THE ENGINEER'S THUMB... At last, a better compressor!

[musiclikscreams]

^Amazing

[merlinb]

I liked the original version of The Engineer's Thumb so much that I had to build the 5-knob version.  I guess you could say I am "all Thumbs" now

Looks stunning! Glad you like it 

[InLimbo]

Hey guys,

First off, props to merlinb for this awesome design.

I've recently decided that I'd like to try to build my own pedal and thought that this project would be a great starter. I apologize for the total noob question, but I have absolutely no idea on how to wire up the input and output jacks to the vero layout (I'm using stereo jacks). I've stared and wondered at the picture of the PCB version with stereo jacks (on page 5) without having any luck. I really like how the vero layout has the wiring for the switch and the pots, and was wondering if there was a way that someone could quickly throw the input jacks and their wiring in the same way. Really all the wiring would be extremely helpful.

Here's what I have so far:



*Note that the bottom row of the vero layout actually starts on the second from the bottom on my layout.

Also, this is my first post after being a long time lurker and drooler at some of these creations.

Any help will be greatly appreciated!

[psychedelicfish]

This page should be helpful.
If your jacks are both metal, only connect one of the sleeve tabs to the ground, and leave the other one hanging. That way you won't get a ground loop through your enclosure (ground loops act as aerials and pick up tonnes of nasty hum and radio interference). Make sure your power jack is a plastic one if you're planning to wire it center negative (what seems to be the standard for pedals).

What you have there looks pretty good for a first project!

[InLimbo]

Oh, that link is super helpful. My jacks are plastic with 6 metal tabs. Looking at the picture on page 5 or so, I have the same jacks as those. There's a tan wire, and two black wires going straight from the jacks to the PCB. I'm not sure where they are going to.

Thanks for the reply. I've already learned a lot!

[InLimbo]

Also, on that link you sent me, it has the wiring for a battery clip, which I will not be using any batteries for this build. So should I just wire the negative off the center and leave the other hanging, or jump them together?

[merlinb]

Oh, that link is super helpful. My jacks are plastic with 6 metal tabs.

[InLimbo]

Awesome! Thanks so much. I can't wait to get this thing rolling over the weekend!

[laird]

A few months ago I built an Engineer's Thumb but haven't been able to get it working quite right. I followed Merlin's vero board layout (on the last page of the PDF) with three modifications: Adding a release control (replace R12 w/ pot), a threshold control (replace R5 w/ pot), and a positive battery disconnect when the power jack is in use.

With the controls set at their defaults (volume and release maxed, ratio and threshold minimized) it passes audio through at unity gain with no compression. That's the closest it gets to behaving correctly. As soon as the ratio is turned above dead zero I get a significant hiss, and the output (quiet and loud alike) goes down as the knob goes up. No compression, just attenuation. Weird noises happen when the release is set to zero, but that's to be expected.

When I first built it I used a 2N3906 as the PNP transistor in Q1 and a JRC13600D as a sub for the LM13700. I might've had the 2N3906 installed backwards - it looks like its pin arrangement is opposite the BC327. A few weeks ago I put in a BC327 in Q1 and a LM13700, as well as replacing the TL074 just in case. The voltage readings are practically unchanged before vs after.

Supply: 9.34v
Q1e: 2.97
Q1b: 2.36
Q1c: 1.40

IC1 (TL074):
Op1 (constant voltage source)
1 (1OUT) 4.67
2 (1IN-) 4.67
3 (1IN+) 4.47
4 (VCC+) 9.34
Op2 (main gain stage)
5 (2IN+) 4.32
6 (2IN-) 4.67
7 (2OUT) 4.70
Op3 (side chain 1 - charger)
8 (3OUT) 4.97
9 (3IN-) 4.67
10 (3IN+) 4.67
11 (VCC-) 0
Op4 (side chain 2 - bias control for lm13700)
12 (4IN+) 2.90
13 (4IN-) 2.97
14 (4OUT) 2.36

IC2 (LM13700)
pins 1-7,10 are all 0v
pins 8 and 9 are not connected and read floating/leaking voltage that stabilizes down to around 0.3v with the multimeter connected
11 (V+) 9.34
12 (2OUT) 4.67
13 (2IN-) 4.67
14 (2IN+) 4.67
15 (2D bias) 0
16 (2A bias) 1.40

Running a square-wave signal generator into the input (2v P-P @1khz, which should be WAY more than enough to trigger compression) I don't see any change in the bias voltage going from Q1 to the LM13700. This points to something wrong with the side chain... based on the voltage readings I'd guess there's a lot of constant current flow going on there. Does anyone have any idea what I should look at next?

Thanks,
-Laird

[InLimbo]

Alright, I need a little bit of trouble shooting guidance. A few posts above, you can see what my layout looks like for reference.

The issue is that when the pedal is engaged, I get no audio. When bypassed, my signal runs through just fine, as it should. So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1. Thinking that it may have been a bad resistor, I replaced it, checked the new one, same thing - 0 value. I checked the old one and it right around 10M as it should. The majority of the other resistors I've checked have been reading correctly as well.

