Lumpy's Lemon Drop with Pre-gain

[tracer03]

I had the opportunity to get my hands on a Lumpy's Lemon Drop with an added pre-gain pot, so I traced the circuit and measured components, and here we are. It's built on stripboard, and I'll be building one today to verify.

There is an onboard CLR and connection to the LED, which I omitted (as it was at a weird angle - top 2 rows between the 47k and the trimmer), but this is traced and 1:1 with the existing pedal. I'm sure it could be tidied up, so if anyone wants to have a go at it...

[HamishR]

CONTENTS DELETED

The author has deleted this message.

[tracer03]

Well, I tried to build mine last night, and no sound. Didn't have time to debug, so not sure if it's a component/solder joint or the layout. I did compare to the existing pedal and it looks good, so I'll dig today and see if I can puzzle it out. May also try to build your version, just to see.

[tracer03]

Found a link that I missed, tried again, still no luck. I retraced the circuit, and laid it out exactly as it is on the working version. Still not sure what's wrong (if it's builder error, bad component, etc.) but will try to debug tomorrow. In the meantime, here's the layout 1:1 with the working 4 knob version.

EDIT: Removed old layout...

[tracer03]

Pics of the board:

[Frank_NH]

I think the 10K resistor after the JFET should be connected to Vol 3.  That hopefully will fix it.

[tracer03]

-- removed non-working layout --

Adjusted the layout, going to try building tonight.

[tracer03]

Still not working. I retraced and copied, and I'm stumped. There are a couple of resistors on the board that measure different than what their color codes show, so I'm not sure what's going on.

Edit: Pic of board.

[tracer03]

And a final layout, 1:1 with the board as I could see it. The resistor values R1 and R2 - I measured them and checked the color code, and they don't correspond.

(incorrect layout removed)

[Travis]

Measuring components in circuit tends to be inaccurate. “R2” should be your typical 1M hanging off the input. 2.2r will dump most of the signal to ground

The measurement of that resistor should change depending on the pregain setting, but I do not think you have the pregain correct

[SixStringTickler]

It looks like the cut directly above the 22n (on the upper right of the board), needs to go down two rows - between the JFET source and the 3n3 cap.

[induction]

Comparing your final trace to the working board:
1. The 47k resistor should be 470k (bias for the bjt gate)
2. The 43k resistor should 47k (bias for the bjt gate)
3. The 2r2 resistor should 1M (pulldown resistor. A 2r2 here will definitely kill your signal)
4. The 4n7 in the middle of the board should be a larger electro, possibly 4u7 (treble gain for the FET)
5. You don't have a ground connection (on the layout, not sure about your build)

Edit: The 'should be' values mostly match the original Lemon Drop schematic in addition to the markings on the components.

[tracer03]

Awesome, I'll make the corrections. (as for the ground wire, just forgot to add it - should be bottom row, right side).

[tracer03]

removed non-working layout

Changes and corrections made (cut under 22n, ground wire added, resistor values corrected, cap, etc.). I removed the onboard CLR and +LED connection for the moment.

Will try and build it up tonight and confirm it works.

[tracer03]

welp, no joy. I've double and triple checked the last layout against the existing board, and I'm stumped.

[induction]

How did you set the trimmer?

[tracer03]

induction wrote

How did you set the trimmer?

I tried it through the whole sweep. Didn't audio probe it (can't seem to find my probe atm) but I knifed strips, checked for bridges, etc. Had to step away from the bench before I could measure voltages (my daughter is home from college and we're 'sharing' the basement so I got kicked out...)

[induction]

The layout looks fine to me. I don't have a schematic to compare the pregain to, but this looks like it should work. The rest of it matches the lemon drop schematic I found.

Post photos and voltages if you like. I'm happy to take a look.

[Hozy31]

There is a layout from 2017 here. Seems some people find it hard to dial in initially.
http://tagboardeffects.blogspot.com/2017/09/lumpys-tone-shop-lemon-dropziiseries-7.html

[tracer03]

induction wrote

The layout looks fine to me. I don't have a schematic to compare the pregain to, but this looks like it should work. The rest of it matches the lemon drop schematic I found.

Post photos and voltages if you like. I'm happy to take a look.

Photos coming (phone died), but I measured the original unit I have (a fix for a friend):

D:5.94
S:0.9
G:0

and my build:
D: 6.05
S: 0.78
G: 0

I know I could likely dial it in closer to the OG unit voltages, but I think it's a component issue that's causing the lack of sound. I've double-checked/reflowed joints, checked/measured/resoldered pots, checked for bridges/knifed strips, etc.

Will post board photos tomorrow once my phone charges up.