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

[Josh Hastick]

Hello I recently finished my build of the Hairball Audio 1176 rev a but I have been having trouble with the calibration with the q-bias i feeding it the recommended .775Vac at the xlr input and its passing signal I tried both ways of doing the q-bias but the variable resistor is not effecting the VU meter. Any suggestions?

Thanks

 

[Djankies]

Hello I recently finished my build of the Hairball Audio 1176 rev a but I have been having trouble with the calibration with the q-bias i feeding it the recommended .775Vac at the xlr input and its passing signal I tried both ways of doing the q-bias but the variable resistor is not effecting the VU meter. Any suggestions?

Thanks

Is it possible that the resistor is broken/faulty? I've seen a lot of people really stress the sensitivity to breaking on those things here. Maybe try taking it out and testing it with your multi?

Daniel

 

[Josh Hastick]

Hello I recently finished my build of the Hairball Audio 1176 rev a but I have been having trouble with the calibration with the q-bias i feeding it the recommended .775Vac at the xlr input and its passing signal I tried both ways of doing the q-bias but the variable resistor is not effecting the VU meter. Any suggestions?

Thanks

Is it possible that the resistor is broken/faulty? I've seen a lot of people really stress the sensitivity to breaking on those things here. Maybe try taking it out and testing it with your multi?

Daniel

true but I tested everything before installing it into the unit and we test that variable resistor multiple times and it tested ok. Its just when we're doing the mnats calibration for the q-bias its not doing anything when turned to knock down the need 1dB. Right now me and my principle of electronics lab instructors are stumped. Any suggestions? 

 

[mnats]

true but I tested everything before installing it into the unit and we test that variable resistor multiple times and it tested ok. Its just when we're doing the mnats calibration for the q-bias its not doing anything when turned to knock down the need 1dB. Right now me and my principle of electronics lab instructors are stumped. Any suggestions?

Besides the trimmer what else have you and the lab instructor checked? Most issues are due to things covered in the FAQ linked from the first post of this thread. Voltages in that section are ok? All transistors measure 0.6 volt drop between base and emitter?

 

[hymentoptera]

One way to check if the QBias trimmer is even doing anything at all would be to measure the voltage between the gate of Q1 and GND and (it should read a negative DC voltage) turning the pot while watching the meter. The trimmer should cause a tiny change in voltage for even a small turn of the pot.

 

[NashvilleDrumStudio]

I have just completed my 4th Rev A 1176 build from Hairball. All the others have gone perfectly until this one.

When I go to calibrate, I'm getting the 0.775VAC signal into the input XLR.  Even with the input turned all the way up and output turned all the way up, I get 0.01vac at most on the output.

If I put the compressor in GR mode, the meter stays all the way down as I increase the output, until I get to around the 1 o'clock position and then it pegs.

Mike at hairball had suggested a potential bad component, joint or fried transistor in the signal or line amp section, and that it would be fairly easy to trace with a DMM. I haven't had to trouble shoot one of these yet, and I have to admit, I could use some guidance as to how to go about this trouble shooting process.  Any and all help will be appreciated.

 

[hymentoptera]

...

Mike at hairball had suggested a potential bad component, joint or fried transistor in the signal or line amp section, and that it would be fairly easy to trace with a DMM. I haven't had to trouble shoot one of these yet, and I have to admit, I could use some guidance as to how to go about this trouble shooting process.  Any and all help will be appreciated.

It's easy, just follow along with the schematic from junction to junction. Once you've got a .77v signal the the input XLR, just move along the signal path, following the schematic. Leave your meter on vAC. Check the ins of the input attenuator for signal. Move along to input transformer. Then to the junction of R5 and R4 (at this point you'll need to ground the black lead to the ground plane). Next to the junction of C1 and the drain of Q1. The onwards to the junction of C2 and R8, etc. At some point the signal will disappear or become severely attentuated. This helps to narrow down where the problem is.

If you have an oscilloscope or signal tracer this is even easier.

 

[NashvilleDrumStudio]

...

Mike at hairball had suggested a potential bad component, joint or fried transistor in the signal or line amp section, and that it would be fairly easy to trace with a DMM. I haven't had to trouble shoot one of these yet, and I have to admit, I could use some guidance as to how to go about this trouble shooting process.  Any and all help will be appreciated.

It's easy, just follow along with the schematic from junction to junction. Once you've got a .77v signal the the input XLR, just move along the signal path, following the schematic. Leave your meter on vAC. Check the ins of the input attenuator for signal. Move along to input transformer. Then to the junction of R5 and R4 (at this point you'll need to ground the black lead to the ground plane). Next to the junction of C1 and the drain of Q1. The onwards to the junction of C2 and R8, etc. At some point the signal will disappear or become severely attentuated. This helps to narrow down where the problem is.

