Tonepad MXR Envelope Filter issue

[jbolin]

Building this for a good friend of mine.  This is about my 10th pedal build and was feeling pretty confident until I finished and plugged it in and I got nothing when switched on...  I followed the instructions to a T and nothing.  I've built one other Tonepad pedal and that was the Ross compressor and it turned out fine.  But...  What I do remember was, on the Ross compressor, there was a jumper that was not noted in the instructions.  While working on the envelope filter, I noticed that there were two jumpers marked, what was noted was for the mods.  I put a jumper on them and the pedal works while turned on...  But, there is no effect.  What on earth could I have done wrong?  I used RCA chips and not TI's.  Here's a couple of pics.  If anyone else has run into this issue, please let me know. 

[Kipper4]

Welcome Jbolin.

Perhaps you could help us to help you.

Go here and supply more information please.

https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Rich

[Mark Hammer]

I typed this out once before, but lost it.  So we'll see if this post gets through.

1) There are three major sections to the circuit: the envelope extraction used to govern/vary the HF clock, the HF clock used to change the pulse-width of the 4066 switches, and the filter it controls.  Troubleshooting begins with assessing that each section is or isn't functioning as it should.

2) The junction of D2 and C9 should show a change in DC voltage as you play, and which corresponds to the Threshold control setting.  If not then either something is amiss with the diodes or the invertor sections feeding it.  The subsequent invertor sections shape that envelope into something a little smoother, whose rise can be slowed down via the Attack control.  You should be able to measure a rising DC at pin 10 of that chip, whose rise time corresponds to the Attack setting.

3) People have noted issues with some brands of chips that require tweaking the triggering of the clock.  But the photo of my old 1978 MXR circuit board shows RCA chips, so you should be good there.  I.e., it's not likely the brand of chips used.

4)  I believe it has been corrected and updated, but the earlier files for the Tonepad A-Gua mistakenly showed only one cap being changed for the filter-range mod.  That mod requires changing *both* C6 and C7 to move the range higher or lower.

[jbolin]

Thanks for the info Mark Hammer. 
and Kipper4, I will report back my findings later on.  I am going to pick up a meter this afternoon.  Thanks again. 

[Slowpoke101]

The links can make for some confusion. The links are mainly for the modifications - which are worth doing once you get the basic effect to work.
These links should be installed just to get it to go as an unmodified unit;
  F - E
  G - H

From your pictures I see that you have cut link G-H. Reconnect it and try again.

Edit: Oops, G - H is linked. Camera angle hid it.

[jbo]

This is jbolin...  I've had to make another account.  I tried to change my email address, and it has never sent the verification email.  I've tried resending the verification email several times and it has not sent.  Anyway, just would like to catch you all up. 

So...  I scrapped the first board (the pics that I posted) and bought another board.  The first board, I tried changing some components and wound up unintentionally breaking some of the pads off and it just would not work after that. 

Anywho, I've got the new board populated and I was extremely careful with all of my soldering and wiring.  So, the pedal is working, but still no effect  . 
The mods/changes I made were:
R16 to 62k
Emphasis control mod: R19 to 47k and added a 500k pot in F&E pads as variable resistor
C2 to 1uF
C4 to .01uF

I just saw @Slowpoke101's post about linking the unmodified pads.  When I get home tonight, I'll try linking G-H and see if that makes the effect work. 

Thank you all for your time!  I'll let you all know if it worked. 

[reddesert]

I have built this effect on perf from the Tonepad layout. Reading the comments/build reports on the Tonepad website is useful. The links are the first issue.  The jumper from pad G to H is necessary because that's how the clock signal gets from the clock (IC2 pin 8 ) to the switches.  If this link is not in place there will be no filtering. The reverse sweep mod switches between a link and an inverter to invert the clock signal.

After that, the main thing that trips people up, I think, is getting the ultrasonic clock to run. If it doesn't run, the effect won't do anything.

There are two unusual aspects of this effect:
1. It has a rather large voltage dropping resistor of 3Kohms immediately after the voltage input, R4 on the Tonepad schematic. This makes the supply voltage Vs dependent on the current draw of the chips.
2. The clock needs a bias voltage supplied by a voltage divider of R14 and R16. Several people in the Tonepad comments found that in order to get the clock to run (especially with TI chips), the values of this divider needed to be changed.

You're using RCA chips, not TI, but these comments still apply. The simple-ish way to test the function is to: 1. test the value of Vs - it should be around 5-6 volts. If it's well outside this range it may not work. 2. Use a trimpot in the R14/R16 voltage divider or swap out resistors until you get the effect to work.

The less simple but better way to verify the operation of the clock is to use an oscilloscope. If you put the scope on the output of the clock at IC2 pin 8, you should see a square-ish wave at around 50 kHz. So for example if you had a trimpot in the voltage divider, you could turn the trimpot until the square wave appeared.

Many people don't have oscilloscopes, but you can now get a DIY kit for a mini oscilloscope for just $20 or so. I have a build report for the Jye-Tech DSO150 at http://www.madbeanpedals.com/forum/index.php?topic=26815.msg259591 . It's pretty easy to do. The build instructions are good. Make sure you get it from an authorized seller.

[Fp-www.Tonepad.com]

Having the ICs in sockets will make it easy for you to try other ICs. This circuit uses the IC in a less conventional way and sometimes it won't work unless you got the right ICs.
Make sure you add the jumpers as shown on the layout image.
I suggest you try without the mods first, it can make a cleaner build without the switches and emphasis control.

[jbo]

Thank you all!  Well, after I originally posted this, I bought another circuit board from Tonepad, built it and it worked.  So...  I thought I'd try and etch the board myself and give it a go.  The first board I etched, I used sockets and, well...  It sort of worked, but had some issues.  I etched another one without the sockets and it had the same exact issues.  The effect kind of worked, but not good enough.  Very frustrating.  There seems to be a grounding issue somewhere.  When I roll the volume knob on my guitar on/off it makes the God awfullest noise.  I've had two different switches connected to it and the same results.  Like I said, I've etched two circuit boards and got the same results.  I'm just going to move on to a different circuit.  Want to thank everyone who participated in giving me answers!