[BUILD] 1176LN Rev D DIY

[Sillen]

Photo of top pcb:

http://cdn.imghack.se/images/b916a5271e23115aeccadd5a2e0d292f.jpg

 

[jplebre]

At first glance C7 is the wrong way around. which transistors did you use?

 

[Sillen]

I used 3708's.

 

[ln76d]

I assume that you checked all resistors and capacitor values...
Transistors:
2n3708 are well placed
Did you use 2n3391 or equivalent?
Did you placed in proper order all bipolar transistors?
What FET did you use? If 2n5457 - both are wrong placed.
Yes, C7 is wrong placed. Also check tantal capacitors polarization, cause i don't see them from this angle.
For C7, C10, C17 is better to use film caps.

 

[Sillen]

I assume that you checked all resistors and capacitor values...
Transistors:
2n3708 are well placed
Did you use 2n3391 or equivalent?
Did you placed in proper order all bipolar transistors?
What FET did you use? If 2n5457 - both are wrong placed.
Yes, C7 is wrong placed. Also check tantal capacitors polarization, cause i don't see them from this angle.
For C7, C10, C17 is better to use film caps.

Fixed C7 polarity.
Tantalum caps are set with correct polarity.
Yeah it's 2n5457s. How should they be placed? Just the other way arround?

 

[ln76d]

Yes, only reversed. You have drawings of proper placement on pcb. Half of the circle which looks like transistor from the top.

 

[Sillen]

Something is still weird  :-\ The gate of Fet Q1 has a negative value now though. The Ac of xlr output should differ whatever way I turn the Q bias trimmer I think, ye?

 

[jplebre]

The Ac of xlr output should differ whatever way I turn the Q bias trimmer I think, ye?

not exactly. The bias could be above the signal and that way the fet won't be conducting.

Turning it will only affect the o/p signal (more or less signal) if it's in the fet conductive range. it would be quite a few turns before it happens.

Make sure you are feeding hot enough signal as well (see Mnats guides)

 

[Sillen]

Do you mean in his calibration videos? There is no calibration-guide else from mnats that I found. How do I know if it's hot enough?

 

[ln76d]

Do you mean in his calibration videos? There is no calibration-guide else from mnats that I found. How do I know if it's hot enough?

This will be usefull:

http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/UREI-1176LNmanual.pdf

 

[Sillen]

yey I managed to do the qbias adjustment now Finished step 2 as well! But there's a problem at the Gain reduction meter tracking adjustment. Ihave troubles zeroing the meter with R71. It just goes up to -4 when it's fully CW.

 

[jplebre]

did you do null adjustment correctly and then put the jumper back in place? (just covering all bases)

 

[Sillen]

Yeah null adjustment was done correctly and tracking adjustment trimmer was put back in circuit afterwards.

 

[mitsos]

Thanks for the confirmation... working fine now.. I did have a toggle switch for the link, and it worked fine, but something was not right about the unit.  It actually worked fine at my place, but I had it at my friend's for a few months and it would act up there.  Once in a while the VU would go from 0 to about -3 and sort of fluctuate back forth a bit (like between -2.5 and -3.5 or so). This was with the meter in GR (of course) with or without signal, sort of like -3 was the new 0.  In the end, I think it was compressing, I'm waiting for my friend to send me a vocal he ran through this unit where it happened in the middle of it.

Anyway, I can't say for sure that it was the link circuit, but with so many wires in this box (2 channels in 2U), one less thing will at least make it easier to troubleshoot if it happens again.  So far though it's been on for a couple of hours and needles are set at 0. Fingers crossed.

thanks!

OK, left the unit at "friend A's" studio for a few days. That's where it was having the problem. Presented the VU issue after a couple of days, I picked it up and left it at Friend B's studio to rule out studio/power issues because he's had some PSU problems in a couple of other pieces of gear.  Anyway, here again, it was working fine for a couple of days, then, yesterday, while I was there, I glanced down, and the needles were at -3... This is with VU in GR mode, no input, controls have no affect.  I opened it up as quickly as possible to take some voltages, and proceeded to check the PSU first.  As soon as I touched my DMM probe to the -10V output (mnats PSU), the needles went back to 0...  all transistor voltages were in line with voltage chart... but I expected as much because the VUs were already back to normal.

