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

[R.G.]

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.

OK, let's take stock. I'll tell you what I think you told me, and you correct me if I'm wrong. As verified by audio probe, the audio comes into the input jack, hits R4, and also appears on the output side. The JFET drain also gets audio, and the sound (at the output jack?? I guess.) gets louder and softer depending on the setting of (a) the depth pot and (b) the trim pot, each independently and in concert. Right?

If so, we are quite nearly there. Correcting the jack wiring was a big step forward. I can appreciate that to you it may still be "It don't work.", but in fact, much more of it works than did before. Getting audio through the audio path, and verifying that the depth pot and the trim pot both affect loudness at the output jack checks out the whole modulation path and the biasing for it. That leaves only the LFO oscillator.

As you may remember, the LFO oscillator had problems in the past as well. We're going to go back and settle those out. We were handicapped by the input jack confounding audio and power together. That may now be sorted out.

So let's see. Get out your voltmeter. Plug the black lead into the common or negative/black plug hole in the meter, and the red probe into the volts/ohms or red plug hole in the meter. Set the meter to be able to read 9V dc (probably a 20Vdc scale). Plug a guitar cord into the input jack to turn power on to the circuit, and clip your black meter lead to the lug of the input jack that connects to the sleeve of the jack.

Using your red probe, measure and record the following voltages:
- Tip and ring lugs on the input jack
- both ends of R4
- Both sides of capacitors C5, 6, 7, 8
- All three leads of the transistor
- both ends of R9, 10,11,12,13,14,15

Now unplug the guitar cord, set your meter to read ohms (100K or 200K scale). Leave the black probe on the input jack lug. Connect the red probe to the end of R9 nearest the center of the PCB (i.e., away from the wires).  Turn the speed pot and report whether the resistance changes smoothly from about 4.7k to 55K as you turn the pot. Now repeat that, but put the probe on the end of R10 nearest the center of the board, away from the wires.

I told you to measure a bunch of stuff, but I think the problem will pop out of that set of measurements.

[Toddy]

I only got a chance to do the ohm tests on R9 and R10 this morning before my son woke up. Both R9 and R10 change ohmage just as you described when the rate pot is rotated. So at least that's good!

I will get a chance to finish the voltage testing later this morning. A wire came loose and I have to resolder it back on the jack. That's what I get for trying to do things in a hurry!

Patiently awaiting free time,
Toddy

[R.G.]

No problem, do it when you can.

I have a herd of sheep to feed doses of wormer and trim hooves on, so I'm tied up for a while. 

[Toddy]

Had a chance to resolder my wires. I measured the voltages with the switch on and the guitar cord in. My results are pretty poor. The battery has 9.1 volts. When I measured the input jack ring it measured 1.1v, and the tip (going to R4) measured 0.0v. Therefore the rest of the circuit had no voltage running through it on any of the caps, R4, or the transistor.
I measured to make sure the battery connector was hooked up and there was 9.1v measured on the board so I know somehow the input jack has to be a problem still.
Please don't tell me I have the wrong input jack again...

Still puzzled,
Toddy

[R.G.]

Please don't tell me I have the wrong input jack again...

I won't - unless you do.   

It's picture time again. Take and post a picture of what you have. That worked great last time!

Now for the knowledge part, Go here: http://en.wikipedia.org/wiki/TRS_connector and read the background on that tip, ring, and sleeve are. What you want is a TRS (tip/ring/sleeve) jack that has no shorting/shunting contacts or switches, also known as an "open circuit TRS" or "stereo open circuit" jack.

The principle behind the use of this jack is that all normal guitar cords are mono, tip-sleeve, and not tip-ring-sleeve. The sleeve is just longer, covering where the ring contact would be. When you put a mono plug into a Tip-Ring-Sleeve jack, the tip and the sleeve lugs on the jack work just fine. The ring contact on the jack however, contacts the longer sleeve. In effect, the wire connected to the ring lug of the jack is shorted to the sleeve lug.

