[BUILD] FET/500 Official Support Thread

[boneindian]

Try inserting a signal at TP15 and testing the output at output tx brown first, before removing the input tx.  That'll bypass the input and test to see if the line amp and your test setup is working.

First thing I decided to do this morning was look through my signal generator setup.  I've mentioned this a few times, but I'm using the OSC XLR out on the back of my SSL console and routing it to a signal tracer, where I'm clipping the black probe to D4 and putting the probe on whichever point I'm injecting signal at. 

The mnats calibration guide is very adamant about not sending signal to ground and Mike, your description of a signal generator was a little different from my set up so I decided to get into my signal tracer and make sure everything was going where it was supposed to and found that the signal on one pin was markedly weaker than the other so I rebuilt it for this application and now my testing is going a little better.

I went back and tried injecting  a 400mVAC signal at TP1 (I wanted to do 100mVAC but was having trouble getting my voltage reading low enough and I thought it would work well enough to see what I could see)

That now gives me 6VAC at TP15 and 225mVAC on either side of  R5

Injecting 2VAC at TP15 gives me about 9VAC at the Brown wire of the Output TX.

It seems like the later stages are acting as expected to me !

Still, with one probe clipped to pin 2 of the input xlr and the other to pin 3 a .775VAC signal drops to  12mVAC unless the unit is in Full Bypass.  (In Full bypass out put XLR pins 2&3 read .775VAC). I tried this with both the signal from the onboard OSC and from a DAW just to make sure there's not something weird going on with my test setup

 

[Echo North]

Progress! The grounding on this unit is very weird, so I'm trying to consider all of that.

Try inserting that signal into Pin 1 (dotted) of the input transformer.  Try it with the black probe on pin 4 of the transformer (same side, at the other end of the row) and then with the black probe at D4.  See if either of those give you signal through the unit.

Mike

 

[boneindian]

Progress! The grounding on this unit is very weird, so I'm trying to consider all of that.

Try inserting that signal into Pin 1 (dotted) of the input transformer.  Try it with the black probe on pin 4 of the transformer (same side, at the other end of the row) and then with the black probe at D4.  See if either of those give you signal through the unit.

Mike

Ok, with Input and Output knobs at noon .775VAC into pin 1(dotted) of Input TX with black probe on pin 4 I get 2.5VAC at the out put XLR. 

With the black probe at D4 I get 50mVAC at output (turning input and output fully CW raises that to .665VAC)

 

[Echo North]

Ok, with Input and Output knobs at noon .775VAC into pin 1(dotted) of Input TX with black probe on pin 4 I get 2.5VAC at the out put XLR. 

With the black probe at D4 I get 50mVAC at output (turning input and output fully CW raises that to .665VAC)

That makes sense.  It's probably an unbalanced signal so you're getting 1/2 the level.  So what happens if you connect that signal across pin 2 and 3 of the input XLR? Set the signal to 2VAC if you can.

Mike

 

[boneindian]

That makes sense.  It's probably an unbalanced signal so you're getting 1/2 the level.  So what happens if you connect that signal across pin 2 and 3 of the input XLR? Set the signal to 2VAC if you can.

Mike

Sending 2VAC I get 400mVAC at XLR output with input and output knobs at 12 o'clock.

This is with ground clip of signal at pin 3 and signal probe tip at pin 2

 

[Echo North]

Sending 2VAC I get 400mVAC at XLR output with input and output knobs at 12 o'clock.

This is with ground clip of signal at pin 3 and signal probe tip at pin 2

Have you run audio through it?  Does it pass signal?

 

[boneindian]

Have you run audio through it?  Does it pass signal?

Yeah, like I said it's been passing signal the whole time.

Just can't get above 148mv with DMM leads on pins 2 & 3 of the input  even using multiple gain stages to pump as hot of a signal as I can into this thing.

 

[Echo North]

Yeah, like I said it's been passing signal the whole time.

Just can't get above 148mv with DMM leads on pins 2 & 3 of the input  even using multiple gain stages to pump as hot of a signal as I can into this thing.

Ya but if you run audio through it,  like you’re recording or mixing.  Is the signal weak or normal?

 

[boneindian]

Ya but if you run audio through it,  like you’re recording or mixing.  Is the signal weak or normal?

Well it's set up on the work bench now which makes that just a little difficult, but I just tried running song audio through it and it sounded....fine.  A little thin maybe. I was on headphones and only hearing one channel,  but I can take a few and get it set up to run both units in stereo out of the monitors and see how it sounds.

This is weird though, I just set it up to run the unbalanced signal into pins 1&2 hands free, and  I can easily get .775VAC (which I guess makes sense since I was able to get that between pin 1 and pin 2, or pin 1 and pin 3 in the very beginning). I'm just unable to calibrate using a balanced signal for some reason.  Which is why I couldn't get past step 1 in the calibration with DAW video.

If I send a hot unbalanced signal to pins 2 and 3 it seems to behave normally.

Does that trigger any thoughts?

I'm gonna set them up and report back with quality of passed audio in GR off mode

 

[boneindian]

Not thin at all actually, audio sounds fine...normal. Wish I hadn’t removed that 100ohm input mod in the early stages of my troubleshooting though.

 

[Echo North]

Not thin at all actually, audio sounds fine...normal

I think your test setup is weird and I can figure it out.  Can you send a test tone from your DAW like in my video and calibrate?

 

[boneindian]

I think your test setup is weird and I can figure it out.  Can you send a test tone from your DAW like in my video and calibrate?

