[BUILD] 1176 Rev A - Back to the beginning...

[skidmorebay]

I'd ignore the meter section for now and focus on the no compression issue.  Have you confirmed by measuring the output that you're not getting compression?

If you're not getting compression check:
With in/out knobs mid way apply a 1khz 0dB signal and adjust the output to 0dB on the output
- that you see ac at pad 22 that starts larger and get's smaller as you move from ratio 20 to 4.
- that you have a negative DC voltage at pad 21 that starts larger and get's smaller as you move from ratio 20 to 4.

Mike

Mike,
Thanks for following this thread closely. I waited until I was at my wit's end to post a question….

I didn't want to fill up the post with all the measurements I had taken…
Good news is I re-set the Q-bias and I believe I am getting compression now.

I checked for compression by setting the longest release time, sending a 0dbu 1khz tone in, and cranking the input while lowering the output. While switching the Attack knob from "on" to "off" I can see the waveform rise either slowly or relatively quickly, depending on where I set the Release knob. So that's good.

Applying a 0dbu signal, adjust in/out knobs so that Channels 1 and 2 on oscilliscope are both showing a sine wave at 0.775V. (Ch1 on 1176 input xlr, Ch2 on output xlr) Using the DMM I got:

Ratio AC@pad22 DC@pad21
20:1 0.701V -5.85V output goes to 0.922V
12:1 0.342V -3.25V output goes to 0.775V
8:1 0.228V -2.45V output stays about 0.775V
4:1 0.114 -1.63V output goes to 0.738V

But the VU meter still stays stuck below -20db when switched to GR mode. While trying to get some life out of the VU needle I found I was able to dial up the drain voltage of Q11 by fiddling with the Null Adjust and Zero Set pots. I was only getting about 4V at Q11 but now I have good voltages on Q11 and Q12. But Q13 shows -1.3V at the Base, -0.1V at the Collector, and -1.6V at the Emitter. I have 8.98V at TP10 and -0.8V at TP11.
Like I said earlier, the VU works great at +4 and +8, but is dead on GR.
I've checked the wiring again and again.
Think I'll call it a day...

 

[lukidewa]

So  you see 0dB signal between pin 2-3 of the output?

Connect the meter terminals (big lower ones) directly to pin 2-3 of the output and see if you get a reading.

i can see signal in pin 2 (blue) 3 (red). when i connect output direct to VU in +4 mode with ratio 20, the VU condition same when i not connect output direct to VU.

Here the condition (attack and release fully CW).
1. Input CW, Output CW
    pin 2 0,92VAC, VU fully right position.
2. Input CCW, Output CW
    pin 2 0,79VAC, VU fully right position.
3. Input CW, Output CCW
    pin 2 0,47VAC, VU -18

 

[sage]

Thank you Mike

I was able to set the Q Bias alright following your instructions !

Now I went to adjust the NULL ADJ R75 - I follow the instructions from Mnat video - so I connected the DMM to the legs of R74 and i immediately see 0.40V on the meter - I am able from the front plate to adjust R71 to zero the VU Meter but when I go move R75 nothing happens, in other words the DMM it is stuck at 0.40....

I checked all the voltages compared to the schematics with volatges and my measurements are pretty close or exact except than in the GR Meter Driver section...

In fact Q11 reads:

D 16.13
S -0.69
G -0.96

Q12 :

D -1.26
S 15.69
G -0.69

Q13:

D -1.33
S 16.10
G -0.95

I will appreciate some suggestions and thank you for the patience -

 

[Janzoulou]

You have testpoint 10 and 11 on the pcb. Inthe video it shows an older board.
Use these points and it should work.

 

[Janzoulou]

Thanks a lot Mike for posting the voltage check for pad 20/21... That helped me a lot!!!
I measured them today with clear head again both units...

And what happened? The unit I thought was working well had no connection from ratio-board to pad 21. (pad 21 had no voltage - change at all)

Then i checked everything again on both units and found some unstable ground connection at pad 22 on the other one.. lol, as always if you think you are right you mostly aren't...  :

So both units seem to work well. checking now voltages again and then go for connecting the link pcb´s... yippee!  :-X

 

[Echo North]

Thank you Mike

I was able to set the Q Bias alright following your instructions !

Now I went to adjust the NULL ADJ R75 - I follow the instructions from Mnat video - so I connected the DMM to the legs of R74 and i immediately see 0.40V on the meter - I am able from the front plate to adjust R71 to zero the VU Meter but when I go move R75 nothing happens, in other words the DMM it is stuck at 0.40....

I checked all the voltages compared to the schematics with volatges and my measurements are pretty close or exact except than in the GR Meter Driver section...

