All things G1176 - the new "repost" thread.

[myker]

Gain Reduction Meter Tracking
1. Set the controls as follows:
Control
Set to
Input middle
Output fully CW
Attack fully CCW (switched to OFF)
Release fully CW
Compression ratio 20:1
Meter mode GR
VR54 trimmer 1/4 turn from fully CCW

2. With no signal applied, adjust VR55 so that the meter reads 0VU.
3. Apply a 0.245Vrms (-10dB) 1kHz sine wave signal to the input.
4. Switch the meter mode to +4dB.
5. Turn the output level control CW until the meter reads 0VU.

Number 5 says turn output CW to zero-out the meter when above it says to start with the output pot fully CW.
Can i do the signal generating in PT?
Thank you for all the info,
mike

 

[gswan]

I think it's a typo and I start about halfway.

 

[myker]

thank you, i got stuck on the next step. i get no drop when i turn the attack knob "ON" is is because i dont have a switch on mine, mine is just a regular potentiometer?

if the FETS are matched from Hairball, is this step not necessary?

thank you for your time,
mike

 

[gswan]

thank you, i got stuck on the next step. i get no drop when i turn the attack knob "ON" is is because i dont have a switch on mine, mine is just a regular potentiometer?

Then you will have to adjust to suit your own build. You want to be able to switch GR on and off somehow whilst watching the meter.

if the FETS are matched from Hairball, is this step not necessary?

It is necessary, there are other things that need to be compensated for in the GR meter tracking besides the FET curves.

 

[dgoszillai]

Thx mac ! I'll try all this soon

 

[myker]

appears that shunting point 22 on the PCB would be the equivalent, im going to go try right now

 

[myker]

well, that didnt work either, i cant get that needle to drop....

 

[myker]

am i retarded?

 

[Biasrocks]

am i retarded?

No, just lazy.  :

Mark

 

[gswan]

am i retarded?

Electronics-knowledge-deficiency could be considered a form of retardation.
What setup and test procedures did you follow to test each part of your unit?
What trouble-shooting process have you attempted to ascertain the source of the problem?

 

[myker]

sorry guys, i am a bit lazy, and coupled with my lack of time during the week i was looking for an easy out. sorry about that :-[ i suck!

Gain Reduction Meter Tracking
1. Set the controls as follows:
Control
Set to
Input  middle
Output  fully CW
Attack  fully CCW (switched to OFF)
Release  fully CW
Compression ratio  20:1
Meter mode  GR
VR54 trimmer  1/4 turn from fully CCW

2. With no signal applied, adjust VR55 so that the meter reads 0VU.
3. Apply a 0.245Vrms (-10dB) 1kHz sine wave signal to the input.
4. Switch the meter mode to +4dB.
5. Turn the output level control CW until the meter reads 0VU.

this is the procedure i am using, i believe that all of them are going to involve disabling the GR circuit.
i have an mnats rev j and hairball pushbutton switches, hopefully i will have time with the schematic tonight.
-mike

 

[gswan]

Before you attempt calibration, have you performed tests to confirm basic operation of the various stages?

 

[myker]

I did the bias q and it went well, so i fired it up and it passed signal. Then i ran a guitar track through it and back into pro tools with good results. The needle is just goofy.

 

[gswan]

Without proper testing you have zero confidence that it is actually working correctly.
Passing audio through it and listening to the output is not a quantitative test to confirm correct operation.

 

[Chrome Heart]

Is anyone using the Hairball 600ohm attenuator with the Rev J board and Lundahl LL1540 input transformer?
Does it work?

 

[mac]

Hi guys,
I am buliding another J board 1176. All has gone well, Q voltages all seem normal and Qbias adjust all went as per normal - good.

But I cant seem to get the tracking trimmer to do anything.

Gates of Q1 and Q10 seem OK carrying bias signal -0.8v with Q1 zero on the source and the drain. Q10 have -0.52v on the source and 18.7v on the drain. Correct value resistors at R53, R58 and R59, but no matter what I do, in GR mode i have a solid 0.775v at pad 29.

The unit seems to compress perfectly and behave like my other builds, with the exception of not showing me any GR, so I know the fault has to be here in the GR amp section somewhere.

Pulled R54 to double check the R54 trimpot was OK and is all good - but adjusting from CW to full CCW makes no change to the output at pad 29.

Any pointers on what to pull next would be appreciated.

Mac.

 

[gswan]

But I cant seem to get the tracking trimmer to do anything.

Gates of Q1 and Q10 seem OK carrying bias signal -0.8v with Q1 zero on the source and the drain. Q10 have -0.52v on the source and 18.7v on the drain. Correct value resistors at R53, R58 and R59, but no matter what I do, in GR mode i have a solid 0.775v at pad 29.

The unit seems to compress perfectly and behave like my other builds, with the exception of not showing me any GR, so I know the fault has to be here in the GR amp section somewhere.

Pulled R54 to double check the R54 trimpot was OK and is all good - but adjusting from CW to full CCW makes no change to the output at pad 29.

Have you got the diode in the correct way around?

Check pin 6 of the TL071. As you adjust the offset pot (R55) the output of the op amp should also change. If not then you may have a dud op amp.

 

[mac]

Hey Geoff, 

Sorry for you having to bail me out again!  ;D
Yeah CR11 is orientated correctly and in GR mode I have 1.1v at the anode and 1.7v at the cathode. In VU mode I have -3.9v at the anode and 1.3v at the cathode.

TL071 looks healthy with pin 6 changing voltage as I move the Zero adjust trimmer. Zero adjust moves the meter needle as per normal too, so all is good here. Replaced and resoldered connections around TL071 just to be sure - no change.

Obviously something I am overlooking here.

Mac

 

[gswan]

Mac,
Sounds like the TL071 is OK then.
What do you see on the FET source (Q10)? This should change as you adjust Qbias.
Is R54 in the correct holes? Any linking for the style of pot being used?
Does adjusting VR54 change the voltage on pin 6 of the TL071?

 

[mac]

Found it! Bad connection between R54 and R58 (lifted pad).

;D
Thanks for your help Geoff.

Mac