[BUILD] 1176 Rev F/G - new board, new transformer!

[buildafriend]

Hi, I just put together two Rev F hairball kits with MNATS new boards. I have to trouble shoot my mistakes ( im a new builder ). Does anyone know any voltages that I could test for when pumping in .0775V?

Are you trying to test with a 0db input?  You want .775VAC not .0775.

Yep! I want to test the circuit at 0db from the input with a 1k sinusoidal waveform. I'll put the voltage from the generator at 0.775v. Voltage test points would be helpful and greatly appreciated.

 

[mnats]

Voltage test points would be helpful and greatly appreciated.

Expected voltages are printed on the G1176 schematic posted on Jakob's site.

 

[agauchede]

I've built the Rev G and get 22v where 30v should be.  -10v is fine.  I've checked all components against the schematic and can't seem to trace the problem.  I know others have had this issue.  What was the problem?

the problem could be that your particular power transformer is not putting out a high enough voltage.  this could happen with the wrong transformer, or if something is hooked up incorrectly, or if you have particularly low line voltage in your area.

measure the AC voltage at the secondary side of the power transformer... you should get something over 40VAC.

and what is the unregulated DC voltage before the 7824 or 317... here you must have at least 35VDC to reliably get 30VDC after regulation.

ed

Thanks, Ed,

I measure 40v going in and 26v coming out of the LM317.  I'll try changing this first.

Thanks!

BTW: is it my imagination?  In the photo that heads this thread, C26 appears to be backwards, no?

 

[Echo North]

I see what you're saying about C26.  Could have been an earlier prototype/revision.

 

[buildafriend]

Okay, so the output on my Rev F is sort of boat motoring. What measurements can I give you guys to help me get to the bottom of this? I seem to have some kind of oscillations in my circuit. I was able to trace this past the input gain stage but I don't have a good enough understanding of the circuit to get past that in terms of what is really effecting what. What would be your first few guesses for things that could cause this? I don't think it's super obvious because my friend took a look a look at it. He has much more build experience than I do, but who knows. Maybe it's right in front of our faces.

Here is a pic that I snapped really fast just to show friends. I will take better photos and post them.

<a href="http://smg.photobucket.com/albums/v207/whpnewjersey/?action=view&amp;current=IMG_0519.jpg" target="_blank"><img src="http://img.photobucket.com/albums/v207/whpnewjersey/IMG_0519.jpg" border="0" alt="Photobucket"></a>

 

[agauchede]

Hi gang,

Speaking of obvious problems . . . I had LM317 in backwards!  That solved my power problem.  Thanks for your help!

I can adjust q-bias, but cannot adjust GR meter tracking, i.e., I am getting no compression.  Are there common things to check for this problem?  I will search the threads again.

Thanks again!
Chris

 

[buildafriend]

If I remember right, that was my problem with the other one that I have no really started trouble shooting yet. Signal passes but gets no compression. Let me know what your problem is.

 

[agauchede]

Meter responds to level changes in +4 and +8.

Q12-Q15 voltages measure okay.

Voltage levels at points 7, 19, and 21 show no change with input level changes.

any thoughts?

 

[agauchede]

Hot damn!

Had the the wires to points 19 and 21 reversed at the attack pot lugs B and C.

Works like a charm, now!

Thanks everyone,
Chris

edit: except for calibrating meter tracking.  When I switch the meter on, it falls to -15 w/ input up all the way.

 

[agauchede]

Concerning input gain and low threshold, I have read about changing the values of R26 and R1A (w/ the IC balanced Input).  Does anyone have experience with changing both?  I'll do some experimenting this weekend.

Thanks!
Chris

 

[ruckus328]

Alright guys, help me out, debating between doing this one or a Rev D - recommendations?  Any opinions on sound comparison?  Already have the output trannies on hand for this version since they're same used on LA3A so that's the only reason I was leaning towards this one.

 

[kquick]

I finished my Hairball's 1176 Rev F compressor a couple of weeks ago,
but I am having a problem calibrating it.  I hope I can explain this so some one can understand me .
I have set Q bias and The GR meter adjustments with no problems; but when I try to do the tracking adjustment,
this is where my problems start.
These are the instructions I followed
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.
6. Turn the attack control ON (CW) and observe the drop in the meter reading.
7. Adjust the input level control until -10dB is indicated on the VU meter.
8. Turn the attack control OFF (CCW) and re-adjust the output level control for 0VU meter reading if necessary.
9. Repeat steps 7 and 8 until the output drops 10dB whenever the attack control is turned ON.

