[OneRoomStudios]

Did you already replace the broken Q12 ?

No, once I switched the wires I had reversed, the voltages all settled down to be close to the ones on Mnats labelled schematic  (http://mnats.net/files/1176REVD_VOLTS.pdf).

Do you think Q12 could have been damaged if it’s now reading the correct voltages?

[Harpo]

Do you think Q12 could have been damaged if it’s now reading the correct voltages?

From your 

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

you have exceeded the 30 V_CEO abs.max.rating of the 2N3707.
Considering your not correctly working circuit, assuming this part to be blown isn't this far off, but YMMV ...

[OneRoomStudios]

you have exceeded the 30 V_CEO abs.max.rating of the 2N3707.
Considering your not correctly working circuit, assuming this part to be blown isn't this far off, but YMMV ...

You're right, it was worth a shot. I replaced it, but get the same readings as before and the meter is still not working. The circuit appears to be loaded down by the meter.

[OneRoomStudios]

Progress.

I got a new meter. I can now get the meter to zero when I bypass R44, but not when it's in circuit. I read that occasionally a 2K trimmer isn't enough to get it there, depending on the JFET, so I replaced it with a 5K, and I'm closer....but still not there. I can only get the meter to around -1.25dBVU at the extreme end of the 5K trim. Should I order a 10K trimmer and see if that will get me there, or should I be looking for some kind of issue that's causing the problem?

[OneRoomStudios]

One other thing to confirm. I'm building the rotary version, but not using the rotary meter board (only the rotary ratio board). Instead, I'm using a DPDT toggle for the meter (either GR or +4 output), and a SPDT for Bypass. I believe I have the bypass switched wired correctly, but now I'm questioning myself. In bypass, pin 22 is shorted to ground, and when not bypassed, pin 22 is connected to pin 4 from the rotary ratio board. Is that correct?

[Purplenoise]

Hi guys, first post here and a complete newbie to DIY. I am starting my second hairball 1176 and I already have a utc o-12 and a UA 5002. After gathering as much info as I could I'd really appreciate it if someone could double-check my findings as far as wiring the transformers goes. so here it goes:
- utc pin1 to pcb pin1
  utc pin5 to pcb pin4
  utc pin6 to pcb pin5
  utc pin8 to pcb pin8
  utc pin3 to pcb pin7

i am assuming that where the dot is on the pcb its pin 1 and then? clockwise or anti clockwise for consecutive numbers?

As far as the output I see that UA has the same color wiring as EA correct?

Thanks in advance.

[Alistair]

Hi all, apologies if something similar has been addressed in the thread- at 270+ pages it's a bit of a read and I haven't found anything in searches.

I've had a Mnats 1176 for years that has been operating correctly with no issues.
I recently bought a half finished kit from someone who ran out of time to finish it, and have been having nothing but trouble getting it to operate correctly.
It passes signal and compresses, however level is considerably lower than on my other working 1176- often 12 to 20db lower with identical signals.

I've tried the following to rectify the issue:

- swapped t-pad with known working
- swapped input tx with known working
- replaced full PCB (I had a spare stuffed one, so used this. I haven't replaced the meter or ratio boards)
- checked all resistors and other parts visually
- checked voltages (all within 5% of each other)
- replaced 0 set (it was an incorrect pot, but I can't imagine this would effect anything)
- checked and rechecked all wiring
- confirmed output pot is correct spec (again, about 5% out of tolerance with my other unit, but fine)

The only elements that have remained consistent are the output tx, power tx, ratio and power boards, and the 2N5457 JFETs as I didn't have spares of those.

As the issue is present even with compression off, I'm assuming it has to be occurring in the preamp or line amp, and as the metering is showing this signal as significantly lower I'm assuming it has to be in the preamp PRIOR to signal being passed on to the meter circuit. As I've swapped out the PCB, I've essentially replaced all parts in the preamp, with the exception of Q1, one of the 2N5457 JFETs.

Is it possible for Q1 to be having this much impact on gain? 

Thanks in advance.

[Hairball Audio]

Hi all, apologies if something similar has been addressed in the thread- at 270+ pages it's a bit of a read and I haven't found anything in searches.