If you have an oscilloscope or signal tracer this is even easier.

So, I traced the signal from the XLR input (0.775vac) to the input of the T-Pad attenuator, where it still reads 0.775vAC.

However, the joints at the output of the T-Pad Attenuator have zero signal. I tried this with the switch both fully CW and CCW to be sure. Just to be certain, I unhooked the 2 conductor shielded cable that runs from the output of the T-Pad to the Input of the Input Transformer, and tested that end of the cable as well, also with a reading of 0.00 vAC.

The solder joints to the T-Pad attenuator appear to be good. I'm wondering if I've shorted the cable where the two shields are tied together? Or could it be the T-Pad attenuator itself?

Thoughts?

 

[Echo North]

If that's the case, it could be something next in line, like if the input transformer is shorted.  Try disconnecting the two wires from the input transformer and then measure the AC between the disconnected wires.  Anything?

Mike

 

[keevhren]

Hi Mike!

I recently finished building 2 rev A's. I've had the kits for ages but have been super busy with life so they fell by the wayside for a while. I had originally posted some issues earlier this year in the thread here but am still unresolved on them so hopefully you can shed some light on what step to take next.

My current issue is that neither unit is able to complete (well, really i cant start this step...) the 3rd calibration step.  In both the hairball guide and mnats, upon moving the shorting pin back to normal position next to r44, the meter should drop. This happens on both my units. However, I run out of headroom on r71 when I try to re-zero the meter before attempting this calibration step. My first unit taps out at -3 and the other at -1 on the meter.

Qbias and null adjust calibration steps were a breeze.  I've measured all the voltages in the power supply, signal preamp, signal line amp, gr control amp, and gr meter driver and they are all looking fairly close to dead on with the numbers listed in the voltage guide. Both units are also passing signal fully and cleanly by the sounds of it.  Thoughts?

If it's any help I've also just built the signal tracer designed by Mark burnley to help me sort this out if needed, so I have that at my disposal.

Thanks in advance for the help! Let me know of any other pertinent information that might help.

 

[Echo North]

Hi Mike!

I recently finished building 2 rev A's. I've had the kits for ages but have been super busy with life so they fell by the wayside for a while. I had originally posted some issues earlier this year in the thread here but am still unresolved on them so hopefully you can shed some light on what step to take next.

My current issue is that neither unit is able to complete (well, really i cant start this step...) the 3rd calibration step.  In both the hairball guide and mnats, upon moving the shorting pin back to normal position next to r44, the meter should drop. This happens on both my units. However, I run out of headroom on r71 when I try to re-zero the meter before attempting this calibration step. My first unit taps out at -3 and the other at -1 on the meter.

Qbias and null adjust calibration steps were a breeze.  I've measured all the voltages in the power supply, signal preamp, signal line amp, gr control amp, and gr meter driver and they are all looking fairly close to dead on with the numbers listed in the voltage guide. Both units are also passing signal fully and cleanly by the sounds of it.  Thoughts?

If it's any help I've also just built the signal tracer designed by Mark burnley to help me sort this out if needed, so I have that at my disposal.

Thanks in advance for the help! Let me know of any other pertinent information that might help.

Hmmmmm.

Did you have all of your trimmers centered when you did calibration? If they are not centered they can run out of room. Is the value correct?

Are you sure your measuring DC in the null step and using the proper test points?

If you have the same issue in both units I would suspect the same stuffing/wiring error, or cal procedure. 

If you haven't done so yet, walk away for a bit and come back to it later in the day with fresh eyes.

Mike

 

[keevhren]

Hi Mike!

I recently finished building 2 rev A's. I've had the kits for ages but have been super busy with life so they fell by the wayside for a while. I had originally posted some issues earlier this year in the thread here but am still unresolved on them so hopefully you can shed some light on what step to take next.

My current issue is that neither unit is able to complete (well, really i cant start this step...) the 3rd calibration step.  In both the hairball guide and mnats, upon moving the shorting pin back to normal position next to r44, the meter should drop. This happens on both my units. However, I run out of headroom on r71 when I try to re-zero the meter before attempting this calibration step. My first unit taps out at -3 and the other at -1 on the meter.

Qbias and null adjust calibration steps were a breeze.  I've measured all the voltages in the power supply, signal preamp, signal line amp, gr control amp, and gr meter driver and they are all looking fairly close to dead on with the numbers listed in the voltage guide. Both units are also passing signal fully and cleanly by the sounds of it.  Thoughts?

