Vintage Zipper Envelope Filter

This topic has 18 replies, 4 voices, and was last updated 4 years, 6 months ago by tomituominen.

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June 23, 2016 at 8:12 pm #84454

Camarada78
Participant

Hi,

This is my first post, thanks for this great forum.

I live in a small town in Brazil, with little (near zero) guitar/pedal services available.

I was gifted with an old EH Zipper Envelope Filter pedal from the late 70s i think and I am having a hard time to fix it. Currently I cant send them to bigger towns due to low budget.

The pedal was complete mute, with the bypass working well.
I managed to get some audio but it is an intermittent clipping sound with a little filter in it, but it seems to me that it is not mixing with the guitar tone.

I dont want to mess too much around in fear of losing its vintage feel, so do you guys would know what could be?

I have beginner-to-medium knowledge of electronics, enough to fix my pedals so far.

The DC power is normal, jacks too.

Thanks

Have a good day.

June 23, 2016 at 9:42 pm #121651

Scruffie
Member

Start by posting the voltages of all the ICs and FETs please.

June 24, 2016 at 7:42 pm #121657

Camarada78
Participant

IC 1 (14 pins)

1 = 7.05 8 = nothing
2 = 6.95 9 = nothing
3 = nothing 10 = 3.61
4 = 8.29 11 = 0.71
5 = 0.07 12 = nothing
6 = 7.01 13 = 6.53
7 = 7.01 14 = 7.03

IC 2 (8 pins)

1 = 2.45 5 = nothing
2 = 2.55 6 = starts and 2.20 and drops to 1.39 and stabilize
3 = 1.33 7 = 7.52
4 = 0.71 8 = 8.29

IC 3 (8 pins)

1 = 2.57 5 = nothing
2 = 2.59 6 = starts and 2.31 and drops to 1.40 and stabilize
3 = nothing 7 = 6.52
4 = 0.71 8 = 8.29

FETs

T1 = 6.95
T2 = 0.15
T3 = 0.11

those were the readings. triple checked.

Thanks for your help!

June 27, 2016 at 9:46 pm #121673

Scruffie
Member

By the looks of it (and assuming the PCB pin outs match up to the schematic) either the 324 is dead or the 100uF cap coming off pin 8 has gone bad and become a short.

So give the cap a test for continuity and then i’d swap out the 324 if that’s not the case. You could also check for continuity between the 324 pins and the PCB, the traces on the old EHX boards do have a habit of breaking.

June 28, 2016 at 9:22 pm #121690

Camarada78
Participant

Thanks, i’ll test and give feedback. My guess would be the caps. The ICs are so old it is impossible to read if they are the correct ones, but i guess they were never changed, same as in the circuit.

July 5, 2016 at 8:47 pm #121708

Camarada78
Participant

Quote:

By the looks of it (and assuming the PCB pin outs match up to the schematic) either the 324 is dead or the 100uF cap coming off pin 8 has gone bad and become a short.

So give the cap a test for continuity and then i’d swap out the 324 if that’s not the case. You could also check for continuity between the 324 pins and the PCB, the traces on the old EHX boards do have a habit of breaking.

Hi, thanks for the help. Changed the 324 and the 100uF cap and the problem remained the same: intermitent sound, like if the oscilation was working, but it is not affecting the guitar sound, so i only receive the “empty” output sign of the pedal itself, without the guitar sound.

the bypass works btw.

July 5, 2016 at 9:11 pm #121709

Scruffie
Member

Have the voltages changed? On the 324 you should be seeing roughly the same voltage on pins 8 & 9 as you are on pin 10 (it’s a buffer for the reference voltage which should be half supply, pin 10 where the voltage reference enters is a little low but that could just be down to tolerances or value drift) hence why I suggested that cap and the 324 its self.

On your voltages where you list ‘nothing’ on the ICs that’s where the bias voltage should be seen so something is causing an issue there.

Here’s my redraw of the factory schematic for reference;

July 6, 2016 at 3:38 pm #121710

HollyJuster
Member

Hi..i am new user here. As per my knowledge either the 324 is dead or the 100uF cap coming off pin 8 has gone bad and become a short.So give the cap a test for continuity and then i’d swap out the 324 if that’s not the case. You could also check for continuity between the 324 pins and the PCB, the traces on the old EHX boards do have a habit of breaking.

turnkey pcb

July 6, 2016 at 5:45 pm #121711

Camarada78
Participant

Quote:

Have the voltages changed? On the 324 you should be seeing roughly the same voltage on pins 8 & 9 as you are on pin 10 (it’s a buffer for the reference voltage which should be half supply, pin 10 where the voltage reference enters is a little low but that could just be down to tolerances or value drift) hence why I suggested that cap and the 324 its self.

On your voltages where you list ‘nothing’ on the ICs that’s where the bias voltage should be seen so something is causing an issue there.

Here’s my redraw of the factory schematic for reference;

Thanks for the schematics. I have the old one (hand written).

Now the pedal is completely dead and I dont know why. After I changed the CI and 100uF cap it – as i said – remained with the same problem as before (i could hear the oscilator filter but it was not affecting the guitar sound). But now is dead. No voltage in any CI.

I’m going to check the caps or check every resistor to see if any has broken and opened the circuit.

July 8, 2016 at 2:13 am #121713

Camarada78
Participant

My friend. Thanks again for the help. I’m learning a lot about this pedal.

It is still dead.

there is no voltage after the C15 (Capacitor 0.1uF). I tested it and it is reading right, 0.107uF as it should.

But there is no voltage after it anywhere in the circuit.

No voltage is getting to any IC as it did before.

It is very weird.

July 8, 2016 at 10:25 am #121714

Scruffie
Member

How are you powering the circuit? Battery or adapter?

It sounds like Q4/2N5088 has blown.

March 30, 2017 at 6:31 pm #122735

Camarada78
Participant

Hello again scruffie.

I’ve managed to make the pedal work again, but now it only works with batteries, not with the DC power supply.

I’m trying to rebuild this pedal on Proteus using your schematic, but some points are a little confusing.

Can’t understand the power section to proper translate it to Proteus. Where it is written AC adaptor, should i put an AC 9V power source?

April 26, 2017 at 9:31 am #122817

Scruffie
Member

If you PM me your e-mail address I have a copy of the original PCB art work.

And no, this pedal takes DC, it’s just called an AC Adaptor because it changes the wall AC to DC.

August 22, 2018 at 9:44 pm #124221

Camarada78
Participant

Hello again Scruffie,

So long no see.

After almost two years of studying other things and abbandoning that pedal, i’m back at it again (a matter of honour).

so, the pedal is now dead both in battery and power supply. I did not touch it since those days. Anyway.

thanks for the help btw.

weird things:

1. I get 9v on 2n5088 collector, but not on the emitter. I changed the transistor, the problem remained.
2. Therefore i get no power after the transistor. no matter what i do, i tested another two npns and the same.
3. changed the capacitor (c15) and nothing.

Should i bypass this transistor, remove the battery and feed the DC signal straight to the voltage divider (r29)?

August 23, 2018 at 9:53 pm #124226

Camarada78
Participant

Quick update.

I manage to make the pedal work as intended, but it only works on 9v battery, not on DC power supply.

I need to make it to work on DC PS.

1. the DC is working and sending 9v to the diode (D6).
2. I get 8.8v on the emitter and nothing after that.
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