[BUILD] 1176LN Rev D DIY

[Echo North]

I just tried this and it made no difference; still measuring 0.07 VDC at TP1.

But... R4 is measuring 12.5Ω instead of 270Ω. The color coding is the same as R41, so I don't think I swapped resistors with another one somewhere in the circuit. Guess I missed it when originally checking the resistor values.

You should be measuring for AC at TP1. 0.07 V AC at TP 1 wouldn't be that odd, usually it's closer to 0.1 but you probably have the older blue tpad so 0.07 AC would be ok.

You can't measure resistors in circuit unless you're willing to figure out the parallel resistance math. You'd have to left a leg off the PCB to measure it.

Mike

 

[jefepeters]

You should be measuring for AC at TP1. 0.07 V AC at TP 1 wouldn't be that odd, usually it's closer to 0.1 but you probably have the older blue tpad so 0.07 AC would be ok.

You can't measure resistors in circuit unless you're willing to figure out the parallel resistance math. You'd have to left a leg off the PCB to measure it.

Mike

Thanks for the corrections, Mike. I guess I shouldn't be troubleshooting at 11pm on a Sunday night.

Although I wrote DC, I was actually measuring AC volts. So, just to clarify, as you saying the AC voltages for the amplification stage (which remained the same when Q1 was removed from the circuit) are ok?


TP1  : 0.67 VAC
TP15 : 1.40 VAC
TP17 : 0.16 VAC
BRN  : 2.98 VAC
XLR  : 2.97 VAC

 

[Echo North]

Hard to say because you have an older unit and the pots have a different sweep.

What are those measurements if you rotate the input and the output up to the next dot on the scale?  One dot higher.

Mike

 

[jefepeters]

Hard to say because you have an older unit and the pots have a different sweep.

What are those measurements if you rotate the input and the output up to the next dot on the scale?  One dot higher.

Mike

With both the input and output one dot higher I get:

TP1  : 0.088 VAC
TP15 : 1.732 VAC
TP17 : 0.233 VAC
BRN  : 4.289 VAC
XLR  : 4.276 VAC

 

[Echo North]

With both the input and output one dot higher I get:

TP1  : 0.088 VAC
TP15 : 1.732 VAC
TP17 : 0.233 VAC
BRN  : 4.289 VAC
XLR  : 4.276 VAC

All that seems ok to me.  If it was one of our current units, I'd say it was a little low, but these older units have different pots and this all seems within reason.

So let's reset.

1. Based on this, you should be passing decent clean signal with GR off correct?
2. What is your current issue/problem with the unit?

Mike

 

[dcjams]

Hello

Apologies in advance if I'm polluting this thread with something OT.

Is this the correct build thread for the "Mnats" 1176 clone PCB marked "revision H"?

I realise it says "rev d" up at the top there but I'm not sure if this refers to original Urei revisions or Mnats revisions.

If it os then I'll go to page 1 and start reading ... all 273 pages ...  :-\

Thanks
Jim

 

[Echo North]

Hello

Apologies in advance if I'm polluting this thread with something OT.

Is this the correct build thread for the "Mnats" 1176 clone PCB marked "revision H"?

I realise it says "rev d" up at the top there but I'm not sure if this refers to original Urei revisions or Mnats revisions.

If it os then I'll go to page 1 and start reading ... all 273 pages ...  :-\

Thanks
Jim

Sounds like a really old MNATS PCB.

The best place to post would be the All Things G1176 thread:

https://groupdiy.com/index.php?topic=646.0

Mike

 

[dcjams]

Sounds like a really old MNATS PCB.

Very!

Thanks Mike

 

[jefepeters]

All that seems ok to me.  If it was one of our current units, I'd say it was a little low, but these older units have different pots and this all seems within reason.

So let's reset.

1. Based on this, you should be passing decent clean signal with GR off correct?
2. What is your current issue/problem with the unit?

Mike

1. Yes
2. When I removed Q1 I damaged one of the legs. After installing a new matched pair of FETs and doing the alignment, the compressor is behaving much more as expected -- I don't have to turn the input past 1 o'clock or so to begin compressing.  The output pot is still scratchy, but that's more annoying than causing problems.

So, I guess I'm good to go. I'm going to run it a bit, and then try aligning again. I couldn't get the meter to accurately measure both 0dB and -10dB of compression. But I won't worry about it for now.

Thanks for all your help, Mike.

