My studio Mic compressor build

[jfrabat]

I ordered from OSH Park, so I will check once I get home to see if they have the file (site is blocked form the office)

If you uploaded a KiCad .pcb_layout or an Eagle .brd file instead of gerbers, you might even be able to recover your original files. Ask them (I cannot check as I never ordered at OSH park).

I used Eagle .brd file.  I tried looking online in their site, but I do not see any option to download the .brd file.

I have been checking the board, and it seems it is a mess...  From SK10tn, the signal SHOULD go to C8- and from C8+ to R64, and, from there, R65 and 66.  But in REALITY, it is going from SK10tn to R64, and from (the other side of) R64 to C8+.  Then, C8- is connected to IC5 pin 2 on the bottom side (all the previous traces are in the bottom side), and on the top side, connecting to the same pin that connects R64 to SK10tn, there is a trace that connects to C8-, R65 and R66.

Bottom layer


Top Layer


So, obviously that is the issue.  Now, what is the best way to fix this?  I do not want to spend $125 more on more boards, and, on top of that, loose all the components already soldered, so I want to try to fix these 2 boards!  And obviously it is not as simple as cutting a trace, as this thing is bad in several places.  I was thinking of using a set of hand drill bits I have (no power tools!) to sever (not make a hole; just dig deep enough to sever the trace) the connections to C8- and then wiring them with wires from the bottom.  Would there be a negative effect in having C8 and R64 inverted in the circuit (resistor before capacitor instead of how it is in the schematic)?  If that is an issue, I would need to sever also the trace going from SK10tn to R64, and from R64 to C8+ and also wire them from the bottom...

As to WHY it happened, I have NO IDEA.  The schematic is obviously not like that, so I am not sure why eagle made that mess!

[Rob Strand]

C8+ to R64

The C8 vs R64 swap isn't a big issue in itself.   In a compact layout it wouldn't make much difference.

The big issue is the PCB doesn't match schematic.   That means you don't really know what the PCB is doing when you look at the schematic.

There could be more differences that just R64 and C8.

I haven't gone through the details of your R64 and C8  traces but it  sure looks like the cause.

Now, what is the best way to fix this? 

Definitely no need to do a new PCBs.    I've seen production board with less mods 

Cutting a few a tracks and adding a few wires is no big deal.

The important thing is to make sure the mods are correct.  It's very easy to fix C8 and R64 but still have wrong tracks going to C8 or R64.   Just take your time and convince yourself it's correct.

As to WHY it happened, I have NO IDEA.  The schematic is obviously not like that, so I am not sure why eagle made that mess!

Most PCB packages allow you  to make changes *at the PCB level*.   I don't like doing this but some people work like that.  In normal circumstances you would update the schematic to match the PCB.    In your case you have probably inadvertently changed something on the PCB.   The packages offer a number of ways to check the PCB and schematic to make sure they are consistent.   If you aren't aware that such a problem can occur you wouldn't do that extra check step at the end.

The good thing is we found something!

[jfrabat]

As far as I can tell, the traces marked in green are the issue.  If swapping thenresistor and cap is not a problem, that means less corrections.  Anyway, I will try to correct 1 board tonight, and will report back.

[Rob Strand]

As far as I can tell, the traces marked in green are the issue.  If swapping thenresistor and cap is not a problem, that means less corrections.  Anyway, I will try to correct 1 board tonight, and will report back.

If you leave the C8 R64 ordering I think you only have to cut one trace.  The lower trace on the Top Layer pic, the between C8 and R64.

Is that how you see it?

[jfrabat]

As far as I can tell, the traces marked in green are the issue.  If swapping thenresistor and cap is not a problem, that means less corrections.  Anyway, I will try to correct 1 board tonight, and will report back.

If you leave the C8 R64 ordering I think you only have to cut one trace.  The lower trace on the Top Layer pic, the between C8 and R64.

Is that how you see it?

I was thinking of cutting these (red):

Bottom:

So, sever the connection between Pin 2 and C8-, and the connection between R64 and C8+ (I need it to go to -, right?)

Top:

Sever the connection between R64 (SK10tn side) and C8-, and that same trace, but between C8- and R65.

So 4 cuts total according to my estimations.  I have 3 empty boards to test cutting techniques, which I plan to do!

[jfrabat]

Did some testing with an empty board.  3 out of the 4 cuts are fairly simple to do.  But I need advice on the 4th!





I checked continuity on the traces and from each end of the trace to GND (in that plane, so typically, the nearest GND via).  It checks out.