If the sleeve lug is grounded - and it always is in guitar use - then inserting the mono guitar plug connects the wire from the ring lug to ground. By making that the wire from the battery which you want to ground - the positive/red one in this particular pedal - the battery is turned on by inserting the plug. More importantly, it's turned off by removing it, and no external switch is needed.

It's worth noting that this is going to be one of those positive-ground pedals that cannot share a power supply with a negative ground pedal.

[Toddy]

Here are the pictures of the "stereo" jack from my town's Tandy Corporation store that sells Realistic products.



The red wire goes to battery (+) positive and the green wire goes to R4.



I know, I know...I'm not a photographer, but I play one on TV.
Toddy

[R.G.]

That does look like the right kind of jack. Easy to tell if it's wired right. Take the battery out of the battery clip. Connect your meter set to ohms to the external sleeve contact. Now probe first one, then the other lug. Both should be open circuit with no plug in. Now stick a plug in. One of the two lugs will now be shorted to the sleeve. The other, the tip contact, will not be shorted to the sleeve. The shorted one is the ring contact, and that's the one which should contact the battery positive lead through the PCB.

Having identified that, let's test it. Pull the plug out of the input jack, put the battery back into the battery clip. Turn your meter to measure volts, and put the black lead on the sleeve/ground contact of the input jack. Now touch the other lead to the terminal you identified as the ring lug. Does it measure -9v (battery voltage)?

If not, your wiring is incorrect from battery to the input jack.

[newfish]

...I'm hooked on this thread.  It's like a science-based Soap Opera!

[R.G.]

...I'm hooked on this thread.  It's like a science-based Soap Opera!

Yeah, but who's the mysterious stranger in town that everyone almost recognizes, but can't quite?

[Toddy]

Glad you guys are entertained. I am at wits end about this thing and I feel sorry for RG who has to deal with me!

Anyway, I broke out the alligator connectors, desoldered all the input jack wires and did the tests that you said. I found the ring, tip and sleeve. Then I clipped the clips on as instructed after identifying them. Now here comes the screwy part. The battery reads 9.0v at the board and from the negative battery connection up through the wire to the input jack. When the guitar jack is in and I measure the voltage it drops down to 1.1v no matter how I clip or unclip and rearrange the wires on the input jack.

What can be causing the voltage to drop 8.0 volts?

Yes, I fiddled with the depth and trim pots but still only 1.1 volts are reaching the board at R4. And yes, I measured the voltage with and without the guitar plug inserted.

I want comedian Steven Wright to play my part in this soap opera.
Toddy

[R.G.]

Glad you guys are entertained. I am at wits end about this thing and I feel sorry for RG who has to deal with me!

Entertained is not really the word, I guess. Are you familiar with the term "gallows humor", that being the action of making jokes just before one gets hanged? Making jokes when things look really bad is a good way of dealing with the emotional issues that can get in the way of good thinking.

The battery reads 9.0v at the board and from the negative battery connection up through the wire to the input jack. When the guitar jack is in and I measure the voltage it drops down to 1.1v no matter how I clip or unclip and rearrange the wires on the input jack.

What can be causing the voltage to drop 8.0 volts?

We're getting close to the center of the onion. We've already found that the LFO transistor was turned around backwards, and that the input jack (and power wiring) was the wrong type. We're getting close.

Batteries have an internal resistance. They cannot hold up their full voltage if they have to supply too much current. If you have a problem where the circuit pulls too much current, the battery will sag.

So now we have to check out the battery wiring. Remove the guitar cord from the input, and remove the battery from the battery clip. Set your meter to ohms and measure the resistance between the jumper J1 on the board and the two battery contacts on the battery clip. One should show zero ohms as well as your meter can measure it, the other should show more megohms than your meter can measure. Note which one is shorted to J1. Now measure the resistance between the ring contact on the input jack and the other terminal on the battery clip. This should be shorted.

Finally, measure between the jumper J1 and the ring terminal on the input jack, first with the red lead on J1, then with the black lead on J1 (this is because meters supply a DC voltage on the leads to measure resistance).

Report back what you find.

[Toddy]

OK,
J1 was shorted to the (-) negative battery terminal.