-Justin

 

[EUC]

I have a Rev D that I built back in 2013 and sadly haven't used all that often. I'm in the process of trying to use it some more and have some issues. First off I can calibrate it just fine through all three steps. All dc voltages are where they should be according to the schematic. Here's the thing that is bizarre. I turn on the unit and let it warm up. Sometimes the meter when in GR pings the +3 db and stays there. If I  push on the the GR button in and out or wiggle it around it resolves back to 0db and all the readings work great. However, if I move it back to +4 then push GR button again often times it goes to +3 and stays or sometimes it goes to  0db. If it's pinged to +3 the gr metering still works it's just obviously off.  This also can happen sometimes if I turn the attack off or if I tap on the unit casing.  I thought maybe it was an issue with the GR Meter board but all seems good on the solders there. Any thoughts?

 

[weiss]

I have a Rev D that I built back in 2013 and sadly haven't used all that often. I'm in the process of trying to use it some more and have some issues. First off I can calibrate it just fine through all three steps. All dc voltages are where they should be according to the schematic. Here's the thing that is bizarre. I turn on the unit and let it warm up. Sometimes the meter when in GR pings the +3 db and stays there. If I  push on the the GR button in and out or wiggle it around it resolves back to 0db and all the readings work great. However, if I move it back to +4 then push GR button again often times it goes to +3 and stays or sometimes it goes to  0db. If it's pinged to +3 the gr metering still works it's just obviously off.  This also can happen sometimes if I turn the attack off or if I tap on the unit casing.  I thought maybe it was an issue with the GR Meter board but all seems good on the solders there. Any thoughts?

did you check your grounds?

 

[weiss]

does anybody know how i have to wire this older H Pad?
i can't see +/- on the markings..

 

[EUC]

Yes I did check grounds but I'll give them another look over

 

[weiss]

does anybody know how i have to wire this older H Pad?
i can't see +/- on the markings..

anyone?  ???

 

[scott2000]

I don't have one....found this though????

https://groupdiy.com/index.php?topic=20058.1340

If I see something , I'll post...I'm sure Mike will jump in after the bump.....

you have this board???

 

[weiss]

I don't have one....found this though????

https://groupdiy.com/index.php?topic=20058.1340

If I see something , I'll post...I'm sure Mike will jump in after the bump.....

you have this board???

oh yes!! exactly what i have although i'm still not sure about the J2 connection on the right..  ???

 

[scott2000]

I hope you figure it out...

This one post said....

If you aren't using the Altran you will have to refer to your particular transformer datasheet. That is one reason why the polarity of these early boards is not marked, while the current ones supplied by Hairball - which are only designed for the Altran - are.

 

[ilfungo]

Hi
C3 and C6 are 200pf mica.
I've 250pf mica caps, could work?
Thanks!

 

[Echo North]

Hi
C3 and C6 are 200pf mica.
I've 250pf mica caps, could work?
Thanks!

I think that would fine.

 

[trashcanman]

I'm working on a build of the Rev D that I started from scratch using my own boards. I used mnats Rev D schematic as reference and copied his layout quite a bit minus the power supply as I'm building a dual unit and have a single supply for both channels. I initially had no trouble with it and recall being able to complete the first calibration step but I've since tidied up the wiring a bit and now my preamp section doesn't seem to be preamping.
If I input a .776VAC 1Khz sine I get about 100mV at the positive input of the board with the input attenuator up to max. I'm using a stepped attenuator that I made myself so that may be why it's not 129mV at midpoint as suggested by the Hairball troubleshooting guide.
My input transformer is a Lundahl 1540 in 2:1 step-down configuration. With the input attenuator at max I get 776mV at the + transformer input and ~100mV at + output of transformer. Not sure if this is too low and the cause of the problem.

Following the troubleshooting guide but with input and output controls at max my readings are:

TP1 = ~100mV AC
TP15 = ~110mV AC
TP17 = ~110mV AC
Output TX Brown = 2V AC

So it seems like the Line Amp is working. I checked DC voltages for the preamp transistors and they all seem to be within tolerance

Q2 - C=1.77V,  B=1.02V,  E=0.49V
Q3 - C=12.52V,  B=1.77V,  E=1.13V
Q14 - C=30.11V,  B=12.52V,  E=11.89V

My Q-bias voltage at Pad 18 is -3.1VDC fully CCW and goes to 0VDC fully CW and affects the voltage at Pad 15.
Q1 gate voltage is -2.6VDC.
I'm thinking there's a problem with Q1 or my input transformer/attenuator but before I take everything apart to test it I thought I'd see if anyone had a second opinion.

Also I may have an issue with my grounding. I have the main pcb ground wired to the chassis at the IEC ground point and with power off I'm getting 0ohms from ground to chassis everywhere, but when powered on it's almost an ohm on the main board and goes negative at 0V on the psu. Is that normal?