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I've got a bunch of TLE2074, OPA4134 and TLC2264 that I thought I'd be able to use for the Kingslayer project but...well...

Anyway, anybody have an idea about what sort of decent overdrive projects I might use these for?

In looking at the schematic for the old Schaller "Bow Wow Yoy Yoy", it has a lot in common with the schematic for the Weener Wah.  Here is the schematic for the Schaller:



Some minor topology changes notwithstanding, it looks like the main differences are:

1.  The Schaller has a second inductor going to a .22 cap, going to a 1M resistor to GND...I am guessing that these additional components are what create the "yoy" sound (a switch bypasses the 1M to GND, is this what changes it back to more of a "wah" sound?). 

2.  The Schaller has a third transistor stage at the end (1M between B and C, 6.8K on C, 2.2K on E to GND), leading to a 10uF output cap, with the output taken between a 4.7K and a 6.8K (which I guess could just be replaced with a 10K "volume" pot).  Is this a boost stage?

I'd like to mod the Weener Wah to be able to capture the Schaller's "yoy effect.  I guess it wouldn't be too difficult to hack in the additional inductor and relates components...but how important is that third transistor stage? 

Actually, I think I know really do understand what's going on here. With all of the different options, and the fact that I want to use this as an overdrive rather than as a boost, I think simply powering the entire circuit (both plates and heaters) at 12 V from a wall wart will be the best option.

Now -- anybody have any suggestions for a preferred 12v DC wall wart to use with this thing?  :-)

Actually, Scruffie, I looked at the Road Rage at it puts out a maximum current of 100mA.  If I understand the Valvecaster-type devices correctly, they require more than that...about 300-500mA or so, or more.  If you think using a RR-type charge pump will sufficiently power the circuit at 12V, why is there such concern that the circuit be run at 300-500mA?

So Scruffie and Jon...do you think it would be more advisable to power this with a charge pump changing 9V into 12V, or would it be better to power it with a 12V wall wart? 

(and if the charge pump is okay, could I then just use the Road Rage and modify the regular to an LM78L12 or something else like it?)

The reason I ask is because if there isn't that much of a difference, I'd rather just be able to power the effect from the powr supply I use for most of my 9V pedals (a Dunlop DC Power Brick) because then I don't need to worry about carrying a separate wall wart.

So Jon, since I am interested in using this primarily as an overdrive -- powering the entire circuit at 12V will work?  I want to avoid the problems people report with running it at 9V, which is why I thought 18V would provide better clarity and punch (while still yielding good drive characteristics).  But if I can get that with hitting both the plates and the heaters at 12V and avoiding having to use the heat sink...

Alright...I will move on from the charge pump option.  So my question now is...what must I do to feed 12V to the heaters but 18V to the plates?

So Jon, what if I wanted to run the valvecaster plates at 18V, but run the heaters at 12V (which one of the other forums suggests is a good option for better tone/headroom)...could I use the RoadRage for that (and modify the LM78L15 to a LM78L12)?  Or are you saying that even the Road Rage wouldn't work in this scenario for all the reasons you noted regarding charge pumps?

Okay...so if I understand correctly, then something like this would work:

1.  9V power supply to an 18V charge pump.
2.  18V out from the charge pump to the IN of the regulator; GND pin of the regulator grounded.
3. the OUT pin of the regular will provide 12V of power, which can then go to the circuit.

If I have that right (I hope I do!) would it be advisable to insert some power filtering caps between the regulator and the Power IN of the circuit, or should the power filtering be done before the current hits the regulator (or, for that matter, the charge pump)?

So, take the18V lead, feed it to the input pin on the regulator, take a wire from the output pin and feed it to the circuit, and then ground the GND pin?  Dumb question (the pinouts seem fairly intuitive) but I'd rather sound dumb than make a dumb error.

Note -- I'm doing this to try to run a Valvecaster circuit at 12V.  It just occurred to me...do I even need the 18V charge pump, or can I feed the 78L12 regulator the regular 9V source...that is, if I power the 78L12 from a 9V source, will it still put out 12V to feed the circuit?

Can anybody suggest a way to modify this little daughterboard so that it puts out 12V instead of the 18V?  I suspect it may just be a latter of choosing different diodes (and possibly doubling them up), but I'm a novice to futzing with this sort of thing, and don't want to make a really bad mistake!

I'm having trouble uploading a picture, so here's the URL link to the vero layout I'm hoping to modify:

http://4.bp.blogspot.com/-SHcE0P5tEao/U9rvGU589eI/AAAAAAAAIX0/hO5n62dQ2cs/s1600/Toneczar+Openhaur+charge+pump.png

Of course, if anybody has an existing vero layout they can share for a 9V to 12V charge pump, that would be great too.

Thanks in advance.

You cannot fake an audio taper with a variable resistor. You can if it's a voltage divider.

Putting the resistor from 1 to 3 will give you a smaller value pot but the overall taper will be reverse log-ish.

So John, would it be best, then, to take a 250KA pot and just tack a 100K resistor to lug 3?

Oh...no, it's a fuzz face, and I tried a 500K which was too muddy, and a 250K which was not "full" enough, so I figured 350K would be a good compromise!

John, thanks for the insight.  How would you suggest I then go about modifying a fuzz volume control to approximate a 350K audio taper if I've got a 500KB pot or a 1MB pot?

Am I right that if I take a 500KB pot and put a 1.2M fixed resistor across lugs 1 and 3 of the pot, the result will basically be a 350KA pot?

Or am I miscalculating things in terms of the taper/curve?