[myers1st]

Hi-

So I'm working on an older dual rev D with the mnats power supply.  I had the PSU working and trimmed to +30 and -10.  I finished one channel and applied power to test it, but forgot to disconnect the unfinished second channel from the psu and there must have been a short somewhere.  LEDs on the PSU went on briefly, heard a pop, lights out, I killed power after about two seconds.  Nothing smoked or looks fried.

Now the power trafo is acting funny.  Before, I was getting 25v between secondary ends and center tap.  Now I measure 0V between secondary ends and center tap, but I measure 75V between secondary ends and chassis.  Could I have fried the power transformer?  I should be able to read the correct transformer output voltage without the psu connected right? 

Thanks for any help.

[weiss]

hey guys, can you answer a quick question for me?
if the rotary meter switch is set to GR off, should pad 22 show continuity to ground?

thanks

[Hairball Audio]

hey guys, can you answer a quick question for me?
if the rotary meter switch is set to GR off, should pad 22 show continuity to ground?

thanks

Yes.

[Alexwfm]

Hello!

Weird thing happening to my RevD 1176: without any input signal the output self oscillates bring the output volume towards fully clockwise.

Things I found out:
-Disconnecting the output XLR or using a short 1 metre XLR of stops the oscillation.
-Different XLR produce different frequencies that vary 25Khz - 150Khz  about 4Vpp.
-Grounding output + doesn't do anything while grounding the output - produces the same high freq oscillation.
-Lifting the PCB and moving it around I could vary the frequency and amplitude.

Checked transformer wiring multiple times..

For the rest the 1176 works well, calibration was fairly straightforward. Tested earth points with multimeter and all earthing was good.

I'm desperate as I'm not sure what else to check!

Any help will be greatly appreciated!
Cheers!

ps. if anyone fancies the challenge there's another paranormal situation needing debunk:  if I disconnect the wire going to pin 17 -basically disconnecting the return signal from the output volume pot- the signal still passes through the line amp section, lower in volume and in low end but I can't understand how that's possible as that circuit is not connected to the other sections in any way but for that wire?

[Hairball Audio]

Hello!

Weird thing happening to my RevD 1176: without any input signal the output self oscillates bring the output volume towards fully clockwise.

Things I found out:
-Disconnecting the output XLR or using a short 1 metre XLR of stops the oscillation.
-Different XLR produce different frequencies that vary 25Khz - 150Khz  about 4Vpp.
-Grounding output + doesn't do anything while grounding the output - produces the same high freq oscillation.
-Lifting the PCB and moving it around I could vary the frequency and amplitude.

Checked transformer wiring multiple times..

For the rest the 1176 works well, calibration was fairly straightforward. Tested earth points with multimeter and all earthing was good.

I'm desperate as I'm not sure what else to check!

Any help will be greatly appreciated!
Cheers!

ps. if anyone fancies the challenge there's another paranormal situation needing debunk:  if I disconnect the wire going to pin 17 -basically disconnecting the return signal from the output volume pot- the signal still passes through the line amp section, lower in volume and in low end but I can't understand how that's possible as that circuit is not connected to the other sections in any way but for that wire?

That's usual caused by the wires from the meter PCB to the XLR output.  Keep them away from the PCB and/or shield them.

[Alexwfm]

I see! Though I get that issue also when the meter is on GR? I’ll try anyway!

[Hairball Audio]

I see! Though I get that issue also when the meter is on GR? I’ll try anyway!

Yup you will. 

[Alexwfm]

Hello Hairball Audio,

I've tried removing the wire from the XLR to the meter but it didn't help.
Though what resolved the issue was rewiring both of the XLRs ground to the main PCB  star ground instead of using the wire coming out of the output transformer chassis. It seems so strange how that could be affecting the circuit, as the transformer chassis is physically connected to the case as well as the star ground just a few cm away!

Cheers

[Alexwfm]

Happened to fit the top panel finally!
There are still minor noise issues to fix but I’m quite happy!

The extra features are just a switch to reverse the order of compression and eq, and another rotary to send the sidechain through a high pass or to send it to the eq circuit.

Frontpanel made from frontpanels.de from a inkscape design I’ve drawn.

Cheers!

[Hairball Audio]

Happened to fit the top panel finally!
There are still minor noise issues to fix but I’m quite happy!

The extra features are just a switch to reverse the order of compression and eq, and another rotary to send the sidechain through a high pass or to send it to the eq circuit.

Frontpanel made from frontpanels.de from a inkscape design I’ve drawn.

Cheers!

Nice!

[trashcanman]

I've got my stereo build of this about 95% working now but have a few kinks to sort out. I can do most of the calibrations and get it to compress well, all transistor voltages are good but I seem to be getting high gain at the input  stage. Is there an expected AC voltage output for a 0dbu 1k sine at input and controls at 12?
I built my own stepped t-pad for the inputs and think they might be the problem though they seem to be working, as in the volume increases as I would expect as I rotate the switch. With a 0dbu 1k sine at input and controls at 12 I get ~14VAC on one and ~20VAC on the other. I've swapped t-pads between boards and the difference seems to be from them so I'm going to take a look at them again but is that higher than expected? If I turn the ins/outs past 12 the noise floor is very noticeable.
I know there's a lot of variables including  gain staging etc. but wanted to ask.

edit: I found a loose connection on one of the t-pads and the outputs are even now but still about 13VAC when loaded which is much higher than it should be according to the hairball troubleshooting guide.  Guess I'll just work my way through until I figure it out.

