All things G1176 - the new "repost" thread.

[gswan]

Yes, I've even resoldered many connections just in case. The problem is my limited understanding of the compressor's topology. Am I correct in assuming that no actual audio signal runs through the GR amp, just a control signal? Where on the board does this control signal actually 'happen' to the audio signal?

Not quite.
The GR Amp is a rectifier and integrator. It ends up generating a time-varying waveform that changes the FET Vgs value, which affects the FET Ids (ie the amount of current between drain and source).
The GR amp is fed from the audio source, so audio does pass into it. This is amplified and full-wave rectified, summed with a bias offset (set by the ratio switches) and then integrated (smoothed) by the attack/release settings. This affects how quickly the change in Vgs occurs and how quickly it is removed.

The details you have provided to date are that the GR meter is showing the correct gain reduction (ie the GR amp is working) and that the same signal can be seen on the GR FET. If this is the case then, unless the FET is not connected properly, it is operating as expected.

 

[user 37518]

Ok folks i think i found the problem on my 4:1 ratio, the thing is this, the cable that goes from pad 4 from the meter board to the ratio board is like an anthenna, everytime i get my hand closer the unit will go bad, specially on 4:1 ratio so the needle moves all the way to the left (on GR mode). Im guessing it is a grounding problem, but still after grounding everything the cable still acts that way, so i changed the cable, and now it seems to be working more like a real 1176 although the cable still reacts a lot to my hand approaching to it. The other thing is this, when i move the release pot and the Meter is on GR mode, the needle will go like half a db up or down from Zero depending where you move it, to a slower position it moves down, to a faster position it moves up, this happens even when theres no signal present. I guess thats normal but i wanted to double check with you guys first. So is it normal?

 

[gswan]

Doesn't sound normal,I've not seen this behaviour.
Are you sure you haven't got your GR amp oscillating? That might account for your weird behaviour and the fact that your hand acts like a big capacitor.

 

[joulien3]

Hi guy!!
I need help...
I have mount 1176 mnats rev j.
When I switch to gr ,vu is fully on the right...?
And when i try to adjust with trim (q bias or zero adjust) nothing happened...?
Do you know what's the problem?
Thanx a lot!

 

[user 37518]

Doesn't sound normal,I've not seen this behaviour.
Are you sure you haven't got your GR amp oscillating? That might account for your weird behaviour and the fact that your hand acts like a big capacitor.

How can i find if my GR amp is oscillating?

 

[gswan]

Stick a CRO on it and see what the output looks like.

 

[user 37518]

Stick a CRO on it and see what the output looks like.

Man sorry for my ignorance and thank you for your help, but i have no idea what a CRO is. I have electronic knowledge but everything is mostly empirical, so an oscillator, a multimeter and some other instruments like a THD meter is all i know. Sorry for all this questions you've been really patient and helpful.

 

[Echo North]

Cathode Ray Oscilloscope I think.

Mike

 

[user 37518]

Hi guy!!
I need help...
I have mount 1176 mnats rev j.
When I switch to gr ,vu is fully on the right...?
And when i try to adjust with trim (q bias or zero adjust) nothing happened...?
Do you know what's the problem?
Thanx a lot!

Exactly that happened to me once, and i think there could be two different reasons (in my case they were both): 1st.-the unit is in short, i tested some spots like transistors and input stages and i had 0v, did you tested every component before soldering into the board? if everything is ok then check the PSU, most of the problems i've had, have something to do with the PSU, perhaps a broken copper track due to coldsoldering or a component being twisted several times, find the posible problem, and verify you have continuity in those places you are checking, as i said perhaps the PSU is not feeding some components, or the psu is bad, or you have some cold soldering
2nd.- I couldnt find a 2k pot for the zero adjust, so it thought of using a 2.5k, i dont know if this have a big impact, but after i fixed the shorts, i replaced the pot and its ok now.

 

[user 37518]

Cathode Ray Oscilloscope I think.

