Trem Face...someone please, please help me! RG Keen, this involves you!

[R.G.]

Test #2 (test of trimpot on gate)
G varies smoothly from -0.02v to 5.6v as trimpot is turned.

You know, I was assuming that the power supply polarity was correct, but it finally soaked through to me that it may not be. This pedal uses a perverse power supply arrangement of positive ground with NPN and N-channel devices to get the JFET to work with its source and drain effectively grounded. Maybe it's just that I've had my first cup of coffee, but you say the gate varies from -0.02V to 5.6V. That should be -5.6V because all voltages in this thing are negative with respect to ground.

I have violated my own rule of first checking the power supply voltage and polarity. So from here on, put the black lead of your meter on signal ground (sleeve contact on the input or output jack will do nicely) and measure all voltages with the red probe. They should all measure negative with respect to ground. If they don't, your problem could be a reversed power supply connection. If so, I'm slapping myself in the forehead for not doing this first. It's something I yell at other people for not doing at my instructions (in What To Do When It Doesn't Work). Mother Nature has just reminded me not to get sloppy and skip steps myself.

Test #4 (test of trimpot effect on depth pot)
Turning the trimpot has absolutely no effect in volume or ossilation on the depth pot no matter what position either pot is in.

And that is a decisive test. With the JFET source and drain at 0V, if its gate WERE going between 0V and MINUS 5.6V, at some point it would turn off and the depth pot would no longer work as a volume pot. So the JFET is always conducting signal through the depth pot, and that means that it is either always turned on (i.e. the power supplies are incorrect, per above) or it is damaged.

[Toddy]

OK, assuming the JFET was bad, I swapped it out with another brand new 2N5485 I happened to have. Same exact result! The depth pot was still a volume pot with no oscillation. I tested the voltage on the gate and it reads the same -0.002v to 5.6v while turning the trimpot. I do have the positive red probe on the ground and the black negative probe on the part while testing. I checked the battery polarity and it is correct to the diagram on page 7.

How can I have two bad 2N5485 JFETs? My guess is it has to be something else. I do not have time tonight to do an audio probe test but I guess it's not worth it right now.

Pulling the hair out of my receeding hairline,
Toddy

[R.G.]

I tested the voltage on the gate and it reads the same -0.002v to 5.6v while turning the trimpot. I do have the positive red probe on the ground and the black negative probe on the part while testing. I checked the battery polarity and it is correct to the diagram on page 7.

OK, humor me on this. Use the black probe on ground and the red probe to measure with. It'll help keep us from being confused.

So you were getting +0.002V to -5.6V on the JFET gate lead, with the source and drain held to 0V. When that happens, a properly working JFET goes from fully off (near -5.6V) to fully on (about 200ohms). So the only possibilities are:
(1) the JFET is damaged, and is always shorted; this is the least likely of all these possibilities
(2) the JFET is connected improperly, with the wrong pins in the holes so a good JFET acts bad
(3) the JFET is shorted *externally* by perhaps a solder thread or other fault, which could include a thread of copper invisible to the human eye left on the PCB (I mention that because I tore all of my hair out finding one of those one time) or other external flaw
(4) the depth pot is either hooked up incorrectly or damaged so the part which should connect to the JFET is shorted to ground all the time.

This is what I was trying to get at with the audio test, finding whether the audio ever made it to the JFET.

But while you're waiting to get to the audio test, try this: Turn the thing on and put no signal into it. Set your meter to read ohms and connect the red lead to ground and the black lead to the wiper of the depth pot. Now rotate the depth pot and read resistance. It will likely go from 0 (or nearly) to about 20K. Now leave it set at some convenient value, like 10K. Rotate the trimpot. Any change in resistance? If yes, the JFET is working. If no, the problem is closer to the JFET.

