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

[phatmateo]

hmm Im having trouble calibrating the meter as well.  I even bought matched fets from hairball.  You have matched fets and swapping them enables you to calibrate it?

 

[Rob Flinn]

hmm Im having trouble calibrating the meter as well.  I even bought matched fets from hairball.  You have matched fets and swapping them enables you to calibrate it?

Yes, sometimes that has been the case !

Have you replaced the 2K trimmer with a 5k (as detailed elsewhere) to give you some extra range ??

 

[phatmateo]

yes, I have the 5k meter in place of the 2k.  I can never get tp10 and 11 to measure 0 volts.  I'll try swapping the fets to see if it makes a difference.  I'm using 3708's everywhere else.  I wish I had access to some 3707's with a high enough HFE.  Anyone have extras?  Im not sure if thats causing the problem, but I figured its worth a shot.

 

[regularjohn]

Wait...only the 2n5457's need to be matched right?  Or do the two 2n3708's (2n3707's) in the meter circuit also need to be matched?

I went as high as a 10K trimmer and it was almost enough range to get me to zero.  But then the actual gain reduction metering was no where near accurate. 

I also can't get tp10 and tp11 to zero.

This thing is a pain in the heine!  

 

[regularjohn]

Haha...SUCCESS!

I realized that the tracking adjust was maxed out and was keeping me from being able to properly calibrate the GR settings.  I'm now accurately metering GR, and I was able to get TP10 and TP11 down to .01VDC.  That was as close as I could get it to zero...in my opinion one one-hundredth of a volt is pretty darn close.  I still had to use a 10K trimmer for the zero adjust though.

 

[phatmateo]

hmmm I might try the 10k trimmer instead of the 5k.  Thanks John

 

[spica]

Meter calibration frustrations...

Hi Gents, I'm wrapping up my second dual unit - the first one was a bit tricky to calibrate but worked.  I'm getting absolutely no joy with either channel on this one.  The Q bias calibration went fine but I can not get my Null Adj pot to do ANYTHING.  The voltage across points 10 and 11 do not budge at any position of the trim pot.  I also can't zero the meter with the "0" adjust pot.  Both are 5k's and both test fine.

I checked the continuity between the trim pots and everything they are connected to... and that seems fine.  I've tested each component in the GR Meter Driver and everything tests fine as well as has continuity to the next component in the schematic.  I've quadruple checked the wiring.  I replaced Q12 and Q13.  The only thing I haven't done is swap out Q11-the 2n5457. 

In my initial fire up, I did have a couple foul ups.  First I had the output transformer wired incorrectly and blew up R32.  I have replaced the resistor and everything tested fine around it.  The transformer wasn't damaged.  Next I did have some wiring issues - 1.  I had pads 21 and 19 switched as well as pads 15 and 17.  When these were switched I could zero the meter and get the voltage across t10 and t11 down to zero.  I only noticed the wiring issue because the Q bias adjustment wouldn't work and re-checked my wiring.  I don't think I damaged anything with the wrong wiring as I have checked most of the components on the board.

Almost certainly no one has made the same wiring mistake, but has anyone experienced the problem of the Null Adj not doing anything to the voltage across t10 and t11?  Any ideas?

Thanks.

 

[Rob Flinn]

Almost certainly no one has made the same wiring mistake, but has anyone experienced the problem of the Null Adj not doing anything to the voltage across t10 and t11?  Any ideas?

Thanks.

Yes, the trimmer was dead in my case !!

 

[spica]

I wish that was the case with mine - this is the second trimmer I've tried and both have tested ok. 

 

[Rob Flinn]

In that case all I can suggest is that you recheck everything again.  Did you check the transistors ??

 

[regularjohn]

I wish that was the case with mine - this is the second trimmer I've tried and both have tested ok.  

This is exactly the problem I had.  Mess with your tracking adjust trimmer until you see either a change in volts across TP10 and 11 OR the VU meter start to move in GR mode.  Once you see the tracking adjust trimmer changing the volts there or moving the meter, your null adjust trimmer should start to work and eventually you'll be able to zero the meter as well. At least that's what got me out of the weeds!  Best of luck!

 

[spica]

Thanks guys.  It just got a little better and a little more frustrating.  I switched out the Q12 and Q13 transistors earlier today on one channel and didn't do anything else than poke around and check continuity and wiring.  I tried again to no avail and made my above post.  That channel just started to work 3 hours later... for no reason.  I didn't even adjust the tracking adj (although I don't think this should have any effect as it should be out of circuit at this point) as suggested by regularjohn.  I did, however, go grocery shopping and watch a half of monday night football. 

The other channel won't budge even with playing with all the trim pots... maybe I should go get ice cream and watch a movie.

Physics has to win here! There must have been some loose connection or something that I bumped on the now-working channel.  Just can't find it...

I'll try swapping out Q12 and Q13 on the non-working channel and do a tribute dance to the compressor gods (Bill Putnam and Rupert Neve).

Thanks.

 

[ilfungo]

Hi guys
I just finished the calibration of the first blue stripe
everything works fine except the display output to +4
I have about 5 dB difference between the VU meter of the blue stripe and in pro tools

pro tools 0dB
blue stripe-5db
you have any idea about?

thanks

 

[regularjohn]

Hi guys
I just finished the calibration of the first blue stripe
everything works fine except the display output to +4
I have about 5 dB difference between the VU meter of the blue stripe and in pro tools

pro tools 0dB
blue stripe-5db
you have any idea about?

thanks

What resistor did you use for the VU meter?  3.6K or 8.2K?

 

[ilfungo]

Ciao Regularjohn
I used the  hairball schematics  and there are both resistances 3.6ke 8.2K ???

 

[spica]

Hi Ilfungo,

Looking at the schematic, it should be 3.6k for +4 on the meter (R18).  Is that what you have in that position? 

I finally got my other channel to work.  There is some intersection of the 0 set pot and null adj pot where things start working and I just had to play with both to find it.  Maybe the transistors are picky about the resistances they see for both pots before they will do anything.  Everything is cool now.  Hours spent and it was just the trim pots working together.  Talk about wonky.  All's well that ends well. 

 

[regularjohn]

Ciao Regularjohn
I used the  hairball schematics  and there are both resistances 3.6ke 8.2K ???

You probably have your +4 and +8 reversed.  The same signal will meter lower at +8 than at +4.

 

[ilfungo]

I checked the resistors value and they are correct
I tried to do this mod ( see the picture) and now the 0db in protools is 0db on blue stripe
the only problem I have it's on +8  the difference is 6db instead 4db
Any suggestion?
Thanks

 

[mnats]

I checked the resistors value and they are correct
I tried to do this mod ( see the picture) and now the 0db in protools is 0db on blue stripe
the only problem I have it's on +8  the difference is 6db instead 4db
Any suggestion?
Thanks

Yes - learn the definition of "Decibel", then find out what 0dB refers to in your Protools setup.

The "mod" you show only bypasses the required 3.6k resistor in the VU meter circuit. Without it your VU meter is surely displaying incorrect information unless the meter is faulty or is not a true VU meter.

 

[ilfungo]

Mnats thanks for your help ...
I just finished calibrating the blue stripe with a multimeter
and it seems okay except half dB above zero on the meter output
could be the resistance of 3.6K?
I saw that you were talking to a 3.9k resistor to +4 (hairball VU meter) instead of 3.6K. 
Right?
sorry but I am a beginner ...
anyway thanks for your work, the blue stripe sounds so amazing!!

There is a system to test the compressor and its calibration with ProTools?
THANKS