The positive (+) battery terminal shorts to the ring of the input jack.

J1 reads 1.1ohms with red lead on J1 and black lead on ring lug. With black lead on J1 and red lead on ring lug it cannot get a reading.

After this is done I'm going to make some onion soup!!
Toddy

[R.G.]

J1 was shorted to the (-) negative battery terminal.
The positive (+) battery terminal shorts to the ring of the input jack.

OK, so far so good.

J1 reads 1.1ohms with red lead on J1 and black lead on ring lug. With black lead on J1 and red lead on ring lug it cannot get a reading.

I believe something is pulling too much current from the battery, but can't tell exactly which.

Try this:
1. Remove C4, C9, J1 and Q3. Do this by using your soldering iron to melt both leads of the caps and all three of the transistor legs simultaneously. Be sure your iron is tinned and shiny-bright across the whole width you use to melt the solder on the leads. On J1, clip it in the middle of the wire, and just bend up the left hand side for measuring voltages. You will later remove each half one at a time when we get to that. Note very carefully before pulling the caps and transistor out which way round they are turned. My knee-jerk reaction is that perhaps C4 is backwards, so check that to be sure. The + end goes away from the wire side.

Open the holes on the solder side by taking a sharp pointed wooden toothpick, then melting the solder on each pad and poking the toothpick into the hole. This will leave a nice ring of solder around a clear hole for reinstallation.

2. Put the battery back in the clip, and insert the guitar cord plug in the input jack.

3. Measure the DC voltage between the black wire from the battery clip where it goes onto the board, or the bent-up left hand side of J1, to the bottom/ground side of one of these: R5, R6, R7, R14, or R15. This should be the battery voltage, a bit over 9Vdc.

4. If so,  (a) remove the battery from the clip (b) remove the halves of J1 and clear the holes (c ) solder in a new J1 wire.
5. Now, check again. Still 9V? go to step 6. If not, yell.
6. Solder in C4, being sure that the polarity is correct. Re measure voltage. Still OK? Yell if not.
7. Solder in C9, measure voltage. Still OK? Yell if not.
8. Solder in q3, measure voltage. Still OK? Yell if not.

In fact yell anyway. 

After this is done I'm going to make some onion soup!!

I was thinking more of onion beer. 

[Toddy]

Had a chance today to work on it and test it as you instructed. I have good news and not-so-good news. The good news is that as I went step by step (disassembling and reassembling) all the voltages measured a touch over 9V on all of the points you said to measure. Then I checked the voltage to the input jack and now THAT now measures a touch over 9V. I got excited when I saw that! So I decided to plug it in to my guitar and amp to truly see if that was the problem. That's where the not-so-good news happened. There still is no tremolo oscillation.

OK, keep on truckin'.
Toddy

[R.G.]

Had a chance today to work on it and test it as you instructed. I have good news and not-so-good news. The good news is that as I went step by step (disassembling and reassembling) all the voltages measured a touch over 9V on all of the points you said to measure. Then I checked the voltage to the input jack and now THAT now measures a touch over 9V. I got excited when I saw that! So I decided to plug it in to my guitar and amp to truly see if that was the problem. That's where the not-so-good news happened. There still is no tremolo oscillation.

Acutally, the not-so-good news is good news. You appear to now be getting correct voltage to the PCB.

Since we have worked our way through getting the depth pot and JFET to work, we only need to get the LFO to work. We've eliminated - what, three or four defects so far? - and have one or two more to go.

Here's the next set of tests. For reference, we are going to refer to directions as following:
like the picture in the article on my web page, the side of the board with wires exiting the board is "up". The non-wires long side is "down". Left and right are then correct per the picture.

1. Keep a battery in the clip, plug in a guitar cord to the input jack to let battery voltage go to the PCB.
2. Clip your meter's *black* lead to the sleeve/ground connection of the input jack, making sure it does not short to other parts of the jack/plug.
3. Use the *red* lead only and measure the DC voltages on both top and bottom ends of
- R8, R9, R10, R11, R12, R13, R14, R15 and Z1, and list each voltage as top or bottom voltage.
- left and right ends of C5, 6, 7 and 8, again listing voltage as "left" or "right".
- all four transistor pads from right to left: e, b, c, and the other b which should not be being used. List the letter with the voltage.