Assuming No, unsolder the JFET end of the depth pot. Move the red probe to the drain of the JFET. Read resistance there while rotating the trimpot. Any resistance change? If yes, the fault was the depth pot connection. If it's always low resistance to ground, either the JFET is bad (which we doubt very, very much because two new JFETs have been tried) or there is a problem on the PCB. So a sharp knife (X-ACTO is great for this!) and cut around the pad the drain is on, and the entire connected copper to eliminate the possibility of a copper or solder thread. Measure again. Still tied to ground? Then remove the JFET and measure from the drain PAD where the JFET used to be to ground. It should measure the 2.2M of the pulldown resistor. If it's less, there is a circuit board flaw. You have to be careful doing this, because if the problem was the solder, you're modifying it to make this test.

OK, assuming the JFET was bad, I swapped it out with another brand new 2N5485 I happened to have. Same exact result!
How can I have two bad 2N5485 JFETs? My guess is it has to be something else. I do not have time tonight to do an audio probe test but I guess it's not worth it right now.

Testing with a new part is pretty telling, but I would have said (I think I did, somewhere) that the JFET is likely not the problem. I only include "damaged JFET" for completion. That's the least likely part to be bad. Experience shows that probably 95% of all flaws in newly built effects is from wrong orientation/pinout, bad soldering, and improper wiring.

[Toddy]

OK, I tried the resistance test on the depth pot to the trim pot. All went well. The resistances on the pot went from 0 to 25K ohms on the depth pot (I obviously have a 25k pot). Then I tested the depth wiper to the trim pot and the resistances on the depth pot changed as I turned the trim pot.    Yeay! The JFET is good!!

I am going to have to wait to do the audio test tomorrow because I have other (personal) stuff to do tonight. This is just too CRAZY!!

Still recovering from the headspin,
Toddy

[R.G.]

OK, I tried the resistance test on the depth pot to the trim pot. All went well. The resistances on the pot went from 0 to 25K ohms on the depth pot (I obviously have a 25k pot). Then I tested the depth wiper to the trim pot and the resistances on the depth pot changed as I turned the trim pot.    Yeay! The JFET is good!!

OK, we're making progress. The JFET should have been able to make the resistance very, very high as the voltage got over about -3V or so.

If that's the case, then there are two remaining possibilities. Either the audio's not getting there, or the LFO is still not running. Audio test will help eliminate things.

Yell when you can work some more.

[trendyironicname]

R.G., you kick ass.  seriously. 

[Toddy]

I finally got a chance to do the audio test. Here are my results.

Input jack loud sound on outer lug and middle lug but nothing on the inner center lug.

Output jack loud sound with switch on and switch off.

R4 no sound on input side (on either input wire connection or resistor itself). Loud sound on output side.

Depth pot empty lug was a very faint sound. Wiper varied with turn of the depth pot itself. Lug to capacitor constant loud.

JFET drain constant loud no variations.

I tried turning the trim pot and it had no effect on the loudness of the sound either at the depth pot, which I turned all the way up and all the way down, or on any of the three JFET legs. The rate pot works as the sound gets louder and softer on the wiper as I turn it. I measured the voltage on the JFET gate again and it still changed with the turn of the trimpot as before.

How could the trimpot have an effect on the voltage but not the sound signal?

Is R4 the problem? I reheated the solder on the board with the iron to make sure it wasn't a cold joint.

Awaiting the score of my test, (I hope I got at least an A-.)
Toddy

I have only 24 hours to see if I can fix it. Then I'm going to be away for six days.

[R.G.]

Input jack loud sound on outer lug and middle lug but nothing on the inner center lug.

I'm not sure what you mean by inner, middle, and outer.Can you do a picture, or perhaps use your meter to tell me which of these lugs connect to what?
Two of the lugs should have no signal on them, only one should have signal. One is the sleeve, and is grounded. One is ring, which also connects to ground when a plug is inserted and switches the battery on, and only the one which connects to the tip of the plug should have signal on it. This is at least a wiring problem.

Output jack loud sound with switch on and switch off.

That's OK.

R4 no sound on input side (on either input wire connection or resistor itself). Loud sound on output side.

This is very strange. It indicates a probable wiring problem, possibly to the input jack.

