Callate 2 (MXR Gate)

[Fender3D]

Sorry guys, this a very basic circuit...
first, lift the damn 10uF and see if signal passes.

There are just 2 stages in signal path, Q1's buffer and IC1b's buffer, what can go wrong?

[Rob Strand]

first, lift the damn 10uF and see if signal passes

Actually his JFET is socketed so pulling it out would also work.

I think removing the JFET and shorting the CE terminals are both worth trying.
The CE short needs a bit more circuit working and checks the JFET.
If the CE short still doesn't pass the signal but removing the JFET does then that narrows the problem to around the JFET.

[jfrabat]

Leave the links across AB and CD (and leave the EF link in too ). You only remove them if you are wanting to use the attack and release modifications - don't bother with those mods at the moment.

I really did think that there was a definite solder bridge where the middle arrow was pointing. Oh well.

Try the short across Q2 and see if audio can get through. If it doesn't it is time to do some checks with an audio probe to see where it's getting lost.

OK, made sure to clean up the suspected bridges.  The middle one is not an issue because it is traced anyway...  Also bridged the Emiter and collector of Q2.  Still no sound coming through (regardless of pot position).

Solder joints today (including bridge) - NOTE, IMAGES ARE 180* FROM PREVIOUS!:



And with backlight to see the traces:

[Rob Strand]

Still no sound coming through (regardless of pot position).

So try pulling the JFET out.

[duck_arse]

try resoldering your pot legs - there is what looks like a cracked solder in your backlight pic. test the resistance across the pots legs ON THE BOARD, see if there is connection or not.

[Fender3D]

I think removing the JFET and shorting the CE terminals are both worth trying.
The CE short needs a bit more circuit working and checks the JFET.

Removing the FET should have been the first thing to do... 2 days are passed...

I know it may be anything when a builder has no experience, but a circuit analysis should be explained...

There are 2 buffers in series and in between them there's 1 cap shorting signal to GND through the FET switching job.
Assuming input, output and footswitch are correctly connected, no signal whatsoever means one or both the buffers are failing their duty...
Lift the cap or remove the FET and check, possibly with a signal probe.

[jfrabat]

OK, hold up; I shorted Q2 as stated, but keep in mind Q2 is the 2N3904 (same as Q1) and not the NTE451!  The one that is socketed is the NTE451.

Now, I did try to play it with the NTE451 taken out, and it is not playing.  Tonight I will break out the audio probe and try to follow the signal and see where it is disappearing.  I will also re-solder the pot, just to rule that out.

[Fender3D]

Now, I did try to play it with the NTE451 taken out, and it is not playing.

Pot has nothing to do with signal path. Don't look for minor issues 'till you don't sort out why signal does not pass trough 2 basic buffers...

If it does not work, check the 2 buffers, assuming your solder bridges quest is actually ended and assuming input, output and footswitch are correctly connected.

[Rob Strand]

Now, I did try to play it with the NTE451 taken out, and it is not playing.  Tonight I will break out the audio probe and try to follow the signal and see where it is disappearing.  I will also re-solder the pot, just to rule that out.

Don't bother putting the JFET back until you get the signal to pass.

Something odd is going on as your DC voltages seemed OK. Although I did note this before,

One thing that's weird is most of your measurements show a your multimeter loading voltages but pin 5 doesn't show this effect!    Are the resistors on pin 5 1M?

I know your resistors are 1M but maybe the 10nF cap to the 1M has an issue.  That however is unlikely to be the cause of no signal!

Audio probe would be helpful especially to see if you are getting signal from the output of the first opamp.

[jfrabat]

I will check it with the audio probe in Saturday (just got home today and I got a client coming in tomorrow, so no pdals until the weekend!).

[jfrabat]

I will check it with the audio probe in Saturday (just got home today and I got a client coming in tomorrow, so no pdals until the weekend!).

Well, client cancelled.  Brought out the audio probe.  Traced the input signal.  This is where I could hear the audio signal (I used a clean tone, for this purpose, 500Hz):



This means the signal is making it into the board, going down the 1K resistor, up the 0.047 cap, into Q1, out of Q1, past the 0.01 cap and into the pot, out of the pot and onto pin 3 of the 072, Out Pin 1, across the 0.047 cap, and nowhere else.  Am I tracing it right?

Now, is it me, or should I not have sound coming out of pins 6 and 7 of the 072?

[Rob Strand]

What you have done so far is good.

There's another audio path to check - see below.

