(Solved) Release pot on G-1176 moves g.r. pointer. Any help?

[FrankoPanko]

I have built over twenty of these gyraf 1176 compressors and never had a similar problem. Everything works, but when I turn the release pot left and right, the pointer on the gain reduction meter moves even though there is no input signal. The voltages on the transistors are ok, except for Q15, which has 1 v lower on the emitter. Can anyone help me where to start looking for the error? Thanks in advance!

 

[timpanic]

I have built over twenty of these gyraf 1176 compressors and never had a similar problem. Everything works, but when I turn the release pot left and right, the pointer on the gain reduction meter moves even though there is no input signal. The voltages on the transistors are ok, except for Q15, which has 1 v lower on the emitter. Can anyone help me where to start looking for the error? Thanks in advance!

Hi, I´ve the same prob with one unit here. I replaced the diodes and the 0,022 cap as mentioned in other threads but it didn´t change anything. Did you find anything in the meantime? I had a lot of trouble this time with the FETs...I had to replace a lot to get the unit working but in the end that´s the only issue left.

 

[saint gillis]

Sounds silly, but did you triple check the way the attack and release pots are wired?

 

[gyraf]

perhaps leakage in C19-c20 - the two 6u8 caps feeding the sidechain rectifier?

I mostly see this if the FD333 low-leakage diodes are not quite right, but I've also seen it on genuine/original rev F´s..

/Jakob E.

 

[timpanic]

perhaps leakage in C19-c20 - the two 6u8 caps feeding the sidechain rectifier?

I mostly see this if the FD333 low-leakage diodes are not quite right, but I've also seen it on genuine/original rev F´s..

/Jakob E.

Thank you so much Jakob E.
It´s not 20 db or something but around a 3-5db drop on the GR meter. I am also wondering if it is inside
a "normal vintage" range because it´s not the end of the world. It doesn´t sound "wrong" and I don´t use these slower releases not that often and one can just increase the output level but it´s still strange.

I already replaced the 6u8 tantal caps during the build cause they were only 16v rated so the 30v ones used now are quite new.
The build here is based on the stereo 1176MS, Both channels show the same phenomena. I have another mono G1176 pcb based here, a very old build by me, which does not show this at all but I also remember another mono build from the past where it was also shown.

I´ve used FD300a diodes on both channels here now and already replaced these with 4148 for testing on one side but it shows the same behavior when turning the release pot. The multimeter and my china component tester shows no defekts so far with these diodes. I can try to order FDH333 and again new tantals and see what happens and will report.

This phenomena is often discribed here in the forum. Leakage is the obvious answer here but it turns out people have all kinds of traps here from caps in the input, around the pot, in the output section, sockets used etc...yeah really a rabbit hole.

It seems that with the 1176 its not often done with just buying new parts...there are always Diva-parts involved here

 

[timpanic]

Sounds silly, but did you triple check the way the attack and release pots are wired?

Maybe not so silly....I must check this out further. I had to change the direction and had to rotate the pots because in the front I had the original placement of slow/fast position in the scale but for the ms1176s pcb it´s meant to be the opposite ( like in a ssl etc) way. Beside that it should be okay.

update: checked it and that´s not the issue here. Will go on searching....

 

[timpanic]

perhaps leakage in C19-c20 - the two 6u8 caps feeding the sidechain rectifier?

I mostly see this if the FD333 low-leakage diodes are not quite right, but I've also seen it on genuine/original rev F´s..

/Jakob E.

Hi Jakob. I replaced the Diodes and nothing changes. I took them out of an old mono g1176 where the release has no effekt on the GR. In the meanwhile I populated a completly new 1176MS pcbgrinder board..new tantals 35v, all caps new...same problem. Really strange. Could it be something with the 2N5457? Or that I used a 5k trimpot instead of the 2,5k for the qbias?

When I take out all 107 and the diodes the "problem" is still there. Turn down release pot drops also the GR. Do you have any Idea what I can replace or check? Thanks in advance.

 

[gyraf]

If it still does this without the FD333 diodes in place, there is something leaking DC into the Q-bias system

Perhaps leakage in C5 or C27 (lift one end and try)? Alternatively some leakage or partial short from chassis to pot (attack or release)? Contamination on PCB(clean)?

