[BUILD] 1176LN Rev D DIY

[Che_Guitarra]

Trace your signal through the circuit.  Feed a 1khz 1VAC signal into the input and set the in/out knobs to the middle.  (couldn't get it hot enough from my UFX, so stuck with 0.775V)

Measure the AC voltage at these points using GROUND as the reference.

1. Input XLR pin 2  767mV
2. + input at the PCB (by C1)  6mV
3. - of C7  6mV
4. Output XLR pin 2  25mV

That's pretty conclusive.  I'm pretty much convinced it's the T-pad now due to the inability to vary the input signal.

 

[Echo North]

Your AC will be a lot smaller at the input (step down TX, balance loss, and attenuation) but 6mV is waaaaaaay too low.  You wanna see something in the 100-300mV range IIRC.

Mike

 

[Echo North]

You can do the same thing with the input.  Measure the AC at the XLR, TPAD XLR side +/-, TPAD TX side +/-, primary of the input tx, then the secondary...which is the same as the PCB.

 

[Che_Guitarra]

Firstly, I appreciate your help here Mike, thanks for walking me through this.  You've offered me a big a-ha moment in how to troubleshoot circuit issues with your advice 

So it appears the T-pad is working fine (although it behaves quite strangely compared to a regular pot)... that leaves me with the IT.  The orientation is correct, and with a DMM I can see all is not well on the output side of the trafo.  I'm only getting a reading on one of the four output pins (a constant 104mV) and it's not responding on queue with the input control.

Maybe not what I wanted to find, but at least I know what the problem is now.

 

[Echo North]

Firstly, I appreciate your help here Mike, thanks for walking me through this.  You've offered me a big a-ha moment in how to troubleshoot circuit issues with your advice 

So it appears the T-pad is working fine (although it behaves quite strangely compared to a regular pot)... that leaves me with the IT.  The orientation is correct, and with a DMM I can see all is not well on the output side of the trafo.  I'm only getting a reading on one of the four output pins (a constant 104mV) and it's not responding on queue with the input control.

Maybe not what I wanted to find, but at least I know what the problem is now.

Well one pin is not connected to anything, one is connected to the shield and then your case (ground), the third is connected to ground at your PCB, and the fourth should have a signal.  I'm not sure the issue in your input transformer. 

Disconnect the transformer from the PCB and t-pad.  You can keep it on the PCB.

1. What is your DC resistance in ohms between the two outside pins on the SEC? (+ and - on the PCB)
2. What is your DC resistance between either outside pin and the  inside pin with the wire attached to the can on the SEC?
3. What is your DC resistance between the two outside pins on the PRI? (+ and - on the PCB)
4. What is your DC resistance between either outside pin on the SEC and either outside pin on the PRI?

Should be:
1. 13Ω ish
2. Infinity
3. 50Ω ish
4. Infinity

This is not a definitive test to confirm the transformer is ok, but it's a good baseline.

Mike

 

[Che_Guitarra]

Should be:
1. 13Ω ish 13.7
2. Infinity  √
3. 50Ω ish 52.1
4. Infinity √

This is not a definitive test to confirm the transformer is ok, but it's a good baseline.

Mike

It's looking good then.  I'll reinstall the trafo and reheat all the solders on the input chain... you never know, whilst they look OK it may just be a cold solder (edit - solders reheated, still an issue).

 

[Echo North]

I think the issue somewhere in the first stage of your PCB.

Are you sure the + and - are right on both sides of the transformer.  Note on either side of the PCB the are flipped. 

Is your R4/R5 the right value?

What is your DC voltage at Q1 gate right now?

 

[Che_Guitarra]

I think the issue somewhere in the first stage of your PCB.

Are you sure the + and - are right on both sides of the transformer.  Note on either side of the PCB the are flipped. 
Yes, red wire to positive at each point on the input chain, white to negative

Is your R4/R5 the right value?  Going off the colour coding R4 = 270Ω, R5 = 27KΩ

What is your DC voltage at Q1 gate right now?  670mV

 

[Echo North]

If your Q1 gate voltage is positive that is a problem and would explain why you're dumping so much signal.  That voltage needs to be negative and in the 0.5-1.5V range.  Are you sure you have a positive DC voltage there?

 

[Che_Guitarra]

Sorry, that was a typo - it's definitely a negative reading.

 

[Echo North]

Sorry, that was a typo - it's definitely a negative reading.

Wacky man.  Stumped.  Anyone? Anyone?

Check the continuity in the wires between the input parts for a break or bad joint?  Maybe a bad component/FET.

So with the input tx disconnected from the PCB and a 0.775 VAC signal applied to the input xlr you see how much ACV between the transformer sec + and -?

