[BUILD] 1176 Rev A - Back to the beginning...

[ChrioN]

No that was my bad. The signal disapears at secondary side of the transformer.

This is really driving me nuts. I've completed four 1176s over the years, so I know this project fairly well.

Anyways, I've attached a picture of how I've wired the input.

So signal from transformer PCB until you connect it to the main PCB at which point you know longer get signal from the output of transformer PCB... Must be shorted PCB input +- no?  Or the signal from transformer PCB isn't actually connecting to the PCB input.. ie.  lifted trace/dodgy wire/dogdy molex etc...  Or the 270R is a stupidly low value

When main PCB is connected have you tested whether there's signal from a point on the transformer PCB ?

 

[Rybow]

Do the primaries and/or secondaries need to be jumpered in any fashion? I had a similar problem on a 312 build, and it was because I had jumpered the transformer primaries incorrectly.

 

[ChrioN]

When hooking up the transformer unbalanced outside the box, it works perfectly.

 

[Rybow]

Oh sorry. I just re read everything you posted.

 

[MicDaddy]

Did you verify that you have PIN 2 from input XLR terminated to the + pad?  Your diagram shows PIN 3 going to +

 

[ChrioN]

Did you verify that you have PIN 2 from input XLR terminated to the + pad?  Your diagram shows PIN 3 going to +

Not following.

 

[Hank Dussen]

Did you verify that you have PIN 2 from input XLR terminated to the + pad?  Your diagram shows PIN 3 going to +

Not following.

MicDaddy's right: on your drawing you have the + and - of the input XLR reversed.

 

[ChrioN]

I'm not using xlrs. Just illustrating the solderjoints. Also, it seems like I'm getting the signal through when using unbalanced cable between signal gen and 1176.
Everything works as it should when using unbalanced input cable it seems...

 

[Thunder Audio]

Hello all!  New member - 1st post, although I have been watching and reading activity here for MONTHS!  You have shared so much invaluable info that it's staggering.  To my point, tho...  I am in the final throws of a Hairball 1176 Rev A build and everything has (mostly!) gone quite smoothly.  I am in the calibration stage and was immediately (but temporarily) stymied when I got no reaction when attempting to adjust the Q bias.  Discovered that the trim pots DO NOT mount on the main PCB ion the orientation depicted.  Problem solved - Q bias now set.  I am now running into a situation where, in attempting to calibrate the discrete meter circuit, I get NO CHANGE in the DC voltage across R74 when adjusting R75.  Drat!!!  I do get full deflection of the meter (in GR mode) in both directions, but no change in the voltage reading.  This is on the mnats V1.2.5 PCB.  I do indeed have the jumper placed to remove R44 from the circuit.  I have double checked that there are no apparent shorts or bridged solder points.  No matter what I do, I'm getting a fairly constant reading of 0.468 VDC across R74.  Any thoughts?  I've been able to work my way through every issue which has confronted me thus far on this journey (my "maiden voyage", if you will!), but this has got me stumped...  HELP!, oh wise forusm denizens...  I've attached a photo

Cheers,

Joe

 

[MicDaddy]

I think you want to take your Voltage measurements across TP10 and TP11 instead of R74.

 

[Thunder Audio]

MicDaddy, you are absolutely correct.  It kinda freaked me out when the value was decending, decending and then JUMPED!  After a few tries realization dawned that my meter was changing to mV...  All is well.  Now, onward to Gain Reduction Meter Tracking adjustment.  This is exciting!  I'll post more photos upon completion - I'll be curious to see peoples reaction to my "Tie Dye" front panel finish...

Cheers,

Joe

 

[Thunder Audio]

Well, this is pesky...  Following mnats video on Gain Reduction Meter Tracking adjustment, I get precious little drop on my VU meter when I re-engage the GR - like a half dB or so.  No combination of input/output gain settings yields much, if any change in that reading.  Even wide open gain with the 1kHz tone shows no gain reduction.  Excitement quelled momentarily...  Any thoughts?

 

[MicDaddy]

What Voltage of the Sine wave are you feeding the input, and are you measuring the same voltage at the output?  i.e. .775V @ input XLR with input knob at 12 O'clock, measure the output XLR adjust Output control until you read .775V @ output XLR.  See Below...  let us know how it goes.


from nimbleswitch-

Step 3: Adjust Gain Reduction Meter Tracking

Ok. .775v coming in.

    * In GRmode, Input control at 12 o'clock, and adjust output control
      to give .775v coming out of the unit.
    * Now, switch to bypass, and adjust the input control(the t-pad)till
      your output of the 1176 reads 10db(2.4495).
    * Then switch back into GRmode and again readjust the output
      control(of the unit) to read .775v at the unit's output.
    * Then switch to bypass yet again, and readjust the input
      control(t-pad) till the unit's output reads 10db(2.4495).
    * This goes back and forth a few times till the 10db swing
      holds...i.e, in bypass mode you have 2.4495v coming out, and then
      switching into GRmode, you have .775v coming out. Thus the 10db
      swing...10db of gain reduction.
    * Immediately insert R44 with input signal still present and adjust
      it till your internal VU meter rests at -10dB. You'll probably be
      quite close to this setting without adjustment.


