All things G1176 - the new "repost" thread.

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Hello I am having a issue with a new rev f/g it seems to be filtering highs off pretty dramatically anyone ever seen this? It's calibrated and compressing sooooo I don't know where to start looking?

Thanks
 
claudio.accatino said:
Hi everyone,

Problem is, I'm having some strange behaviour on the input stage.
Briefly, it seems that the input is about 10 dB more sensitive than I remember, as the unit starts compressing way too early (referring to knob position) compared to the silverface one I used often in the last few years. I admit that I haven't been able to A/B them yet.

My G1176 has the same issue. Can someone help us?
 
pedroplanet said:
claudio.accatino said:
Hi everyone,

Problem is, I'm having some strange behaviour on the input stage.
Briefly, it seems that the input is about 10 dB more sensitive than I remember, as the unit starts compressing way too early (referring to knob position) compared to the silverface one I used often in the last few years. I admit that I haven't been able to A/B them yet.

My G1176 has the same issue. Can someone help us?

If you look on the schematic you will see a "T&C" part across S4B.
This part is a resistor that is selected to set the threshold,at which compression starts (for the 20:1 ratio).
An easy way to do this is to use a resistor decade box clipped across here and select the appropriate value after setting up the unit with the input knob at the position you want for compression to start.
 
gswan said:
pedroplanet said:
claudio.accatino said:
Hi everyone,

Problem is, I'm having some strange behaviour on the input stage.
Briefly, it seems that the input is about 10 dB more sensitive than I remember, as the unit starts compressing way too early (referring to knob position) compared to the silverface one I used often in the last few years. I admit that I haven't been able to A/B them yet.

My G1176 has the same issue. Can someone help us?

If you look on the schematic you will see a "T&C" part across S4B.
This part is a resistor that is selected to set the threshold,at which compression starts (for the 20:1 ratio).
An easy way to do this is to use a resistor decade box clipped across here and select the appropriate value after setting up the unit with the input knob at the position you want for compression to start.
Hey gswan
I dont see that on the schematic I have. Can you post a copy?
 
Chrome Heart said:
gswan said:
If you look on the schematic you will see a "T&C" part across S4B.
This part is a resistor that is selected to set the threshold,at which compression starts (for the 20:1 ratio).
An easy way to do this is to use a resistor decade box clipped across here and select the appropriate value after setting up the unit with the input knob at the position you want for compression to start.
Hey gswan
I dont see that on the schematic I have. Can you post a copy?

Draw it in then. Stick a resistor (S.O.T.) across S4B.
 
gswan said:
Chrome Heart said:
gswan said:
If you look on the schematic you will see a "T&C" part across S4B.
This part is a resistor that is selected to set the threshold,at which compression starts (for the 20:1 ratio).
An easy way to do this is to use a resistor decade box clipped across here and select the appropriate value after setting up the unit with the input knob at the position you want for compression to start.
Hey gswan
I dont see that on the schematic I have. Can you post a copy?

Draw it in then. Stick a resistor (S.O.T.) across S4B.
What I meant is I dont see S4B
 
Hmmm. I didn't put that resistor on the the ratio switch either.

Gswan, I wonder if the lack of that resistor is what was causing this problem a few posts back?: 

"Sounds great on anything without fast transients. I'm noticing, though, that with drums, the fast transients seem to be causing a nasty peaky distortion." This occurs right on the transient. It sounds like I'm overloading the input but no amount of reduction (prior to hitting the 1176) seems to remedy this problem.

Anyway, I also having a 2nd problem that has started. I'm having some very audible ringing on both channels of my dual G1176. It started after I was using the slam mode function quite heavily on both channels. I'm not sure what's causing it. Any ideas?


 
JW said:
Hmmm. I didn't put that resistor on the the ratio switch either.

Gswan, I wonder if the lack of that resistor is what was causing this problem a few posts back?: 

"Sounds great on anything without fast transients. I'm noticing, though, that with drums, the fast transients seem to be causing a nasty peaky distortion." This occurs right on the transient. It sounds like I'm overloading the input but no amount of reduction (prior to hitting the 1176) seems to remedy this problem.

I very much doubt it. This is a SOT part, it does not affect anything other than the threshold at which compression starts. Any other problem is due to faulty contruction and/or wiring. It sounds like you need to get a scope onto it and do some troubleshooting.

JW said:
Anyway, I also having a 2nd problem that has started. I'm having some very audible ringing on both channels of my dual G1176. It started after I was using the slam mode function quite heavily on both channels. I'm not sure what's causing it. Any ideas?

Not sure what you mean by 'ringing'. If it is real ringing then check the termination of the transformer. Get a scope onto it and see how it reacts to a single burst at the output. Tune the termination to match your transformer.
 
