[BUILD] 1176LN Rev D DIY

[Echo North]

I used 3707's , bought about 60 of them , went through them for hFE , my Fluke meter doesn't check hFE , I got a cheep meter that does from eBay - maybe its not accurate 

I doubt it's that but I'll figure out a way to test that.

 

[Echo North]

This weekend I'll get a spare second and I'll go test what the control voltage and threshhold voltages should be and we'll see if maybe your control V is too low or your treshhold voltages is too high (meaning too low).

Mike

 

[audiophreak]

Awesome !!!  Thank You   

EDIT :  I'll continue to read and search too ... ( you know ... endlessly starring at the schematic waiting for something to jump out and smack me in head ) 

 

[audiophreak]

well ... nothing smacked me in the head ,  but thought about a few things , thought I would share my unverified thoughts to see what you think.

  In reading the conversations indicated and re-reading this "

Ok, here is how I understand it. 

There are two ladders/voltage dividers in the ratio switch.  Referring to the MNATS schematic,  divider A acts as a voltage divider for the AC leaving the preamp and entering the control amp.  As you decrease the ratio 20 to 4 you incorporate more resistors and decrease the AC level.  This effectively sets the ratio.  Without getting too much into it, a smaller AC level in this control amp in conjunction with the threshold, will yield a lower ratio.  This is fine with your circuit I believe.  With an input signal, switching the ratios down, you should see decreased AC at pad 22.

Ok now on to divider B.  This sets the threshold which is basically a negative DC offset voltage.  The threshold is fixed.  It decreases with the 20-4 ratio selection.  See the image below.  The -10VDC rail is connected to this network.  The lower the ratio, the lower the offset (more resistors to go through).  At a ratio of 20, this offset must travel through R64.  In my circuit, I get a 4VDC drop across this resistor.  You are getting none.  This is a huge issue, because having a -10VDC offset will mean it'll be impossible to get over the threshold.  It'll just be set way too high.  The more negative the offset the higher the threshold.

So what's the problem?

Well your negative rail could be shorted to that point somehow.  R64 could be shorted but then switching ratio's would get the other resistors involved.  You might not have a DC path to ground and have no flowing current.  Check your current through R64.  You should have like 3.2mA.

Start fishing around that part of the circuit.

      In the above quote if the negative DC offset voltage sets internal threshold, maybe I could lower my -10vdc from PSU ( using mnats alt PSU with trimmers )  in theory lowering the threshold, then doing the calibrations to see if there is a difference ... not sure if this will damage any components or not. 

  In the test Mike gave me with measuring input and output voltage , the meter was reading the proper GR as voltages indicated.

    so I was thinking ( Dangerous )  ;D  that if the 3k6 resistor sets the meter for +4 , maybe my meter already has  some sort of internal resistor and with the 3k6 makes its reading more like +8 , therefore throwing off calibrations and needing a huge input signal to achieve a slight amount of GR. would I damage anything by removing the 3k6 resistor ?

  any thoughts on these sort of tests ???

    EDIT : not necessarily to solve anything , just for more data as to where the problem may be.

 

[Echo North]

Don't mess with your supply rail, it also sets your Qbias.

I forget that you do have a unknown meter.  Switch it to +4. Feed in a signal and do what ever you need to do in GR off to see 1.24VAC between output pins 2 and 3.  What so you see on your meter in +4?  Should be 0.

Also set you Qbias using your DMM rather than your meter.  Follow these steps to set your Qbias:

If you have a version with the "off" switch on the attack pot, you can just switch that.  Otherwise short pads 22 to ground.  Feed a 1khz signal into the input at about 0dBu.  You can put your DMM across input xlr pin 2 and 3 and look for 0.775VAC which is about 0dbu.  Your DAW might say it's sending out a -16dBu FS signal or something.  Just do what ever you need to do to get 0.775 VAC across 2 and 3 at the input.  Again you'll see impedance loss no matter what with a 600Ω input like the 1176.

Now put your DMM across pin 2 and 3 on the output xlr and turn the qbias (in and out knob mid way).  You should see the output moving up or down.  Turn the bias until it gets to the max and doesn't get any higher. 