In fact Q11 reads:

D 16.13
S -0.69
G -0.96

Q12 :

D -1.26
S 15.69
G -0.69

Q13:

D -1.33
S 16.10
G -0.95

I will appreciate some suggestions and thank you for the patience -

Have you pulled R44 out of circuit using the jumper?  As you rotate R75 do you see a DC change at the base of Q13?

Note Q12 and Q13 are bipolar transistors, they have a BCE rather than GDS.

Mike

 

[Echo North]

But the VU meter still stays stuck below -20db when switched to GR mode. While trying to get some life out of the VU needle I found I was able to dial up the drain voltage of Q11 by fiddling with the Null Adjust and Zero Set pots. I was only getting about 4V at Q11 but now I have good voltages on Q11 and Q12. But Q13 shows -1.3V at the Base, -0.1V at the Collector, and -1.6V at the Emitter. I have 8.98V at TP10 and -0.8V at TP11.
Like I said earlier, the VU works great at +4 and +8, but is dead on GR.
I've checked the wiring again and again.
Think I'll call it a day...

Are you able to set the null adjust and calibrate the tracking?

 

[Echo North]

So  you see 0dB signal between pin 2-3 of the output?

Connect the meter terminals (big lower ones) directly to pin 2-3 of the output and see if you get a reading.

i can see signal in pin 2 (blue) 3 (red). when i connect output direct to VU in +4 mode with ratio 20, the VU condition same when i not connect output direct to VU.

Here the condition (attack and release fully CW).
1. Input CW, Output CW
    pin 2 0,92VAC, VU fully right position.
2. Input CCW, Output CW
    pin 2 0,79VAC, VU fully right position.
3. Input CW, Output CCW
    pin 2 0,47VAC, VU -18

I'm not sure what you mean.  Just remove the meter and feed 0.775VAC into the terminals.  Does the needle go to around zero? 

Mike

 

[sage]

Now I went to adjust the NULL ADJ R75 - I follow the instructions from Mnat video - so I connected the DMM to the legs of R74 and i immediately see 0.40V on the meter - I am able from the front plate to adjust R71 to zero the VU Meter but when I go move R75 nothing happens, in other words the DMM it is stuck at 0.40....

I checked all the voltages compared to the schematics with volatges and my measurements are pretty close or exact except than in the GR Meter Driver section...

In fact Q11 reads:

D 16.13
S -0.69
G -0.96

Q12 :

D -1.26
S 15.69
G -0.69

Q13:

D -1.33
S 16.10
G -0.95

I will appreciate some suggestions and thank you for the patience -
[/quote]

Have you pulled R44 out of circuit using the jumper?  As you rotate R75 do you see a DC change at the base of Q13?

Note Q12 and Q13 are bipolar transistors, they have a BCE rather than GDS.

Mike
[/quote]

Yes I did pull R44 out - I will check if the voltage change at the base of Q13 - thank you for the note.

So am I understanding right that instead of connecting the legs of R74 i should use the test points???

Mike shall I be worried about the fact that those voltages in the Meter section are all different than the indicated voltage on the schematics with voltages?
I was thinking about pulling all resistors out of the Meter Section and triple check them again...

 

[Echo North]

Mike shall I be worried about the fact that those voltages in the Meter section are all different than the indicated voltage on the schematics with voltages?
I was thinking about pulling all resistors out of the Meter Section and triple check them again...

The voltages in the schematic are for a calibrated unit.  Your unit is not calibrated so you'll see some difference.

 

[lukidewa]

Update in my case. VU meter still does not respond with 0dB signal directly.
Is VU meter broken?

 

[skidmorebay]

Are you able to set the null adjust and calibrate the tracking?
Report to moderator  Logged


SOLVED!

I just found that I had a broken trace on the meter board, between the pad for 28 and the VU meter.
I noticed I had continuity between pad 29 on the main board and one side of the VU meter, but none between pad 28 and the other side of the VU meter. Also, I had wildly different voltages on pads 28 and 29 when the meter was switched to GR.
I did a re-flow of the pads on the meter board, but that didn't help so I soldered a jumper wire between the pad for 28 and the upper VU pad. And voila - the meter came to life. I just finished the meter calibration and all is well. The unit sounds great, too.

Great project. This is my second one. I hope to build at least a few more as money and time permit....
thanks for looking into this, Mike.

Justin

 

[sage]

Have you pulled R44 out of circuit using the jumper?  As you rotate R75 do you see a DC change at the base of Q13?

Note Q12 and Q13 are bipolar transistors, they have a BCE rather than GDS.

Mike
[/quote]

Yes R44 is off and yes I do get Voltage changing in the Base of Q13 - gonna try using TP10 and TP11 now - does that mean that i put Black DDM probe on TP10 and Red on TP11 ?