Now, is it me, or should I not have sound coming out of pins 6 and 7 of the 072?

yes.

So now follow the part from the emitter of Q1.

Q1.emitter ---> 22k  ---> 10nF --->  IC2 pin 3 ---> IC2 pin 6,7

Also,
(Q1.emitter ---> 22k)  ---> 10uF ---> 1M

See where the sound stops in each case.

[jfrabat]

I tested all traces.  Those are the only ones with signal.

[Rob Strand]

I tested all traces.  Those are the only ones with signal.

Hmmm.  Was that with the JFET in or out?

[Rob Strand]

One thing that's weird is you are getting signal on the emitter of Q1 but not on the base.
I'm assuming you just forgot to color those traces in red?

The key problem is why the signal is on one side of the 22k but not the other.
This part,
Q1.emitter ---> 22k  ---> 10nF --->  IC2 pin 3 ---> IC2 pin 6,7

EDIT:
OK, as a short cut perhaps try resoldering that 22k, the horizontal one just above Q1.

[jfrabat]

I tested all traces.  Those are the only ones with signal.

Hmmm.  Was that with the JFET in or out?

In

[Rob Strand]

In

Leave it out for now it makes it harder to debug.
There could even be two problems: the one stopping the audio (when the JFET is out), then another related to the JFET.

You need to get it to pass audio with the JFET out.

With the JFET out, use the audio probe to find at what point in this chain the signal stops:
Q1.emitter ---> 22k  ---> 10nF --->  IC2 pin 3 ---> IC2 pin 6,7

[jfrabat]

OK, with JFET out, the signal is going through (note: I still have a jumper from collector to emitter of Q2).  But as soon as I put the JFET in, the signal dies...  If I plug it in backwards, it lets the signal through, but no effect (no gating).

Here is where I found signal (not I mirrored the image to have it in the same direction as the build doc):



Orange is regular signal, red is amplified signal, yellow is somewhat muted signal.
Light blue is where I should have signal according to build docs, but I do not due to the jumpers (expected loss of signal)
Purple is where I cannot understand why I do not have signal.

Here is the original image from the build doc:

[Rob Strand]

OK, with JFET out, the signal is going through (note: I still have a jumper from collector to emitter of Q2).  But as soon as I put the JFET in, the signal dies...  If I plug it in backwards, it lets the signal through, but no effect (no gating).

Despite not working those measurements look a *lot* better.    Putting the JFET in backwards is probably looking similar to like it's not there.   So the good thing is the audio is passing through.

Don't worry about your purple traces (yet).  I would have expected some signal on a few of those points as well.  Perhaps it's because the 1M divides the signal down by a large factor.  The good thing is signal is coming out on pin 1 of the IC.   Just put that result on the shelf for now until we need it.

The point we are at is the JFET is shorting out the signal despite the fact Q2 has its CE terminals shorted.

So next steps are is to check the DC level on the gate with the JFET removed.  I'd expect about 2V (depending on you meter impedance it could be a bit lower).

Beyond that I'd start thinking the JFET is not turning off because the VP (Vgs_off) for that JFET is too high.

So if the DC on the gate looks OK you should:
-  lift one end of the 100k located near the Output connection
- Remeasure the DC on the gate (with the JFET removed).

Now you should see about 3.9V (perhaps a little lower).
If that new voltage looks OK, put the JFET back in and confirm the unit it passes signal.
Also try listening to it with your guitar and amp to judge is your getting any signal drop.

If you get this far the problem is the VP (Vgs_off) for the JFET is too high to work in the circuit.
If it were me at this point I would try to measure the VP of the JFET to confirm that.

Wait a sec I will find the thread on how to do it:

So, in this thread, see reply 1 and the test circuit is the left hand side.  I recommend adding a 220 ohm resistor in series with the power to prevent damage if you connect the JFET incorrectly.

https://www.diystompboxes.com/smfforum/index.php?topic=122138.0

[jfrabat]

So next steps are is to check the DC level on the gate with the JFET removed.  I'd expect about 2V (depending on you meter impedance it could be a bit lower).

1.767V I am reading at the gate.  I am guessing that is within the OK range, right?

So if the DC on the gate looks OK you should:
-  lift one end of the 100k located near the Output connection
- Remeasure the DC on the gate (with the JFET removed).

Now you should see about 3.9V (perhaps a little lower).

You mean this one?



If so...  Actually, a whole LOT lower...  0V at the gate.  Source 3.88V, D 3.82V the drops to 3.53V.