Author Topic: Engineer's Thumb: Is this issue normal?  (Read 1257 times)

JackSkellington

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Engineer's Thumb: Is this issue normal?
« on: November 05, 2018, 11:27:11 AM »
Hello, I have a problem with the Engineer's Thumb using Sabrotone layout.
https://www.sabrotone.com/?p=2901
All the informations about it, here:
http://www.valvewizard.co.uk/engineersthumb.html

The effect seems work, a sort of, indeed I get the compression, but with some weird issues.
When I don't hit the strings I can hear the hiss and the volume rise up, and when I hit the strings I get a loud attack, then the compression act and I can play normally, though I got another strange thing: depends by the settings, but if I hit the strings harder the compression low the volume more than when I play softly.
I think this depends from the volume that rise up too much, it cause the loud attack and the loud volume when I play softly.
This issue cause a third problem. When I wired it into the box with footswitch and all the rest, this loud attack cause a high pitch snap when I switch off the effect, especially after I waited 6-7 seconds the release time.
This snap is barely audible when I engage the Vemuram Jan Ray (in the same box).
I tried anyway to use a pulldown resistor input or output, but the problem is in that big boost of the compressor.

I really need help, the pedal is for a friend.

Thanks!
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zombiesonore

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Re: Engineer's Thumb: Is this issue normal?
« Reply #1 on: November 05, 2018, 11:42:12 AM »
Hi.
I've build one this summer, maybe I'll be able to give you some help.
Do you have build the full 5 pots version?
I remember, when using this version, that a good clean compression could be hard to get. The pots interacts at lot.
Please let me know how you sets each pots.
 

JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #2 on: November 05, 2018, 11:52:41 AM »
I'm using just three pots. Ratio and Volume and Attack. I followed the instruction to exclude, or better to keep the fix value for the other pots.

The compression sounds clean and nice (not distorted), but I get this thing really strange to me, that make this compressor a bit hard to play without the right touch. And I get this loud volume after the release time. This cause the loud attack of the first hit, and probably the loud snap when I switch off.
I guess that the overdrive effect after the Engineer's Thumb attenuates the snap becuase it attenuates even the compression.

Edit: The LM13700 come from Tayda. Some bad experience with this chip from Tayda?
« Last Edit: November 05, 2018, 01:02:42 PM by JackSkellington »
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zombiesonore

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Re: Engineer's Thumb: Is this issue normal?
« Reply #3 on: November 05, 2018, 01:14:46 PM »
What value did you used for the "Release" resistor?

JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #4 on: November 05, 2018, 03:38:27 PM »
You can find the instructions to exclude the Release, Threshold and Attack pot on the Sabrotone page.
Anyway, I used 1M resistors for Threshold and Release, I guess it should be like if both was at max.

By the way, this kind of reaction I found it some years ago when I tried to build an auto wah DOD FX25, using an LM13700. Even this effect was sensitive to the picking (like the compressor). When I let it for a few seconds and then I hit the strings I got a quick loud bump of low frequency before the normal volume wah sound of the effect. The same things when I let the strings release by their self, the same loud bump of low frequency in the tail of the decay of the wah. Unusable, so I rejected.

Thinking this now I get the exact thing, though with a different effect: in this case I have a bump of volume.

Unfortunately, I have just another LM13700, even this bought from Tayda, it is right that LM13700 coming from the dismissed DOD FX255, now used for a Snow White Auto Wah, without this bad issue but with an unexplained not working Decay pot that I left anyway.

Or both this LM13700s bought with at least three years of distance are defeated, or all the LM13700s coming from Tayda are defeated. Or all this behaviour is normal and I don't know what mess I did.
Anyway, my Engineer's Thumb sounds too weird to be normal and usable with no worries.

This building is enough urgent. :-[ :-[
Thanks for the help.
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jkokura

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Re: Engineer's Thumb: Is this issue normal?
« Reply #5 on: November 05, 2018, 08:25:38 PM »
My first thought was either your chip is bad or you've got parts in the wrong places. Perhaps you've got the wrong value in one of the key places?

Perhaps walking through the debugging steps and ensuring the parts values and orientations, swapping out the chip, taking some measurements might help.

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midwayfair

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Re: Engineer's Thumb: Is this issue normal?
« Reply #6 on: November 05, 2018, 10:28:05 PM »
The thumb clamps down pretty hard after the initial attack. I'm not sure if that's what you're talking about.

There's absolutely a compression artifact where the first note's attack is significantly louder than the rest of the compression. I didn't notice it as much with my guitars but with higher output pickups I can't unhear it.

I stopped building these because I wasn't able to satisfactorily deal with it without using the input LEDs, which will add distortion with high-output pickups.

If you didn't use the input LEDs, add those first and see if they help.
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JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #7 on: November 06, 2018, 02:09:27 AM »
I prefer the chip is bad, because I didn't see anything wrong. But I'll check again.
I'll take out the chip for the measurement, too.

What I get is right a loud initial attack. When I play harder I get less volume than when I play softly, but this maybe depend from the settings, and this could be almost handle. But the loud attack is a bigger problem, especially when cause the loud snap when I turn off the effect. It's not the usually pop, but an high pitch click.

