Old School

[Kipper4]

Hey Guys
Ben N bought this circuit to my attention in a recent thread.
Ever willing to learn I'd like to understand how it all work better.
In a true Kipper style thread I'll post up the drawing I found.
Googles great innit.

Then I'll attempt to explain what I think I see and how I imagine the circuit "Stamps" (ref R G Keen) interact.

There will be some mistakes, laughs hopefully and most of all some learning.

Here goes strap in.


The drawing

[Kipper4]

What I think  see

Centre top
555 chip +-18V charge pump. Surely there's a more elegant less parts way of doing this.

Middle left
N channel J fet buffer. I get it. Simple low parts and high input Z

Centre
2N5088 looks very similar to the ea tremolo wobbled bit (technical term)
Q1 here

http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf
Then there's the starve feature pot which I imagine introduced more resistance to ground between the emitter and gnd.

Centre right
2N5088 phase shift oscillator
I can see the J fet on the output of the lfo doing wobble duties as it does the same in the above ea tremolo.

Brb needs more coffee.

[vigilante397]

Surely there's a more elegant less parts way of doing this.

My reaction to basically everything

Brb needs more coffee.

I'll stick around, nowhere else to be

[Kipper4]

Pull up a pew Nathan your more than welcome.

So I also see the fet below the PSO which presumably goes open when activated by the opto isolator. I'd hazard a H11F1 not sure I haven't looked into it yet.

Bottom left
I see what looks similar to the dyna comp peak detector but with op amps.
I kinda like this portion of the circuit (no surprise there. I'm sure a version will pop up in a future design tbc.)

Obviously the peak detector is controlling said opto.

Thanks guys.
Chip in if you wanna come along for the ride.

[Kipper4]

Link to dyna comp peak detector

https://www.electrosmash.com/images/tech/mxr-dyna-comp/mxr-dyna-comp-envelope-detector.png

[samhay]

Edit - spoiler warning. Rich, it you're trying to work this out for yourself, my apologies. Don't read on.

It's a tremolo that uses a JFET as a variable resistor.

The demo here shows what everything does:
https://www.youtube.com/watch?v=Se_grzo9QzM

In your/Madbean's schematic the switch is drawn strangely, but is an on-off-on connected to the LDR (it's not a photoFET). The peak detector sets the resistance of the LDR, which switches in parallel with the depth or speed control so you get a 'dynamic tremolo'.

Starve changes the bias point of T1 to add dirt.

[Kipper4]

Heres a clearer pdf

http://www.madbeanpedals.com/projects/_folders/VFE/pdf/VFE_OldSchool.pdf#page=1&zoom=auto,-13,792

I thought the ldr went to a j fet. Not so It appears.

1    How should ldr be wired please? Is that the switching?

on1 off on2


on1 to 6k8?

off not connected

on2 to 470 Ohms

2    what is the function of the ldr? how does that work. Curious.

Certainly looks like a magnavibe type circuit might work with this too by replacing Q1 with another led ldr combo and the wobbled T1 replaced with a concertina splitter arrangement.

3    Is it really worth having the charge pump?

Can it work from just a split supply +9V, 4V5, 0V?

And btw is Vr = +18V? Not familiar with 555 charge pumps.


Thanks guys
Rich

[Kipper4]

Heres an idea for a vibrato along the same lines unverified as yet..




edited to add output cap, good catch Stephen. Thanks

[duck_arse]

yule want to add a blocking cap before the output level pot.

[Kipper4]

Thank you mate.

[Ben N]

Yeah, my understanding was that it's a tricked out EA trem.

[Kipper4]

Who needs old school when you can have new school


A bit of a work in progress
Enveloped tremolo

Drawing update since the led driver was drawn wrong.
Also the tap tempo was ineffective so removed

[Ben N]

Noice!