Help troubleshooting DIY Tonebender MKII

[John Nada]

Hi there,

I'm having trouble building a Tonebender MKII kit from Das Musikding. This the the schematic:



Alright, the Tonebender MKII is the second kit I'm building from Das Musikding, so I'm kind of a newbie to the world of DIY pedals. The first one I did was the Plexi-Drive, which worked at the second attempt, after I figured out I did the classic thing of soldering the in and output the wrong way around.

With the MKII I get sound in bypass, but when I engage the pedal the sound is gone but the LED is working. I've used an audio probe to find the issue while using a frequency generator. When I test at the output the frequency is still there but very quiet. I'm sure it's the frequency I'm sending to the pedal, since I can hear the frequency changing when I use the slider on the generator. After going through the signal path, I noticed a drop in volume when it gets to Q2, the second transistor, the capacitor before that (C4) is still loud. When I check with a multimeter (measuring from the bottom side at the solder joints), all three points of the transistor show up to 9v (shouldn't that be half of that?!) and the same goes for R8. However, on R6 I only get a reading on the multimeter on the side closest to the second resistor, the other side stays at 0 both from the solder point as well as the lead of the resistor on the other side.

Is R6 the problem (resistor not working) or might it be somethig with the transistor itself? From here on the sound is very weakend but still there up to the output, at least as tested with the audio probe. With a guitar I hear nothing though. Who can help me figure out what to do next?

Kind regards,

John Nada

[John Nada]

By the way, , for what it's worth, this is the solder side of my PCB:




This is the component side:




And this is the wiring with the casing:

[Electric Warrior]

You're getting 9V where the transistor should be connected with ground and 0V on a lead that should connect with -9V. I bet it's neither the transistor nor a resistor.

What do you measure on Q1E and on R9 and R4 on the leads that should connect with the battery?

[thermionix]

I think the footswitch is wired wrong.  Remove the short black wire that runs between opposite corners, then report back.

[Electric Warrior]

I think the footswitch is wired wrong.  Remove the short black wire that runs between opposite corners, then report back.

That connects the circuit input to ground when the pedal is off. It should be correct.

[John Nada]

Might be an optical illusion by my image. The link goes from the left bottom to the one in the middle next to it. The one in the right bottom corner is linked to the one in the left top corner. This is according to the wiring diagram:



I should note that I did not attach anything for the battery, since I would never use that. So it's running on a power supply.

Q1E = 8.99
R4 = 0.47 at the transistor's side, 0 on the other
R9 = 0 left , 0.03 right (as seen from atop the components)

[thermionix]

The one in the right bottom corner is linked to the one in the left top corner.

Remove that one.  The wiring diagram is wrong, and doesn't jive with the schematic.  It connects board input to + voltage (not ground) in bypass, which may have killed C2 or Q1.

[John Nada]

EDIT!

I redid my measurements. The first time I did them, I grounded to the ground tip of the DC-jack, which turned out not to be the correct way of doing this. Sorry guys, I'm a rookie. I did all of it again with the ground to the enclosure. Here are the new results:

R1 (top): 0
R1 (bottom): 0
R2 (top): -0.08
R2 (bottom): 0
R3 (left): -8.99
R3 (right): -1.82
R4 (top): -8.99
R4 (bottom): -8.30
R6 (top): -8.99
R6 (bottom): -0.15
R8 (left): -0.07
R8 (right): -0.07
R9 (left): -8.99
R9 (right): -8.96
R10 (left): -8.45
R10 (right): -8.96

C1 (top): 0
C1 (bottom): 0
C2 (plus): 0
C2 (minus): -0.08
C3 (plus): 0
C3 (minus): -8.99
C4 (top): -8.11
C4 (bottom): -0.07
C5 (plus): 0
C5 (minus): -0.03
C6 (top): 0
C6 (bottom): -8.96

Q1C: -8.46
Q1B: -0.07
Q1E: 0
Q2C: -0.16
Q2B: -0.08
Q2E: 0
Q3C: -8.17
Q3B: -0.16
Q3E: -0.08

D1 (ring side): 0
D1 (plain side): -8.99

And once again as a reminder, I get a full sound until I get into Q2, there the sound starts to get a lot weaker.

