johnnybregar said: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
johnnybregar said:Did you receive my missing parts request? Just checkin.... Thx.
EmoRiot said: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!
Hairball Audio said:Sounds good.
dbmorton said: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.
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
JMan said: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!)
Hairball Audio said:If your TP22, 21, and CR2 voltages all look decent you pot is fine.
You were able to set Qbias?