Maestro Envelope Modifier - ME-1 debugging

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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bandus
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Post by bandus »

Dear reader!

I have a vintage Maestro Envelope Modifier on my bench. It acts strangely and doesn't really match my expectations.
In my understanding it should retrigger the ADSR cycle as you pluck a string (seeing the vintage EHX Attack Decay and Boss Slow Gear on youtube). For example set a slow attack, long sustain and fast decay and as i hit a note the volume starts to increase than it sustains and after that quickly mutes as it reaches the decay part of the envelope.

That's fair, you might think that quite normal, right?! But when i hit a note let's say in the long sustain phase of the envelope i hear a "normal" volume guitar pluck and it fades when it reaches the decay phase. My Pigtronix Philosophers King and Attack Decay pedals (also ADSR units) works like as i hit a string the ADSR cycle retriggers (if the sensitivity was set correctly) and a slow attack appears any time i hit a new note.

Do you think my Maestro pedal is broken or this is the normal operation?
Here is the schematic:
https://files.effectsdatabase.com/docs/s ... difier.jpg

As you can see there is a sealed LED/LDR in the circuit and as i connect a different led to the see how it lights up i see exactly as i described the sound of the pedal: trigger - the led start to lights up slowly and if the cycle is completed i can retrigger it to start all over again.

Image

Let me know what do you think!
András
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Maestro Envelope Modifier schematic
Maestro Envelope Modifier schematic

aka180
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Post by aka180 »

Hey all,

Just trying to get one of these going. There was a couple cold solder joints which I reflowed so it works now but its effect is very inconsistent. There's literally nothing out there on this pedal. If someone out has one of these that they know is working as it should, could you post some aidoo clips of it.

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modman
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Post by modman »

from 2005:
Screen Shot 2020-02-22 at 09.03.51.png
https://www.harmonycentral.com/forums/t ... need-help/

You are not alone - but a schematic is here: https://www.freestompboxes.org/viewtopi ... 19&t=29943
But indeed - this is the one pedal that hasn't been demoed on youtube yet.
Would be nice it you could share some gut shots...
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aka180
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Post by aka180 »

So I think it is going well now. I had a bad solder joint at C4 which could explain why nothing as working. Cleaned it all up and tweaked the trimmer a bit and it seems to be fine. I've been watching demos of the boss slow gear and mooer slow engine and it seems there is bit of a learning curve to using it. For sure as cool as it is, I definitely still prefer using volume pedal.

Anyway, here's some gut shots for now. I'm putting in 70+ hours at work this week but maybe next week I'll thave time to upload a video too. At least we can get something out there. Worse case, some may be able to say if it isnt working right.
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Manfred
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Post by Manfred »

Hi aka180,
I am intending to make a pcb-clone could you please tell me the board dimensions.

aka180
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Post by aka180 »

So the board about 2.5" x 6.5".
Out of curiosity, any idea what you'll be using for the led/ldr? There's no markings on it so I'd be curious to know what could be used as a replacement should I ever need one.

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modman
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Post by modman »

aka180 wrote:So the board about 2.5" x 6.5".
Thanks!
aka180 wrote:Out of curiosity, any idea what you'll be using for the led/ldr? There's no markings on it so I'd be curious to know what could be used as a replacement should I ever need one.
Ready here some suggestions: https://music-electronics-forum.com/sho ... #post40367
Could you tell us the markings on the transistors?
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Manfred
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Post by Manfred »

Out of curiosity, any idea what you'll be using for the led/ldr? There's no markings on it so I'd be curious to know what could be used as a replacement should I ever need one.
Can you measure the resistance when the LED is on and off. To make your own optocoupler it is important to know the light resistance and the dark resistance.
https://sound-au.com/project200.htm

aka180
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Post by aka180 »

Manfred wrote:Can you measure the resistance when the LED is on and off. To make your own optocoupler it is important to know the light resistance and the dark resistance.
https://sound-au.com/project200.htm
I get 30 MegOhm when dark.
I jumpered the C and E of q13 to keep the light on and cranked the trimmer down to get maximum light and measured 1kohm

I found the optimal trimmer adjustment gave me 3kohm at the ldr. Lower value makes it a little too sensitive and higher makes it too quiet or doesn't trigger at all.

aka180
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Post by aka180 »

modman wrote:Ready here some suggestions: https://music-electronics-forum.com/sho ... #post40367
Could you tell us the markings on the transistors?
Not familiar with Q1 and Q5 so I included pictures
Q1: A139 208
Q5: f115-2 903 (check the pics but I'm pretty sure that's an F)
Everything else: 2N3565 327
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