mxr envelope filter doesn't work

9 volts · February 14, 2006, 06:18:52 AM

Hello there, Ive just completed building an mxr envelope filter clone and having a little trouble. Basically I get an unaffected signal. The potentiometers don't effect the sound and but the signal is strong. I've based the circuit board on ggg project and would appreciate any feedback. I've looked through past messages in regards to the choice of ic's. Mine were from small bear. Weirdly if I touch between and connect r16 (100k) and c4 ((.1uf) the wah kind of works in relation to the pressure.......anyway greatly appreciate any feedback.

Mark Hammer · February 14, 2006, 04:21:02 PM

I've built maybe 4 of these things, 2 with the A-Gua layout, and 2 with the original MXR layout (photocopied from the one I bought in 1978 or so). I don't think any have worked right away. Too damn many pins and CMOS requirements. For starters, make a version with no mods whatsoever, just to be sure you weren't confused by any of the alternate pads. second, make sure you are getting good contact between the chips and sockets. The chips could be seated wrong (ever had a pin bend under the chip and sit on top of the socket *looking* like it was inserted?)

Arn C. · February 15, 2006, 08:46:31 AM

Mark Hammer wrote:

Quotesecond, make sure you are getting good contact between the chips and sockets. The chips could be seated wrong (ever had a pin bend under the chip and sit on top of the socket *looking* like it was inserted?)

I know what you are saying Mark. I built the XORUS Ultra Sick and couldn't get it to work properly. So, I decided to strip it down and start over. After I cut off all the wires I noticed that one end of the IC was hung up on one of those little box caps. One end of the (14 pin?) chip was seated and the other end was popped up and not seated. So, the IC was only half working. I almost have it all back together and will try it out again soon.

Sucked that I cut all the wires before I noticed the improperly seated IC.

Peace!
Arn C.

hank reynolds 3rd · February 15, 2006, 01:16:56 PM

this has happened to me in the past too...
What I do now is put one side of the Ic in the socket a tiny bit first, then do the other side...

mrsage · February 15, 2006, 04:19:51 PM

Quote from: 9 volts on February 14, 2006, 06:18:52 AM
I've looked through past messages in regards to the choice of ic's. Mine were from small bear.

That could well be your problem.

This circuit is very particular when it comes to ICs. I've heard of people having trouble with the SmallBear chips before.

Try some fairchilds from www.mouser.com (make sure you get the DIP style, not the surface-mount SOIC ones).

9 volts · February 16, 2006, 12:45:57 AM

Hi there, well I checked the pins on the ic's and they all seem ok. I've noted that someone wrote earlier this-

"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)"

I'm wondering if this is the next step I'm to try though i'll certainly look around for some extra ic's to try. I've got an audio probe wired up and know how to check voltages at ic pins but to be honest don't really have the knowedge base to problem solve the situation. Anyway thanks again for the feed back.

StephenGiles · February 16, 2006, 08:17:04 AM

When I breadboarded this a few years back, I just used whatever inverter Cmos I had at the time which happened to be a mix of 4069 and 4049. I worked first time, now that may just be luck, but I'm not so sure it's down to particular makes of cmos. I still have the components I used in a bag so if I have time I may rebreadboard it.
Stephen

9 volts · February 18, 2006, 03:18:22 AM

Well. I've now replaced the ic's and am using those which have ube written after the the number and have also tried replacing the 62k resistor with a higher value (92) and both these changes haven't changed the units behaviour..I'm still getting an uneffected signal...I've reread mark hammers article on the geo website about the workings of the envelope filter and at least am getting a better understanding about how these things work. Welcome any other feedback

9 volts · February 18, 2006, 06:00:03 AM

ps I've just noticed that when I connect and the disconnect the battery the signal makes a wah sound. I suppose this is manually altering the voltage.

9 volts · May 27, 2006, 07:26:32 AM

Just a note to say I finally bought Phillips ic's (ubn I think) and the effect worked immediately. I then added some of the mods on the tonepad page and its become a great simple to use envelope filter.

Mark Hammer · May 27, 2006, 08:41:39 AM

Congratulations. I loved this puppy when I got one around 1978 or so, and still do. Now you can love it too.

Many many thanks for providing followup. Like with any DIY pedal, there are always all sorts of unsuspected sources of difficulty, but with some there are some things one needs to look at first because of the frequency with which that problem occurs. When people write back and indicate that approach X cures problem Y, that ends up helping lots of other folks in the future who may not be sure where to start troubleshooting. It's nice when the solution involves a couple of dollars, a couple of socketed parts, and only a couple of days wait..

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mxr envelope filter doesn't work