Engineer's thumb distortion : a further attempt to solve the issue.

[eh la bas ma]

Hello,

Seeing how Engineer's Thumb distortion has been quite fashionable for some time now, I thought I would join the party.
I mean it's now or never, right?

I will race with Wook22 and Matopotato, let see who will solve this first !

We all seem to have the same symptom, I wonder if we all made the same mistake.

I built a kit from musikding :

https://www.musikding.de/docs/musikding/engineer/engineer_schalt.pdf

Here is a sound clip of my distortion :
https://soundcloud.com/ehlabas-ma-chaussure/engineersthumb-distortingwav-1

And here is a picture of the inside of my build :



Every suggestion is welcome !

[puretube]

You solve it first: lift off pins 8 & 9 of the LM13700.
These are the buffer outputs.
Should not be grounded directly!
Leave open when buffer is not used!
The Pedal-PCB "Thumbsucker" shows them grounded in the schemo: fail!
The Musikding kit seems to show them grounded in the pcb-layout: fail! (if they are).
The Valve-Wizards original schemo shows them unused or does not even show them (n.c.).
His (old PCB - 2012) seems to show them grounded as well, however. (overseen?).

There you go.



ps: grounding the buffer-outputs does not ruin the chip, because they can withstand it according to the datasheet, but I think it can cause some "irritation" inside the IC...
https://www.ti.com/lit/ds/symlink/lm13700.pdf

(maybe by measuring the current-consumption of the whole pedal and comparing un-/grounded buffer-outputs reveals a significant difference?)
(the buffer-inputs may be grounded, however, when not in use).

[Wook22]

Hello,

Seeing how Engineer's Thumb distortion has been quite fashionable for some time now, I thought I would join the party.
I mean it's now or never, right?

I will race with Wook22 and Matopotato, let see who will solve this first !

We all seem to have the same symptom, I wonder if we all made the same mistake.

Hopefully the suggestion above will assist you. Having listened to your audio clip, your distortion sounds very similar to mine, although mine is more pronounced on the lower (thicker) strings for some reason.

Unfortunately it doesn't appear on my build that the pins mentioned are grounded, confirmed with a multimeter.

Good luck. Hopefully there is a simple answer to this!

[eh la bas ma]

You solve it first: lift off pins 8 & 9 of the LM13700.
These are the buffer outputs.
Should not be grounded directly!
Leave open when buffer is not used!
The Pedal-PCB "Thumbsucker" shows them grounded in the schemo: fail!
The Musikding kit seems to show them grounded in the pcb-layout: fail! (if they are).
The Valve-Wizards original schemo shows them unused or does not even show them (n.c.).
His (old PCB - 2012) seems to show them grounded as well, however. (overseen?).

Thanks for your help !

I checked with a multimeter, and pin 8 and 9 aren't grounded. Pin 6, for exemple, does ring if I do a continuity test with Ground. I am not sure how to read what the schematics is showing though, looks like they are going nowhere, meaning "unconnected" ?



DrALx suggested in Wook22's thread :

"(...) If i was going to play with things, I would add a 1k trimmer in series with that 1k resistor on the emitter of the PNP (so you can vary the total resistance from 1k to 2k) and see how things behave with increased resistance there."

I guess it's R11 on my shematics. I will try this with a B1k pot as variable resistor, instead of a trimmer, and report.

Edit : looks like i'm slightly behind Matopotato and Wook22 in this distortion quest... I ll do my best to get to the final boss and the treasure chest first...

[duck_arse]

if the buffer inputs are also grounded, it doesn't matter that the outputs are ground, because the transistors that make-up the darlington pair buffer will then never turn on. looking at the musicding schem shows those 4 pins not connected, yet looking at the pcb trace in their docs, they all seem to share the pin 6 [V-] copper. they ought to correct their docs. anyone building that pcb should show 0 Ohms between pins 6, 7, 8, 9, 10. [I think. from what I can see. I'm standing to be corrected ....... ]

the thumbsucker docs don't show the pcb traces, and the circuit diagram shows the mechanical drawing instead of the electrical drawing of the lm13700 [tsk tsk, really?], but at least they show that those pins 6 - 10 are all grounded. see previous paragraph.

but never mind my blather, the rules still apply - we want to see your IC voltages, transistors etc. always.