Depth pot empty lug was a very faint sound.

Odd, but not very telling.

Wiper varied with turn of the depth pot itself. Lug to capacitor constant loud.

Isn't the wiper the same as the lug to capacitor C8? How are those different?

JFET drain constant loud no variations.

Does this remain constant as you diddle the trimmer?

I tried turning the trim pot and it had no effect on the loudness of the sound either at the depth pot, which I turned all the way up and all the way down, or on any of the three JFET legs. The rate pot works as the sound gets louder and softer on the wiper as I turn it. I measured the voltage on the JFET gate again and it still changed with the turn of the trimpot as before.

How could the trimpot have an effect on the voltage but not the sound signal?

I'm wondering if a wiring problem with the input jack could do this. Let's look there first and see if that helps us peel another layer off the onion. We're pretty sure that there is some problem there. It may be masking yet another problem. Solving these things is like peeling onions. You remove a layer at a time and cry a lot. 

Is R4 the problem? I reheated the solder on the board with the iron to make sure it wasn't a cold joint.

Can't tell. I'm more inclined to get the input jack fixed first.

Awaiting the score of my test, (I hope I got at least an A-.)

Can't tell yet. The input jack thing may be a big step forward. I can't come up with any plausible way that a correct wiring would give what you're telling me, so I think either the jack is wired incorrectly or we're measuring incorrectly. Can you post pictures of the input jack?

I have only 24 hours to see if I can fix it. Then I'm going to be away for six days.

It's a really bad practice to set yourself limits like that. As you've pointed out, you've actually been working on this for three years. Another six days won't hurt, especially since you're making great strides.

[Toddy]

Sorry. Trying to do ten things at once goofs me up sometimes.

Input jack is hooked up like this.
-Outer sleeve goes to outer sleeve of output jack and to ground.
-Innermost ring goes to R4.
-Remaining lug goes to battery positive.

My goof on the depth pot. The wiper goes to the C8 as you said. The other lug goes to the middle lug on the switch.

JFET remains constant loudness even while turning the trim pot.

Self-correcting my test errors,
Toddy

[R.G.]

Input jack is hooked up like this.
-Outer sleeve goes to outer sleeve of output jack and to ground.
-Innermost ring goes to R4.
-Remaining lug goes to battery positive.

OK, When you stick the plug into the jack, the very tip of the plug touches a contact. Set your meter to ohms, and verify whether the internal contact which touches the very tip of a guitar cord plug goes to the "innermost ring" or the "remaining ring".

[Toddy]

When I put the guitar plug into the input jack there is an ohm reading on the innermost ring and no ohms on the "remaining" ring. Is that good or wrong?

Toddy

[Toddy]

I went ahead and switched the "innermost" and "remaining" wires on the input jack. I tested it and no signal was going through the circuit at all so I switched them back and we are back to where we were.

So what would be another hypothesis about why R4 had no sound where it connected to the input?

Toddy

[R.G.]

I went ahead and switched the "innermost" and "remaining" wires on the input jack. I tested it and no signal was going through the circuit at all so I switched them back and we are back to where we were.

So what would be another hypothesis about why R4 had no sound where it connected to the input?

Yeah, that one's got me confused. If the two points are ...really... connected by a wire, seems like they should both have the same audio on them right?

All I can suppose is that they are not, in fact, connected by a wire. If there appears to be a wire between them, then the wire must be open. That then begs the question of how audio gets to the rest of the circuit. That's why I mentioned pictures, because "innermost" and "remaining" lugs form no picture in my mind that I can relate to a jack. I'm going on faith that those may be correct places for wires.

As Arthur Conan Doyle said, through Sherlock to Watson "Eliminate the impossible, Watson. What you have left, no matter how improbable, must be - the truth."

[Toddy]

Toddy

[Toddy]

This is how I wired the input jack.

This is how the Trem Face looks so you can see all the wiring connections.

This is how I looked when I switched the two input jack wires and it didn't work.


Toddy

[R.G.]

OK, we have a winner. 

