[BUILD] 1176LN Rev D DIY

[Echo North]

Good afternoon Mike and all DIY'ers

I am still scratching my head with this REV D.

checked the GR pcb no shorts(solder connections) all correct resistors.
checked the GR Meter Driver Section - Confirmed each resistor is correct and no shorts.

I am able calibrate the Q Bias
I have swing on the Null adjust and on R71 - But I still +3 volts at the end of the trimmer and the needle at +3VU

Pad 28 and 29 show high volts of +21vdc.

What is the typical volts at pad 28 and 29 with the GR PCB disconnected?

I am trying to find other avenues to look down for build errors based on what I have.

Any hunches or thoughts would be appreciated.

That's pretty normal.  They are near the V rail. You can see them noted here on the mnats site.

http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

Can you remind me of your problem symptoms? Considered sending it in for repair?

Mike

 

[bxershrts]

Thanks for your fast reply Mike,

The problem or symptoms are the high voltage at Q11 / Pad 28 I believe.

Thanks for the link  - it is what I have been using confirm my build.

The circuit is in range except at Q11, Q12 ,Q13.

It passes audio - all pots work, trim pots ,Qbias Is easily set - but I run out of range on the null adjust and front pot "balance". I have switched the null adjust to 5K and R71 to 5K - I even went to 10K on both to see if it just a bias range of the particular Fets I am using - but it always ends up 3 volts out at the end of the trim pot.

 

[Echo North]

Thanks for your fast reply Mike,

The problem or symptoms are the high voltage at Q11 / Pad 28 I believe.

Thanks for the link  - it is what I have been using confirm my build.

The circuit is in range except at Q11, Q12 ,Q13.

It passes audio - all pots work, trim pots ,Qbias Is easily set - but I run out of range on the null adjust and front pot "balance". I have switched the null adjust to 5K and R71 to 5K - I even went to 10K on both to see if it just a bias range of the particular Fets I am using - but it always ends up 3 volts out at the end of the trim pot.

Re-flow joints, even if they look good. Clean ALL flux off the PCB, it's a huge factor if you have flux in those high impedance areas.

Mike

 

[felix1988]

Hi everybody, hi mike.

I still have some problems with my rev d build i think.
i can fully calibrate it without any problems and i guess it works but  i feel like there must be something off because it sounds distorted on the shortest release setting. not just on bass-heavy stuff but also on vocals. when i send a sine wave to it i can see the harmonics in a frequency analyser. the harmonics are higher than on my rev a which i think should normally be the other way round, right?

how should i check for problems?

Thanks!

 

[ln76d]

Check all wires connections. I had similar problems on my rev F where i used connectors instead soldering wires to the PCB.
Two wires weren't contacting properly.

 

[bxershrts]

OK Mike, heres what I have done.

I have replaced Q12 - Q13 the meter is somewhat closer - yet still very off and out of range on the null adjust and Front panel balance. 

I have reflowed all GR Meter joints.

here are my measurements...and perhaps you can point me in another direction to try.


Q11 D:    21.84 vac
          S:      -5.92

Q12  C:      21.84 vac
            B:      -5.92
            E:      -6.10

Q13  C:      21.05 vac
            B:    -5.35
            E:      -5.91


I have checked attack and release pot wiring and find it to be correct.
Pad 28 and 29 are correct from GR PCB.
All resistors are quadruple checked.
Short of putting in 20K pots in null adjust and R71 I am stumped.

One thing I do notice - I can hear the build compress , except that in GR mode the needle does not move. In +4 and +8 the needle is pretty typical of movement. The attack and release pot are both showing fast and slow in regards to pot movement and needle reaction.

Thanks for your ideas

I am stumped. 

 

[Echo North]

Just a reminder, in case you have a unit available!
FET bias is adjusted correctly, I suppose the distortion occurs because of a superimposed ripple on the control (gate) voltage.

Did somebody ever measure the distortion at 40 Hz, with a gain reduction of 4 or 5 dB?
With a bass guitar I get audible distortion, even at longer release times.
Just curious...

(In the 'off' position, - so with the signal going through the circuit-, the distortion is very low.)