[puretube]

Yes, duck_arse: it`s very irritating that we`re dealing with 5 slightly different schemos
(ValveWizard"E.T.2012"; ValveWizard"E.T.2016"; PedalPCB"Thumb Sucker"; Musikding"E.T. Kit"; "Supreme Compressor")
with at least 3 differentpcb-layouts (ValveWizard; PedalPCB; Musikding),
where the schemos don`t all agree with their corresponding PCBs for 100%
and all bear different or no component-designators ...

[duck_arse]

for eh la bas ma, wook22, matopotato - where did each of you source those lm13700's from? and just for fun, could you all each please enter here the markings on your parts, including any batch or date codes, please?

and eh las bas, don't be shy with those voltages.

[matopotato]

Yes, duck_arse: it`s very irritating that we`re dealing with 5 slightly different schemos
(ValveWizard"E.T.2012"; ValveWizard"E.T.2016"; PedalPCB"Thumb Sucker"; Musikding"E.T. Kit"; "Supreme Compressor")
with at least 3 differentpcb-layouts (ValveWizard; PedalPCB; Musikding),
where the schemos don`t all agree with their corresponding PCBs for 100%
and all bear different or no component-designators ...

Yes, it adds to confusion not having one schema and one layout. Especially if you do not have the build yourself.
On the other hand, despite those variations, I am leaning more and more towards that we have the same problem. So I  would vote for the culprit being in what is in common between the three. Or five...
I will try to measure and tweak the current to the LM13700. I guess it is on pin 1?

[eh la bas ma]

Hi Duck_Arse, I wonder how your Flying Spanner is doing ?

for eh la bas ma, wook22, matopotato - where did each of you source those lm13700's from? and just for fun, could you all each please enter here the markings on your parts, including any batch or date codes, please?

Coming from musikding's kit. On the chip I can read 557LRJ4E0   LM13700N
Edit : On the back i read : Phillipines 08 or 04 (not sure, number is hard to read) and BG O in the other circle.

and eh las bas, don't be shy with those voltages.

Here are my readings, pedal switched off, all controls at 12' :

DC 9V+ = 9.50 V

BC327

E= 4.60 V
B= 4.19 V
c= 1.122 V

TL74 ACN

1= 4.62 V      14 = 4.61 V
2= 4.61 V      13 = 4.62 V
3= 4.36 V      12= 4.15 V
4= 9.23 V      11= 0 V
5= 4.37 V      10= 4.42 V
6= 4.62 V      9= 4.62 V
7= 4.63 V      8= 4.19 V

LM13700N

1= 1.120 V     16= 0 V
2= 0.6 V         15= 0.8 V
3= 4.62  V      14= 0.5 V
4= 4.62  V      13= 0.6 V
5= 4.62 V       12= 0.7 V
6= 0  V           11= 9.23 V
7= 0  V           10= 0 V
8= 0.5 V          9= 0.650 V

I also read this thread from reply #31 :

https://www.diystompboxes.com/smfforum/index.php?topic=105610.20

It seems Rankot had a similar issue, and he managed to solve it by "skipping the buffer"

OK, I have just tried with TL071 instead of NE5534 in my second build and it sounds the same. Then I tried to remove the JFET input buffer, proposed by Jonny Reckless in some of the posts of the main thread, because that was the last thing not the same comparing builds one and two. And it seems that skipping the buffer did the trick - it works as expected! I just notice some faint rattling on the very end of the note decay when Threshold pot is at minimum - pin 3 of B is at 4.23V. When turned to max, pin 3 gets at 3.83V and no rattling at all. Is that normal, or I have to look for something else? Maybe cause I used 100n instead of 10n for C3?

I will try to put NE5534 back and see what happens now. Maybe the input buffer was the only problem!

I wonder how I could try that on my build ? What should I do to skip this buffer ?

[matopotato]

for eh la bas ma, wook22, matopotato - where did each of you source those lm13700's from? and just for fun, could you all each please enter here the markings on your parts, including any batch or date codes, please?

and eh las bas, don't be shy with those voltages.