If it's any help I've also just built the signal tracer designed by Mark burnley to help me sort this out if needed, so I have that at my disposal.

Thanks in advance for the help! Let me know of any other pertinent information that might help.

Hmmmmm.

Did you have all of your trimmers centered when you did calibration? If they are not centered they can run out of room. Is the value correct?

Are you sure your measuring DC in the null step and using the proper test points?

If you have the same issue in both units I would suspect the same stuffing/wiring error, or cal procedure. 

If you haven't done so yet, walk away for a bit and come back to it later in the day with fresh eyes.

Mike

When you're asking if my trimmers are centered, are you saying that I should be starting my overall calibration with the tracking adjust, Q bias, and Null adjust trimmers turned about half way up?  I definitely have been attempting to do this with them all turned as far clockwise as they could go... after reading through the build guide spot on trimmers just now I see that they were supposed to be started in the middle.  I'm sure I did this during my build (months ago!) but in my frustrations of a failed first few attempts of calibration I must have forgotten this.  I'll give it another shot and report back if the problem still persists.  Thanks!

 

[Echo North]

I'm sure if this will solve the issue, but I would definitely start there.

 

[thomasdf]

As I never use the +4 or +8 functions much, I was thinking of getting rid of the one of both I don't use, and use that position to trigger a relay true bypass. Has anybody done that before? I could really use a hard bypass on that unit in the environment I am working on (hybrid setup with hardware inserts in Protools + summing). DAW bypass cuts the signal for a short period, making it hard to really stay focused on the tiny changes, precise level matching etc

 

[Potato Cakes]

Hello, everyone!

I finished a stereo 1176 Rev D which is working great so I decided to proceed with building a Rev A. I just got it put together and the one thing I seem to be stuck on is I can't seem to the VU meter needle to move anywhere close to zero when GR is selected. It seems that I can't get there to be a difference in voltage between pads 28 and 29 that are connected to the meter PCB. Each of these pads in relation to ground do give me voltage and it increases and decreases when I turn the zero adjust 2k potentiometer. I was very careful with component placement and giving it a quick glance it everything seems to be in order. I've narrowed it down to Q13. I'm getting -2V on the emitter and 0V on the base. So either BJT is bad or the null adjustment 2k trimmer that proceeds it. The voltages on R76 proceeding the null adjustment seem fine. I think I have another 2K trimmer somewhere and maybe another 2N3708. Has anyone had a transistor or Bourns trimmer to be DOA?

Thanks!

Paul

 

[keevhren]

I'm sure if this will solve the issue, but I would definitely start there.

Okay!  I'm glad to report that one of my Rev A's successfully went through all 3 calibration steps after I started the process with the wipers in the center position.  I followed along to the Don Bonin youtube videos ( https://www.youtube.com/user/dbonin360 ) for all three steps and it worked like a charm.  However, on my second unit, I'm not able to finish the final calibration step for the Tracking Adjustment.  Here's a step by step of what I was doing:

1. I started out with the input and output controls all the way down.  20:1 was selected, GR was the meter mode, Attack off, and release all the way clockwise. 

2. I confirmed .775VAC on my input XLR.  With this signal coming in, my VU meter was hitting at about -1.5 so I zero'd it out using the front adjustment pot on the unit. 

3. Switch to VU mode (+4) on the unit.  The needle drops to around -20dB.  I now crank my input up to about "12" (at this point, my DMM reads .736VAC at the input XLR as it drops when I turn up the input from -infinity).  I turn my output knob up to just shy of "48" to zero out the needle on the VU meter. 

4. I now turn on my attack knob all the way clockwise and the VU needle drops to about -6 on the meter.  This was where things started to go differently from unit 1 (which successfully calibrated) vs unit 2 (which didn't).  On my first unit at this point, the needle dropped to about -14 on the meter.  This was what happened to Don's needle as well in his calibration video. 

5. From here, I attempted to adjust the input and output knobs in order to have the needle at 0 when attack is off, and -10 when attack is on.  It worked on unit 1 like a charm, but with endless fidgeting on unit 2 I was never able to get the meter to hit both.  It seemed as though I was in an endless circle of having the needle at -10,  turning the attack off, the needle would fall to -20 then jump up to about +2.5.  From here, it would very, very slowly pull back down to about -1 on the meter.  I would re-adjust the output control to zero the meter, turn attack on, the needle would drop to -20, then move up to -7, and slowly fall down to about -8 where it would find its resting point.  From here I would adjust the input to get it to -10, turn attack off and the cycle would repeat endlessly with almost the exact same readings every time despite the input knob and output knobs changing each cycle. 