 

[Che_Guitarra]

I may try a new tact - I have a Rev A board sitting here just waiting to be stuffed with components.  I'll populate the board and then switch out with the Rev D PCB - at least that way the problem can be isolated to being either on the PCB or within the input circuit. 

Due to the observed behaviour, my immediate thought is that it's an issue within the input chain.  No matter how minuscule the difference, if I tweak the input control I should be able to hear the signal morphing, but I can't get an iota of change.  I tested all the PCB components for value before soldering into place so i'm confident they're OK.

Give me a day or two, but if you think of anything in the meantime i'm all ears.

 

[braeden]

Well, I turned my 1176 back on today expecting hours of troubleshooting. I don't know what has occurred between then and now but I am seeing compression in both stereo link mode and normal mono GR operation.

I think there is still a crappy soldering job on some of the output wiring resulting in a thin sound and a 'buzz' in the right channel, but other than that the compression seems to be functioning okay.

But, I am only seeing GR when the slam rotary switch is set to the slam mode (all buttons-in). Is it possible that I have wired my slam switch upside down? I've looked at all of the pictures from mnats but it isn't really conclusive, maybe I should have used some common sense when I put the switch in.

4, 8, 12, 20:1 all show no sign of GR, only all-buttons in (which sounds amazing by the way).

Same for both channels so I'm guessing this is the culprit!

Thanks

 

[Echo North]

I may try a new tact - I have a Rev A board sitting here just waiting to be stuffed with components.  I'll populate the board and then switch out with the Rev D PCB - at least that way the problem can be isolated to being either on the PCB or within the input circuit. 

Due to the observed behaviour, my immediate thought is that it's an issue within the input chain.  No matter how minuscule the difference, if I tweak the input control I should be able to hear the signal morphing, but I can't get an iota of change.  I tested all the PCB components for value before soldering into place so i'm confident they're OK.

Give me a day or two, but if you think of anything in the meantime i'm all ears.

Not a bad idea.

Well for reference I measured my input circuit disconnected from the PCB (you don't even need power on).  With 0.775 VAC across input pin 2 and 3 I get 0.130VAC at the transformer output between + and -.  In the full CW position I get 0.5VAC.  Check yours, that will tell you if the tx is passing signal correctly.

Mike

 

[Echo North]

Well, I turned my 1176 back on today expecting hours of troubleshooting. I don't know what has occurred between then and now but I am seeing compression in both stereo link mode and normal mono GR operation.

I think there is still a crappy soldering job on some of the output wiring resulting in a thin sound and a 'buzz' in the right channel, but other than that the compression seems to be functioning okay.

But, I am only seeing GR when the slam rotary switch is set to the slam mode (all buttons-in). Is it possible that I have wired my slam switch upside down? I've looked at all of the pictures from mnats but it isn't really conclusive, maybe I should have used some common sense when I put the switch in.

4, 8, 12, 20:1 all show no sign of GR, only all-buttons in (which sounds amazing by the way).

Same for both channels so I'm guessing this is the culprit!

Thanks

Is this a rotary version?

 

[Che_Guitarra]

Awesomeness  8)

My Rev A Hairball kit arrived in the mail today, so I just rigged up the input chain (t-pad/input trafo) and fed it into my D.  Hail Mary, I have signal and a moving meter!  Woohoo!

So that's good news... kinda.  At least my Rev D problem is off the PCB and can be isolated to the t-pad or trafo... or my wiring thereof.  I'll strip off the existing wiring, reinstall it, and if I still have a problem there'll be no doubt it's a component issue.

 

[braeden]

Is this a rotary version?

Yeah it is, I don't think I've wired the rotary switch around the wrong way, but I've desoldered everything and I'll try again, hopefully no cold solder joints.
But it beats me as to why the same problem would exist on both channels.

Stumped for now.

 

[Echo North]

Awesomeness  8)

My Rev A Hairball kit arrived in the mail today, so I just rigged up the input chain (t-pad/input trafo) and fed it into my D.  Hail Mary, I have signal and a moving meter!  Woohoo!

So that's good news... kinda.  At least my Rev D problem is off the PCB and can be isolated to the t-pad or trafo... or my wiring thereof.  I'll strip off the existing wiring, reinstall it, and if I still have a problem there'll be no doubt it's a component issue.

Interesting!  Well see if you can isolate it to the t-pad or tx (or either of their PCBs) and I'll get it replaced.

Mike

 

[Sitral]

Hi Guys, I am putting together my order at Mouser (replacing the backordered parts in the linked rev D cart). Unfortunately, the FDH333 diode is not available, which in the BOM is marked with "do not substitute". At Mouser I found the FDH300 diode, which seems to have the same specs. Still no possible substitution? Any experiences or information?

Thanks, Mattia

 

[berkleystudios]

are jensen jt-11p-1 compatible for the input transformers for the rev D? http://www.jensen-transformers.com/datashts/11p1.pdf