All things G1176 - the new "repost" thread.

[gswan]

From your previous image, I saw these two potential problems.
1) Bad solder joints.


2) potential solder bridge.


The significant voltage drop across R17 is where you should be looking. Is R17 correct in value?
If so, what is drawing excess current through this resistor?
Even with a reduced voltage, the DC bias of Q2 seems elevated. Is R12 really 1M?

 

[Whoops]

I agree with what member gswan said,
these 3 joints look really bad:

 

[gswan]

That's exactly what I was pointing out.

 

[sodastereo]

I have reviewed your photos and components, and there does not seem to be an assembly error. I check your compression rotary wrench? and the cables from the pcb to it? Is that key well welded?

 

[mks]

Can anyone point me to the reason why I get a lot more harmonic distortion when metering is set to output vs GR metering. It’s quite significant and would like to fix this rather than simply not use output metering. It has been years since I built these and it’s tricky finding my way back into these designs

 

[gyraf]

..it was always like that - have you tried the original?

 

[mks]

..it was always like that - have you tried the original?

Thanks gyraf. I guess I had never noticed since I rarely leave them on output metering or injected a test tone in real-world use to notice how much distortion there is when switching away from GR. So clear. Super interesting though and fun quirks

I did some harmonic measurements on an older build I’m just bringing back to life. One at each metering setting is attached. Interesting harmonics around the fundamental too. Looks a lot like some other measurements I’ve seen out there. Does this look like “healthy” behavior in terms of distortion differences?

 

[cprins]

I have reviewed your photos and components, and there does not seem to be an assembly error. I check your compression rotary wrench? and the cables from the pcb to it? Is that key well welded?

Hi sodastereo,
Thanks again for your feedback. I've checked all previous points, including the values for R12 and R17, and those don' t seem to be the problem. The joints looked a bit weird after resoldering them, but I' ve checked and double-checked them and they are fine. For now I' m out of ideas. I feel I have already taken up too much of your and everybody else's time, and therefore have decided to scrap the project. In any case thanks a lot (to all!) for your ideas and suggestions!

 

[Whoops]

Can anyone point me to the reason why I get a lot more harmonic distortion when metering is set to output vs GR metering

..it was always like that - have you tried the original?

I was not aware of that, I guess I never noticed since I always use the meter in GR mode.
But I really want to try it as sometimes I really want more Harmonic Distortion

 

[gswan]

It's because the direct metering mode of the output attaches a diode bridge (via a resistor) across your signal bus. This results in additional distortion. It's the reason why most modern metering is decoupled using op-amps and precision rectifier circuitry. The GR metering passes through an op amp before arriving at the rectifiers in the meter.

 

[Whoops]

It's because the direct metering mode of the output attaches a diode bridge (via a resistor) across your signal bus.

Thats great, I will use it in Output metering next time I use it, always looking for more dirtiness.
Thanks for explaining

 

[raoul1983]

Hi All,
It's not fixed yet, so I post my question again, hope someone can help me out
I just finished my build, the power rail was like it should be +30v and -10v. I think I've shorted something during calibration. The 220ohm resistor burned... Now I only get like over 60v and no -10(or anything there) I replaced the resistor and the voltage regulator, but stil got the same values.
Does anyone know what to do or what to replace?
It is a Gyraf pcb with a separate power transformer.
cheers!

 

[gswan]

If you've really got 60VDC where 30VDC is supposed to be (and I doubt that you have) then you have probably cooked most of your board. It's more likely that your measurement technique is broken, amongst other things on the board. Why would you try calibration before you have verified that your board is actually operating with the correct DC operating points?

 

[Whoops]

Now I only get like over 60v and no -10(or anything there) I replaced the resistor and the voltage regulator, but stil got the same values.

That's really strange.
Whats the voltage you have before the 7824 regulator?

Measure and test all the rectifier diodes (CR7,CR8,CR9,CR10)

Very important also, measure and test the Zener Diode (CR6) in the -10V rail

Measure resistors R85, R86, R87

After that you should do a video showing how you taking the voltage measurments and also some photos of that part of the PCB

 

[spoontex]

Hi,

I'm planning to build a 1176 compressor, and I read some threads that is need to match two fet transistors. So, my question is:


Is enough measure only the Vp and Idss ( attach schematic )


Or I need to measure at diferent Vgs values, how is described here:

https://www.axtsystems.com/joomla31...76ln-audio-compressor/4-art-1176-fet-matching

 

[gyraf]

I think we discussed this earlier in the thread?

 

[spoontex]

Hi,

somebody can tell me if this meter work with this build?

Description:

Panel-VU-Meter with Frame
Part-Nr. : SD-740 -B
Dual-dB: -20~+3dB
with 12V Color=Amber Bulb lamp
with black plastic mounting frame
DC 500uA Full Scale, DCR=650Ω
(Item is only for a display meter, design the driver board by yourself, not included, please understand)

Thanks!

 

[spoontex]

Hi,

I'm trying to match some fet's BF245A, and I get very high values, comparing VGS 0V to -0,250V. I don't think it is normal. I stop on 0,750v.

I use this method:

https://www.axtsystems.com/joomla31...76ln-audio-compressor/4-art-1176-fet-matching
Is necessary this method to match the fet's? or I can use a simple method. Second attached circuit.

 

[spoontex]

Confirmed, this are fake jfet.

Anyone can tell me if I can use a 2n5952 for this build?

Thanks.

 

[gswan]

Hi,

I'm trying to match some fet's BF245A, and I get very high values, comparing VGS 0V to -0,250V. I don't think it is normal. I stop on 0,750v.

I use this method:

https://www.axtsystems.com/joomla31...76ln-audio-compressor/4-art-1176-fet-matching
Is necessary this method to match the fet's? or I can use a simple method. Second attached circuit.

You can match the slope of the transfer curve so that the metering more accurately reflects the gain reduction. It's not critical though.