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

[auden100]

I had a similar issue. This was the reply at the time.

Is there any thing in the circuit that could be changed that would provide more volume?

I *think* if you change R8 from 220R to 100R you will get a 6dB boost.

[EeroN]

I had a similar issue. This was the reply at the time.

Is there any thing in the circuit that could be changed that would provide more volume?

I *think* if you change R8 from 220R to 100R you will get a 6dB boost.

Thanks! I'll try that, it's easy enough to tack another 220 in parallel and see what happens.

[EeroN]

Yeah, that did it.

Thanks!

[suryabeep]

Hello!
I built an engineers thumb redux as made by jonny.reckless,  but it is not working. Bypass works fine, but switching it on creates a very loud pop (even though I'm using a switching board that has almost eliminated that from all my other builds). There is no sound when I'm strumming at a low volume, but strumming hard produces a loud crackling noise. I can't really tell if the gate on/off switch is having any effect on the noise.
I've gone over the bottom of my board for any solder bridges - none so far.
Here are my voltages:
MAX1044 pins 1-8:
4.57, 4.63, 0, -4.16, -8.22, 4.69, 4.51, 9.32
TL072 1-8:
-4.89, -4.59, 0, -7.29, -4.65, -3.44, -4.54, -5.36
LM833 1-8:
8.44, 8.47, 8--(decreases when I probe it), -7.22, 0, 2.91, -6.21, 9.58
TL074 1-14
-6.29, -5.73, 0, -6.78, 0, -6.33, -6.33, -6.25, 0, 0.56, -7.27, -0.20 (increases slowly to 0), -6.32, -6.31
LM13700 1-16
-6.31, -0.01, 0.18, 0, 8.47, -7.26, 0,0,0.01, 0, 9.57, 8.47, 0, 0.18, -0.01, -6.31
J201 dsg:
9.57, 9.57, 7.25
BC556 (Q3) EBC:
-3.44, -4.19, -3.45
BC556 (Q1) EBC:
-7.28, -7.98, -8.20

I've never had to troubleshoot anything this complicated before, so I don't even know where to start
The schematic i'm using is attached below.
Thanks!

[merlinb]

I've never had to troubleshoot anything this complicated before, so I don't even know where to start
The schematic i'm using is attached below.
Thanks!

Those numbers hurt my eyes. Maybe you could write them on the schematic itself, in the relevant locations, and reattach it? Preferably in a new thread.

[PRR]

> The schematic i'm using is attached below.

Has errors. Missing a ground under LED1 LED2, which is why the JFET voltages are all jammed high.

The parts with more than 3 legs, it is just too tedious to have one finger in your listing counting pin numbers and the other finger on the plan.

And Merlin has a point. This is not *his* ET but a different (derived) project, and maybe best kept apart.

[domestic-bliss]

Hi everyone.... new member [but played guitar on off and always been into effects/tone in general since probably about well 1992 aged 8 lol]
realy want to build the all singing all dancing version of this [with noise gate etc and as best as possible for metal]
I want to use it along with a diy [hopefully although might buy a cheap one and mod it who knows open to suggestions here] tube screamer.....
I play metal [almost djent tbh think obsolete/demanufacture ish era fear factory with a dash of type o yes im a weirdo]
so the usual convention is ....
guitar [with obligatory emg81] - noise gate - compressor  - tube screamer - amp - and an eq in the fx loop.....................
would putting the redux engineers thumb and a tube screamer type unit in one box to go in front of the amp [il be actualy using a line 6 x3 live hopefuly but wel call it the amp for now] be doable?
i see there is a few variable options available which would probably suit me better ?
realy liking this engineers thumb .............. and my close friends circle are not strangers to electronics
massive thanks to all in this forum ive learnt a ton in the day or two ive known about it lol
:-)

[jonny.reckless]

Hello!
I built an engineers thumb redux as made by jonny.reckless,  but it is not working.

In your circuit you are missing the feedback around IC2A. There should be 220 ohm and 10uF in series to ground from the inverting input. The gate won't open without the extra gain. This stage has a gain of several thousand at max.

I think you have also got the +9V to the op amps wired up incorrect. The supply goes to the opamp pin, and the decoupling cap goes from the pin to ground. As shown the decoupling cap is in series with the positive supply.

The input stage ground is missing. Pin 3 of IC3 needs to be grounded. There may be other issues.

I have a fully debugged PCB available if you want to build one. The layout is important if you want to avoid parasitic oscillation or poor noise performance.

[thehallofshields]

I've built 2 of these now that didn't work. 

When 'Ratio' is cranked up, I'm just getting clean + background fuzz with no compression.
I'm hoping that the problem is a bad batch of CA3080 chips.

[thehallofshields]

I'm set on using pots instead of toggles for this build, so I'm going to try this treble control.



If it doesn't have enough of an effect, I'll just put the Treble Boost mod as always on, then put a passive Tone Control at the end of the circuit.

