All things G1176 - the new "repost" thread.

[Biasrocks]

There's no disagreement, it adjusts the threshold of the compressor.

If you must, put a 100K pot in there and adjust until you get the threshold point you like, measure the pot's resistance, insert resistor, done.

I haven't used it in any of my builds.

Mark

 

[niccolo gallio]

Hi there, after hours of headscratching and google searching I've decided to post here in search for assistance with a Mnats Rev. J unit.
I have assembled two units of whom the first one worked ok first try, nothing fancy here: no input trafo and just standard components. The second one (same components) gives strange readings in the marked points on the PSU section: Where it should give +30V it's between 27.6 and 28.7, meaning that the value changes over time..
Where it should read -10V it reads ~ -9V.
The unit doesn't seem to pass audio and it doesn't smoke either..
I've checked this malfunctioning unit side to side to the one that works and it looks like I've not misplaced components..
At first I thought that could be the VR1 gone bad, so I've took it out and checked for shorts but it looks ok, no shorts.
I'm quite sure this question has been posted countless times but couldn't find any info about troubleshooting the PSU specifically.
I'd like to know your opinions about this and if you can suggest other test points for this PSU?
Also, could the VR1 not be functioning correctly even if it has non shorts?
Again please forgive me if I'm making you loose time

sincerely

niccolo gallio

 

[Biasrocks]

Would one leg of the 100k pot go to the selector?

Looking at the schematic, the T&C resistor goes across the last switch (20:1) on the ratio control board ahead of R26 (56K).

Mark

 

[redmojosteve]

Hi
I have just completed my G1176 using MNATS Rev J boards with OEP input and output transformers. I was very careful with checking the component values before soldering them in place and all of the transistor biasing voltages are spot on. So far so good. I have put a OdB 1kHz signal through the input but that is about where it ends! i.e. no signal at input pot. The input test signal is unbalanced and between ground and the XLR +ve connector. This is the first time I have used input transformers and I am thinking that I am sure I am missing something really basic so I apologise in advance. e.g. as tested above, is the input primary voltage just floating and do I need to ground the -ve connection?
regards

 

[Dr-Mbogo]

try mark burnleys signal tracing test probe. I made good experinces using this tool.


I hope you'll find the mistake soon.

Chris

 

[redmojosteve]

Found the problem. I'd used a cheap connector between the sig gen and the input which turned out to be faulty. After correcting this it seems generally OK. I just need to check through the thread as I now need to get the lights in the meters working and I know this has been covered before. (I am using MNATS very useful little PSU rather than the onboard components)

 

[redmojosteve]

I have now finally run audio through my dual channel G1176, in particular drum recordings, and it works superbly and very much as I expected (or hoped!) it would sound. Even the stereo tracking seems OK, and I have only used the simple link. I have the Hairball studio boards but haven't incorporated them yet. On a vaguely related topic concerning matching FETs, has anyone ever tried the "CT100 USB Semiconductor Curve Tracer"? On the face of it, it looks like a useful piece of kit for hobbyist level of matching.

 

[Le Roux]

Is 18 AWG alright for wiring the G1176?

I thought I remember reading that 18 AWG for power supply, and 22 AWG for pots etc.

Thanks

 

[k-los]

Can someone help me out pls. I have been reading and probing for weeks it looks like im having problems in the .....


        B      C    E
q5  1.24  28.6  1.72
q6  28.6  4.44  29.0
q7  29.6  4.44  29.0
q8  3.8    29.0  4.3
q9  3.8    0      3.2

Erea im using the bd139 and  bd140...................... ???

Thx

 

[gswan]

Check the orientation of the BD139 and BD140 and that they are in the correct holes (and you don't have the links in).
Also check the resistor values around Q5.

 

[trapiche2]

Hello!
First, A big thanks to Jakob for the project!
My 1176 is working!  ;D
I have only one question concerning the frequency response:
I have measured and get this:

I feel like I was missing treble ...
Is this normal in 1176?
Thank you very much

 

[Jazzboms]

Hi

Im building 2 units rev J.
I posted a post yesterday but took if of. Wanted to do some more cheking first.
So Im down to the following issues.
The first one:
- It worked when I started it. GR Meter, compressing audio was fine. But after a some testing the secondary voltage(-10) dissapeared. All my reading in the primary(30V: GR control amp, signal line amp, signal pre amp)if fine compared to the measuring on the schematics. Pin1 on tl071 should be -10V, but is 0V. I dont think it is the tl071, I have cheked this lt071 with my second unit, witch works.

For both.
- The VU reading dont work. GR is ok, but no VU. Have tried to fix it with the prim pots. Just stays at -20. The meter Im using is from an old tascam mixer.

Thanks

Update:
Seems like I have resolved my problems with the -V line. I found a tread on the recording.org. Didnt know about this forum....
It was my Zener diode that was bad.
The VU reading still need to be solved.

 

[gswan]

The VU meters are probably DC meters, not AC. You may need to make a bridge using germanium or schottky rectifiers and wire this between your signal and the meter.