On my unit that successfully calibrated, the input knob was just above the dot between 24 and 18 and the output was just shy of 48 when it successfully reached the 0/-10 point.  The successful unit also did not do the drop to -20, then back up, and slowly creep down to its resting place thing that the 2nd unit is doing. 

I've confirmed that r44 is in the middle of it's value prior to starting this calibration step although I don't think that has anything to do with what's wrong.  I'm no expert, but it seems as though the meter is acting finicky but I'm unsure of where to start in troubleshooting this.  The unit is passing signal and (I will triple check this later tonight) to the best of my abilities from a thorough inspection, it appears that the wiring between unit 1 and unit 2 are identical so I don't think anything is backwards.  Suggestions on how to proceed with troubleshooting?

Much thanks!

 

[Echo North]

As I never use the +4 or +8 functions much, I was thinking of getting rid of the one of both I don't use, and use that position to trigger a relay true bypass. Has anybody done that before? I could really use a hard bypass on that unit in the environment I am working on (hybrid setup with hardware inserts in Protools + summing). DAW bypass cuts the signal for a short period, making it hard to really stay focused on the tiny changes, precise level matching etc

Definitely doable.

Cut a few traces and mount a small perf board between the in/out with a 24V relay, dropping resistor, and protection diode.  Switch the 24V rail with the +4 (or +8) and direct wire the ins and outs through the relay.

Mike

 

[Echo North]

Hello, everyone!

I finished a stereo 1176 Rev D which is working great so I decided to proceed with building a Rev A. I just got it put together and the one thing I seem to be stuck on is I can't seem to the VU meter needle to move anywhere close to zero when GR is selected. It seems that I can't get there to be a difference in voltage between pads 28 and 29 that are connected to the meter PCB. Each of these pads in relation to ground do give me voltage and it increases and decreases when I turn the zero adjust 2k potentiometer. I was very careful with component placement and giving it a quick glance it everything seems to be in order. I've narrowed it down to Q13. I'm getting -2V on the emitter and 0V on the base. So either BJT is bad or the null adjustment 2k trimmer that proceeds it. The voltages on R76 proceeding the null adjustment seem fine. I think I have another 2K trimmer somewhere and maybe another 2N3708. Has anyone had a transistor or Bourns trimmer to be DOA?

Thanks!

Paul

DOA parts are actually very rare.  What is VERY common is parts that get damaged during install. Either from excessive heat or static electricity.  Just for reference you should be soldering at 650 for lead and 700 for lead free.  Many users just move to the max setting on the iron.  Many of the repairs that come in have dead transistors. However, when we supply transistors to our assembly house for the JE-990's we've never had a single DOA in thousands of units. The point being transistors are easily damaged when using excessive heat and not grounding yourself.

The trimmer is easy enough to check even in circuit.  You could use an ohm meter across an outer lead and the wiper and see if the resistance changes.  Make sure the trimmer isn't set up as a rheostat and the pin and wiper are not shorted in circuit.

Having 0 at the base of Q13 is an issue as noted here:
http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

R76 ok? R74? Remove the transistor and see if you get a negative voltage at the base pad.

Mike

 

[Echo North]

I'm sure if this will solve the issue, but I would definitely start there.

Okay!  I'm glad to report that one of my Rev A's successfully went through all 3 calibration steps after I started the process with the wipers in the center position.  I followed along to the Don Bonin youtube videos ( https://www.youtube.com/user/dbonin360 ) for all three steps and it worked like a charm.  However, on my second unit, I'm not able to finish the final calibration step for the Tracking Adjustment.  Here's a step by step of what I was doing:

1. I started out with the input and output controls all the way down.  20:1 was selected, GR was the meter mode, Attack off, and release all the way clockwise. 

2. I confirmed .775VAC on my input XLR.  With this signal coming in, my VU meter was hitting at about -1.5 so I zero'd it out using the front adjustment pot on the unit. 

3. Switch to VU mode (+4) on the unit.  The needle drops to around -20dB.  I now crank my input up to about "12" (at this point, my DMM reads .736VAC at the input XLR as it drops when I turn up the input from -infinity).  I turn my output knob up to just shy of "48" to zero out the needle on the VU meter. 

4. I now turn on my attack knob all the way clockwise and the VU needle drops to about -6 on the meter.  This was where things started to go differently from unit 1 (which successfully calibrated) vs unit 2 (which didn't).  On my first unit at this point, the needle dropped to about -14 on the meter.  This was what happened to Don's needle as well in his calibration video. 