Well, at least one more layer off the onion. That's a tip-shunt jack. It's the wrong kind to switch the battery. You need a Tip Ring Sleeve (TRS) jack, also known as a "stereo" jack.

[trixdropd]

Sometime's a picture is worth 1000 words....

[Toddy]

Here are my results from this morning.

Got a "stereo" jack from my favorite Tandy Corporation store and hooked it up. Plugged it into the guitar and amp and I actually got nice variable depth and speed oscillation passing through the circuit!! But no guitar signal. Went back and changed two wires and got no signal passing through the circuit at all, bypass switch on or off. Rewired the input and output jacks again and I get just guitar signal and no oscillation. Then I did it a third time and nothing again. Now I can't remember how I hooked it up the first time!! So...my patience with this Trem Face has gone away for today. And I am leaving now and will be back on Thursday so the Trem Face will have to rest...and so will I!

What I need is a foolproof dummy picture that even a caveman can understand for hooking the input and output jacks up in this Trem Face circuit. Even though I've built about ten pedals and fixed a dozen amps and radios and have done wiring for cars and boats , I still get goofed up on the diagrams on how each individual circuit gets wired up...and I have studied this circuit extensively!!

Once I get the picture I will hook everything up "the right way" when I get home and tell you my results.

Thanks R.G., You are the MAN!! You deserve a break from me for a few days anyway!! (and so does this board!!)
Happy Birthday USA!!
Toddy

[R.G.]

Take a break knowing that it will work shortly after you get back. We've peeled off several layers, and I think we're very close now.

Here's a picture: http://www.switchcraft.com/products/pdf_files/jack-85b_schematic.pdf Go look at 12B, second row down, second from the left. The contacts you want are Tip, Ring, and Sleeve.

Sleeve connects to audio ground, on input and output. Ring is where the red wire from the battery connects. Tip is where the audio signal comes off to go to the PCB, and it winds up connecting to one end of R4.

It can be confusing looking at switches and jacks for wiring. When I was getting started, I figured out what worked for me: using an ohmmeter to actually follow the connection from the end I had identified through the switch/jack/etc to where the wire was going. I could eventually figure out what all the contacts I needed were by keeping a good sketch and writing down notes. There was no internet to ask for help in back then (when dinosaurs roamed the earth).

In your case, I would do this. Remove batteries and power supplies from the circuit. Take a guitar cord and insert it into the input jack just until you feel it snap into position the first click; because of the ring contact, this will NOT be fully inserted, and will be about 1/8" from full insertion. Now use your ohmmeter. Connect one probe to the ground/sleeve on the free end of the guitar cord. Touch each of the lugs on the jack. The one with zero ohms from the far end of the guitar cord is the sleeve contact. Check to see that this one does NOT have continuity to either of the other two lugs. Note down in words/sketches which one this is.

Now put your ohmmeter probe on the tip of the free end of the guitar cord. Touch the two lugs remaining; one of them will have low ohms to the tip contact on the cord. That's the ring contact. Make a note/sketch so you don't lose it. Now push the plug all the way into the jack. With your ohmmeter verify that the newly-identified ring contact is now shorted to the sleeve.

Finally put your ohmmeter probe on the tip of the free end of the guitar cord, and touch the remaining lug on the jack. This should show continuity; if it does, you have correctly identified the tip lug.

I think this procedure will identify the tip, ring and sleeve of any phone jack, even where you can't see the insides to see what touches what.

In any case, go get traveled, get a rest from this, and come back refreshed.

[Toddy]

There, I'm back!

I swapped out the stereo input jack, hooked up the wires correctly now, and the guitar signal still passes right throught the effect without oscillating. I did an audio probe test and at least the input side of R4 works now (as opposed to just the output side). The JFET drain still has sound and the sound gets louder and softer via a turn of the depth pot and the trim pot and both together. But still no oscillation. It was wierd that time I changed the input jack wires around and got just oscillation but no guitar signal passing through it.

Any suggestions?

Still puzzled even after a six day hiatus,
Toddy