I'm at a loss how to proceed with this, I guess next time it does it I'll measure the GR Fet voltages first...  Anyone have an idea?

thanks!

 

[audiophreak]

Well ... I replaced all the the 3707's with 5088's in the correct pads and replaced the 5457's with another matched set purchased from another source, verified all components on ratio board  -  it changed absolutely nothing 
  I then swapped out the ratio PCB with the one from my Rev.Js  as it used the Lorlin switch in stead of the "slam " switch ( in case I wired it wrong )  ... and no change 
  what I am getting is the QBias and Null adjust procedures go as per mnats calibration videos , but the Gain Reduction meter tracking adjustment - I can only get -5db Gain Reduction , measured the output with GR off ( pad 22 shorted ) - 1k 0db on input XLR , IP and OP controls at 12:00 , the OP control adjusted to 0 on meter I read +1.246 on OP XLR ( aprox +4 )  , then unshorted pad 22 engaging GR , input control almost all the way up and out set to 0 on meter ( almost all the way down ) I get -5db on meter , then measured at OP XLR and got +0.694 ( apro. -1db )  , I assume because meter mode is in VU ?

  So today I pulled the main PCB out and verified all resistors in both GR meter driver and GR control amp sections - all checked as they should be, I had a Lytic in C17 , replaced with a poly while I was there , can not test pf caps - DMM doesn't go that low 

  Before I pulled the main PCB I checked all voltages as per mnats schematic  , all the same as I posted back on pages 188 and 190.

  I check and tested all the components before I installed them on the PCBs, not that I couldn't have made a mistake ,  but the test point voltages are either spot on or slightly off .

  are the voltages that are slightly off a concern ??

  before I reinstall main PCB any Idea's on where I should check / test next ?? 

really hitt'n a brick wall here  :-[

would really appreciate any help with this

 
 
   

 

[Echo North]

Well ... I replaced all the the 3707's with 5088's in the correct pads and replaced the 5457's with another matched set purchased from another source, verified all components on ratio board  -  it changed absolutely nothing 
  I then swapped out the ratio PCB with the one from my Rev.Js  as it used the Lorlin switch in stead of the "slam " switch ( in case I wired it wrong )  ... and no change 
  what I am getting is the QBias and Null adjust procedures go as per mnats calibration videos , but the Gain Reduction meter tracking adjustment - I can only get -5db Gain Reduction , measured the output with GR off ( pad 22 shorted ) - 1k 0db on input XLR , IP and OP controls at 12:00 , the OP control adjusted to 0 on meter I read +1.246 on OP XLR ( aprox +4 )  , then unshorted pad 22 engaging GR , input control almost all the way up and out set to 0 on meter ( almost all the way down ) I get -5db on meter , then measured at OP XLR and got +0.694 ( apro. -1db )  , I assume because meter mode is in VU ?

  So today I pulled the main PCB out and verified all resistors in both GR meter driver and GR control amp sections - all checked as they should be, I had a Lytic in C17 , replaced with a poly while I was there , can not test pf caps - DMM doesn't go that low 

  Before I pulled the main PCB I checked all voltages as per mnats schematic  , all the same as I posted back on pages 188 and 190.

  I check and tested all the components before I installed them on the PCBs, not that I couldn't have made a mistake ,  but the test point voltages are either spot on or slightly off .

  are the voltages that are slightly off a concern ??

  before I reinstall main PCB any Idea's on where I should check / test next ?? 

really hitt'n a brick wall here  :-[

would really appreciate any help with this

 
 
 

Did you triple check your ratio PCB resistors?

I actually don't have a D right now.  I'm building one monday.  We can do over some voltages.

Mike

 

[audiophreak]

Yes , all ratio PCB components checked and verified , I'm out till Sunday but have Mon,Tues,Wed off.
  really appreciate the help Mike

 

[mnats]

Well ... I replaced all the the 3707's with 5088's in the correct pads and replaced the 5457's with another matched set purchased from another source, verified all components on ratio board  -  it changed absolutely nothing 
  I then swapped out the ratio PCB with the one from my Rev.Js  as it used the Lorlin switch in stead of the "slam " switch ( in case I wired it wrong )  ... and no change 
  what I am getting is the QBias and Null adjust procedures go as per mnats calibration videos , but the Gain Reduction meter tracking adjustment - I can only get -5db Gain Reduction , measured the output with GR off ( pad 22 shorted ) - 1k 0db on input XLR , IP and OP controls at 12:00 , the OP control adjusted to 0 on meter I read +1.246 on OP XLR ( aprox +4 )  , then unshorted pad 22 engaging GR , input control almost all the way up and out set to 0 on meter ( almost all the way down ) I get -5db on meter , then measured at OP XLR and got +0.694 ( apro. -1db )  , I assume because meter mode is in VU ?

