More MXR envelope filter questions...

[moosteak]

Hi all,

What a great forum...!

I've built the tonepad MXR envelope filter and seem to have different troubles to everyone else. I've used a ST 4066BE and Motorola 4069's UBE (unbuffered?). Now I've installed all the mods and I'm getting sound, but no filter action except if I really hammer the strings on the normal (not reverse mode). I've stayed clear of the R16 bias mod, left it at 100k, as the reverse mode doesn't work if you change this. Now, I've ordered more 4069's and 4066's as reading the posts, this can be a problem. Trouble is, I am getting some sweep when I give it lots of neck pickup and play really hard at the top of the neck (bigger voltages).

The filter range mod works great (as in you can hear output frequency shift), the emphasis makes a little difference to the tone and the reverse mod works (changes the starting filter frequency)... We just don't have any sweep!!!

I've changed the output caps and resistors to the generally preferred non-tonesuck/volume drop values (C2 tantalum 1uF non polarised, C4 to 15nF, R1 1k, R2 100k etc).

Anyone else got/had this problem?

[moosteak]

Ok,

So the chips really do have an effect don't they?!!! Its working great now, and I'm just gonna have a go at a Decay pot too.

These chips DO work in the MXR Envelope Filter;

Philips HEF 4069UBP

Philips 74HCT 4066 N

these, DON'T;

Motorola MC14069UB.

Just thought I'd add these findings! The Motorola looks likes its unbuffered (UB) but still didn't work. Oh well, we're on our way to chewy funk heaven now!

Cheers all.

[jjs]

Just wanted to note that the Motorola MC14069UB worked in my tonepad MXR Envelope Filter clone. Maybe yours is damaged.
I used the Motorola and a Toshiba TC4069UBP.
Here's my original post about the build: http://www.diystompboxes.com/smfforum/index.php?topic=24518.msg159092#msg159092

[Mark Hammer]

This might be empty voodoo handwaving specific to my own personal shortcomings as a builder, but make sure there is good contact between those CMOS chips and their respective tie points.  That could imply using any of: a) good quality machined sockets rather than the spring-leaf type, b) soldering the CMOS chips directly to the board (MXR did, why can't you?), or c) pretreating the pins of the chips in some manner or at least confirming the absence of obstacles to conduction (e.g., scraping any visible tarnish off the leads with a blade).

As people have noted, the circuit does seem to be a little fussy about chips, but I sometimes wonder if the fussiness is not so much the specific brand or lot of chips, but simply the need to have a zero-ohms path between several key IC pins and their respective tie points.  Admittedly that's a naive point of view, but I've built this beast a few times, and also experienced this non-responsiveness to anything but strong input signal, which seemed to go away when better contact was established.  Again, I'm not saying chips are irrelevant.  Rather, it is important to recognize that there may be other factors either separate from chip type, or as adjuncts to chip type, that will not be "fixed" simply by plunking in the right brand of chip.  What can appear as a case of using the "right chips" may well be a misattribution and more likely caused by simply improving the quality of the critical contacts.  The "right chips" may simply end up having cleaner pins or be seated better in their respective sockets.

If this is theoretically impossible (and there are many others whose technical expertise I will gladly defer to), so be it.  I'm just saying what it seems like from my end.

[StephenGiles]

I only ever built this on breadboard and the stock circuit worked first time - even using a 4049 as I mentioned before, because I didn't have any 4069s at the time. I can only guess that you have made a mistake somewhere along the line. When building these sort of circuits, it really is worth testing as you go. In that way, for instance, if you build the envelope generator and see a decent sweep on a volt meter at its output each time you play a note then you could reasonably eliminate that from later troubleshooting.

However, it's often more luck than judgement!

[StephenGiles]

http://elists.resynthesize.com/synth-diy/1998/12/766830/

I found this "how it works" from Mr Haible regarding the MXR Envelope Follower.

[moosteak]

Thanks for your responses.

I always scrape the leads of resistors carefully before inserting them and likewise with anything that hasn't got a problem with static. I couldn't quite believe that the chips were gonna make the difference, but in this case they did. However, I do agree with the spun pin type sockets over the spring type (just better quality and better contacts), and that re-inserting the different chips make have scratched the contacts in the sockets, so that there is a zero-ohms connection.

I dunno... Its being used in two gigs tonight though!

Cheers