?