I can do it, but it'll be a 1-2 weeks as our units are on loan at the moment.

Mike

0.15%.

Within spec and should definitely not be audible. Maybe try re-calibrating the q-bias or a new set of FETs?

Mike

 

[felix1988]

Check all wires connections. I had similar problems on my rev F where i used connectors instead soldering wires to the PCB.
Two wires weren't contacting properly.

Thanks for the hint! I  did and it didn't change. it's weird, my rev d sounds way dirtier than the rev a could the fet be broken or sth?

 

[Echo North]

Check all wires connections. I had similar problems on my rev F where i used connectors instead soldering wires to the PCB.
Two wires weren't contacting properly.

Thanks for the hint! I  did and it didn't change. it's weird, my rev d sounds way dirtier than the rev a could the fet be broken or sth?

Could be a funny joint (re-flow) and make sure it's clean of flux.  Had one in the shop the last week that was acting the same (high distortion) and it ended up being a bad joint in the pre-amp section. The joint looked good, but when I re-flowed it, all the distortion went a way.

Or weird transistor if all else fails. Make sure their DC voltages are right VS schematic.

Mike

 

[Echo North]

OK Mike, heres what I have done.

I have replaced Q12 - Q13 the meter is somewhat closer - yet still very off and out of range on the null adjust and Front panel balance. 

I have reflowed all GR Meter joints.

here are my measurements...and perhaps you can point me in another direction to try.


Q11 D:    21.84 vac
          S:      -5.92

Q12  C:      21.84 vac
            B:      -5.92
            E:      -6.10

Q13  C:      21.05 vac
            B:    -5.35
            E:      -5.91


I have checked attack and release pot wiring and find it to be correct.
Pad 28 and 29 are correct from GR PCB.
All resistors are quadruple checked.
Short of putting in 20K pots in null adjust and R71 I am stumped.

One thing I do notice - I can hear the build compress , except that in GR mode the needle does not move. In +4 and +8 the needle is pretty typical of movement. The attack and release pot are both showing fast and slow in regards to pot movement and needle reaction.

Thanks for your ideas

I am stumped.

21VAC? or do you mean DC?

 

[bxershrts]

My mistake - yes DC volts. Sorry

 

[Echo North]

My mistake - yes DC volts. Sorry

Ya your voltages are crazy off. R79 and R67 are right?

Reflow ALL of those joints in the GR meter section too. Maybe you're missing continuity to ground.

If the R's are right, I'm not sure what to tell you, I'm stumped. Consider sending in to us for repair.

Mike

 

[bxershrts]

Yeah.... When all else fails.  OK,  what is your shop rate?

 

[Echo North]

Yeah.... When all else fails.  OK,  what is your shop rate?

http://www.hairballaudio.com/build-support-services

 

[Echo North]

hello, I'm having trouble with step 1 of the calibration...i've turned the q bias adjust all the way in both directions and nothing happens to either the voltage reading or the vu meter. i,ve checked all of the wiring and solder joints and everything looks good. any hints or advice would be much appreciated.

Start buy measuring the DC voltage at pad 18 as you rotate the qbias. It should go from 0VDC to some negative value like -2.2VDC.

Use the CT/0V of the power supply as your common.

Mike

 

[Dr. Lessley]

ok, voltage reading at pad 18 goes from 0 to -2.9...sounds like its right? i really appreciate your help mike...thanks

 

[Echo North]

ok, voltage reading at pad 18 goes from 0 to -2.9...sounds like its right? i really appreciate your help mike...thanks

Try the same thing on PAD 7.

 

[Dr. Lessley]

pad 7 goes from 0 to 1.0 but drops by itself after i stop turning r59...is that right?

 

[Echo North]

pad 7 goes from 0 to 1.0 but drops by itself after i stop turning r59...is that right?

No. That bias voltage travels from pad 18 through the attack and release pot  wiring to pad 7.  Follow it, make sure that wiring is right and check those joints and header connections.

 

[Dr. Lessley]

ahhh...i had pad 7 and ground reversed...now I'm hung up on the meter tracking part...there seems to be no change in voltage when i turn the attack knob on and off...