  So today I pulled the main PCB out and verified all resistors in both GR meter driver and GR control amp sections - all checked as they should be, I had a Lytic in C17 , replaced with a poly while I was there , can not test pf caps - DMM doesn't go that low 

  Before I pulled the main PCB I checked all voltages as per mnats schematic  , all the same as I posted back on pages 188 and 190.

  I check and tested all the components before I installed them on the PCBs, not that I couldn't have made a mistake ,  but the test point voltages are either spot on or slightly off .

  are the voltages that are slightly off a concern ??

  before I reinstall main PCB any Idea's on where I should check / test next ?? 

really hitt'n a brick wall here  :-[

would really appreciate any help with this
   

That kind of shotgun approach is rarely, if ever, productive. Since your transistor voltages were already within 10% there was never any need to swap them out, as you learned.

To recap, your unit works but with only produce 10dB of gain reduction when the input is extremely high, right?

We determined that your readings are being performed with correctly functioning test equipment, right?

So first measure your gate voltage at the GR FET with no input and the Q bias already adjusted.

Now slam the unit with a signal that will produce 10dB or so of gain reduction. With that in place measure the AC voltage at the XLR input (pins 2 and 3), after the T attenuator/input transformer at the signal preamp input (marked INPUT on my Rev D PCB) referenced to ground, at the input of the GR control amp section (pad 22 on the Rev D PCB) and finally the DC voltage at the gate of the GR FET again.

Then we can compare voltages. That should isolate the problem.

 

[mnats]

Thanks for the confirmation... working fine now.. I did have a toggle switch for the link, and it worked fine, but something was not right about the unit.  It actually worked fine at my place, but I had it at my friend's for a few months and it would act up there.  Once in a while the VU would go from 0 to about -3 and sort of fluctuate back forth a bit (like between -2.5 and -3.5 or so). This was with the meter in GR (of course) with or without signal, sort of like -3 was the new 0.  In the end, I think it was compressing, I'm waiting for my friend to send me a vocal he ran through this unit where it happened in the middle of it.

Anyway, I can't say for sure that it was the link circuit, but with so many wires in this box (2 channels in 2U), one less thing will at least make it easier to troubleshoot if it happens again.  So far though it's been on for a couple of hours and needles are set at 0. Fingers crossed.

thanks!

OK, left the unit at "friend A's" studio for a few days. That's where it was having the problem. Presented the VU issue after a couple of days, I picked it up and left it at Friend B's studio to rule out studio/power issues because he's had some PSU problems in a couple of other pieces of gear.  Anyway, here again, it was working fine for a couple of days, then, yesterday, while I was there, I glanced down, and the needles were at -3... This is with VU in GR mode, no input, controls have no affect.  I opened it up as quickly as possible to take some voltages, and proceeded to check the PSU first.  As soon as I touched my DMM probe to the -10V output (mnats PSU), the needles went back to 0...  all transistor voltages were in line with voltage chart... but I expected as much because the VUs were already back to normal.

I'm at a loss how to proceed with this, I guess next time it does it I'll measure the GR Fet voltages first...  Anyone have an idea?

thanks!

I read back through your earlier posts but can't determine for sure whether only the meter if affected or whether the unit will also reduce the gain when the meter is spontaneously indicating gain reduction.

But it does sound suspiciously like a bad solder joint. I've seen cases less often where components can show signs of intermittent failure under load but far less often then the former.

*edit* Pop the cover, take the blunt rubber end of a screwdriver and start tapping on various parts of the circuit. Move the wiring around with something insulated. Do this until you see the drop occur. You should be able to isolate the bad joint/short this way.

 

[audiophreak]

Thank you mnats 
    That makes total sense , will take measurements and post back on Monday.