MXR Envelope Filter doesn't work

[moeburn]

Hey guys, I just built an MXR Envelope filter.  When i plug it into my amp, I can almost barely hear the guitar, its not wahing, but that sound doesn't change even if i unplug the battery.  I've tried audio-probing it, but I dont really know what I'm looking for.

[markr04]

If I remember correctly, that build is sensitive to the ICs used. TI brand is said to not work. I had a heckuva time with mine for that reason.

[moeburn]

If I remember correctly, that build is sensitive to the ICs used. TI brand is said to not work. I had a heckuva time with mine for that reason.

I've tried 4 4069 and 2 4066 ICs, I have a TI and an "F" version of each, but replacing them doesn't make any audible difference whatsoever.

[Peter Snowberg]

Make sure the 4069 has a "UB" in the suffix. Without that it won't work. The original schematics specified 'RCA chips only'.

After that... check the "what to do when it doesn't work" sticky thread.

[moeburn]

Bottom pic: The red film caps are marked '104K', the four white caps are "563J", the left three caps are "101", "10J", and 47uF.  I am using three 1Mohm pots.  The bottom left IC, although hard to read, has a fancy "f" (Different than the other two), and definately says CD4066BCN.

I also tried cleaning off the flux, but my first attempt was with a cotton pad, hence the little fibers that actually arent solder joints...

When I plug my circuit in, it doesn't appear to make a difference in sound whether or not I even put the chips in.  Its just really really faint unwahed.

[moeburn]

aaaaannyone?

[moeburn]

Please, I really don't want to have to spend money on all these parts to build a new one again.  I've gone through it with an audio probe, and well, of course its not working.  Who the heck sends an audio signal through a 200k resistor, then another 200k resistor?!  The chips don't do anything at all.  From one pin to another as located in the schematic, they just dont do anything.

[StephenGiles]

moeburn - before you run off and shoot yourself, I would take a pointed object and scratch around all the copper traces on the underside of your PCB. Looking at your superb picture with a magnifying glass indicates that there might just be a solder bridge or two. The next thing to do is trace the guitar signal all through the circuit. I'm short of time at the moment so I'm sure someone will provide more help.
Stephen

[moeburn]

Okay, I got a scalpel and scooped out the PCB in between every soldered pin.  No change.  I still get a very faint uneffected guitar sound, regardless of whether the battery is plugged in.

[mrsage]

moeburn - before you run off and shoot yourself, I would take a pointed object and scratch around all the copper traces on the underside of your PCB. Looking at your superb picture with a magnifying glass indicates that there might just be a solder bridge or two. The next thing to do is trace the guitar signal all through the circuit. I'm short of time at the moment so I'm sure someone will provide more help.
Stephen

I would have to concur...

It looks like you may have accidentally connected two pads that shouldn't be connected.

If you have the original PCB trace layout, compare it carefully to your finished product and see if you accidentally connected two pads that shouldn't be connected. That's easy to do, and sometimes it looks so neat that you don't even realize it happened. I've had to de-solder a lot of pedals to check for solder bridges before...It comes with the territory!

In particular, I'd check these spots:

http://tinypic.com/9jobcy.jpg

It looks like there are some solder tails there...little tails of solder connecting things that shouldn't be connected will cause problems!

Also, there are a few spots where bits of solder may have conjoined pads that are near each other. Just use some de-soldering braid and clean those up a bit...desolder and make sure you're not accidentally connecting the wrong things together.

[niftydog]

guys, start at the top and work your way through systematically. Yes, the PCB may have faults, but no one has even asked if he's checked the power supply voltages!

Have you measured any voltages? Like, do the chips have power? Are the biasing resistors doing the right job? etc.

Who the heck sends an audio signal through a 200k resistor, then another 200k resistor?!

if you are talking about R7 and R12, that's not at all what's happening. R12 is in the feedback path of all those op amps, that arrangement is entirely normal.

Seems you may have taken on a challenging project for your skill level - tonepad lists this as an advanced project!

Measure the power supply pins of all the op amps for a start. Measure all the points marked Vs. Then maybe measure (and note carefully) the voltages present on all op amp input pins. Then, armed with that we might be able to get somewhere.

[moeburn]

Thanks Mrsage, I checked all the points you circled, and they were all just photographed at a bad angle or they were connected by bits of fluff (i stupidly used a cotton boll to wipe off the isopropyl).  I think I can safely say there are no solder joints.

Niftydog, thanks for the advice, I do recall checking the voltage the first time it didnt work, and there was voltage on the board, but I will check all the ICs like you mentioned.  There are no opamps (this circuit tends to make the signal quieter), there are two inverters and a ?switch? i think.  

I'm aware that this is a very hard project, but my last project was a tubescreamer, and I found it very easy, it worked on the first try.  That was 'intermediate', so i moved up.  And now its hard

[niftydog]

ok, not op amps, but the CMOS gates being used as amps.

[brett]

Hi.
This is a tricky project.
Thinking back to the problems I had with it, and what I know now that I didn't know then:
1. Save your sanity.  ALWAYS use sockets.  Only buy UBE chips.
2.  Expect CMOS chips to get destroyed in handling (and soldering).  So buy 2 of everything.  
3. Read 1 and 2 again.
4.  Expect to eventualy get a signal through it.  Expect to find it doesn't auto-wah.
5.  Get it wahing by adjusting the bias with those (??) 100k and 62k?? resistors (100k and 91k or 100k will work) (there's several posts on this)
6.  Be disappointed that the reverse-wah thing doesn't work.  Give it a kick.
7.  Congratulations! You've now got an auto-wah that kinda works.
8.  Buy a JH wah on e-bay.
9.  Go wah-crazy!!!

cheers