String damper question

[Mark Hammer]

It's an envelope-controlled pedal, except that it uses your guitar's envelope to trigger its own internal envelope.  Rereading the article, Isee that the author/designer views the pedal as something that could be used in set-and-forget manner, but could also be used with a momentary.  Of course there are two kinds of momentary use.  One would have the envelope-shaping in effect, unless you stepped on the momentary to close SW1B.  The other would have the unit essentially disengaged, until you stepped on SW1B.

I gather that all the magic revolves around C9 getting charged up.  If it is only getting charged up by the gate-like pulse from the rectifier, then it charges up at a rate set by the Attack pot, and discharges at a rate set by the Decay pot.  If the gate is replaced by a signal that is held high (closing SW1B), then it never discharges.  BUt that's why the article alludes to being able to get interesting effects by "pumping" a momentary switch.  When doing so, you are replacing the "on" that would normally come with a hard-picked note, with one that is arbitrarily chosen by the user, using the momentary.

Strikes me that a flexible version of this pedal would be one that had a latched and an unlatched/momentary switch paralleled in the same build.  If you wanted it to stay on, you use the latching stompswitch.  If you wanted to "pump it", you set the latching stompswitch to off, and use the momentary in its place.

[pinkjimiphoton]

that my friend is why i thought i did it wrong

i will hopefully get it working one of these days. winter's here, gigs are fewer, more time to hibernate in my dungeon and cook stuff up.

[lars-musik]

So if I understand the ongoing discussion right, this one generates an envelope depending on the guitar signal. Thus is a gatorish slow gear-like tool? Looks like I have to built it.

Unfortunately I won't be having much time for soldering in the next weeks, so I'll just throw my last night`s work on the market. It is not verified but I've been over it a few times and Diptrace says it's good to go. If someone is a 1590a nerd like me, he/she is very welcome to try it.

It is based on Fransico's layout, I hope that's allright.


Project doc:
https://www.dropbox.com/s/iou8i7gwy7b6h8d/String_Damp.pdf?dl=0

[pinkjimiphoton]

it looks like it has the mistakes from francisco's layout. look at the top right corner, there's a cap labled 180 that does nothing. i believe the top of the cap should be connected to the square pad for the pot next to it, and there should be a break in the trace the cap is currently sitting over. it needs to bridge that gap, right now it's shorted out of the circuit and not connected to anything.
there may be more. should be an easy fix, but that's the first thing i noticed bro

[lars-musik]

Gosh, there I had to look hard. It is the pad for the output.
Turned 180° and some photohop magic applied it looks like this:


In the build document , you'll find the corresponding schematic (that is identical to the layout sais my computer). If you spot a mistake, it should be also in the schematic. Absolutely possible I made an error while copying but then it should be better detectable in the schemo.

But thanks for looking and keep on doing so, I am just a novice!

[Kipper4]

its working in a fashion I may need to tweek the attack decay some but its passing signal which is good news.
I need to replace a wrong cap yet.
heres my voltages
icl7660
1  9
2  4.7
3  4.5
4  -4.5
5  -8.9
6   5
7   7.4
8   9


Tl072

1   0
2   0
3   0
4  -8.9
5   0
6   0.04
7  -7.4
8   9


LM13700
1    -7.9
2     0.7
3     1.5 to 0.2
4     0.3
5     0
6    -8.9
7    -7
8    -7.8
9     0.03
10  -6.8
11   9 
12  -7
13   0.004
14   0
15  -0.9
16  -7.7

just ordered 10x lm13600 so I'll swap that out in a few weeks when they arrive
Good luck Lars and thanks for the help guys

Edit
did i say Im using polarised caps ?

[lars-musik]

Hi Kipper,

I wonder why you have a voltage inverter in there. Maybe I overread it (or most likely I just couldn't follow your discussion with Sam on the first page), but as far as I can see, a negative ground, a positive 9V supply a bias voltage (Vref, or whatever an engineer calls it) suffices. What am I missing?

[bluebunny]

Yeah, me too Rich.     Granted, they are using some perhaps strange terminology: V- instead of GND, and GND instead of Vb.  I say "tomaytoes", you say "tomartoes"... 

[Kipper4]

I don't know why but I thought I'd try and give it some more headroom. Might be my biggest mistake to date

[duck_arse]

hey rich, on yr tl072 voltages, says you've got -7.4 tomatoes on pin 7. that don't look right, even without looking a circuit.

[Groovenut]

hey rich, on yr tl072 voltages, says you've got -7.4 tomatoes on pin 7. that don't look right, even without looking a circuit.

Yup, I would think pin 7 would read zero

[Kipper4]

I see what your saying fellas, but I can also see that pin 6 is attached to +9v via a 1M resistor and to gnd via a 4k7.
Hhhmm more work to do I guess I need to double check my layout and nodes.
Cheers

[samhay]

The op-amp pin 7 voltage might be ok if the numbering corresponds to the schematic as the diodes might make a mess of your voltage readings - no DC feedback in the op-amp.
Can you take voltage measurements while you strum the guitar - the voltage here should change I think.

[Kipper4]

Will do. I'll test that mate.

[Groovenut]

I'm wondering why pin 10/12 are negative, whilst pin 13 is slightly (ever so) positive?

[lars-musik]

Good news, everyone: The layout works. I couldn't leave this one alone, so I finished it last night. It attacked-decayed at first firing up, so I am quite happy with that. But it seems to need some tweaking:

Somehow the triggering doesn't really work. Right now, the decay seems to be fixed by the values dialed in (C9 and VR1) and damping the strings manually doesn't re-set the mechanism. A played note slowly fades in and holds for the dialed-in decay time, then the sound stops and the machine is ready for the next attack. I'd rather have the slow-gearish behaviour that damping the strings manually closes the gate and "arms" the trigger for the next note. As far as I can see in the circuit description this circuit should be able to do that.

I find these two  sentences in the description:

1. "The bi-stable formed around IC1 b is then triggered, its output on pin 7  going positive. This condition is latched for the time being by D3 and R19. C9 will now charge via D5, R21 and the attack pot"

2. "When the voltage is sufficient to forward bias D2, causing current to flow into R17, the bi-stable IC1 b becomes re-set. This signifies the end of the attack period, the length of which is obviously determined by the rate of charge of C9 via RV2"

I wonder if according to (1) a re-sizing of R19 will have a significant effect on the latching time and thus on the re-setting of the trigger

or

relating to (2) a replacement of D2 with a diode of lower Fv (germanium, Schottky) would help.

Unfortunately the new work week just started, so I can only muse about these things whilst commuting and not put them into action on my work bench.

But maybe some of you highly knowledgeable people can give some input?

Thanks, Lars