 

[timpanic]

If it still does this without the FD333 diodes in place, there is something leaking DC into the Q-bias system

Perhaps leakage in C5 or C27 (lift one end and try)? Alternatively some leakage or partial short from chassis to pot (attack or release)? Contamination on PCB(clean)?

Lifted both c5 and c27. Still the same. When I touch the release pot at its contacts ( which is logical cause then there is less ohms than 4m7) the gr reduction reduces but nothing else doing the trick here. I can calibrate the unit, it compress etc everything works beside this problem.

 

[JohnRoberts]

I don't know what an 1176 is, but look for DC voltage on that pot that is causing meter fluctuation.

JR

 

[timpanic]

I don't know what an 1176 is, but look for DC voltage on that pot that is causing meter fluctuation.

JR

Hi, yes there is a little dc there like 0,3v. But that´s the whole question. I measure -1,6v at the negative side of the tantals and this does not change by turning the release knob. I measure 0,2v at the fdh diodes when I turn the release on slow and 0,3 when turning to fast.

Sadly the TO didn´t chime in and tell us what his solution was...

BUT I read in the 1176 help thread somebody had this problem. He made a new board/build EXACTLY the same, same components etc and the problem was suddenly gone and he didn´t know why. He thought it was the FETS on sockets but the new one was also on sockets. What. The. Hell.

 

[Davidgilmour90]

perhaps leakage in C19-c20 - the two 6u8 caps feeding the sidechain rectifier?

I mostly see this if the FD333 low-leakage diodes are not quite right, but I've also seen it on genuine/original rev F´s..

/Jakob E.

Hello Jacob.
I have one question about the metering switch:
At the left position is bypass, center position is GR, and right position?
Because in this position metering not working (go all on the left side).
Is normal?
Thank you.

 

[gyraf]

isn't it for selecting +4 and +8 as vu-meter reference?

 

[Davidgilmour90]

isn't it for selecting +4 and +8 as vu-meter reference?

Hi Jacob, thanks for the reply.
While doing some testing, I realized that you need a really strong signal level to get the vu meter to shake. Indeed, seeing the schematic, I was wondering why the signal for the meter from the output was taken directly from the output transformer, entering the meter AC and without a driver circuit. Why without driver circuit? I noticed that entering the AC directly into the meter, the needle dances a lot and the measurement is not precise.
I was thinking: wouldn't it be better to modify the unit with a driver circuit and maybe a switch so that the input level can be selected on the meter as well as the output level?
From your project, if I'm not mistaken, it seems to me that the +8 output has been omitted and only the +4 output has been left. But I was just thinking about inserting a driver, I think it would be more stable and the meter would work better.. what do you think?

 

[radardoug]

In a word, no. Thousands of 1176s have been built without a meter driver.

 

[Davidgilmour90]

In a word, no. Thousands of 1176s have been built without a meter driver.

Thanks for answer.
I assume though that obviously you need a vu meter with adequate sensitivity to work well with the 1176, correct?

 

[radardoug]

UREI just used a standard VU meter with inbuilt rectifier.

 

[gyraf]

the 1176 requires a VU-meter with a sensitivity of 1.23V AC for a deflection to 0VU when driven through a 3K6 resistor

see e.g. SIFAM VU METER R34A

 

[Davidgilmour90]

the 1176 requires a VU-meter with a sensitivity of 1.23V AC for a deflection to 0VU when driven through a 3K6 resistor

see e.g. SIFAM VU METER R34A

Thanks for the reply Jacob, my meter can't handle it and I think I'll fit a driver circuit.

I also wanted to ask you for the ATTACK and RELEASE potentiometers if they were logarithmic or linear as in the BOM it is reported linear, while in the logarithmic layout. Thank you in advance.

 

[timpanic]

Just want to chime in and tell that my leakage problem is still there but I now think it must be coming from the meter circuit. When I pull out the transistor before the tl071 the problem is gone means the output does not drop when I turn the release pot. Sadly I tried to change other/new transistors there and the problem remains. As the meter circuit works it could not be a wrong component there. I also tried some other tl071, one even makes it worse ( even more drop).