freestompboxes.org

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:
http://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.



Let me know what do you think!
András

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.

from 2005: https://www.harmonycentral.com/forums/t ... need-help/

You are not alone - but a schematic is here: viewtopic.php?f=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...

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.

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

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.

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?

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

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.

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

Hello aka180!

Do you know the types of the diodes? Are silicon or germanium?

Thank you!

I've built a clone (using 1N4148 and BC548B with hFEs between 300 and 350), but it didn't work. The LED lights all the time and with the trimpot I can adjust its intensity.
At Q4's emitter I have almost no signal, but I can't understand why. Anyone can post some voltages, please?

gigelmargel wrote: ↑16 Oct 2020, 22:37 Hello aka180!

Do you know the types of the diodes? Are silicon or germanium?

Thank you!

These are the diodes. I don't see any markings on them but I always assumed these types were germanium...but I'm not that knowledgeable on those things. I'll try to get you some voltages tomorrow. It's been a crazy week

Thank you for your kindness, aka180!

If you have a multimeter with an option for diodes, you can try to measure the diodes (I think that is enough to measure only one, because it seems that all are identical), or, to be more precise, the forward voltage. I think that your assumption is correct, but there are silicon diodes which looks the same.

The voltages of the transistors will be more than welcomed, but you will need more time to do this (but, of course, there is no hurry).

I've look very carefully at the pictures and I think that I found two possible mistakes in the schematic (I marked both in the picture). I hope that I will have a little time to test them tomorrow (anyway, the second one, 47K vs. 4K7, seems to me to have a little influence, but the first one may be more important).

So the forward voltage across each diode is 0.61v and they all give the same reading.

I traced it out and yes, those are r3 and r30 and yes R3 is actually 5.6k and r30 is 47k. Maestro was notorious for mistakes/inconsistencies in their schematics.

Transistor voltages:
Q1
b 1.4, C 3.5,E 0.87
Q2
B4.6, C 0.8, E 1.79
Q3
B6, C0.3, E0
Q4
B8, C 0.2, E1.2
Q5
B8, C 0.2, E 0
Q6
B 1.0, C 0.6, E 0
Q7
B 0.6, C 0.05, E 0
Q8
B 1.1, C 6.5, E 0
Q9
B 8.7, C 8.0, E 8.2
Q10
B 8.6, C 8.0, E 7.5
Q11
B 8.6, C 6.6, E 5.6
Q12
B 6, C 8.6, E 5.8
Q13
B 5, C 7, E 4.5

Hope this helps, let me know if there's anything else

Hello, aka180!

You're my hero!!! I was almost sure that the diodes are germanium ones, but I was wrong. Anyway, I used silicon in my build so it's OK.
The bad news is that almost all my voltages are wrong. I must recheck all, but I hope to find the mistakes. Maybe the schematic has other errors in it. I will try to recheck it from the photos, but I has serious doubts that I will have success because of my poor electronic knowledges. Anyway, I will try.

Your voltages vs. mine are the next ones:

Q1 - OK
C: 3.5
B: 1.4
E: 0.87

Q2 ???
C: 0.8 / 6.35
B: 4.6 / 0.64
E: 1.79 / 0.08

Q3 ???
C: 0.3 / 7.9
B: 6.0 / 0.3
E: 0.0 / 0.0

Q4 ???
C: 0.2 / 7.9
B: 8.0 / 0.23
E: 1.2 / 0.0001

Q5 ???
C: 0.2 / 0.04
B: 8.0 / 0.64
E: 0.0 / 0.0

Q6 ???
C: 0.6 / 7.02
B: 1.0 / 0.06
E: 0.0 / 0.00

Q7 - OK
C: 0.05
B: 0.6
E: 0.0

Q8 ???
C: 6.5 / 0.02
B: 1.1 / 0.58
E: 0.0 / 0.00

Q9 ???
C: 8.0 / 8.0
B: 8.7 / 2.27
E: 8.2 / 1.78

Q10 ???
C: 8.0 / 8.00
B: 8.6 / 1.78
E: 7.5 / 1.17

Q11 ???
C: 6.6 / 8.00
B: 8.6 / 1.18
E: 5.6 / 0.68

Q12 ???
C: 8.6 / 8.00
B: 6.0 / 0.68
E: 5.8 / 0.14

Q13 ???
C: 7.0 / 5.60
B: 5.0 / 0.13
E: 4.5 / 0.01

Thank you a lot!

Hello, aka180!

Even if I tried hard to check the schematic against the posted photos, I had almost no success. If you will have some free time to lose sometime, it will be great to check the schematic.

Thank you a lot!

Hello, aka180!

If you will have some free time, can you try to check the factory schematic, please?

Thank you a lot!

Hi, the complete maestro manual was just posted on the vintage pedals page on Facebook. A user scanned the whole thing in and there is a copy of the schematic of the envelope modifier!



It uses 2n3566 transistors and 1n4148 diodes!

Yes and the schematic is for an older version of the Envelope Modifier, so this particular version of the Envelope Modifier needs to be traced.