[BUILD] New FET/RACK Official Help Thread - Please read first post!

[johnnybregar]

OK - so I verified that the correct Transistor is in place, one of the J309's in Q2.  The DC voltage is:

G = 4.7
S = 8.29
D = 14.62

 

[Echo North]

OK - so I verified that the correct Transistor is in place, one of the J309's in Q2.  The DC voltage is:

G = 4.7
S = 8.29
D = 14.62

https://www.hairballaudio.com/uploads/pdf/fet_rack_a_v1.14_voltages.pdf

Ya they're off.  However Q2 and Q3 interact off the same supply rail, so Q3 being dead could cause issues with Q2.  I would triple check all the R values and soldering. If that all looks good I would replace Q2 and Q3.  You can use the missing parts form and I'll send them to you.

Mike

 

[johnnybregar]

Ok, I just verified all the R values are correct and soldering seems good - so submitted missing parts form for Q2 and Q3. 

Hopefully it’s that easy. 

 

[Echo North]

Ok, I just verified all the R values are correct and soldering seems good - so submitted missing parts form for Q2 and Q3. 

Hopefully it’s that easy. 

Sounds good.

 

[johnnybregar]

Did you receive my missing parts request?  Just checkin.... Thx.

Sounds good.

 

[Echo North]

Did you receive my missing parts request?  Just checkin.... Thx.

I've got some requests, did you get a ship notice? I get a million emails everyday, don't know who is who and what is what.

Email me through the contact form your name, shipping address, and parts and I can see if I got it.  If not I'll ship out.

Mike

 

[johnnybregar]

No ship notice, will do the contact form. Thx, and no worries.

 

[EmoRiot]

I'm building a Rev A and I'd like to add the red neon lamp atop the meter. I have a neon bulb, like the original, that works off  115V AC but I'm not sure where I can best tap off the  power for that.

The Meter switch bank's Off switch has solder tabs and they test for the correct behavior with a continuity tester, where the Off position breaks continuity (lamp off) but any other switch position passes continuity (lamp would be on). But is 115V passing through this switch? Or has it been stepped down or converted to DC by this point in the circuit?

Any help would be greatly appreciated!

 

[EmoRiot]

I'm building a Rev A and I'd like to add the red neon lamp atop the meter. I have a neon bulb, like the original, that works off  115V AC but I'm not sure where I can best tap off the  power for that.

The Meter switch bank's Off switch has solder tabs and they test for the correct behavior with a continuity tester, where the Off position breaks continuity (lamp off) but any other switch position passes continuity (lamp would be on). But is 115V passing through this switch? Or has it been stepped down or converted to DC by this point in the circuit?

Any help would be greatly appreciated!

I'll come back to reply to my own comment for anyone else who might search for something similar. The answer is yes. I got my neon lamp connected to two of the switch tabs on the backside (the side which faces towards the meter). I'm running wires off the main AC input (pre-transformer). Neutral goes to one lead of the neon lamp, Live goes to the switch's 1st tab (closest to the front panel) and then a connector lead goes from the center tab of the switch to the neon lamps other lead. This setup correctly disrupts mains power from reaching the neon when the switch is in the off position but passes power to it for any of the other three positions.

If anyone reads this and notices that I've made a grave error, do let me know but it sure seems to be working as expected.

 

[johnnybregar]

Sounds good.

Well, I give up.  I can’t even get q2 and q3  out of their places.  I have a solder sucker but clearly I don’t have the chops to get these components out cleanly and I’m scared I’m gonna ruin something if I keep it up. 

I can’t find a contact page on your website.  How can I do the flat rate repair?  I can send it to you.  I’m just over on. Bainbridge Island. 

Thanks,

Johnny

 

[adam.schw]

Hey Mike,

Got a Rev A build I have assembled. Seems to have a muffled/ low pass filter going on with both GR on and off. Compression, attack, release and ratios work as about expected. I went through and checked the DC voltages of all the Q points and they seem to be right. I didn’t fully go through auditing the values quite yet, but checked the first stage and all the parts are correctly placed. All my solder joints look good, the few that we’re looking a mediocre I reflowed, with the exception of the transformer. Those don’t look the best, but they don’t look like they should be an issue.