Mine says Philippines 01 on the back and BK  M in the other cricle. But I got it as part of a kit from Das Musikding.
I read it to be:
14ZXK34E3
LM13700N

[matopotato]

I wonder how I could try that on my build ? What should I do to skip this buffer ?

I saw that too, but thought I did not have any buffer. They talked about FET and I thought I had "OTA".

Anyway, measured between my R10/1k/trimpot and pin 4 on OTA, and only got 3.5uA. Seems small. And I disconnected, and the pedal still sounds. So not sure if something basic is missing.
I posted my readings in https://www.diystompboxes.com/smfforum/index.php?topic=129225.0 first post.
And after breadboarding the copy, I took new readings twice, but they were inconsistent IMHO. I will add them to that post if it says anything...

[matopotato]

I wonder how I could try that on my build ? What should I do to skip this buffer ?

I saw that too, but thought I did not have any buffer. They talked about FET and I thought I had "OTA".

Anyway, measured between my R10/1k/trimpot and pin 4 on OTA, and only got 3.5uA. Seems small. And I disconnected, and the pedal still sounds. So not sure if something basic is missing.
I posted my readings in https://www.diystompboxes.com/smfforum/index.php?topic=129225.0 first post.
And after breadboarding the copy, I took new readings twice, but they were inconsistent IMHO. I will add them to that post if it says anything...

I see on https://www.ti.com/lit/ds/symlink/lm13700.pdf that 7,8,9,10 and 11 pins are part of the buffer. So grounded or disconnected, I would guess we have not engaged it. So that should close to what Rankot talked about?

[matopotato]

And it seems both pin 1 and 16 are for the current bias input. And my educated guess is that we are only using one of the two amps, so pin 1 is the one.
In chapter 6.4 of that Texas Instruments pdf, the current is to be 0.4 until max 5uA, so I see no issue there (not knowing what a compressor wants though)
But in 6.2 about config, I would guess we have single supply? Or do we have dual?
Tried pulling the pin 11 VCC, since that said "buffer" and I am soon down to pulling at random hoping for a Bingo, Voila, Heureka or something magic. But no change.
Seems as a strange and not so musical distortion it is pretty well tested and should cope with the hostile environment of a rock club with sweat, beer and what not. And still be on a breadboard...
Maybe it will sell? And we got the only three copies in the world? Bye-bye Klon Centaur, you have just been de-throned! Mu-ha-ha-ha, we are getting filthy rich... I am going to...
What? Sorry? Not my thread? Oh, well.... Sorry? Yes, calming down now. I will find the jacket myself. Yes, the one with the long sleeves... (I'll see myself out...)

[ElectricDruid]

In chapter 6.4 of that Texas Instruments pdf, the current is to be 0.4 until max 5uA, so I see no issue there (not knowing what a compressor wants though)

That's not right. The absolute max I_ABC current is 2mA (Section 6.1). More typical currents are given as 5uA to 500uA. You can use bigger I_ABC currents but the DC offsets that it introduces start to get objectionable in many situations.
I don't know what range the Engineer's Thumb (or derived designs) uses though.

[matopotato]

In chapter 6.4 of that Texas Instruments pdf, the current is to be 0.4 until max 5uA, so I see no issue there (not knowing what a compressor wants though)

That's not right. The absolute max I_ABC current is 2mA (Section 6.1). More typical currents are given as 5uA to 500uA. You can use bigger I_ABC currents but the DC offsets that it introduces start to get objectionable in many situations.
I don't know what range the Engineer's Thumb (or derived designs) uses though.

Sorry, got confused by "Input bias current" in 6.4

[Wook22]

for eh la bas ma, wook22, matopotato - where did each of you source those lm13700's from? and just for fun, could you all each please enter here the markings on your parts, including any batch or date codes, please?

and eh las bas, don't be shy with those voltages.

Mine came with a kit from Effect Pedal Kits

Markings on the back: 05 F7
On front: 04XLD9KE3 LM13700N

My voltages etc are in the post I started.

