Colorsound inductorless (twin-t) wah schematic

[cd]

SSIA - anyone have a schematic for the Colorsound inductorless (twin-t) wah?  NOT the one at Fuzz Central with the inductor in it.

[Ansil]

i asked a year ago and no one had it a few people sent me the one with the inductor in it but so far no luck. if you find it email me it.

[cd]

i asked a year ago and no one had it a few people sent me the one with the inductor in it but so far no luck. if you find it email me it.

Yeah, I found your post when I did a search  If I find it I'll post it up for everyone.

[petemoore]

I built the one from GEO, uses opamp and no inductor...definitely Wahs and is quite 'adjustable'...circuit, box with treadle...only thing it doesn't yet have is a bypass switch...then I can really test it./

[cd]

I built the one from GEO, uses opamp and no inductor...definitely Wahs and is quite 'adjustable'...circuit, box with treadle...only thing it doesn't yet have is a bypass switch...then I can really test it./

Do you have the schematic or not?

[nirvanas silence]

I actually traced one a few months ago and it sounds great.  I don't have the cap value of one tropical fish cap though.  This board looked like a copy of the original though so I can't verify how accurate it is.  I don't have a scanner so if I get a chance to take a picture of it I'll defiantely post it.  Sounds great and is cheap to make.

[cd]

I actually traced one a few months ago and it sounds great.  I don't have the cap value of one tropical fish cap though.  This board looked like a copy of the original though so I can't verify how accurate it is.  I don't have a scanner so if I get a chance to take a picture of it I'll defiantely post it.  Sounds great and is cheap to make.

Great, someone who actually knows what they're talking about!!  NS, I have a circuit drawing with no values below, if you can fill in the values that's good enough for me.  Did you copy down the colors of the tropical fish cap?  If so we can probably decipher the value from that.  OK, check out the pic:

[nirvanas silence]

R1: 5M7  (!!!)
R2: 10K
R3: 330K
R4: 1M
R5: 180K
R6: 180K
R7: 470 ohm with a 100K pot in series
R9: 33K
R10: 100K
R11: 47K

C1: .01
C2: .015
C3: .0022
C4: .0068
C5: .1
C6: .01
C7: .0022

Schematic is probably 100% correct seeing how mine matches yours identically.  C2 was the mystery cap but I must have taken it out and measured it... .  Please give credit if anyone decides to post future info about this pedal...

[cd]

Thanks NS, this nut has finally been cracked!!!  Strange that C3 and C4 are not matched (the same) though.  I will redraw the schematic and post it for all later today.

[nirvanas silence]

Glad you could use it.  I think I'm tossing a switch in my vox wah to change between circuits so I figured I should trace the circuit while I had a colorsound wah here.

[petemoore]

Moot [?]...anyway the schem for the ductorless wah should still be up at GEO...
 Looks like you're gonna use this discrete version...anyway RG does a good runthrough of what the circuit and components do...

[cd]

Moot [?]...anyway the schem for the ductorless wah should still be up at GEO...
 Looks like you're gonna use this discrete version...anyway RG does a good runthrough of what the circuit and components do...

Duh.  Your post was pointless because it didn't answer the question and provided no useful information in any way.  The twin-t wah schem at GEO uses completely different circuit values.  Anyway, here's the full redrawn schem:

[Ansil]

interesting in the fact that it looks alot like the idiot wah......

[cd]

Yup it's a simple Twin-T filter wah, the "trick" is the circuit values that give it the proper frequency range/response.

[Paul Perry (Frostwave)]

In a traditional wah, the Q varies as it sweeps (because, the R in series with the coil varies, I think). What this inductorless one does I can't imagine, anyone simulated it yet??

[cd]

This one varies Q as well, by applying negative feedback around the notch frequency.  RG's Tech of Wah explains it way better than I can:

http://geofex.com/Article_Folders/wahpedl/wahped.htm

Here's the sweep (simulated):



BTW the sim above is with a 2n5088 transistor (high gain).  Lower gain transistors (like 2n3904) have a softer Q (less peaked sweep).  If you're building this, I would suggest using the high gain transistor, then stick a trimpot on the emitter to adjust the Q (soft/sharp) as desired.  Also, see the GEO article above on adding a 2nd transistor to buffer the output, it doesn't change the tone much (if at all) and it helps with other FX after.

[Tim Escobedo]

The Twin T/Bridged T is a great circuit to implement as a wah. Simple and easy to control. Q does vary quite a bit with tuning. It's also a very easy design to play with. I personally think they make cool sounding VCFs, too, if you aren't too concerned with precise control over Q. Lots of design considerations. "Balance" of the RC components in the "T" networks, amount of gain, impedances of gain stage, gain capability of gain stage, allowable amount of distortion, and so on. And all can be explored with a single transistor design.

[Ge_Whiz]

How did you implement it as a VCF, Tim? Just substitute a JFET for the pot, or is there more to it than that?

[R.G.]

The twin T provides high Q only at the specific place where the components are matched per theory. The null gets less deep (that is Q goes down) as you move off the theoretical match. Changing the one resistor to move the frequency counts for that too, so the Q changes.

For another twin T wah, PAIA did one in a Poptronics article in the late 60's and also did a leslie simulator that way. I think it was the "Synthespin".

They're all quite similar. It's an inexpensive (compared to an inductor) way to get a bandpass filter.

[Tim Escobedo]

How did you implement it as a VCF, Tim? Just substitute a JFET for the pot, or is there more to it than that?

I was just being synthesizer-specific. Most typical synth VCFs offer steeper cuttoffs, more consistent Q across tuning range, and superior CV rejection. These are areas where the Twin T really can't compare with other VCF designs regardless of method used to tune the filter. Still, they're simple enough and sound good enough to be useful.