I know it seems like we've done this before - because we have. But we've also changed things in the circuit since we checked last time, and it's only now what we have verified that the correct DC voltage is getting to the PCB. Hang on, have another go.

[Toddy]

I must apologize. My last 9Volt battery in the house is dying at 8.9Volts but I think we recorded enough data (but a bit lower than it should be) to help.

                  top                bottom
R8              0.0                 7.0
R9              0.15               0.15
R10            0.15                0.15
R11            0.16                0.14
R12            0.0                  waivers ~ 0.46
R13            0.47                9.0
R14            0.11                9.0
R15            2.45                9.0
Z1              3.34                9.0

                 right                 left
C5              0.14                 0.11
C6              0.14                 0.15
C7              0.48                 0.15
C8              0.08                 2.45

transistor BC184C
e    0.48
b    0.11
c    0.48
empty b    0.11

Yes, I will get a new battery tonight when I get in from work. I did not get a chance to turn the depth pot or trim pots and do more measurements. Last time we had more waivering going on with C5, C6 and C7.

All right, Clancey. Take the boys and surround the house!
Toddy

[ppatchmods]

The suspense is killing me!!!

[R.G.]

I must apologize. My last 9Volt battery in the house is dying at 8.9Volts but I think we recorded enough data (but a bit lower than it should be) to help.

No biggie. We can work with this. The important thing is that something you did cleared whatever was holding your battery voltage down to 1.1V on the board. We don't know what it was, but now at least there is voltage on the board to work with.

top                bottom
R8              0.0                 7.0

The siren you hear is the sound of a fatal problem. If you connected up probes carefully as I told you and this isn't a measurement problem, then no battery voltage is getting to R8. I tossed this one in just to be sure that we still had good power on the JFET side, and we do not. The top end of R8 should connect to the -9V supply through J1. Did you remember to put another length of wire in for J1? If you did, there is a problem and voltage is not getting from one end of J1 to the other. If you used a 5.7V zener, then the voltages on R8 should be top =-9V and bottom = -5.7V.

Just to save some suspense, here are the voltages you should read on all the components, plus or minus a little for component tolerances:

R9               0.0               0.0
R10             0.0               0.0
R11            -9.0              -7.4
R12            -9.0              -7.8
R13            -6.2              -1.1
R14            -7.4               0.0
R15            -1.1               0.0
Z1              -5.7               0.0

                 right                 left
C5             -7.4                  0.0
C6              0.0                  0.0
C7              0.0                 -6.2
C8             -1.1                 (varies with trimpot)

transistor BC184C
e    -7.9
b    -7.4
c    -6.2
empty b    -7.4

To measure these correctly, it is quite important to put the black probe in the black/common hole in the meter, the red probe in the red/volts-ohms hole in the meter; then to clip the black probe to the ground/sleeve contact on the input jack. If  you do this, the jumper J1 should read -9V (OK, minus the battery voltage whatever that is), as should the top of R8, R11, and R12.

[Toddy]

I re-measured R8 (the 3.6K) today just to make sure. It actually does read -9.0v on top but only -1.7v on the bottom. And, I re-measured its value on the resistor itself and it reads 3.6K as it should. Bad part? Bad soldering job?

Once I my son goes off to his AM activities I will go down into my "Hidey Hole" (my workbench in the cellar), fire up the solder iron and resolder the joints. We'll see if that makes a difference.

It's just a flesh wound,
Toddy

[R.G.]

I re-measured R8 (the 3.6K) today just to make sure. It actually does read -9.0v on top but only -1.7v on the bottom. And, I re-measured its value on the resistor itself and it reads 3.6K as it should. Bad part? Bad soldering job?

Given the number of problems we've already found, could be bad karma too. 

Once I my son goes off to his AM activities I will go down into my "Hidey Hole" (my workbench in the cellar), fire up the solder iron and resolder the joints. We'll see if that makes a difference.

'S'worth a try.