[midwayfair]

I've had some trouble getting my meters to zero since I built a stereo version (on the old boards) and I wanted to try to fix things. The problems are definitely related to my meter drivers since everything works properly in +4 mode. My compression has always worked properly as well.

Going off the schematic here:

http://library.hairballaudio.com/docs/fet_rack_d_doc_v1.11.pdf

I shrank R72 to about the same size as its companion and I got pretty close, with a little extra slop. I still wasn't able to get 0V across R74. So I made it smaller (down to about 500R now), and I was finally able to zero it. I left the righthand channel the same as it was before.

But I can't get the calibration step to work properly anymore. My meter in GR mode barely jumps when I switch the bypass on and off, regardless of the compression ratio (mine goes all the way down to 2:1 with a much lower threshold as well).

What exactly are the consequences of changing R72? It looks to me like it's just a limit on the voltage divider created by the 0 pot, but does it affect the actual meter driver at all? Is there some other place I should be looking to fix these issues (either the inability to zero or the seemingly weak needle bouncy bouncy)?

[trashcanman]

Alright so I'm pretty sure my stepped t-pads are the problem with my gain problem. I built them myself according to this schematic
I've just looked at how it was drawn in the original schematic and seems to be slightly different

Maybe it's just a bad scan but it looks like the left hand end of the top pot is not connected to the wiper, the bottom pot doesn't have it's bottom end connected to the com and the wiper is connected to the opposite end. I drew a altered version below


Anyone know if that's how it should be?

Edit: I tried a few different ways or wiring it and none of them worked so I'm thinking I had them right the first time. I've found that if I send it a -10dbu signal from my interface the noise floor is much lower and more usable. There must be something wrong regardless but it's at least usable that way.

[babaorum]

Hello,

My 1176 (old rotary version) doesn't compress, only INPUT and OUTPUT seems to have an action on the signal.
What can I check first to debug it ?

Thanks,

[Hairball Audio]

Hello,

My 1176 (old rotary version) doesn't compress, only INPUT and OUTPUT seems to have an action on the signal.
What can I check first to debug it ?

Thanks,

Most off this stuff applies:
https://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

Likely a Pad 22/21 issue.

Mike

[OneRoomStudios]

I'm working on a Rev D V2.2 board and having some issues. All the voltages are reading fine except for the GR Meter Driver section, which is way off, and I can't get the Q Bias control to decrease the level when trying to calibrate. I tried searching through this thread and doing the usual stuff (reflowing solder, checking component values, etc), but no luck. Maybe when someone sees these wacky voltages, they'll know what the issue is (bad Q11 FET maybe?).

Q11:
D: 24.8V
S: -6.3V
G: -5.0V

Q12:
B: -6.3V
C: 24.8V
E: -2.0V

Q13:
B: -1.15V
C: -1.77V
E: -1.78V

If it makes any difference, my B+ is a hair low at 29.8V. Any help would be super appreciated.

[Harpo]

Q12:
B: -6.3V
C: 24.8V
E: -2.0V

if voltage readout was correct, I'd expect a broken or wrong part or Q12 placed with wrong orientation and now broken because of this.

[OneRoomStudios]

if voltage readout was correct, I'd expect a broken or wrong part or Q12 placed with wrong orientation and now broken because of this.

Thanks Harpo. It turns out I made a bone-head mistake and switched wires 18 and 20. The voltages all read correctly now (or close enough).

I'm having another issue now though - I can't seem to get my meter to work.

It's an old vintage meter that I like the look of, but it's a DC meter, and it reads  0dB at around 110mVDC. I built a half-wave rectifier for the output, and it reads that well enough, but it doesn't react at all in GR mode (doesn't go to "0," doesn't move).

I'm assuming the output of the GR meter circuit is DC and doesn't need to be rectified (I'm reading DC across points 28 & 29). When have the meter set to +4/Output, I read 1.1VDC across 28 & 29, but when I switch into GR mode, it drops to 0VDC.  It's almost like the meter is loading down the driver circuit. I measure around 300 Ohms across the meter pins. Is that too low? Does the GR meter signal voltage have to be buffered or something?

[OneRoomStudios]

More experimenting. I built a FWB rectifier for the meter (which seems to be a 300uA DC meter), and get pretty close to 0dB at 1.223V with a 3K6 resistor. All good on the output metering.

The GR metering still isn't working though. When switched into GR mode, I measure around 300mV across points 28/29, which feed the meter in that setting, but see nothing on the meter (doesn't go to "0," stays at -inf). It shouldn't matter with a FWB rectifier, but I checked the DC polarity, and it's correct. I'm at a loss now.

This is a DC meter, but I can only get it to read AC (with a rectifier), and it doesn't seem to be reacting to the DC  coming from the meter driver circuit. Any ideas?

[Harpo]

Did you already replace the broken Q12 ?

1176ln rev.7 help

Started by fuzzbox The Lab

What am I missing in my tools list for building my 1176LN Rev D?

Started by canidoit The Lab

Early 1176ln rev.F uses O-17 ?

Started by listen202 The Lab

Suggest 1.8K for R12 in mnats and other 1176LN Rev D DIY builds

Started by David Kulka « 1 2 » The Lab