Hello DIY'ers,

I've been working on Mnats rev j 1176 for some time now (6 months now, 1 to build 5 to troubleshoot), and have read through most of this thread. I have a problem, my 1176 has not been compressing since the day I finished assembling it, and as of yesterday I know what the problem is! My electronics knowledge is what we'll call beginner, all I've learned has been from working on this project, but this is beyond me....

I've traced the signal and all is well until I hit the 2 FDH333 diodes, signal enters the diodes but does not come out on either of them, I've tried replacing them and the same problem occurs, I'm stumped on what to do about this (they were measured before hand to ensure they were functional). Is there a possibility that a damaged component somewhere else in the circuit is causing the signal to stop here? Has anyone else experienced this?

Thanks in advance.
 
What signal exactly do you have at the diodes (Anode side)? Remember to include the DC offset, which is negative. It is likely that you don't have enough signal to get above +0.5V and through the diodes. This could be due to many things, most likley a wrong resistor in one of the stages.

Have you performed DC bias checks?
Have you performed stage gain checks?
Have you performed Qbias calibration?
 
Have you performed DC bias checks? NO
Have you performed stage gain checks? NO
Have you performed Qbias calibration? YES

Could you please enlighten me as to what dc bias checks are and how I can do them?

I forgot to mention, I did check transistor voltages, everything looked good in that area. I also checked the voltages at the points designated by Gyraf, also good.

For gain stage checks, this is referring to the test signal? If so could you specify at what points in the schematics I should be probing for changes.

Thanks

 
The transistor voltages you mention are the DC bias checks for the circuitry.

To test the AC characteristics of the signal amp stages, apply a signal to the unit and check the gain through the first stage (should be about 26dB). The output driver stage should be about 10dB.

Some details here:
http://www.axtsystems.com/index.php?option=com_content&view=article&id=57:1176lnproblems&catid=34:1176ln&Itemid=62

How about the signal on the diodes? What do you have there?
 
goldenGeek said:
Hello!
I`m trying to troubleshoot my 1176 (built on a PCB from Gustav). The problem is that it doesn`t compress, and the levels are varying every time it`s powered up. I`m tring to learn how to use my scope, and I`m feeding a 1k sine to the input. I get a sine also on the output, but as I said the level vary from time to time its powered up. I`ve disconnected the OEP output iron just to rule that out (it did make the signal about half in power from before the transformer, but that`s varying with the "normal" signal strength so I guess that`s fair enough).

Should I read a clear sine at the attack pot? I read a fine sine on the rest of the pots though. It seems like there`s something happening around the 333-diodes... anyone who maybe has a hint for me?

Thanks :)

I finally figured out what was wrong with my 1176, so I thought I'd post the solution in case someone elese has the same problem. After changing all the transistors and diodes it was still not working, the problem was as stated earlier that it didn't compress and that the levels dropped drastically after being on for about half a minute. Well, what I did wrong (I'm really upset with my self for overlooking this simple yet fatal error) was that I didn't wire the ground/0v wires to the attack and threshold pots. You may ask why... the reason was that in the PDF it said that *=optional, but I guess that only applied to the PCB. So I figured that the * on the pots was optional as well. Guess what it wasn't. Maybe the PDF should have been updated with a different symbol to mark ground/0v on the pots... or maybe noobs like me should stay away from electronics ;) After all I'm really happy now that everything is working, and I guess I learned my lesson  :)
 
I've redone the dc bias test and put my results in the test spreadsheet, and it's not as good as I had previously thought!

Q2 0.979 2 0.481
Q3 2 11.25 1.13
Q4 11.22 28.9 10.6
Q5 4.6 27.2 4.2
Q6 27.2 13.9 27.8
Q7 27.8 13.9 28.4
Q8 13.9 28.9 28.4
Q9 12.6 0 13.2
Q12 4.3 14.7 3.8
Q13 14.7 28.9 14.1
Q14 3.3 16.1 2.8

Sorry it takes so long to reply but work keeps me busy..
Q15 16.1 28.9 15.6
 
Hi all,
I thought that all the 1176 pros would be hangin' out in this thread so I'll bring my issue here
and see if anyone has any suggestions:
When I connect '17', the output pot works but a get a weird thumpy oscillation.
Disconnect, and the unit passes audio fine.

Any thoughts?

Cheers!
 
Interesting and thank you, Gswan!
I will go back and check. I have a suspicion you could be correct
as the wiring diagram I referenced (I'm building a REVA version)
was found to be incorrect AFTER I wired everything.
I've been troubleshooting ever since.

So I'm on the same page: '17' from the PCB goes to the center lug of the output pot correct?
 
stitch-o said:
So I'm on the same page: '17' from the PCB goes to the center lug of the output pot correct?
Correct.

Don't use a wiring diagram. Use the circuit diagram.
Anything else is a derivative from the circuit and may have errors.
 
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