I will try now -

 

[Echo North]

Update in my case. VU meter still does not respond with 0dB signal directly.
Is VU meter broken?

Sounds like it.  Is it a Hairball meter?

If so email me:  info at hairballaudio dot com

Mike

 

[Echo North]

Yes R44 is off and yes I do get Voltage changing in the Base of Q13 - gonna try using TP10 and TP11 now - does that mean that i put Black DDM probe on TP10 and Red on TP11 ?

I will try now -

Doesn't mater which TP you use as common.

 

[Echo North]

Are you able to set the null adjust and calibrate the tracking?
Report to moderator  Logged


SOLVED!

I just found that I had a broken trace on the meter board, between the pad for 28 and the VU meter.
I noticed I had continuity between pad 29 on the main board and one side of the VU meter, but none between pad 28 and the other side of the VU meter. Also, I had wildly different voltages on pads 28 and 29 when the meter was switched to GR.
I did a re-flow of the pads on the meter board, but that didn't help so I soldered a jumper wire between the pad for 28 and the upper VU pad. And voila - the meter came to life. I just finished the meter calibration and all is well. The unit sounds great, too.

Great project. This is my second one. I hope to build at least a few more as money and time permit....
thanks for looking into this, Mike.

Justin

Awesome!  8)

 

[Janzoulou]

Finally finished my1176 Rev A Dual and somehow it works. Had to tweak around a lot until it was finished and regarding me being a numb in electronics I must say I would not have come that far without this forum and all this information I found here. Thanks a lot to all of you!!!

I regret I did not order the VU-Meters from mike at Hairball Audio, when I purchased the transformers, Fets etc.!!!! I went with this one:

http://elcodis.com/parts/2464254/SQ10.html.
It is quite big and looks nice but is not a true VU which i found out when it arrived.. I built a rectifier with germanium diodes and put a cap (470uf !) after lots of try and error..

I also had to put the ratio-board apart from the switch so i could get everything placed on the panel regarding to these big meters...

The black knobs will be replaced with silver ones... ordered them wrong.
Anyway there are some errors in the design. The switch supposed to be between the meters did not fit... argghh.
I was to fast...

I got a question and would be really glad if someone could help me... !! ?

Is there a way in getting a reasonable tracking on the meters with measuring and putting the right diodes/caps on the meter, without try and error?
The meters i got are not precise and one of them I cant get into right GR- tracking. Or maybe change the trim to a different one? (i need more negative tracking as the GR-meter only goes up to -3 ) What makes me suspicioous is that this is only on one of them, the other one is doing a better job (up till -7)

Thanks a lot!!!

BTW: The toroid is doing a buzz - like there is moving something inside. Is that normal? I only know this from really big ones. It is not that loud but in my control-room I will be able to hear it.

 

[sage]

Finally I was able to calibrate the unit!!!

I went thru each step and indeed using TP10 and TP11 it all made sense...
The 3 videos helped - the only question was about the fact that I have a push version not a rotary to selct VU operations and so I used +4 for the tracking adjustment - it seems to make sense, I hope that is the right way.

I checked the voltages again and they are a lot closer ! Here and there they are off a little bit, for example R27 reads 4.4 and not 6.6 but that is the most off i have - everything else is very close, identical or just 1 volt off, mostly over the values indicated on the schematic.

Shall I assume it's all good to go? Or shall the voltages BE EXACTLY the same?

Mike your instructions and suggestions helped so much - thank you - can't wait to get the Rev D....

 

[sage]

Tried on BASS AND WORKS GREAT !!!!!
STRANGE THING: with no audio passing thru when the releasse is at its max (7 fully CW) the VU meter indicates 0 - when we move the relase knob to CCW the VU meter grows a whole db and  a half ....

is that normal?

 

[Janzoulou]

I got a question and would be really glad if someone could help me... !! ?

Is there a way in getting a reasonable tracking on the meters with measuring and putting the right diodes/caps on the meter, without try and error?
The meters i got are not precise and one of them I cant get into right GR- tracking. Or maybe change the trim to a different one? (i need more negative tracking as the GR-meter only goes up to -3 ) What makes me suspicioous is that this is only on one of them, the other one is doing a better job (up till -7)

Thanks a lot!!!

BTW: The toroid is doing a buzz - like there is moving something inside. Is that normal? I only know this from really big ones. It is not that loud but in my control-room I will be able to hear it.

The question is how exactly I could check if something on the meter board is wrong, if i cant get the Meter tracking right? In +4-mode it works quite well and the calibration - steps before tracking (bias and null-adjust) worked fine.

Thanks again. And excuse me if my question may sound silly.. I am really not an electronic-crack but doing recording and mixing...  :-[