My problem is that, it always only changed 1.5 db drop with the switch on and 1.5db Gain with switch off so it would never
adjust out properly.The input and output pots were very touchy, I checked and found that I had
wires reversed on pads 15 and 17 from the input pot.  I have corrected that and now the input and output pots make adjustments nice and smooth, but when I turn attack switch on I get no change. The meter does nothing not drop or movment at all.  So I went back over the whole pcb, and double checked everything a hundred times.  I have checked my wiring using Skylars rev D wiring diagram and Mnats wiring the Hairball case instructions. I had another rev F Board so I installed that and same problem; I can set q bias and adjust GR meter, but when I turn attack switch on- same problem.I checked and compared voltages on both boards against the schematic and they are very close. I see no problem there What I don't understand is why when the wires on pad 15 and 17 were reveresed it allowed the attack switch turned to on to make the meter drop like it's supposed to but when the wires are correct it stops.  Everything else seems fine,it passes audio and compresses.
Any help would be appreciated. 

 

[kquick]

BUMP:
  Anybody? Help!

 

[mnats]

The meter does nothing not drop or movment at all...Everything else seems fine,it passes audio and compresses. 

Are you saying that the meter does not sit at zero or that it does zero but doesn't otherwise move?

If it sits at zero and you can hear the unit compressing the audio then you should check Q10 and the surrounding components. This FET controls the meter. On the Rev F boards the area that contains these components is marked GR METER DRIVER AMP.

[quote author=kquick]I had another rev F Board so I installed that and same problem; I can set q bias and adjust GR meter, but when I turn attack switch on- same problem.[/quote]

This suggests a wiring error. But since the signal that affects both the compression and the meter movement connects to pad 7 it's not really possible that the same signal can affect one thing (compression) and not the other (metering). Therefore it is more likely that there is an incorrect component or components on both boards. Did you stuff them at the same time?

[quote author=kquick]What I don't understand is why when the wires on pad 15 and 17 were reveresed it allowed the attack switch turned to on to make the meter drop like it's supposed to but when the wires are correct it stops.  [/quote]

But you said it only dropped 1.5dB, didn't you? If there is 10dB limiting the meter should be able to be adjusted to show the full 10dB.

 

[kquick]

Are you saying that the meter does not sit at zero or that it does zero but doesn't otherwise move?

The meter zero's but it will not drop when I turn the attack switch on or rise when the attack switch is turned off. to do the calibration.

If it sits at zero and you can hear the unit compressing the audio then you should check Q10 and the surrounding components. This FET controls the meter. On the Rev F boards the area that contains these components is marked GR METER DRIVER AMP.

I checked all of the resistors to make sure they are correct and the voltage on the FET matches the second PCB. all of the solder connections look good no shorts.

This suggests a wiring error. But since the signal that affects both the compression and the meter movement connects to pad 7 it's not really possible that the same signal can affect one thing (compression) and not the other (metering). Therefore it is more likely that there is an incorrect component or components on both boards. Did you stuff them at the same time?

Since your post I rewired and used new pots from the second build. I stuffed the second board after I could not figure out the problem to see if it was something I did and to have something to compare to.


After I rewired same problem, but I did find that if I turn the input all of the way up instead of half way like the calibration suggests the meter started dropping like it was supposed when I turn the attack switch on then adjusting input to -10db and turning attack switch off it returns to zero like it was suppose to.  I never had to adjust R54 or R55 trim pots to get those reading.  So now I am wondering if I got lucky and finally got it, or do I still have a problem because I had to have the input all of the way up to do the calibration and did not have to adjust the trim pots. My guess is the original wiring was fine I never turned the input all of the way up to do the calibration.

 

[mnats]

3. Apply a 0.245Vrms (-10dB) 1kHz sine wave signal to the input.

Sorry, I missed this the first time I read your post. Try 0.775 VRMS

 

[okgb]

0.775 VRMS  is what peak -peak when looking at the scope ?
[ i 've seen a few formula's , would like to get your learned advice ]

 

[kquick]

Sorry, I missed this the first time I read your post. Try 0.775 VRMS

That seems to have done the trick, had to adjust R55 and R54 just a tad but it is working fine. Mako I appreciate your help with this thank you. Now I think I have enough confidence to try a stereo build with the rev J boards I got from you.  Thanks again.

 

[mnats]

Glad that worked. Now that I think about it that's why I quoted 0dBm in my calibration video rather than "-10dB" as mentioned in section 5.3.3 of the service manual.

0.775 VRMS  is what peak -peak when looking at the scope ?
[ i 've seen a few formula's , would like to get your learned advice ]

Learned? You're joking, right?

For sine waves I just use (RMS x 1.414) x 2 = P-P as I was taught.

 

[buildafriend]

Hey, sorry for being a hardcore newb.

My 1176 was working well but all of a sudden it got really crunchy and low in volume unless you have both the GR and +8 buttons engaged. Then it works fine.

Any quick ideas of what it could be?