This is where it gets a bit more tricky because the trace is very close to another one:



Any suggestions on how to sever ONLY the trace I need severed and not the one beneath it?

I was going to cut the traces on the built boards, but I figured I better wait to be sure I am cutting the right traces!

[Rob Strand]

Looks like a lot of cuts.

Do you intend to wire C8 or R64 to pin 2 IC5a ?

For the cuts, the only around the home item for cutting tracks is,
https://duckduckgo.com/?q=box+cutter&iax=images&ia=images

Do you have a scalpel?

[jfrabat]

Do you intend to wire C8 or R64 to pin 2 IC5a ?

C8, but the + side has to go to Pin 2, right?  My intention is to make those 4 cuts, and then wire R64 to C8-, and C8+ to Pin 2 and R65 (which has a trace to R66).  So 4 cuts and 4 external wires.  Does that sound right?

For the cuts, the only around the home item for cutting tracks is,
https://duckduckgo.com/?q=box+cutter&iax=images&ia=images

Do you have a scalpel?

I am sure I can do better...  RC Airplanes and boats (all scratch built) as well as guitar building are some of my other hobbies.  I got all kinds of X-Acto knives and blades.  Also got some small chisels and punches (may still be too pig for this). And I got a scratch owl as well.  My worry is not so much the tool as the eye sight...  I am thinking of trying the same technique, just being careful with the diameter of bit used (I got 4 sizes smaller than the one used).

[PRR]

> So what is the best way to fix it considering the boards are already printed?

Get a sharp knife and small sharp screwdriver (chisel). Remove the offending copper.

Small wire jumper to where it is supposed to connect.

In the old days I recovered screw-ups and damage where half the board was bad. More jumpers than chisel-out, but I've done enuff of both.

NEVER say "it can't be wrong, it is just like the plan".

[Rob Strand]

I got all kinds of X-Acto knives and blades.

X-Acto knives are excellent.

C8, but the + side has to go to Pin 2, right?  My intention is to make those 4 cuts, and then wire R64 to C8-, and C8+ to Pin 2 and R65 (which has a trace to R66).  So 4 cuts and 4 external wires.  Does that sound right?

It's hard for me to make it out.

What might be complicating it for you is the polarity of C8.  C8 can go in anyway.
(and FWIW, your schematic has C8 flipped from the original article anyway.)

My understanding is most of the circuit is already connected correctly.    Especially if you are going to wire C8 to pin 2.

In reply #124, the lower pic "Top", the lowest red wire going from C8- to R64 is the only wire which is incorrect.   Currently, that pin of R64 goes to both C8- and pin 2.  If you cut the C8- to R64 track then it fixes everything.   C8- then connects to pin 2 and to all the right places and C8+ only goes to R64.

I might be wrong since it's hard to trace accurately from those pics but the main point is the board already has all the right connections.

[jfrabat]

I got all kinds of X-Acto knives and blades.

X-Acto knives are excellent.

C8, but the + side has to go to Pin 2, right?  My intention is to make those 4 cuts, and then wire R64 to C8-, and C8+ to Pin 2 and R65 (which has a trace to R66).  So 4 cuts and 4 external wires.  Does that sound right?

It's hard for me to make it out.

What might be complicating it for you is the polarity of C8.  C8 can go in anyway.
(and FWIW, your schematic has C8 flipped from the original article anyway.)

My understanding is most of the circuit is already connected correctly.    Especially if you are going to wire C8 to pin 2.

In reply #124, the lower pic "Top", the lowest red wire going from C8- to R64 is the only wire which is incorrect.   Currently, that pin of R64 goes to both C8- and pin 2.  If you cut the C8- to R64 track then it fixes everything.   C8- then connects to pin 2 and to all the right places and C8+ only goes to R64.

I might be wrong since it's hard to trace accurately from those pics but the main point is the board already has all the right connections.

No, you are absolutely right!  I just saw it.  Of course!

Flip C8, and cut one trace (from C8 to R64).  All the other traces work perfectly!

I got so excited, I tried it in one of the boards (1st board).  It still has the diode jumpers and all the caps in, but these are the voltages (no signal) I took quickly before heading out to the office:

Pin 12: 1.3mV
Pin 13: 3.4mV
Pin 14: 5.5mV

I also had the trigger pot set more than halfway.  When I turned it counter clockwise, the LED turned red, which is another good sign (trigger was lowered, the gate activated!).  Also, the DEPTH pot affected the color of the LED (so the more the gate closes, the more red the LED becomes!).