I started working through the troubleshooting guide and my Q3 base is reading at about .13 instead of .05. Q2 gate and TP15 test about right.  My unit isn’t perfectly calibrated at the moment because I moved around my Qbias, etc but it’s in the neighborhood.

When I go onto the next step, in order for me to set the measurement to .200 VAC at TP17, the guide says pot should be at middle of the scale, but my output  is at -36 on output.
Is this related to input mod being done? In order to get my input to the proper level to do the step before it’s at -12, aka about 3 o clock.
TP17 and Q4 read right, but Q5 and 6 are both .105 instead of .173.

Did I burn out a component or do I maybe have a bad component somewhere? I’ll go through and audit the rest of the component values.

 

[adam.schw]

Update. Just discovered I mixed up 33n and 33J capacitor  ;D. I’m assuming that’ll fix it. If it doesn’t I’ll post back!

 

[johnnybregar]

I need help getting my rack unit going.  Is anyone willing and able to assist?  I need q2 and 3 replaced, then just need to make sure it’s all working.  I have the parts, and can send it your way.  Happy to pay for your time. 

 

[dbmorton]

Hey Gang,
This is my first post on this forum, and I look forward to whatever insight you might provide.

I have built 3 1176's in the past (original versions, 2 rev Ds and 1 rev A) and had absolutely no problems. I have recently completed a recent issue Rev D for a friend and, although assembly was no problem, attempts to calibrate have been another matter.

I noticed immediately that is seemed to be VERY touchy when I moved the input knob; the TINIEST movements led to large voltage changes. Got Q bias in range, but could not get next 2 steps to work properly. Null Adjust was OK, but reduction meter tracking adjustment was impossible to achieve...time to check voltages.

Q bias voltage in range, but signal preamp readings were as follows:
TP1          0.100 VAC
Q2 Base    0.063 VAC
Q3 Base    0.006 VAC
Q14 Base  cycling up & down (& OL)

I have triple checked component placement and found 2 resistors that had been accidentally swapped by me, which has been corrected.

At this point, I could really use some guidance on what to do.

Sincerely,
dbmorton

 

[Echo North]

Hey Gang,
This is my first post on this forum, and I look forward to whatever insight you might provide.

I have built 3 1176's in the past (original versions, 2 rev Ds and 1 rev A) and had absolutely no problems. I have recently completed a recent issue Rev D for a friend and, although assembly was no problem, attempts to calibrate have been another matter.

I noticed immediately that is seemed to be VERY touchy when I moved the input knob; the TINIEST movements led to large voltage changes. Got Q bias in range, but could not get next 2 steps to work properly. Null Adjust was OK, but reduction meter tracking adjustment was impossible to achieve...time to check voltages.

Q bias voltage in range, but signal preamp readings were as follows:
TP1          0.100 VAC
Q2 Base    0.063 VAC
Q3 Base    0.006 VAC
Q14 Base  cycling up & down (& OL)

I have triple checked component placement and found 2 resistors that had been accidentally swapped by me, which has been corrected.

At this point, I could really use some guidance on what to do.

Sincerely,
dbmorton

I would look thought the complete troubleshooting guide.  It almost always comes down to a mis-placed component or bad solder joint.

https://help.hairballaudio.com/hc/en-us/categories/360003562093-Technical-Support

Mike

 

[JMan]

My Rev D is assembled, the power supply is working with correct voltages, and it passes audio!  It does seem to do gain reduction as well, but I'm having some issues that I'm trying to pin down.

I went through and checked all of my voltages against the expected numbers on the Hairball troubleshooting guide, and although I am pretty good with the soldering iron, I did find a couple imperfect joints and cleaned them up.  I'm mostly good on voltages (never more than 10% off), except at Q5 where I'm getting about 0.255v at the base (compared to the stated 0.195v). 

Weirdly, as I move along, the voltages get back to normal again pretty much right away (I haven't measured Q6 because I stuck the supplied spacer under it, which made it inaccessible for probing, but aside from that it's back to normal readings after Q5).  I do have some variation when measuring in the GR control amp, with the different ratios having varying amounts of discrepancy from the anticipated voltages, but nothing that seems TOO far out.