5. From here, I attempted to adjust the input and output knobs in order to have the needle at 0 when attack is off, and -10 when attack is on.  It worked on unit 1 like a charm, but with endless fidgeting on unit 2 I was never able to get the meter to hit both.  It seemed as though I was in an endless circle of having the needle at -10,  turning the attack off, the needle would fall to -20 then jump up to about +2.5.  From here, it would very, very slowly pull back down to about -1 on the meter.  I would re-adjust the output control to zero the meter, turn attack on, the needle would drop to -20, then move up to -7, and slowly fall down to about -8 where it would find its resting point.  From here I would adjust the input to get it to -10, turn attack off and the cycle would repeat endlessly with almost the exact same readings every time despite the input knob and output knobs changing each cycle. 

On my unit that successfully calibrated, the input knob was just above the dot between 24 and 18 and the output was just shy of 48 when it successfully reached the 0/-10 point.  The successful unit also did not do the drop to -20, then back up, and slowly creep down to its resting place thing that the 2nd unit is doing. 

I've confirmed that r44 is in the middle of it's value prior to starting this calibration step although I don't think that has anything to do with what's wrong.  I'm no expert, but it seems as though the meter is acting finicky but I'm unsure of where to start in troubleshooting this.  The unit is passing signal and (I will triple check this later tonight) to the best of my abilities from a thorough inspection, it appears that the wiring between unit 1 and unit 2 are identical so I don't think anything is backwards.  Suggestions on how to proceed with troubleshooting?

Much thanks!

You lost me at about set 1.

Simple version:

1. Attack switched off, release full CW. Input and output mid way.
2. Feed is somewhere around a line level 1K signal.  Level isn't really important. Just switch to +4 mode and turn up the signal until its hit 0 on the meter.
3. Flip back into GR metering, and switch attack ON to full CW and adjust the output control so you see 0.775 VAC on the output between pin 2 and 3. (0dB).
4. Turn attack to OFF position and adjust input till you see 2.44VAC on the out (+10).
5. Adjust you trimmers.

If you can't accomplish this, you probably have a circuit issue.  Check against the schematic with voltages.

Mike

 

[keevhren]

If you can't accomplish this, you probably have a circuit issue.  Check against the schematic with voltages.

Mike

Tried the hairball method this morning and still had the same issue where I cannot get the 0 to -10db drop on the meter.  Measured all my voltages and came up with the following (note... I flagged anything that was more than .5V off from the schematic):

Part:
(schematic voltage) - My Voltage reading

SIGNAL PREAMP

Q2

• (6.73V) - 7.28V
• (2.22V) - 2.52V
• (4.51V) - 4.38V

Q3

• (13.74V) - 13.18V
• (6.13V) - 6.70V

SIGNAL LINE AMP

Q4

• (13.72V) - 13.11V
• (6.6V) - 4.22V - off by more than 2V

Q5

• (3.42V) - 3.30V
• (2.7V) - 2.76V
• (25.15V) - 24.29V - off by almost 1V

Q6

• (27.58V) - 27.15V
• (2.2V) - 2.14V

GAIN REDUCTION CONTROL AMP

Q7

• (5.22V) - 5.16V
• (4.71V) - 4.63V

Q8

• (16.93V) - 17.02V
• (16.31V) - 16.38V

Q9

• (3.65V) - 3.68V
• (3.09V) - 3.11V

Q10

• (14.96V) - 14.41V
• (14.39V) - 13.82V

GAIN REDUCTION METER DRIVER

Q11

• (10.52V) - 9.21V - off by more than 1V

Q12

• (-0.81V) - -0.76V
• (-1.41V) - -1.35V
• (9.5V) - 8.14V - off by more than 1V

Q13

• (-0.88V) - -0.83V
• (-1.46V) - -1.40V
• (9.76V) - 8.46V - off by more than 1V

POWER SUPPLY

• (29.75V) - 29.79V
• (-9.85V) - -9.57V

Based on all of these readings, I'm under the impression that something is wrong leading into the GR METER DRIVER and possibly the SIGNAL LINE AMP.  However, in tracing through the schematic, I'm unsure of what could possibly be making these readings be off.  I also compared the voltages with those I read on my first 1176 that calibrated correctly and they are definitely not as close as the voltages on my first unit (with the exception of Q5... my first unit measured 24.35V at the same spot where unit #2 measured 24.29V for what should be, according to the schematic, 25.15V).  Thoughts on where to proceed from here? Thanks for the help thus far Mike!