This looks VERY promising (but I still need to do some final tests)!  Thanks guys!

[11-90-an]

This is probably gonna be the "longest" workday of your life, Felipe...

[Rob Strand]

Pin 12: 1.3mV
Pin 13: 3.4mV
Pin 14: 5.5mV

This looks VERY promising (but I still need to do some final tests)!  Thanks guys!

Very promising indeed!

I got so excited,

To tell you the truth I was excited about it as well.
This problem has been a tough one to crack and finally something that makes sense.

[jfrabat]

If you had not picked out the trace error, I would never have found it!  Thanks a million!

Regarding the diode jumpers, I should take them out now, right?  How about the 3 caps?  Or should I fix the other board and the compare that one with no caps to this one with caps?

[jfrabat]

This is probably gonna be the "longest" workday of your life, Felipe...

That thing was fricking HARD to find!  Would have never gotten to it by myself!!!

[Rob Strand]

If you had not picked out the trace error, I would never have found it!  Thanks a million!

And if 11-90-an didn't post the link to the layout I probably wouldn't have check it.

Regarding the diode jumpers, I should take them out now, right?  How about the 3 caps?  Or should I fix the other board and the compare that one with no caps to this one with caps?

Yes, you can take all that out.

FWIW, the problem was C8 was shorting R64.  That causes a very high gain on IC5A.  Any small signals around C8/R64 and the input socket got amplified by a very large gain - that's going to be mains hum.  That caused IC5a to have a AC signal on the output, which looked like oscillation but wasn't actually oscillation.   The whole circuit just rectified the massive signal and produced a large (rectified) negative voltage on pin 14.

[jfrabat]

If you had not picked out the trace error, I would never have found it!  Thanks a million!

And if 11-90-an didn't post the link to the layout I probably wouldn't have check it.

Yup.  11-90an and Rob Strand both need partial credit in all my pedals.  You guys always help dig me out of the wholes I tend tondig myself into!  Lol!

]
Yes, you can take all that out.

FWIW, the problem was C8 was shorting R64.  That causes a very high gain on IC5A.  Any small signals around C8/R64 and the input socket got amplified by a very large gain - that's going to be mains hum.  That caused IC5a to have a AC signal on the output, which looked like oscillation but wasn't actually oscillation.   The whole circuit just rectified the massive signal and produced a large (rectified) negative voltage on pin 14.

I take it is good that I do not feel completely like Charlie Brown listenibg to her teacher ("wah wah wah wah..."), right?  At least now after reading a couple of times I understand a little!

[11-90-an]

If you had not picked out the trace error, I would never have found it!  Thanks a million!

And if 11-90-an didn't post the link to the layout I probably wouldn't have check it.

Yup.  11-90an and Rob Strand both need partial credit in all my pedals.  You guys always help dig me out of the wholes I tend tondig myself into!  Lol!

Bah. Rob and you did all the work. Think of me as an audience trying to keep track of what's happening, shouting the occasional "look out!", "over there!"

p.s. you can just call me "the other" nathan... 

[Rob Strand]

Yup.  11-90an and Rob Strand both need partial credit in all my pedals.  You guys always help dig me out of the wholes I tend tondig myself into!  Lol!

You seem to get an unfair share of weird problems.    The MXR Noise-gate was another crazy one.   If it wasn't for the other forum member re-designing the circuit it would never have worked.

Bah. Rob and you did all the work. Think of me as an audience trying to keep track of what's happening, shouting the occasional "look out!", "over there!"

Every bit helps, that's what's good about having more heads thinking about crazy problems.

[jfrabat]

OK, did some real sound testing today.  We are closer, but not there yet!  Gate seems to be on all the time now, and hence, the DEPTH pot works kind of as a volume.  But TRIGGER pot is not working as intended.  At least I can now test the GATE BYPASS switch, and that is working!

Anyway, here are some new voltages (no signal) with the TRIGGER pot at full (-12.19V) and the DEPTH pot at half way (7.11V):

IC5:
Pin 1: 29.4mV
Pin 2: 1.4mV
Pin 3: 0V
Pin 4: 15.34V
Pin 5: 142.8mV
Pin 6: -13.38V
Pin 7: 14.74V
Pin 8: -13.67V
Pin 9: 1mV
Pin 10: -12.19V
Pin 11: -15V
Pin 12: -3.9mV
Pin 13: 2.9mV
Pin 14: 1.9mV