Later, I included even the two LEDs, but the problem was the same. Initially I didn't think this issue was a thing so bad. But now with the footswitch... I can't give this pedal to my friend.
He should engage the overdrive before to turn off the compressor. Not so cool.

Edit: I bought these two LM13700 from tayda, when the cost was 1,50 $. Now it's 2,02 $. Musikding has it at 1,75 €.
« Last Edit: November 06, 2018, 03:16:20 AM by JackSkellington »
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JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #8 on: November 06, 2018, 04:05:09 AM »
Voltage LM13700:
1 - 2.24v
2 - 0v
3 - 4.50v
4 - 4.49v
5 - 4.49v
6 - 0v
7 - 0v
8 - 0v
9 - 0v
10 - 0v
11 - 0v
12 - 0v
13 - 0v
14 - 8.99v
15 - 0v
16 - 0v

I measured it without the LM13700 and without cables.

Resistors value are correct, as well the orientation of the BC327 and the diodes. Caps orientation and value correct. Position of the components is right.
« Last Edit: November 06, 2018, 11:39:58 AM by JackSkellington »
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midwayfair

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Re: Engineer's Thumb: Is this issue normal?
« Reply #9 on: November 06, 2018, 07:52:50 PM »
I prefer the chip is bad, because I didn't see anything wrong. But I'll check again.
I'll take out the chip for the measurement, too.

What I get is right a loud initial attack. When I play harder I get less volume than when I play softly, but this maybe depend from the settings, and this could be almost handle. But the loud attack is a bigger problem, especially when cause the loud snap when I turn off the effect. It's not the usually pop, but an high pitch click.

Later, I included even the two LEDs, but the problem was the same. Initially I didn't think this issue was a thing so bad. But now with the footswitch... I can't give this pedal to my friend.
He should engage the overdrive before to turn off the compressor. Not so cool.

Edit: I bought these two LM13700 from tayda, when the cost was 1,50 $. Now it's 2,02 $. Musikding has it at 1,75 €.

It actually sounds like you might be talking about something different from what I was, then. The click I was talking about was fairly subtle and the LEDs clip the initial signal a bit to prevent it, so if it's really that noticeable you might have something else going on.

I've definitely had bad 13700s from Tayda. To the point where I wasn't sure they really were what they said on the package.
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JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #10 on: November 07, 2018, 02:25:27 AM »
I really would like to solve changing the LM13700. That will be so easy!
By the way, I tried, just to be sure, the other LM13700 (Tayda) from the Snow White (without this issue, but with a not working Decay pot, as I said. Maybe there's a link?) and the result is the same.

To tell this issue with few words the effect (the LM13700?) work, but bad. Because I guess it boosts too much, so I got this very loud initial attack (at least three time the normal volume), and, I'm trying to guess, for the same reason I heard this high pitch click when I switch off the effect after the release time, and a bit when I turn on, It's not the usually bump when we got without the pulldown resistor. And I got a bit too much volume jump: louder when I play softly (because the too much boost) and less loud when I play harder (because the compression, perhaps the good working part).

This issue is absurd, the Engineer's Thumb has pro and cons, but I get an effect unusable, I don't think that nobody notice this, except me. :o

The funny thing is that the same loud initial attack I got in the Auto Wah DOD FX25 I dismessed, it was loud even in the decay, just with a bunch of low frequency, but that was the wah effect like in the heel position.

Midwayfair, how did you realize that Tayda had bad LM13700 chip? It doesn't work at all or you got a sort of issue like me?

By the way, I even more sure I'll never buy transistors or ICs from Tayda.
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JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #11 on: November 09, 2018, 03:33:24 AM »
I ordered a new LM13700 from Musikding. Waiting to test it. ::)

I also ordered some stuff I usually order from Tayda.
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JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #12 on: November 16, 2018, 09:04:04 AM »
Hello guys, I'm really disappointed, mad and desperate with this effect. I replaced the Tayda's LM13700 with a Musikding's LM13700 (it looks printed finer), but the problem persists.
It's like a big boost that causes a really too loud initial attack and the snap when I disengage the effect.
I tried even to replace the BC327 with another one bought from Musikding. But nothing.
« Last Edit: November 16, 2018, 10:57:10 AM by JackSkellington »
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jkokura

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Re: Engineer's Thumb: Is this issue normal?
« Reply #13 on: November 18, 2018, 07:09:03 AM »
I wish I could offer more for you than to keep working the debugging steps, or try again. I don't know if the Sabrotone layout is verified or not, I suspect it is, but you can never rule out our own mistakes. I'd try it again at the stage you're at now, although I'd reuse whichever parts you can from the first try.

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JackSkellington

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Re: Engineer's Thumb: Is this issue normal?
« Reply #14 on: November 18, 2018, 12:58:12 PM »
Sabrotone layour is verified, there's even the image of a pedal built. I really can't imagine what is the mistake, indeed, I imagine there's no mistake.
Probably I'll try it on breadboard, if I can trust of my breadboard, it's really cheap, I could try to build it again, but with new parts, I guess I can use the LM13700 and the transistor, and the pots. But I am really disconsolate about this effect. And I can't understand how I could get the same issue with the same IC but a different effect. ???
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