Autowah Tone Modding?

[Arn C.]

http://www.geocities.com/diygescorp/autowah.gif

Howdy All and Happy Friday!
 
I made the above autowah quite awhile ago now and was wondering if anyone could tell me where I could make some mods to vary to sound of this wah(ex: make more of a vocal sound, etc...)

It already sounds nice, but I would just like to see what different sounds I can get out of this circuit.

Thanks!
Arn C.

ps  Thanks for the schematic Marcos!

[Arn C.]

BUMP!

Any suggestions?  Anyone?

Thanks!
Arn C.

[earthtonesaudio]

That circuit is crazy.  I have no idea how it works!  Is that the whole schematic?

[Arn C.]

Yes, that is the whole circuit and it does work fine.  Just wanted to see if I could do more with it.

Thanks!
Arn C.

[earthtonesaudio]

Whew, a second look at it and I see it's a voltage controlled bridged-T wah!  That really wasn't obvious at first, wow.  Looks like the input signal tunes the oscillator of that NAND gate circuit which somehow puts out a DC voltage...

Anyway, you could probably get a better range of "wah" by mis-matching the two 10n capacitors in the feedback loop of the top BC549.  I would just replace one of them with a 6n8 or 4n7 cap.  Also you could split the 68k into two 33k resistors, and at their junction place a small (51-100pF) cap to ground.  (but use a socket or a switch cause it could self-oscillate with this mod)

Good luck!

[petemoore]

  Last transisitor gain stage, all the usual mods [such as cut and paste in alternative gain stage..or any of the typical mods.
 

[Arn C.]

Thanks a bunch Gents!   I will give these things a try.   

Peace!
Arn C.

[earthtonesaudio]

Another cool thing to do would be replace just one of the 10n caps with a bunch on a rotary switch, like 2n2, 4n7, 6n8, 10n, 22n, etc.  Larger values will make it more bass-like.

[Arn C.]

Exactly what I was planning on doing!   Thanks again!

Arn C.

[snap]

which components are the T, and which is the bridge?

[earthtonesaudio]

I still don't get what the NAND gates are doing, but to answer Snap's question:

The components that connect collector to base on the top transistor form the "bridged T" network.  This is a variation of the "Twin T" filter, so called because it has 2 series caps with a resistor to ground between them ("T" number one), and 2 series resistors with a cap to ground between ("T" number two).  The Bridged T is a variation on this filter which merges 2 of the series components and eliminates the shunt component.  In this case, the 2 series resistors are combined into the 68k resistor from collector to base (That's the bridged part) and the 2 10n caps which connect at the collector of the bottom transistor form the other "T" part. 

If you vary the resistors you can sweep the filter, and in this case the bottom transistor is used as a variable, voltage controlled resistor to ground.

A much better explanation (with pictures) is here: http://www.geofex.com/Article_Folders/EQs/paramet.htm#bridged_t

[snap]

ahh - I was being blind. Thank you for opening up my eyes Alex!

[Arn C.]

I tried the rotary switch using 1nf up to 50nf.   Below 10nf sound got thinner and wah was less pronounced.   10nf and above got bassier and the wah was more pronounced.   I believe I need a booster(clean) attached to the end of the circuit with a volume control. 

Any suggestioons for a clean booster(basic one) that may work with this circuit?

Thanks!
Arn C.

[earthtonesaudio]

Gus' NPN boost (in the "Beginner Project" section of this forum) has excellent instructions and support, but any 1-transistor boost would work... LPB-1, Sparkle Boost, SHO, AMZ Mosfet Booster, etc.

[Arn C.]

Thanks Alex!   Yes, I just want a simple clean small parts count booster.  I will check out the ones you mentioned.

Thanks!
Arn C.

[Marcos - Munky]

Hey Arn. How´s going? For a booster, I suggest you the SHO and AMZ Mosfet Booster, I built both on breadboard and both are simple and good clean boosters.

[Arn C.]

Thank you Marcos!   I hope you are doing fine!

Peace!
Arn C.

[Arn C.]

This schematic calls for a 4M7 Pot for the speed.   I find it is very touchy.   Is there a way I can make this more usuable?   It goes from slow to fast in a short range and has to be turned very slowly to find the right spots. Don't get me wrong, it works, just want to see if I could get it to react more gradual.   

Any suggestions will be helpful..
Thanks!
Arn C.

ps.  I did put in a boost circuit and it is much better now!

[Arn C.]

Do you think that if I use a 1 M pot with a 3.9M resistor across center to one side that I could get a smoother transistion?

Arn C.

[earthtonesaudio]

If the variation is all bunched up to one side of the pot's rotation, making it semi-logarithmic with that paralleled resistor you mention might help.  If part of the pot's rotation is unusable, you could try using a smaller value pot, and sticking some 1M resistors in series (i.e. from lug 3 to the rest of the circuit).