Mike

So im guessing that by Cathode Ray Oscilloscope you mean a regular, ordinary oscilloscope?, supposing it is, then on what should i focus my attention?

 

[gswan]

That's right, CRO or scope are interchangeable terms for the same piece of test equipment. Have a look at the output of your GR amp, particularly on the piece of cable you wave your hand near. See if there's any HF oscillation on it. Also see what is happening to the signal on it when you do wave your hand near it.

 

[joulien3]

Hi guy!!
I need help...
I have mount 1176 mnats rev j.
When I switch to gr ,vu is fully on the right...?
And when i try to adjust with trim (q bias or zero adjust) nothing happened...?
Do you know what's the problem?
Thanx a lot!

Exactly that happened to me once, and i think there could be two different reasons (in my case they were both): 1st.-the unit is in short, i tested some spots like transistors and input stages and i had 0v, did you tested every component before soldering into the board? if everything is ok then check the PSU, most of the problems i've had, have something to do with the PSU, perhaps a broken copper track due to coldsoldering or a component being twisted several times, find the posible problem, and verify you have continuity in those places you are checking, as i said perhaps the PSU is not feeding some components, or the psu is bad, or you have some cold soldering
2nd.- I couldnt find a 2k pot for the zero adjust, so it thought of using a 2.5k, i dont know if this have a big impact, but after i fixed the shorts, i replaced the pot and its ok now.

Hi!
OK, I have problem with cut trace and I solve that with strap.
However, My input and output it's ok (With my IN and output pot, I can grown up gain, and sound look good)
But , when I switch to GR, VU is on the right!!!
I've tried to adjust with zero adjust and I arrive to 0VU....but meter don't still at 0 VU ....  It growing down....
And when I adjust q bias trim nothing happend....
But I have found 2,2K trim?
Thanx a lot for your response....

 

[Chrome Heart]

Hey all
Im using the 62065 Amveco toroid for my 1176. Im checking all the voltages from the connector (not plugged into the PCB) and Im getting some strange readings. What should the readings for this transformer be. Im wired for US red/brn on center pin and BL and GRN on the outsides. Did I wire this incorrectly?

 

[gswan]

From the data sheet, this is a 2 x 22V 10VA toroid.
For 100VAC operation, the primaries are in parallel (ie yellow+red, black+violet)
You should get around 22-27VAC (load regulation is quoted as 20%) from each secondary (red to green, blue to brown).
Connect the red and brown together to form a center tap.

 

[Chrome Heart]

Fast. Thanks gswan. I have the transformer wired as you describe and Im using a Fluke 87 to measure. I measure each pin against GND correct? If so something is out of whack. Outside pin BL is -.40, outside GRN is -.05, and center is -.18 at the connector. I checked voltage at the back of the IEC where it feeds to the torroid and it reads 117, so its getting power.  ???

 

[gswan]

No, you do not measure WRT GND. The transformer knows nothing about GND. The voltages will appear across the secondaries, so you must measure across the secondaries.

 

[Chrome Heart]

OK. I read this, "Please check all voltages! -10V, +30V ... 24V against GND" on the nrgrecording page. I guess I misunderstood what it meant. So, if thats the case what are they referring to? Heres the link, http://www.nrgrecording.de/html/problems.html I guess they are referring to the 7824.

 

[Chrome Heart]

Thanks gswan, Im getting 25.73 on the secondaries. This seems to be in spec. Im still a bit green at this so thanks for responding.

 

[gswan]

Those voltages you refer to are DC voltages, which are measured WRT GND. The transformer center tap, once connected to the PSU module is also connected to GND and the other ends of the windings are rectified and smoothed to create a DC rail prior to regulation.

 

[k-los]

:-\  Can someone pls help........... I have the mnats rev J board and the problem is when I run audio thru the IC balanced input  only low frequency signal come out no highs, but if I run audio thru the input transformer everything sounds fine................... :'(