Need Help: Escobedo PWM Build

[turdadactyl]

Hey guys,
I'm a relative noob, so there's probably something dumb/simple to blame for this thing not working, but...it's not.  I've laid out the Tim Escobedo PWM (without the LFO) on a breadboard.  It's passing signal, but there's no effect and the output is at a very low level.  The volume pot seems to work.  The PW pot does nothing.  Anybody have a clue what I'm screwing up?

Here's the original schematic:


I'm referring to the numbers as they are labeled in InSonicBloom's layout, which is here:


I MADE ONE SUBSTITUTION:  I didn't have a 5nF cap, so C1 is 10nF/.01uF.  (Also using an LM386 rather than 386D if that counts as a substitution.)

Here are the voltages I got off my meter:
Battery: 9.58
D1 = 9.29
C1 = 8.09
C2 = 8.00
C3 = 9.29

VR1 (PW) B500K
1 = 8.10
2 = 8.10
3 = 8.11

VR2 (Vol) A100K
1 = 8.11
2 = 8.02
3 = 8.02

IC1
1 = 8.28
2 = 8.16
3 = 8.06
4 = 8.11
5 = 8.35
6 = 9.29
7 = 8.29
8 = 8.27

IC2
1 = 8.37
2 = 8.10
3 = 8.10
4 = 7.74
5 = 8.11
6 = 7.74
7 = 8.11
8 = 7.73
9 = 8.11
10 = 7.74
11 = 8.11
12 = 7.73
13 = 8.11
14 = 9.29

Here are a couple pics of the rat's nest I built, which may or may not be useful to you.

[bluebunny]

If your battery (or PSU) is connected to the buses at the top of the picture, then you may find there's no continuity all the way to the bottom of the picture where your circuit sits.  The "cuts" in the blue and red lines are real.

[antonis]

Also, pots on layout are reverse working..

There should be VR1 2-3 at j1 and VR2 3 at k1..

[turdadactyl]

I have the positive battery terminal connected to the top positive rail and the negative battery terminal connected to the bottom negative rail. I put a jumper between the two negative rails but no jumper between the two positive rails since the power is only going into the diode and then from there to pin 6 of IC1 then pin 14 of IC2.

[antonis]

Marc told you that there isn't continuity between the sets of 5 pads..

Your diode anode is "foating" because its jumper doesn't conduct with +9V wire..
(6th pad on the upper rows is a CUT..)

[bluebunny]

[turdadactyl]

Well, holy crap.  Thanks Marc.  Now I have a nice fat distortion.  Next step, fix the pot.  Gotta go to work but I'll report back.

[antonis]

Marc is again right..!!!
(by bad..  )

[bluebunny]

Cool.      Can I have the rest of the day off?   

[turdadactyl]

Yes. Let me know if you need a note.

[bluebunny]

I already got home.  I didn't realise I needed a note.   

[turdadactyl]

Works like a champ!  Thanks again, Marc.  I knew there was something minor I was missing.

[turdadactyl]

[turdadactyl]

I got this circuit working and then added the LFO.  That works great as well.  I'm thinking I'd like to add a second footswitch that would engage/bypass the LFO.  That is, the footswitch shown in the original schematic (which I'd replace with a 3PDT so I can add an LED) would be the bypass for the whole effect, but footswitch 2 (another 3PDT) would simply be an on/off for the LFO and related LED.  Can anybody give me some guidance on this?

I found this old thread, which mentions the same idea, but I'm not sure if it's the solution to the same question.
http://www.diystompboxes.com/smfforum/index.php?topic=73540.msg596747#msg596747

[blackieNYC]

I just did one of these. And since there are so many inverters available, I made a "pseudo-random" LFO. Two or more lfos at different freqs blended together. Kind of like sample and hold.
But it's great without the LFO too. Definitely have a switch for that.

[turdadactyl]

Blackie, does that old thread have everything I need to get that second switch into the mix?

[turdadactyl]

So, after a month I'm coming back around to messing with this build.  I may want to mod it a bit.  I want to make sure I fully understand what's going on here from an actual functional standpoint.  Does this all sound right?

The clipped signal output from the 386 clipping stage is passed into the Schmitt Trigger at pin 1 of the 40106.  That goes out of pin 2 and the combination of the .005u cap and the pulse width pot control how quickly the cap discharges and passes the signal into the second Schmitt Trigger at pin 3.  That creates PWM because it controls how quickly the second trigger reaches the threshold needed to put it into its high output state and then drops back down to the threshold triggering its return to the low output state.  This results in the clipped signal from the clipping stage, mixed with the PWM being outputted at pin 4.  The 100K pot is a simple volume control, as it controls how much of the signal from pin 4 passes to ground versus how much passes to the output.

Question  : Assuming the above is correct, why bother with the first Schmitt Trigger (pins 1 & 2) at all?  Why not just go from the 386 output, through the .005u cap and PW pot directly?

Next, if you add in the LFO, I understand the working of the 47k/500K combination as the rate of the LFO.  I also understand the 2N3904 is just a booster to add some current to the LFO output. 

Question  : Is the 10k pot/33k resistor combo just an output level control of the LFO to the booster (and in turn the 40106)?

[anotherjim]

How good a range of pulse widths the PWM will deal out depends on how fast the input switches between logic levels. The LM386 can't switch its output between low and high very quickly, since it's an audio part. Adding another inverter corrects that issue.

The transistor is used as a variable resistor, controlled by the LFO, it duplicates the existing Pulse Width pot. This is a crude implementation, because if the pot is set low to zero resistance, the LFO will have little to no effect.

[turdadactyl]

How good a range of pulse widths the PWM will deal out depends on how fast the input switches between logic levels. The LM386 can't switch its output between low and high very quickly, since it's an audio part. Adding another inverter corrects that issue.

In this case, will the first inverter always be at its high output level and the level of the second inverter be solely controlled by the cap and pot?

[turdadactyl]

The transistor is used as a variable resistor, controlled by the LFO, it duplicates the existing Pulse Width pot. This is a crude implementation, because if the pot is set low to zero resistance, the LFO will have little to no effect.

I just re-read this.  Isn't this accounted for by the 33k resistor between the LFO pot and the transistor?