Then adjust the output knob so you see +11dbu (2.75VAC) at the output pin 2 and 3.  Now pull the qbias back until you get a 1dbu drop 10dbu (2.45VAC).  That will set your bias.

 

[Che_Guitarra]

Just wanting to say I got my rev D back today.  I spent 4 months looking at it trying to work out the bug in the system before I finally gave up and took it to a pro audio repairer.  Turns out I had two broken traces/tracks on the PCB... that'll do it.

Anyway, it's fixed now and sounding fantastic  8)

 

[jplebre]

Just wanting to say I got my rev D back today.  I spent 4 months looking at it trying to work out the bug in the system before I finally gave up and took it to a pro audio repairer.  Turns out I had two broken traces/tracks on the PCB... that'll do it.

Anyway, it's fixed now and sounding fantastic  8)

was your problem only loss of input, or were there other issues?

 

[Che_Guitarra]

I never got to ask to the repairer (he has monday's off), but the receipt notes say 'found two broken tracks on PCB, repaired broken tracks'.

 

[audiophreak]

Hi Mike ,
            I'm back and was able to do the tests you described, adjusted to get +1.24vac at output and meter reads "0" , so i think the meter is ok.

    I did the QBias as you described and then the Discrete Meter circuit adjustment , but when I did the Gain Reduction meter tracking I got about a 6db GR with input almost all the way up and output almost all the way down ... so about a 1db difference from before.

  I continued with my thoughts that the " Internal Threshold"  is somehow too high and did the Gain Reduction meter tracking with +4 ( 1.23vac ) was juuuust able to get -10db in the  Gain Reduction meter tracking calibration procedure with input almost all the way up and output almost all the way down, then went to +6 ( 1.55vac) and was able to get the -10db with input control at 2:30 position and output at 8:00 position , then +8db (1.94vac) input at  1:30 position and output at 8:00 position , then at +10db ( 2.45vac) input at 1:00 position and output at 8:00 position.

  So it seems to me that the internal threshold seems to be too high there for needing a huge input signal to see any GR , I have verified all the resistors and the cap on the ratio PCB ,  what else would make the threshold too high ??

  or any other thoughts ...


  Thanks so much

 

[Echo North]

It's not necessarily  a threshold issue.  A lot of amplification happens to your signal before it gets set against the threshold so it may be an amplification issue.

Do all of your transistor DC values check out against the MNATS schematic w/ voltages?

Mike

 

[audiophreak]

Yes, a few were a little off , I posted my voltages a page or two back , there were a couple that were like 1v off but none more than that.
   
  I will re-check and post back.

Thanks

 

[audiophreak]

Yes, re-checked all listed voltages on mnats schematic , all within a few 10ths of what I previously posted :

Q3 - C=11.58vdc ( schematic states 12.58vdc )
Q14 - B = 11.58vdc  ( schematic states 12.58vdc )
Q4 - C = 4.91vdc  ( schematic states 4.2vdc )
Q5 - C = 25.09vdc ( schematic states 26.18vdc )
Q6 - C = 27.44vdc  ( schematic states 28.93vdc )
Q11 - D = 11.21vdc ( schematic states 10.56vdc )
Q12 - C = 10.43vdc ( schematic states 9.28vdc )
Q13 - B = -0.94vdc ( schematic states -1.04vdc ) and C = 10.58 ( schematic states 9.75vdc ) and E = -1.51 ( schematic states -1.63vdc )
Q7 - C = 14.86vdc ( schematic states 15.25vdc )
Q8 - B = 14.86 ( schematic states 15.25vdc ) and E = 14.23vdc ( schematic states 14.7vdc )

  ... it doesn't seem like they're off by much
 
  All other  voltages are spot on or off by a few 10ths

    is this out of tolerance ??? 


EDIT :  tested with no input signal IP and OP controls at 12:00  attack full CCW ( does NOT have the " OFF " switch ) release at full CW  and meter mode in GR

 

[Echo North]

Sorry for the delays.  I'll get some tests in this weekend and we'll figure out if it's a threshold or GR amp issue.