[duck_arse]

.... hoping for a Bingo, Voila, Heureka or something magic.... (I'll see myself out...)

well, me too, but we/you've lucked out - from the numbers you've all provided, there seems no obvious common dud batch or magik bad day's production.

[eh la bas ma]

In matopotato's PedadlPCB's forum's thread, I read reply #16 :

"RATIO sets the max gain. Turning RATIO up increases the maximum available gain.
THRESHOLD sets the sensitivity of the peak detector. The peak detector measures the loudness and uses that information to turn down the gain. Turning THRESHOLD down makes the peak detector less sensitive and it is therefore not going to reduce the gain as much.

Bottom line: setting THRESHOLD low and RATIO high is not a good combination. You are causing the pedal to overdrive itself. Your pedal is working as it should. "

Moreover :

The Thumb-Sucker is not a bad design, but its use of an OTA driven by a half-wave rectifier makes the instantaneous response of the OTA susceptible to envelope ripple.  That's one of the good things about using LDRs in compressors and auto-wahs: they "smooth out the glitches" arising from half-wave rectifiers...at least if you let them.

The solution is usually either shortening the gain recovery time, so that one leaves ripple behind quickly, or lengthening gain-recovery time so that the circuit behaves like a slow-to-respond LDR.

So, unless there is a demo of a 5 knobs version that doesn't distort like our builds, with Threshold set under let's say 10', Ratio set around 2' or 3', guitar volume fully CW,

unless someone can find a quote from Merlin saying that this compressor can't possibly distort the signal with a high Ratio and a low Threshold,

I tend to think there is in fact nothing wrong with our builds. This compressor does distort the signal at some settings, like the soundclip linked in my first post.

ElectricDruid, with all respect, is it possible that you are slightly mistaken ? Did you build this compressor ?

Are we sure this distortion issue is actually an issue ?  Many circuits need to be carefully adjusted, or they won't be very useful, compressors would be among them in my experience.

You should be able to use a circuit with the controls in any position without something sounding terrible. Ok, certain settings are better than others, and extreme settings might not be that "musical", but the circuit should continue to function correctly. If  a compressor only works with the knobs within a certain range, either there's something wrong with it or the design isn't much good, in my view. So, yes, I think there's an issue.

On the other hand, I did find some incongruities on my build :

Both R10 pads are showing continuity with E, B and C. One R10 side reads 4.57 V, the other 1.117 V. From the schematic I didn't expect both R10 pads to be connected with all transistor's pads.

I have also continuity between D4 negative side, one R10 pad (the one at 4.57 V) and both R11 pads, I wouldn't expect that either.

But this is what puzzles me the most : these connections happen only when the DC power jack is inserted.

If I unplugg the power jack, connections are as shown in schematics, no more strange continuities. They just disappear...*

I also have continuity between E and C sockets , only when power DC jack is plugged, switched on or off. No longer when unplugged.

I can't see any explanation for this...of course I reflowed, checked for shorts, nothing I can find, and without the BC237 transistors, the same behavior happens with sockets too.

*DMM is Vici VC97A, power supply is Boss PSA adapter. Nothing hidden inside my sleeves, nothing under my aluminium hat (full face, greec hoplite version).

As strange and mysterious as it seems, it doesn't change reply #16 from PedalPCB and the points raised by Mark, though... I 'd say Merlin is indeed a wizard and leave it alone...

First I thought there was nothing wrong, then I have been convinced there was an issue somewhere, now I think there is nothing wrong again...
I went full circle.

What do you think ?

[idy]

You can't use continuity function (or ohm reading either) when a circuit has power!
You can't.
It doesn't work.'
You will get crazy results.
The results will make you crazy.

[eh la bas ma]

Thanks, I didn't know that.

What about just plugging the power supply ? Can this modify continuity results too ?

Unexpected connections above-mentioned occur also when the circuit is switched off.

Edit: No need to answer that... I guess when a circuit is switched on, it just means that the signal is allowed to go through the circuit.
Once the power supply is connected, the circuit is powered. All is clear now. I always thought it was a bad practice because it could damage some sensitive components, but it wasn't the only reason.