I've had a Mnats 1176 for years that has been operating correctly with no issues.
I recently bought a half finished kit from someone who ran out of time to finish it, and have been having nothing but trouble getting it to operate correctly.
It passes signal and compresses, however level is considerably lower than on my other working 1176- often 12 to 20db lower with identical signals.

I've tried the following to rectify the issue:

- swapped t-pad with known working
- swapped input tx with known working
- replaced full PCB (I had a spare stuffed one, so used this. I haven't replaced the meter or ratio boards)
- checked all resistors and other parts visually
- checked voltages (all within 5% of each other)
- replaced 0 set (it was an incorrect pot, but I can't imagine this would effect anything)
- checked and rechecked all wiring
- confirmed output pot is correct spec (again, about 5% out of tolerance with my other unit, but fine)

The only elements that have remained consistent are the output tx, power tx, ratio and power boards, and the 2N5457 JFETs as I didn't have spares of those.

As the issue is present even with compression off, I'm assuming it has to be occurring in the preamp or line amp, and as the metering is showing this signal as significantly lower I'm assuming it has to be in the preamp PRIOR to signal being passed on to the meter circuit. As I've swapped out the PCB, I've essentially replaced all parts in the preamp, with the exception of Q1, one of the 2N5457 JFETs.

Is it possible for Q1 to be having this much impact on gain? 

Thanks in advance.

This will still apply to older boards:
https://help.hairballaudio.com/hc/en-us/articles/360045942974-FET-RACK-Troubleshooting-Guide

And will help you find exactly where the error is.

Mike

[mrclunk]

Hi chaps,
I building a my first Rev D and my output transistor is very hot.
How hot do they generally get?
I have a small heatsink in mine but it's too hot to holda  finger on.
Is that normal??
thanks

[Hairball Audio]

Hi chaps,
I building a my first Rev D and my output transistor is very hot.
How hot do they generally get?
I have a small heatsink in mine but it's too hot to holda  finger on.
Is that normal??
thanks

Yes.

https://help.hairballaudio.com/hc/en-us/articles/360049490733-FET-RACK-Operational-FAQ

[Alistair]

Thanks for the quick reply Mike.

I've followed that guide through and am only getting 0VD to -1.2VDC at TP18, so I am assuming the issue is within the q-bias circuit as I can't get it to the approx  -3VDC suggested.
The -10VDC supply is looking fine, as are R35, R59 and R60 (I've pulled all of them from the circuit and tested resistance).

My other voltages are massively off from those AC voltages listed in your troubleshooting guide, however the DC voltages on all transistors are within 15% of those listed by mnats here: http://mnats.net/files/1176REVD_VOLTS.pdf

Looking at the schem I'm still wondering if Q1 and Q11 might be the issue, but very happy to hear if anyone has any other suggestions.

Thanks all

This will still apply to older boards:
https://help.hairballaudio.com/hc/en-us/articles/360045942974-FET-RACK-Troubleshooting-Guide

And will help you find exactly where the error is.

Mike

[Hairball Audio]

Thanks for the quick reply Mike.

I've followed that guide through and am only getting 0VD to -1.2VDC at TP18, so I am assuming the issue is within the q-bias circuit as I can't get it to the approx  -3VDC suggested.
The -10VDC supply is looking fine, as are R35, R59 and R60 (I've pulled all of them from the circuit and tested resistance).

My other voltages are massively off from those AC voltages listed in your troubleshooting guide, however the DC voltages on all transistors are within 15% of those listed by mnats here: http://mnats.net/files/1176REVD_VOLTS.pdf

Looking at the schem I'm still wondering if Q1 and Q11 might be the issue, but very happy to hear if anyone has any other suggestions.

Thanks all

That Qbias voltage is bumped lower by the - DC resistors on the ratio PCB.  I would check all of those values.

[mrclunk]

Yes.

https://help.hairballaudio.com/hc/en-us/articles/360049490733-FET-RACK-Operational-FAQ

thankyou 

Also kids, check you resistors before populating ya boards. All my 10k's turned out to be 1K's... 

[Alistair]

That Qbias voltage is bumped lower by the - DC resistors on the ratio PCB.  I would check all of those values.

Thanks Mike- there was a burnt trace on one leg of a resistor on the ratio board (that I received already completed). Fixed and calibrated and the unit is working as it should. Thanks for the assistance, would have taken me forever to find that by myself.

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