PS - 8.95

Q1
e - 4.52
b - 4.05
c - 1.09

Q2
e - 6.44
b - 0
c - 8.93

IC1
1 - 4.52
2 - 4.52
3 - 4.30
4 - 8.92
5 - 4.10
6 - 4.50
7 - 4.50
8 - 4.52
9 - 4.52
10 - 4.09
11 - 0
12 - 4.1
13 - 4.51
14 - 4.04

IC2

1 - 0
2 - 0
3 - 0
4 - 0
5 - 0.01
6 - 0.01
7 - 0.01
8 - 0
9 - 0.98
10 - 0.01
11 - 8.88
12 - 4.50
13 - 4.50
14 - 4.50
15 - 0.01
16 - 1.09

Any help would be greatly appreciated!

[waltk]

The issue is that when the pedal is engaged, I get no audio. When bypassed, my signal runs through just fine, as it should. So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1. Thinking that it may have been a bad resistor, I replaced it, checked the new one, same thing - 0 value. I checked the old one and it right around 10M as it should. The majority of the other resistors I've checked have been reading correctly as well.

I didn't look at your voltages, and don't know anything about vero, but can explain something about measuring that 10M resistor.  If you're trying to measure it in-circuit, and getting zero resistance, that just means your input is shorted to ground.  That resistor goes directly from input to ground, and is unlikely to be bad (as you found when you measured it out of circuit).  When you measure something in-circuit, you're really measuring it and everything it's connected to.  So it could be that your input is being shorted to ground somewhere off-board (like in your switch or jacks), or it could be a solder bridge or misconnection elsewhere on the board.

[garcho]

So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1.

Was the pedal powered when you measured resistance? It has to be on to measure voltages but it has to be off to measure resistance.

What layout or schematic are you referring to?

[InLimbo]

The issue is that when the pedal is engaged, I get no audio. When bypassed, my signal runs through just fine, as it should. So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1. Thinking that it may have been a bad resistor, I replaced it, checked the new one, same thing - 0 value. I checked the old one and it right around 10M as it should. The majority of the other resistors I've checked have been reading correctly as well.

I didn't look at your voltages, and don't know anything about vero, but can explain something about measuring that 10M resistor.  If you're trying to measure it in-circuit, and getting zero resistance, that just means your input is shorted to ground.  That resistor goes directly from input to ground, and is unlikely to be bad (as you found when you measured it out of circuit).  When you measure something in-circuit, you're really measuring it and everything it's connected to.  So it could be that your input is being shorted to ground somewhere off-board (like in your switch or jacks), or it could be a solder bridge or misconnection elsewhere on the board.

Ah, I see. I'm using the layout that merlib gave - it's a few posts above, and also on the first page which also has the schematic. It goes straight from input to the ground, as you can see in the layout, which explains the 0 value. A solder bridge is what I'm afraid of, but there doesn't seem to be anything that I can see.

I apologize, this is my first build so I'm still trying to learn how these things work.

So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1.

Was the pedal powered when you measured resistance? It has to be on to measure voltages but it has to be off to measure resistance.

What layout or schematic are you referring to?

The pedal was powered on when I measure the voltages I listed, but was unpowered when I measured the resistance. So, I at least did that right.

[deadastronaut]

just a note on why my attempts to breadboard this, and the mutron v, and ms20,  failed :  fake bloody 13700's ...man those snide chips can really waste a LOT of time and effort..

i have new IC's now.. buy cheap, pay twice i guess.

[InLimbo]

just a note on why my attempts to breadboard this, and the mutron v, and ms20,  failed :  fake bloody 13700's ...man those snide chips can really waste a LOT of time and effort..

i have new IC's now.. buy cheap, pay twice i guess.

At this point, I'm hoping that it's a solder bridge rather than that. Fortunately, I believe I have 4 other 13700's lying around, so hopefully I have at least one good one if that is the case.

[garcho]

just a note on why my attempts to breadboard this, and the mutron v, and ms20,  failed :  fake bloody 13700's
i have new IC's now.. buy cheap, pay twice i guess.

Booya! Happy to see D'Astro back in the OTA game. Quite a chip...

[deadastronaut]

@inlimbo:  yep hopefully.

i had 4 that were ....... .......

@gary: yep just finishing up some stuff, then i'll be back on these projects.. 

[merlinb]

At this point, I'm hoping that it's a solder bridge rather than that.

Your voltages look OK, and I can't see any problems with the top side of the board. Did you add a status LED and does it work?

Most common things to look for:

• A trace that is supposed to be cut but hasn't.
• A trace that has been cut in the wrong place.
• Incorrectly wired off-board components.

[InLimbo]

At this point, I'm hoping that it's a solder bridge rather than that.

Your voltages look OK, and I can't see any problems with the top side of the board. Did you add a status LED and does it work?

Most common things to look for:

• A trace that is supposed to be cut but hasn't.
• A trace that has been cut in the wrong place.
• Incorrectly wired off-board components.

Thanks for the reply, Merlin. I tried both with and without an LED. I'm using the same LED for this as the protection LEDs for testing, and it does light up when the pedal is engaged.

So far, the thought about the input going straight to ground seems to be the most plausible. When I get a chance over the next day or so, I'm going to try and get a shot of the underneath side of the board along with the off-board components I have soldered for testing purposes.

Thanks for your help so far - I'm glad I've chosen this as a first try as you've been extremely helpful.

[InLimbo]

Here's the pics of the bottom side of the board and the off-board wiring. Please note that the janky Radio Shack battery clip cable broke while positioning it for the picture. This battery clip is for testing purposes only - my final build will not have any battery capacity, as I have a powered pedal board. On the underside of the board, I left R1 leads uncut to easier test the resistance with a meter.

Any feedback will again be appreciated!