So I thought, well, it seems like things are close enough for jazz (this might not be the compressor for jazz), let's try the calibration.  First two steps went smooth as butter, but I got stuck on the 3rd (GR meter tracking adjustment).  When trying to set the 10dB drop measured at the output, I am finding that my attack knob/switch does not really do anything when switched between the off and on positions.  With the 1 kHz test tone coming in (tested at input XLR), I set the output for 0.775 VAC with the attack turned full CW (and the other controls set according to instructions); turn the attack control to the "off" position, hear/feel the click and everything, and set the input control for 2.44 VAC at the output.  But now, if I turn the attack control back on, my output voltage only drops to about 2.35 VAC, so basically, not at all.  The good news is that my meter moves a very lazy millimeter, so I guess it's showing that bit of GR, but it seems to me like my attack pot isn't working correctly.  I've double checked/reflowed my joints on the attack/release board, but that hasn't changed anything.

Sorry for the very long post, I'm just trying to be as precise as I can.  Any ideas where I should look?  Could it just be a bad pot?  (I know, I know, the build guide and everything else really wants me to know that I shouldn't make that assumption, but I've already explored all the other options I can think of!)

 

[YoDudeRock]

Mike,
    I am working on a stereo pair of Rev A's.  I was able to calibrate both units.  One of the units calibrated perfectly, the other was a little screwy, the input and output knobs ended up in much different places than the other unit.
Well, I noticed I had the capacitor at C18 in backwards and it was on for 24 hours, so it was bulging like it had botulism! 
So I changed that out for a brand new one.  I double checked the locations/values of all my resistors and they are all correct. 
So I checked the voltages. The voltages are a significantly off in the GR Control Amp and GR Meter Drive Amp  sections. 
Q7-Q10 are off, so I changed them all, still off.
So I also changed C17 and diodes (CR2, CR3, CR10) since those can be sensitive.
Still didn't solve the problem.

Here's the voltages from Q7-Q10...

Q7    B = 3.356  C = 11.21  E = 2.783
Q8    B = 11.20    C = 30.78  E = 10.60
Q9    B = 3.074  C = 21.46  E =2.536
Q10  B= 21.45  C = 30.77  E = 20.92

Any ideas?

Thanks,
Chris

 

[Echo North]

Mike,
    I am working on a stereo pair of Rev A's.  I was able to calibrate both units.  One of the units calibrated perfectly, the other was a little screwy, the input and output knobs ended up in much different places than the other unit.
Well, I noticed I had the capacitor at C18 in backwards and it was on for 24 hours, so it was bulging like it had botulism! 
So I changed that out for a brand new one.  I double checked the locations/values of all my resistors and they are all correct. 
So I checked the voltages. The voltages are a significantly off in the GR Control Amp and GR Meter Drive Amp  sections. 
Q7-Q10 are off, so I changed them all, still off.
So I also changed C17 and diodes (CR2, CR3, CR10) since those can be sensitive.
Still didn't solve the problem.

Here's the voltages from Q7-Q10...

Q7    B = 3.356  C = 11.21  E = 2.783
Q8    B = 11.20    C = 30.78  E = 10.60
Q9    B = 3.074  C = 21.46  E =2.536
Q10  B= 21.45  C = 30.77  E = 20.92

Any ideas?

Thanks,
Chris

Are those voltages off? Sorry I don't have time to look it up. 

Make sure you don't have different output pots.  We just changed our output pots to something more like a traditional log curve.  The are D250K rather than A250K.  If you have one of each they will be different.

Mike

 

[Echo North]

My Rev D is assembled, the power supply is working with correct voltages, and it passes audio!  It does seem to do gain reduction as well, but I'm having some issues that I'm trying to pin down.

I went through and checked all of my voltages against the expected numbers on the Hairball troubleshooting guide, and although I am pretty good with the soldering iron, I did find a couple imperfect joints and cleaned them up.  I'm mostly good on voltages (never more than 10% off), except at Q5 where I'm getting about 0.255v at the base (compared to the stated 0.195v). 

Weirdly, as I move along, the voltages get back to normal again pretty much right away (I haven't measured Q6 because I stuck the supplied spacer under it, which made it inaccessible for probing, but aside from that it's back to normal readings after Q5).  I do have some variation when measuring in the GR control amp, with the different ratios having varying amounts of discrepancy from the anticipated voltages, but nothing that seems TOO far out.