[John Nada]

The one in the right bottom corner is linked to the one in the left top corner.

Remove that one.  The wiring diagram is wrong, and doesn't jive with the schematic.  It connects board input to + voltage (not ground) in bypass, which may have killed C2 or Q1.

That's strange, I'm not the first one building by this schematic and no one has mentioned this in the comments. C2 and Q1 seem to be still working with the audio probe as well as the multimeter.

[Electric Warrior]

The one in the right bottom corner is linked to the one in the left top corner.

Remove that one.  The wiring diagram is wrong, and doesn't jive with the schematic.  It connects board input to + voltage (not ground) in bypass, which may have killed C2 or Q1.

It's a positive ground pedal. +9V connects with ground.

Might be an optical illusion by my image. The link goes from the left bottom to the one in the middle next to it. The one in the right bottom corner is linked to the one in the left top corner. This is according to the wiring diagram:



I should note that I did not attach anything for the battery, since I would never use that. So it's running on a power supply.

Q1E = 8.99
R4 = 0.47 at the transistor's side, 0 on the other
R9 = 0 left , 0.03 right (as seen from atop the components)

You're probably not measuring correctly. One lead of your multimeter should go to ground (enclosure, ground plane on the board, sleeve tab of a jack...).

[John Nada]

Might be an optical illusion by my image. The link goes from the left bottom to the one in the middle next to it. The one in the right bottom corner is linked to the one in the left top corner. This is according to the wiring diagram:



I should note that I did not attach anything for the battery, since I would never use that. So it's running on a power supply.

Q1E = 8.99
R4 = 0.47 at the transistor's side, 0 on the other
R9 = 0 left , 0.03 right (as seen from atop the components)

You're probably not measuring correctly. One lead of your multimeter should go to ground (enclosure, ground plane on the board, sleeve tab of a jack...).
[/quote]

I had the black alligator clamp mounted on the ground of the dc input.

[Electric Warrior]

I had the black alligator clamp mounted on the ground of the dc input.

sounds as if that actually was -9V.

[John Nada]

I had the black alligator clamp mounted on the ground of the dc input.

sounds as if that actually was -9V.

Well I'm new at this, so still learning, still figuring out how to do some things correctly. I did the audio probe with the ground connected to the enclosure, the multimeter testing with ground mounted to the ground tip of the dc-input jack. Should I re-run the multimeter measurements with ground to the enclosure as well?

[Electric Warrior]

Please do. But please don't take so many measurements again now that we've figured out what caused those funky measurements. Voltages on all transistor leads should give us plenty of information.

[thermionix]

It's a positive ground pedal. +9V connects with ground.

Yeah my bad, I came back to correct that.  My post was made before coffee, that's my excuse.

[Electric Warrior]

It's a positive ground pedal. +9V connects with ground.

Yeah my bad, I came back to correct that.  My post was made before coffee, that's my excuse.

"before coffee" is an excellent excuse for just about anything. nearly as good as "well, it was the 60's" 

[John Nada]

Please do. But please don't take so many measurements again now that we've figured out what caused those funky measurements. Voltages on all transistor leads should give us plenty of information.

Pardon me. Here it goes, with ground to the enclosure:

Q1C: -8.46
Q1B: -0.07
Q1E: -0

Q2C: -0.16
Q2B: -0.08
Q2E: -0

Q3C: -8.17
Q3B: -0.16
Q3E: -0.08

[PRR]

My 2 cents says R6 is not really connected at both ends.

[Electric Warrior]

Q1C: -8.46
Q1B: -0.07
Q1E: -0

Q2C: -0.16
Q2B: -0.08
Q2E: -0

Q3C: -8.17
Q3B: -0.16
Q3E: -0.08

That looks spot on. I don't see any obvious issue here...

[John Nada]

Q1C: -8.46
Q1B: -0.07
Q1E: -0

Q2C: -0.16
Q2B: -0.08
Q2E: -0

Q3C: -8.17
Q3B: -0.16
Q3E: -0.08

That looks spot on. I don't see any obvious issue here...

Strange, especially since the volume really drops at the second transistor. What's the next step to check, or are there any other measurement I can take or something else I can check or post here to find the root of the problem?