 

[Beauvais]

Hi everybody

I've built a dual 1176 using mnats rev J boards a while ago and it works perfectly apart from a little hum I can't get rid of. What kind of SNR is there to be expected from this design? I have both OEP input trannies and the electronically balanced input stage on the boards. The output transformers are Lundahl.

When using the EL input I have a 50 Hz (plus harmonics) hum at around -80dB regardless of knob settings, so this must be introduced at the output stage. When using the input transformers the hum depends on the knob settings. With both the input and output knobs at about 2 o'clock, the hum is at about -95dB but rises to about -50dB when turning either knob clockwise or counterclockwise.

Both channels are absolutely identical in behaviour. There must be something wrong with the input transformer wiring or I wouldn't get this changing hum. But are the steady -80dB when using the el balanced inputs normal? I have the grounding scheme as per mnats guide, lifting the input pin1 makes things worse. Connecting pin1 of the outputs to ground doesn't change anything, connecting AC 0V on the board to ground doesn't change anything either.

Do I just have to live with this -80dB hum or should I be able to get rid of it?

Thanks, David

 

[gswan]

50Hz plus harmonics sounds like the power supply.
Check the ripple on the +30V rail of the power supply. Are you using the on-board PSU or an external PSU?

 

[juanjovincenzo]

Hi!! guys

I am preparing the components list to do a G1176. I try to read a lot about the transformers alternatives in this forum, but I dont have the money to buy a lundalhs , OEP, etc..... to compare these in the G1176 circuit.

Please I need help to choose the transformers (IN & OUT). I read about the OEP and the lundahls, but what about the B11148 or cinemags???
I would like the best sound approximation of the original UREI REVISION F using a G1176 circuit.

I self-etched the mnat s REV F PCB http://mnats.net/files/1176Flayout.pdf very similar to REV H or REV J pcbs but I add some traces and pads to update this board for the diferents trasnfo options (like the REV J PCB, adding wire links and cutting traces). I use this old revision because need a small PCB to small enclosure.
I´m confuse about the "Transfo. Options":

1. OUT (original formula Gyraf G1176 2:1 vs the 1:2 Option )

2. IN (the Gyraf G1176 1:1 ratio circuit vs the step down configuration (the 2:1 configuration)

What are the best "Transfo. Options" or the better approximation to the original UREI REVISION F ????

Please, If you have advices, tell me. Thanks a lot

best regards

Juanjo

 

[Echo North]

I would like the best sound approximation of the original UREI REVISION F using a G1176 PCB.

The rev F uses an attenuator/UTC O-12 input and B1114 output.  You could use them on a G1176 with a little effort.

 

[juanjovincenzo]

Hi
thanks Mike
Is correct this wires between J PCB and B1148? http://www.groupdiy.com/index.php?topic=34975.msg428603#msg428603

, so easy?


Is possible use only the OUT TRAFO B11148 without the T attenuator and the TRAFO IN UTC O-12 (or Altran C-3837-1)? So, in the other hand is possible use a IN TRAFO like lundalh LL5402 or OEP A262A2E or a cinemag?

 

[Beauvais]

50Hz plus harmonics sounds like the power supply.
Check the ripple on the +30V rail of the power supply. Are you using the on-board PSU or an external PSU?

I've never measured voltages since the unit works perfectly apart from this little hum. But at the 30V-point on the PCB I have no measurable AC-voltage (the other pin of the multimeter going to ground, right?). Or am I not getting something here?

Also both boards behave exactly the same, which kind of rules out a component problem. I am using the internal power supply, but with a rather expensive shielded toroid made for audio applications. If it was hum introduced by the mains transformer, shouldn't there be minor differences between the channels, one being a little closer or having a different angle etc? But they're exactly the same, -80dB on the frequency analyzer in my DAW.

Actually -86dB right now when I checked again, maybe that's just normal? I had never even noticed it until I patched the 1176 into an LA-2A and used that to boost the signal considerably. Only then the hum rose out of the noise floor. Maybe I'm worrying about something that's just normal behaviour, an 1176 having a SNR of about 85dB?

What's everybody's experience regarding SNR of a 1176?

 

[gswan]

50Hz plus harmonics sounds like the power supply.
Check the ripple on the +30V rail of the power supply. Are you using the on-board PSU or an external PSU?

I've never measured voltages since the unit works perfectly apart from this little hum. But at the 30V-point on the PCB I have no measurable AC-voltage (the other pin of the multimeter going to ground, right?). Or am I not getting something here?

Also both boards behave exactly the same, which kind of rules out a component problem. I am using the internal power supply, but with a rather expensive shielded toroid made for audio applications. If it was hum introduced by the mains transformer, shouldn't there be minor differences between the channels, one being a little closer or having a different angle etc? But they're exactly the same, -80dB on the frequency analyzer in my DAW.

It's not induced. It's actual ripple on the power rail. Moving the wires or transformers won't help in this case. You need to get a scope onto the power rails to view it and measure it correctly. Another quick test is to try adding another 2000uF cap across the rectified DC rail and see if it reduces. Do you have any meter lamps connected to the supply rails?