That's where all the trouble started!  I can't generate a signal from my DAW that hits .775VAC with the DMM on pins 2 & 3 of the input XLR unless the unit is in Full Bypass.

I'm using a Fluke 87V with a newish battery.

 

[Echo North]

That's where all the trouble started!  I can't generate a signal from my DAW that hits .775VAC with the DMM on pins 2 & 3 of the input XLR unless the unit is in Full Bypass.

I'm using a Fluke 87V with a newish battery.

So weird, but you pass audio.  What are you getting?

 

[boneindian]

So weird, but you pass audio.  What are you getting?

I pass audio with very healthy levels...according to my ears and eyes.

with everything cranked I can get up to .180VAC on the input pins....should I just try calibrating with the unbalanced signal from the board applied to pins 2&3?  This is driving me nuts! 

putting the unit in full bypass causes the reading across pins 2&3 to jump to 2.8VAC

Could it be something about my 500 series chassis?

 

[boneindian]

Also, with only 150mv across the input pins I'm getting 1.76VAC at the output with my gain knobs at noon.

For whatever that's worth

 

[Echo North]

Also, with only 150mv across the input pins I'm getting 1.76VAC at the output with my gain knobs at noon.

For whatever that's worth

Ya I'm lost.  I have no idea.  My gut feeling is that your unit is fine, and there is something wrong in your test set up.  Especially since it passes audio at a normal level. I just can't figure it out.  It's super frustrating.  When we test anything on a micro level, it all test normal. 

Maybe your GR Off switch isn't working?  You have your GR off switch in right? Is TP22 shorted to AGND?

Beyond your GR Off not working, I'll have to tap out on remote troubleshooting.  You'll need to send it in and I can fix it in a fraction of the time we've spent.

I doubt it's your chassis, many people with that chassis run these. 

Sorry,

Mike

 

[boneindian]

Ya I'm lost.  I have no idea.  My gut feeling is that your unit is fine, and there is something wrong in your test set up.  Especially since it passes audio at a normal level. I just can't figure it out.  It's super frustrating.  When we test anything on a micro level, it all test normal. 

Maybe your GR Off switch isn't working?  You have your GR off switch in right? Is TP22 shorted to AGND?

Beyond your GR Off not working, I'll have to tap out on remote troubleshooting.  You'll need to send it in and I can fix it in a fraction of the time we've spent.

I doubt it's your chassis, many people with that chassis run these. 

Sorry,

Mike

I'm with you, everything about the unit seems absolutely fine,...I just can't get it calibrated. Ugh.

Yes GR off has been in and TP22 (- side of C17) is shorted to AGND.

I may try calibrating with the unbalanced signal and see if I can get anywhere... and hope that there's just something screwy with my setup.  It seems so straight forward though, I can't imagine what would be different about me running an XLR out of my setup than it would be for anyone else.

Have definitely now spent longer troubleshooting than building the units.  I feel incredibly stupid.

 

[Echo North]

I'm with you, everything about the unit seems absolutely fine,...I just can't get it calibrated. Ugh.

Yes GR off has been in and TP22 (- side of C17) is shorted to AGND.

I may try calibrating with the unbalanced signal and see if I can get anywhere... and hope that there's just something screwy with my setup.  It seems so straight forward though, I can't imagine what would be different about me running an XLR out of my setup than it would be for anyone else.

Have definitely now spent longer troubleshooting than building the units.  I feel incredibly stupid.

Na you're fine.  You seem on top of it.  I trust it's built well.

I'm about to go on vacation for a week with my family and I'll be off email after Monday.  If you can't figure it out by Sunday night, shoot me an email and you can send it in.  I'll figure it out when I get back.

Seems like every year or so there is a weird/frustrating one.  This is it for sure.

In the mean time, I'm here if you have any questions.

Mike

 

[boneindian]

Na you're fine.  You seem on top of it.  I trust it's built well.

I'm about to go on vacation for a week with my family and I'll be off email after Monday.  If you can't figure it out by Sunday night, shoot me an email and you can send it in.  I'll figure it out when I get back.

Seems like every year or so there is a weird/frustrating one.  This is it for sure.

In the mean time, I'm here if you have any questions.

Mike

Well Mike, your suspicion that there was something weird with my test setup proved to be correct. After my last comment about the seeming sameness of running XLRs out of my DAW as any other setup I decided to eliminate that last point of failure and use another of the 480 points on the patchbay and the problem....disappeared. I still have no idea what could have caused a seemingly normal signal to drop like that when the unit is engaged (I suspect it is a grounding issue and I’ll know more when I pull the bay out of the rack to check all the ground bus settings) but, after switching to a more regularly used part of the bay the problem completely disappeared and I was able to calibrate both units in under an hour.

Thank you for your patience and persistence in helping me get to the root of the non-existent problem in my build. 

 

[Echo North]

Well Mike, your suspicion that there was something weird with my test setup proved to be correct. After my last comment about the seeming sameness of running XLRs out of my DAW as any other setup I decided to eliminate that last point of failure and use another of the 480 points on the patchbay and the problem....disappeared. I still have no idea what could have caused a seemingly normal signal to drop like that when the unit is engaged (I suspect it is a grounding issue and I’ll know more when I pull the bay out of the rack to check all the ground bus settings) but, after switching to a more regularly used part of the bay the problem completely disappeared and I was able to calibrate both units in under an hour.

Thank you for your patience and persistence in helping me get to the root of the non-existent problem in my build.

Ah patchbays cause trouble for all of us at some point.

Glad you found it!

Mike