help with Mark Hammer's Woody pedal

[smoguzbenjamin]

Hello guys,

I'm working on mark hammer's woody pedal, but it seems it needs a bipolar PS. I'm putting it onto my breadboard, but I'm not sure what to do. Can't I just give the opamps 4.5v instead of 9v? Or should I apply 4.5v to the unused inputs? I still haven't really got opamps down, I really should study some more sometime, haha.  I'll only be using this off a wallwart, so I don't really ned batteries anymore... :roll:

But anyway, what should I do?

[Nasse]

If I had a working Woody I would be very happy to buy few batteries for it. But I have a faint memory or just a hunch that mr. Hammer had some good reason to use two batteries. Must check the archives maybe...

But for another story I have strong opinion that with such all-opamp design it will be cheaper to use two batteries instead of one. You can suck very much more juice out of batteries that way, they probably last looooonger together than two exhausted one at time

[smoguzbenjamin]

Yeah but I'm kinda short on cash (I don't get that much pocket money) So I was wondering if I could somehow convert it for wallwart use... :roll:

[Nasse]

Why not, sure it can be done, but watch those potentials. I never made my pedals wall powered, because I had one with two nine volters in series and artificial middle and neg ground (old elektro harmonix) and one with "real" +/0/- supply connector in  my setup, and some regular ones... And had that nasty shock from old tube amp when testing... But I dont play live anymore...

Quess Woody uses some regular adequate low noise quality opamp that is not very happy with one nine volter because of current consumption and the opamp may have trouble when voltage drops...

[smoguzbenjamin]

I'm using a TL072 / 4558 for the dual opamp and a TL064 for the quad opamp.... But couldn't I apply 4.5 volts to the unused inputs to feed the opamp correctly?

[Mark Hammer]

First, thanks for being interested.

In principle, you ought to be able to pick your preferred op-amp (I used what I had), figure out how to supply an appropriate reference voltage and run it from a 9v battery.  Personally, I don't know enough about how to do that, so I adopted the dumb-but-it-works approach.  I have a pretty good sense about what it is that different resistor-values do in a Vref divider circuit, but I've never really understood enough about how to determine the appropriate resistor values to use, given the properties of the specific op-amp, gain requirements, etc.

In general, although it does cost more for 2 batteries, and it also needs more room, complicates turning it on and off, etc., if there was ever a circumstance where you wanted more clean headroom, it would be in an acoustic simulator.  The ONLY clipping in the pedal should be from the clipping circuit.  Any clipping in the input, output or bass filter stages will take away from the sound.  

If I knew how to redesign it to accommodate, say, a unipolar 15v supply with a floating ground (Vref, as discussed), then that would solve all the problems, especially being able to power it externally.

Sorry  

[smoguzbenjamin]

Never mind, Mark, thanks for your input.

I'll be trying to float the ground up by having ground at 4.5v. So refereced to ground you have +4.5 and -4.5v which should be ok I guess I've got a breadboard and seas of time so I'll be having fun tweaking the Woody into perfection  Mark, do you want me to email the mods I applied?

[Mark Hammer]

Absolutely!!  I hardly ever consider something "done", and am only too happy to see someone else improve a design or make it more usable/friendly for people.