It's been my experience easier to 'see' what's going on with the DMM than watching the VU

 

[pietro_moog]

hi guys.
i'm looking for a nice power transformer from mouser.
do you have a suggestion?

 

[Thunder Audio]

Some serious head scratching at this point...  With 1kHz sine wave @ 0.775V at the input, I am simply NOT getting the proper behavior when engaging/disengaging GR.  If I start with the input at 12 o'clock, when I adjust output to read 0.775V, my VU meter shows -4dB.  In following nimbleswitch's procedure, I actually get a tiny bump in output - to 0.792V.  At step two, I do not have enough input gain left to achieve 2.449V at output - I can only get 1.425V.  If I start with my input at 10:00, I do not have enough gain at step four to achieve 2.449V at output - I can only get 1.157V.  I've gone back and re-done the Q-bias adjustment and the discrete meter circuit calibration, but am getting nowhere with this step.    Another visual (and poking about) inspection turned up a poor solder point at the input to the PCB, but repairing that has yielded no change...  am fairly perplexed at this point.

 

[benlindell]

hi guys.
i'm looking for a nice power transformer from mouser.
do you have a suggestion?

http://www.antekinc.com/ is where I always buy power transformers from, best prices I've seen.
http://www.mouser.com:80/ProductDetail/Triad-Magnetics/VPT24-2080/?qs=sGAEpiMZZMtlKt%2fhwW%252bxLShKYyyYbCyA if you really want mouser

 

[Gilgamesh]

Some serious head scratching at this point...  With 1kHz sine wave @ 0.775V at the input, I am simply NOT getting the proper behavior when engaging/disengaging GR.  If I start with the input at 12 o'clock, when I adjust output to read 0.775V, my VU meter shows -4dB.  In following nimbleswitch's procedure, I actually get a tiny bump in output - to 0.792V.  At step two, I do not have enough input gain left to achieve 2.449V at output - I can only get 1.425V.  If I start with my input at 10:00, I do not have enough gain at step four to achieve 2.449V at output - I can only get 1.157V.  I've gone back and re-done the Q-bias adjustment and the discrete meter circuit calibration, but am getting nowhere with this step.    Another visual (and poking about) inspection turned up a poor solder point at the input to the PCB, but repairing that has yielded no change...  am fairly perplexed at this point.

I'm having similar problems. If I feed a high enough signal I can do the first part, if I feed a low enough signal I can do the second part but I can't find a medium to be able to do both! I was going to redo the Q bias but it sounds like you had no luck there. I'll try it anwyay. If I find a workaround I'll post back.

 

[Gilgamesh]

Some serious head scratching at this point...  With 1kHz sine wave @ 0.775V at the input, I am simply NOT getting the proper behavior when engaging/disengaging GR.  If I start with the input at 12 o'clock, when I adjust output to read 0.775V, my VU meter shows -4dB.  In following nimbleswitch's procedure, I actually get a tiny bump in output - to 0.792V.  At step two, I do not have enough input gain left to achieve 2.449V at output - I can only get 1.425V.  If I start with my input at 10:00, I do not have enough gain at step four to achieve 2.449V at output - I can only get 1.157V.  I've gone back and re-done the Q-bias adjustment and the discrete meter circuit calibration, but am getting nowhere with this step.    Another visual (and poking about) inspection turned up a poor solder point at the input to the PCB, but repairing that has yielded no change...  am fairly perplexed at this point.

I'm having similar problems. If I feed a high enough signal I can do the first part, if I feed a low enough signal I can do the second part but I can't find a medium to be able to do both! I was going to redo the Q bias but it sounds like you had no luck there. I'll try it anwyay. If I find a workaround I'll post back.

Have been through the Rev D thread. The problem you are describing (if I have interpreted it correctly) appears to have been experienced by a lot of people in that thread as well. One recommendation was to use this guide:

http://www.axtsystems.com/index.php?option=com_content&view=article&id=56:1176lncalibration&catid=34:1176ln&Itemid=62

I'm going to try it using DVM on output rather than observing the meter as I have been and see if I have any more luck.

 

[Thunder Audio]

Well, it seems that the voltages coming off of my power transformer are off - and intermittent, to boot!  Let me chase this down for a while...

 

[Thunder Audio]

A tech friend of mine suggested that the 0 volt taps from the secondaries should be seeing ground, and indeed, my +30V readings became perfectly stable upon doing so...  Now have stable +30/-10V at appropriate test points, but no matter which calibration technique is employed, I get level drops of 0.014V or about a needles' width on the VU meter.  My Q-bias calibration goes perfectly, so it appears that the GR FET is in conduction.  Likewise, calibrating the discrete meter circuit goes without a hitch, but GR meter tracking just aint happening... I'm in beyond my pay grade here.