[Elijah-Baley]

Hi guys, I need help with this compressor.
I'm using the sabrotone veroboard layout, and I included even the two leds that was missing.
I got a bump when I switch the effect, the noise is an high pitch snap amplified from the compressing, indeed with Ratio at zero I have no bump.
I tried to use a 1M resistor from input to ground, but it didn't solve.

Please help, the pedal is for a friend.

Edit: If I put a Jan Ray clone after it I can reduce the bump, but a pull down resistor in the input or in the output, 1M or 39k, don't solve it.

[FlyingWild]

Hello,

I've just read the near 30 pages here and Valve Wizards web page for version II, and I'm pretty much all set, but can I just ask, if I have understood things correctly, it appears that the Threshold and Ratio controls have a similar effect, for those that have built it and used this compressor, is there an advantage to having both the Ratio and the Threshold control? I'm not adverse to putting in the extra pot, but if they effectively achieve the same end result, I'd rather keep it to just four knobs and stick to the 1M resistor for the threshold.

Many thanks, Chris

[rankot]

I've built 2 of these now that didn't work. 

When 'Ratio' is cranked up, I'm just getting clean + background fuzz with no compression.
I'm hoping that the problem is a bad batch of CA3080 chips.

Don't bother using CA3080 ICs, they're most probably fake. Use LM13700 in parallel.

How did your "tone" pot work?

[PRR]

> the Threshold and Ratio controls have a similar effect

They do quite different things, at least for wide dynamic range input.

Look at another "compressor". You want to have a parade. You do not want tall-and-short marchers and a lumpy mob, you want all about the same height.

Threshold: anybody under this height we leave alone.

Anybody over the threshold, we cut some off the top.

Ratio: A 2:1 ratio we cut half the excess. A 10:1 ratio, we cut 90% of the excess.

_I_ would go ahead, blow the buck, have all likely knobs on my first build. Perhaps after extended playing, I might find one or the other can be left pre-set. But until you play a lot (on many types of music) you can't be sure.

[FlyingWild]

Thanks PRP,

Your explanation on how the two controls differ is very useful, the only reason for me asking the questions is this post from Merlinb:

Just wondering what it is about the design that means the threshold control isn't really worthwhile.

Basically because it is soft-knee compression. When you're operating in and around a soft knee, turning down the threhold has a very similar effect on the transfer function as as turning down the ratio. You can see that to the left of the red line (i.e. around the knee) both graphs look very nearly the same, so if your signal spends most of its time in this region, you won't notice the difference between using the threshold control or the ratio control.

But I'll take your advice and build the five knob version, this will be my first project designing a PCB layout! so a lot of learning and no doubt mistakes ahead.

Thanks again, Chris

[FlyingWild]

Hello,

I'm drawing out the schematic for a five knob version of the Engineer's Thumb V2 in Eagle, and I'm struggling with the potentiometers, particularly the threshold knob, knowing whether pin 1 or pin 3 is connected to the 4.5v rail.

The data sheet for the Alpha pot https://www.rapidonline.com/pdf/561734_v2.pdf numbers the pin as shown in my photo:



And here is that section of the schematic I've drawn out:



It would be most helpful if someone could say whether I have got the threshold pot the right way round in the schematic or not. I think the other pots are correct, but happy to told otherwise. My plan is to use PCB mounted pots so it would be nice to get it right first time.

Many thanks, Chris

[rankot]

I've put CCW (1) to 4.5V and CW (3) to C3, so I believe your schematic is OK.

[PRR]

> knowing whether pin 1 or pin 3 is connected to

See the arrow on each pot symbol? This points to the "full up" end of the pot travel.

(I could swear we had this debate already, maybe in this thread.)

[merlinb]

I'm struggling with the potentiometers, particularly the threshold knob, knowing whether pin 1 or pin 3 is connected to the 4.5v rail.

Threshold is a funny one because some people will expect the threshold to be raised as you turn the knob clockwise; like, give it more threshold, man. That means compression kicks in later.
But some people expect knobs to 'do more effect' as you rotate clockwise. That means you want the threshold to lower; like, give it more sensitivity, man.

Which you choose is up to you. If you want the threshold to raise as you turn clockwise, 4.5V goes to CW pin (3).  Otherwise it goes to the CCW pin (1). Guitarists notoriously don't know how to use compressors, so I would choose the latter for a stompbox, and the former for a studio compressor.

EDIT: Not sure if that was the question you were asking 

My plan is to use PCB mounted pots so it would be nice to get it right first time.

You can check for yourself when you lay out the PCB, since you will see the 4.5V net connecting to one pad or the other. You can always switch back to the schematic and reverse the connections.

[bluebunny]

Guitarists notoriously don't know how to use compressors

I lent my ET (and some others) to my tame guitarist to try out...

TG: It doesn't sustain as much as my xxx compressor.

BB: There's no such thing as sustain (explains what compressors actually do...)

TG: It doesn't sustain as much as my xxx compressor...