Strange new problem with Electric Mistress.

[Praying_V]

Hi everyone.  Let me give the whole story.

I'm attempting to build an 9V Electric Mistress from the Tonepad schem: http://www.tonepad.com/getFileInfo.asp?id=102

This is by no means my first project, I've built around 20 pedals over the past few years.  However, this is the first time I'm completely stumped...

I've got the whole thing assembled, and used all the exact values specified in the schem.  All soldering is clean.  I didn't add any custom mods, not even true bypass.  And it ALMOST works- I'm getting sound in bypass, and also a signal when the effect is engaged, but the "flanger sweep" is acting strangely.  Rather than a triange modulation waveform, the flanging is happening in a "square wave".  The effect is alternating between two states, kind of like a step-phaser.  (there could be other problems, but i don't hear any, it sounds like it might be working except for the sweep)

It seems my controls are working- the speed of the square-wave-flanging changes with the "Rate" pot.  I can"t say for cetain if the "feedback" control is doing anything...  But i can say everything seems to be wired & connected correctly.  I've checked everything 10 times now, over 2 days...  I've tried adjusting the trimpots, to bias the BBD & set the clock speed.  Neither seems to help.  I've adjusted them very slowly, (I've done this before in a Small Clone, and a Memory Man without problems), so I think it's not a trimpot issue.

Right now I'm thinking it has to be a bad component.  Maybe a bad IC?  I've checked all my pin voltages, and compared them to the working pin voltages posted here: http://www.diystompboxes.com/smfforum/index.php?topic=46519.0 .....all voltages check out perfectly except for one thing- my LM311 pin7 (tied to 4013's pin3) is a little low (I'm getting 1.6V).  I don't know if this is related, but i figured it's worth mentioning.  There could be a bad component, but I have no idea where to look.  (could a bad BBD do this?)

I don't have an oscilloscope, but i have attempted to see what the LFO is doing using my DMM.  When i set the "Rate" slow on the Mistress, i can see the DC voltage increasing & decreasing slowly in the LFO.  It seems i have a good sine/triangle wave in the first 3 LFO stages (the LM324 stages).  I have a square wave going from the 4013 to the SAD1024 (which i think is expected?). 

I don't know enough about LFO circuits, or BBD cirtuits, to figure out what the problem could be.  I've spent a few days planning & carefully building, and a few more days trying to debug...  And I've reached the point where I'll have to give up & start a new project...  But I REALLY want to finish this one!  If anyone has any ideas, what could possibly cause something like this, let me know, I'll be forever grateful.  Right now my only other option is to buy all new components and start from scratch.  PLEASE HELP!!  thanks ........ken

[darryl]

I don't know if this is the problem, but I change my diode from a 1N4001 to a 1N914 in the loop of the 311IC and then it worked perfect. I was told it should not have made a differents but, I was having the same problem you were and that fixed it. I hope this helps.

darryl

[Praying_V]

Hey, I don't know how to make sense of this...  But it actually worked!!  Theories, anyone??

Thanks a million ..........ken

[gaussmarkov]

here's a theory:  the 1N4001 is a slow diode relative to the 1N914 or 1N4148.  so the timing cap in the VCO does not discharge as much on each oscillation.  that means it takes less time to charge that cap back up so that the output oscillations are faster and have a smaller amplitude.  the amplitude may fall below the level (1/2 supply) required to switch the 4013 on and off.