MicDaddy

Re: 1176 Rev A - Back to the beginning...
« Reply #1040 on: July 14, 2011, 12:47:32 PM »
pictures always help, and are just plain fun to look over  :)


Hairball Audio

Re: 1176 Rev A - Back to the beginning...
« Reply #1041 on: July 14, 2011, 12:51:43 PM »
Double (triple) check your resistor values in the line amp section.  Look for shorts.

Mike
Hairball Audio, LLC
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evilcat

Re: 1176 Rev A - Back to the beginning...
« Reply #1042 on: July 14, 2011, 01:41:00 PM »
Change Q6, if I remember correctly what I read about burning R32, it's a wrong output xfrm wiring or a falsy Q6, so if your wiring is correct, then swap Q6 ! Good luck.

Ben

Re: 1176 Rev A - Back to the beginning...
« Reply #1043 on: July 14, 2011, 03:02:43 PM »
YEP! Q6 was DOA from the factory.

now onto everything else lol.

Chris

Re: 1176 Rev A - Back to the beginning...
« Reply #1044 on: July 15, 2011, 07:58:03 AM »
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


That Helped!!! Thanks a lot!!

Re: 1176 Rev A - Back to the beginning...
« Reply #1045 on: July 16, 2011, 07:19:45 PM »
Hey Guys
So on this very topic.....

I just finally got all the audio passing correctly, no distortion. set the Q bias according to the instructions and also as i did with my two other 1176s now im trying to get the GR tracking happening. ANd no matter what i do i dont get a drop of more than 4db when switching the bypass on and off. Id ont have the unit in front of me at the moment but this sounds like a Ratio board resistor value or something? Anybody had this before?

Thanks!

Chris


ChrioN

Re: 1176 Rev A - Back to the beginning...
« Reply #1046 on: August 09, 2011, 12:45:12 PM »
This is so strange. Signal disappears after the input transformer. All resistor values checks out.

Anything obvious going on?
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

MicDaddy

Re: 1176 Rev A - Back to the beginning...
« Reply #1047 on: August 09, 2011, 01:07:53 PM »
This is so strange. Signal disappears after the input transformer. All resistor values checks out.

Anything obvious going on?

You see audio on the input side of the transformer but not on the other side?

ChrioN

Re: 1176 Rev A - Back to the beginning...
« Reply #1048 on: August 09, 2011, 01:10:16 PM »
Yes, measuring on the pcb at the input pads, no signal. I've tried two transformers, same problem.
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

MicDaddy

Re: 1176 Rev A - Back to the beginning...
« Reply #1049 on: August 09, 2011, 01:14:32 PM »
Yes, measuring on the pcb at the input pads, no signal. I've tried two transformers, same problem.

Transformer is oriented correctly on pcb?  I believe there's a black dot on the sticker side which should face either output or input  (I want to say output side but don't remember).

+/-/shield are terminated properly on the trafo pcb with no shorts? 

Sorry if this is elementary I'm just trying to lay out what I would check.

If you find that everything is oriented and correct, I'd remove the wires from the output side of the input transformer, and make sure I'm seeing audio at this point.
« Last Edit: August 09, 2011, 01:18:23 PM by MicDaddy »


ChrioN

Re: 1176 Rev A - Back to the beginning...
« Reply #1050 on: August 09, 2011, 01:18:04 PM »
Yes to all questions, and yes I've measured at the output pins of the input transformer, so no wire problems.

It often is the elementary parts that is the problem. Any other suggestions? I apreciate it. Thanks.
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

MicDaddy

Re: 1176 Rev A - Back to the beginning...
« Reply #1051 on: August 09, 2011, 01:20:00 PM »
Yes to all questions, and yes I've measured at the output pins of the input transformer, so no wire problems.

It often is the elementary parts that is the problem. Any other suggestions? I apreciate it. Thanks.

Ok I believe next thing in the path is the Tpad?  Do you see the audio on the input/output here?  Is the input knob turned up?

ChrioN

Re: 1176 Rev A - Back to the beginning...
« Reply #1052 on: August 09, 2011, 01:30:01 PM »
Note that the t-pad comes before the input transformer. No problems there. Its after the input transformer the signal gets lost.
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

MicDaddy

Re: 1176 Rev A - Back to the beginning...
« Reply #1053 on: August 09, 2011, 01:39:29 PM »
Note that the t-pad comes before the input transformer. No problems there. Its after the input transformer the signal gets lost.

 ::)  been awhile since I've been inside her...  (insert joke here)

the leads from the input that terminate at the pcb....  with these removed do you see signal on these wires?

ChrioN

Re: 1176 Rev A - Back to the beginning...
« Reply #1054 on: August 09, 2011, 02:10:57 PM »
Note that the t-pad comes before the input transformer. No problems there. Its after the input transformer the signal gets lost.

 ::)  been awhile since I've been inside her...  (insert joke here)

the leads from the input that terminate at the pcb....  with these removed do you see signal on these wires?

Yes, there is a signal when the wires ain't terminated to the pcb so the problem should be somewhere on the pcb.
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

MicDaddy

Re: 1176 Rev A - Back to the beginning...
« Reply #1055 on: August 09, 2011, 02:24:35 PM »

Yes, there is a signal when the wires ain't terminated to the pcb so the problem should be somewhere on the pcb.

And with the wires terminated no signal at those pads?  Sorry for my dragging out of where you seem to have already laid out in your first post, trying to get up to speed and rule out simple stuff.  pics?

ChrioN

Re: 1176 Rev A - Back to the beginning...
« Reply #1056 on: August 09, 2011, 02:36:08 PM »
You got it right.
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

ChrioN

Re: 1176 Rev A - Back to the beginning...
« Reply #1057 on: August 10, 2011, 03:51:08 PM »
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.
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

onlymeeee

Re: 1176 Rev A - Back to the beginning...
« Reply #1058 on: August 10, 2011, 06:49:40 PM »
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 ?

MicDaddy

Re: 1176 Rev A - Back to the beginning...
« Reply #1059 on: August 10, 2011, 06:58:56 PM »
It looks to me, from your diagram, you have pin 3 input XLR terminating to the + side where it should be pin 2 to the +

Maybe it makes no difference...?


 

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