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

[tristanc]

For now, is there anyone left producing circuit boards, preferably V3 or V4?

Is there a Vero layout for either of these versions?

I might have a couple remaining - drop me a DM. Or you can grab the KiCAD source / gerbers from https://github.com/tristancollins/pedals and get your own from PCBway or similar.

[DIY Dood]

For now, is there anyone left producing circuit boards, preferably V3 or V4?

Is there a Vero layout for either of these versions?

I might have a couple remaining - drop me a DM. Or you can grab the KiCAD source / gerbers from https://github.com/tristancollins/pedals and get your own from PCBway or similar.

Thanks... attempted PM, but it says your Inbox is full!

[tristanc]

For anyone else interested I have 5 boards available for the ET issue 2. Details and pics here:

https://www.diystompboxes.com/smfforum/index.php?topic=122355.msg1153513#msg1153513

Merlin has issue 4 boards available at his shop too.

[scott17]

Hello everybody, I'm new here.

Just an FYI for those that might be interested.
I purchased the Engineer's Thumb Compressor "parts only" kit from Das Musikding in Germany.
The kit came with everything except the enclosure and pot knobs, for $33.00 (27,90 EUR) including shipping.
I already had a project box, and including marking and drilling the box, this project took about 3 hours from opening the kit to completion.
YMMV, as I've been doing this kind of thing for a long time. This is a 5-knob kit, and as far as I can tell it is identical to the current schematic on Merlin's website with the exception of the MOSFET Millennium Bypass section, but it is true bypass via the footswitch.
The PC boards included are high quality. All resistors and diodes were soldered first, then IC/transistor sockets, then caps, then pots. I used a 1/8" spacer between the board and pots when soldering in place. Solder the switch to the switch PC board, then mount the LED to the enclosure first, then thread the switch PC board over the LED leads and tighten switch mounting nut before soldering the LED leads. I used different I/O jacks, but there is nothing wrong with the ones that come with the kit.
The circuit worked first time and sounds great! Thanks Merlin!

[mdcmdcmdc]

To the question about board availability, PedalPCB just released one.

[DIY Dood]

Following up on my inquiry... I just ordered the kit from Das Musikding in Germany per @scott17 's suggestion.

I'd need to hunt down buy nearly every component (aside from the box) as my stock is thin (newb). So, the slightly increased cost is worth it for me vs. buying a board from one of the folks here and then all components from a supplier like Mouser.

I'll report back after the build - or maybe before depending on the clarity of the kit.

[garcho]

You made the right choice, nothing wrong with a kit if you don't have many of the parts and aren't sure what you'll need in the future. And it's good to support businesses in the community. Without all the DIY/maker-friendly shops, prices would be higher for the weird old fashioned crap we use to build pedals with, and they would be much harder to find (compounding the price).

[eh la bas ma]

I built the same kit than Scott17.

Despite the controls description in the document, I have some difficulties to hear what is happening, and find the right settings to hear some changes in the guitar's sounds when the pedal is engaged and when it's turned off.
How could I dial the controls to have the most audible setting, aside from the odd clipping effect when Ratio is CW, and Treshold, Release are CCW ?

What settings do you like, to "improve" your sound or to have a nice compression feeling?

I am not sure how the Ratio control works. On my build the sound gets "quieter" going CCW.

"At the extreme we get limiting, where the output signal is maintained at a constant level no matter what the input level. This is exactly what you want for maximum sustain" : "extreme" is fully CCW ?

When Ratio is fully CW, then the sound gets quieter when Treshold is turned CW. Does it mean that compression increases when Ratio is fully CW ?

"Attack- The time it takes for the compression to kick in when a loud sound comes along." CCW is short time CW is longer ?

"Release- The time it takes for the gain to recover after the loud sound has passed" : this one I can hear it allright

"Threshold- How big the input signal has to be before compression can happen" : CCW is "not big" and CW is bigger ?

[Kevin Mitchell]

I am not sure how the Ratio control works. On my build the sound gets "quieter" going CCW.

With less compression it's going to amplify the signal less. So there's less compensation to keep the signal at a steady level.

If your input signal is too low the envelope will not function as strongly so the envelope sweep would be smaller.
If your power supply is too low you'll have less headroom and less of an audible difference, as it would cause a similar issue as I've mentioned above (being less wiggle room for the envelope and your signal)

If you think there's an issue with your pedal feel free to post voltages and photos.

[eh la bas ma]

Thank you, I don't think there is an issue, I'm just a bit confused with the controls...

[Ben N]

Is there some way to eliminate some of that duplication?

Yes, use a switching jack socket:

What is the practical effect (usage) of a side-chain input when we're dealing with a single guitarist and a pedal?

None, AFAIK, but it can be handy when used in a more complex signal chain, for example after a filter or light overdrive, where you specifically want the compression after the other effect, but want to feed it a clean, full-dynamic signal with a minimum of noise. Split & buffer the signal at the top of the chain, sending one signal into the audio chain and the other straight to the compressor sidechain. This approach can be useful for other envelope controlled effects, like a filter after a compressor--normally the compression would make the filter ineffective, but feeding its envelope follower a pristine, unsquashed signal brings back max quack.A clean sidechain into a noise gate is also cool (see Boss NS-2).