So I thought, well, it seems like things are close enough for jazz (this might not be the compressor for jazz), let's try the calibration.  First two steps went smooth as butter, but I got stuck on the 3rd (GR meter tracking adjustment).  When trying to set the 10dB drop measured at the output, I am finding that my attack knob/switch does not really do anything when switched between the off and on positions.  With the 1 kHz test tone coming in (tested at input XLR), I set the output for 0.775 VAC with the attack turned full CW (and the other controls set according to instructions); turn the attack control to the "off" position, hear/feel the click and everything, and set the input control for 2.44 VAC at the output.  But now, if I turn the attack control back on, my output voltage only drops to about 2.35 VAC, so basically, not at all.  The good news is that my meter moves a very lazy millimeter, so I guess it's showing that bit of GR, but it seems to me like my attack pot isn't working correctly.  I've double checked/reflowed my joints on the attack/release board, but that hasn't changed anything.

Sorry for the very long post, I'm just trying to be as precise as I can.  Any ideas where I should look?  Could it just be a bad pot?  (I know, I know, the build guide and everything else really wants me to know that I shouldn't make that assumption, but I've already explored all the other options I can think of!)

If your TP22, 21, and CR2 voltages all look decent you pot is fine. 

You were able to set Qbias?

Mike

 

[JMan]

If your TP22, 21, and CR2 voltages all look decent you pot is fine. 

You were able to set Qbias?

Mike

I was able to set Q bias without issue.  I went through the whole troubleshooting guide again this evening and re-checked/recorded all the voltages.  I noticed that where discrepancies with expected voltages occurred, they were mostly on the high side (only a couple on the low), but there were actually a few slightly larger swings than I remember seeing initially, and sure enough, it was in that TP22/CR2 area.  (TP21 is pretty spot on).

I went all the way through the voltages, steps 1 & 2 of calibration, and ran into the same brick wall when I hit step 3 -- got to the +10 dBu on output part, turned attack on again, and VAC only dropped from 2.44 to 2.39.  Still not fully understanding what's going wrong, but it must be there in the voltage readings, so I'll put them below, with the expected voltages from the troubleshooting guide in italics for comparison.  (Sorry that this is going to make a for long post, but maybe it will help others to see a comparison?).  I think it's pretty clear that if there's an issue here, it's most evident beginning in the GR Control Amp Input.

Values in red = Off by more than I thought was reasonable

Signal Preamp Section (I think this looks okay)

TP1: 0.100 (0.100 VAC)
Q2 Base: 0.095 (0.087 VAC)
Q3 Base: 0.011 (0.010 VAC)
Q14 Base: 1.953 (1.73 VAC)
TP15: 1.947 (1.73 VAC)

Signal Line Amp

TP17: 0.200 (0.200 VAC)
Q4 Base: 0.200 (0.200 VAC)
Q5 Base: 0.254 (0.195 VAC)
Q6 Base: unable to measure due to spacer blocking access, could desolder if needed
Output Transformer Brown Wire: 3.854 (3.65 VAC)

Output Measured Between "+" and "-": 3.725 (3.62 VAC)

Set Q Bias successfully.

GR Control Amp Input (this is where things took a bit of turn)

TP22
20:1 - 0.385 (0.380 VAC)
12:1 - 0.224 (0.180 VAC)
8:1 - 0.148 (0.098 VAC)
4:1 - 0.083 (0.035 VAC)

GR Control Amp

Q7 Base (20:1) - 0.385 (0.377 VAC)
Q8 Base (20:1) - 3.464 (3.62 VAC)
Q9 Base (20:1) - 0.412 (0.430 VAC)
Q10 Base (20:1) - 3.465 (3.68 VAC)

GR Control Amp Output

Anode CR2
20:1 - 3.463 (3.63 VAC)
12:1 - 2.014 (1.78 VAC)
8:1 - 1.336 (1.20 VAC)
4:1 - 0.745 (0.620 VAC)

GR Control Amp Threshold Voltage

TP 21
(20:1)  -6.71 (-6.78 vdc)
(12:1)  -3.82 (-3.83 vdc)
(8:1)  -2.75 (-2.72 vdc)
(4:1)  -1.84 (-1.84 vdc)