Mike

 

[mnats]

I continued with my thoughts that the " Internal Threshold"  is somehow too high and did the Gain Reduction meter tracking with +4 ( 1.23vac ) was juuuust able to get -10db in the  Gain Reduction meter tracking calibration procedure with input almost all the way up and output almost all the way down, then went to +6 ( 1.55vac) and was able to get the -10db with input control at 2:30 position and output at 8:00 position , then +8db (1.94vac) input at  1:30 position and output at 8:00 position , then at +10db ( 2.45vac) input at 1:00 position and output at 8:00 position.

I wonder what you are using to measure the AC voltages in the circuit? In my videos, I use an AC voltmeter that can measure up to 10MHz with precision. Mike often recommends using an ordinary digital multimeter. At the time when I made the video, few DMMs could measure even a 1kHz AC voltage with any accuracy. I'm not sure whether the situation has changed much in the intervening years.

You might have also seen that I use two signal generators in the videos - one an ancient HP unit and another cheap Asian unit purchased locally. Nowhere have I ever suggested you use the output of your computer audio device to do the calibrations. The reason is that many devices simply aren't capable of driving the 600 Ohm input of the limiter as easily as a purpose-made device. I think you saw this earlier when you tried to drive the input to 0dBm.

You've shown that the unit is capable of -10dB gain reduction. What is unclear is whether you have measured the signal levels precisely or not, given the unknown test instruments or lack thereof...

 

[audiophreak]

Thanks mnats,
      I am not testing with with a DAW , this is the multimeter I use - http://www.testequipmentdepot.com/fluke/dmm/115.htm?ref=gbase&gclid=CIvL_vzHmrgCFQ1xQgodM38A0w
( with fresh battery )
  and this is one of two signal generators that I am using- http://www.parts-express.com/pe/showdetl.cfm?partnumber=392-200
  ... I swapped out Q1 and Q11 with two that didnt cut it from the matching processes ... getting some inspiration from your Rev.D page  "  so accurate matching of these parts might not be essential. You may wish to select FETs for a particular threshold range. "  ( thinking I have a Threshold Issue )...and when I readjusted the QBias it only took 10 turns of the trimmer ( from furthest from ground) instead of the 18 turns it took prior, to get the 1db drop on the VU meter ( from +1 to 0db) .
  The NULL adjustment did not change , and when I did the Gain Reduction meter tracking adjustment, this time was able to get -7db with input control almost all the way up and output control almost all the way down, so slightly better, but still not correct.

... as Mike stated a few posts back , I need to step away and clear my head, work is taking my next couple of days, so wont be able to get back to this till Monday or Tuesday. 
  Your documentation and calibration videos are awesome , I just wish my signal tracing and circuit trouble shooting skills ( or lack of ) were a little better  ;D

Thanks,
            Chip


 
 
 

 

[LHS]

Hello,
I'm wiring my ground to chassis and reading the hairball FET guide (which is great btw).
He mentions "the toothed lug included in the mouser cart" but I can't seem to find it in the bom or my mouser invoice. Does anybody have the mouser part # for that lug?

 

[Echo North]

Hello,
I'm wiring my ground to chassis and reading the hairball FET guide (which is great btw).
He mentions "the toothed lug included in the mouser cart" but I can't seem to find it in the bom or my mouser invoice. Does anybody have the mouser part # for that lug?

It was recently added in the past month or so.  Maybe you ordered your kit a few months back?

Mouser part: 534-7316

 

[LHS]

fantastic thanks  8)

 

[mitsos]

I've had some issues with a dual/stereo unit I built ages ago... comes and goes, I've checked it multiple times, and my next step is to remove the stereolink boards to see if they are responsible.. In converting it to dual mono only, after removing the stereo link boards, is it only a matter of reconnecting the output pot wire to the ratio board?

or is there anything else I need to rewire? It's been a while since I've been in this thing and I'm a bit rusty on the wiring..

thanks!

 

[Echo North]

I've had some issues with a dual/stereo unit I built ages ago... comes and goes, I've checked it multiple times, and my next step is to remove the stereolink boards to see if they are responsible.. In converting it to dual mono only, after removing the stereo link boards, is it only a matter of reconnecting the output pot wire to the ratio board?

or is there anything else I need to rewire? It's been a while since I've been in this thing and I'm a bit rusty on the wiring..

thanks!

Yes pad 15.

Are you using a switch?  In "non-link" mode it should be bypassed.