[Mark Abbott]

I have built the Engineers Thumb some years ago and I love how it is quiet, transparent, and provided I have the compression (Ratio) control set above 12 o'clock there is a lot of output.

I initially had an issue with output and I have done the mod recommended by Merlin to increase output and that worked well (decreased the 220 ohm resistor to 100 ohms.

However, I recently played a Mooer Yellow Comp and I was blown away by how much output it had, the EQ control and the great colouring it has. I dare say I will look for a secondhand one, but I thought there was room for improvement with my Engineers Thumb.

What other mods are recommended to boost output without the compressor distorting?

Thanks for your assistance and patience.

Kind Regards

mark

[rankot]

You can always add a simple amplifier after it.

[DIY Dood]

Need troubleshooting help.

I used the 5 knob kit from Das Musikding. Getting sound through, but effect is very crude. Threshhold seems to have limited effect except to push it to dull-mud at fully CW. Attack and Release have no perceptible effect.  Ratio seems to work and blend clean vs "compressed", but fully CW is very harsh. Gain also seems to be working, but at close to fully CW it's breaking up badly. No one would consider the sounds I'm getting usable.

I found a chart of voltages in Valve Wizard V4 circuit PDF.  It includes voltages at the IC's, some of which do not match my measurements of my circuit. Unfortunately the schematic from Das Musikding seems to be slightly different from the Valve Wizard versions 3 and 4 that I found. Some pins are not used in the Das Musikding edition. I started to look for where the feeds were coming from to the various pins where voltage vary, but the circuits vary enough that I'm not confident in my ability to cross interpret (I'm a newb!).

Below are my measurements in a comparative chart from the Valve Wizard V4 circuit. Please note: Das Musikding has swapped the IC designations - IC1 & IC2. The part #'s TL074 and LM13700 obviously apply, but the schematic names IC1/IC2 are flipped. 

If someone can tell me if these voltage measurements indicate issues and where, that would be great. Again, the voltage chart is from the Valve Wizard V4 schematic, not the Kit Schematic.

Readings with significant variation shown in bold. Nothing was plugged into the input or output. All controls were fully CW:



Kit Schematic:



Valve Wizard V4 schematic:

[garcho]

Double/triple check C3, C4, and C5 values, double/triple check C1 and C2 orientation, and double/triple check D4, D5, D6, and D7 orientation. Sorry it's vague, but that's where I would start.

[duck_arse]

Double/triple check C3, C4, and C5 values, double/triple check C1 and C2 orientation, and double/triple check D4, D5, D6, and D7 orientation. Sorry it's vague, but that's where I would start.

no, you'd start by looking at the parts on the board. show some photos so's we can join in, mebbe?

[DIY Dood]

OK... will do both!    I'll pull it out of the box tomorrow and post.

One question: The red diodes in the kit ( d5/d6 on the schematic) were not matched. One has a diffused light head (satin) and the other clear/bright. Obviously the light level doesn't matter inside the box, but clearly they were not the exact same part. Would that be a concern performance wise? Should I measure them with my DVM's diode scale and see how they check out? 

I do have other (new, matched) red diodes that I could swap them too... should I do that and re-test? Would I need to recalculate the value of R1 or is it not key in this sort of design?

[r080]

but clearly they were not the exact same part. Would that be a concern performance wise? Should I measure them with my DVM's diode scale and see how they check out? 

That is probably not necessary. The design page has a note about why they are there. The point is just to clip large incoming signals to prevent them from clipping in a bad way later in the circuit. Slightly different forward voltages will still be okay.

http://www.valvewizard.co.uk/engineersthumb2.html

"However, because of the OTA in the feedback loop, the circuit does not clip at all gracefully, and may even oscillate at some settings if overdriven. With so much headroom no ordinary guitar will manage this, but if you put a booster in front then it could be a problem. To fix this, a pair of standard red LEDs should be added in anti-parallel as shown. These will prevent the input signal from exceeding about 3Vp-p, resulting in graceful overload. "

[Sanguinicus]

Finally got around to finishing this after 1 year at the bottom of my project box. It sounds excellent but I find with the level at max it's a tiny bit above unity volume. Is it possible to bring unity back around half way on the pot? I want to have this as an always on pedal, even when I switch to high gain but I lose too much attack, like I'd have to compensate by increasing amp gain.

[Mark Hammer]

Finally got my own working, long after stuffing the board and wiring it up.  Turned out I had the BS170 flipped around wrong.

Very invisible-sounding.  I installed it in a 1590B box that I had prepped for a 3-knob overdrive that turned out to be disappointing.  In the absence of any legending on the box, I figured I'd re-purpose the box and add a 3rd control.  Decided to use variable Release, which turned out to be useful.  Went with a 20k resistor in series with a 1M pot, in place of the fixed 1M Release resistance.  Worked out well.  Shorter release times (lower resistance) yields a little more dynamics.  Short release with high Ratio settings gives a nice "pulled punch" snap on Tele bridge pickups.