How can I brighten up my Wah Pedal?

[ruepselrum]

I recently modded my Dunlop Crybaby GBC95 to my personal taste. I did the common resistor adjustments (vocal mod, more gain+bass mod), converted to true bypass and added an LED. I also adjusted the gear (full toe=full open pot) to achieve most treble.
Although I really like the mods, I'm still not totally satisfied. After all it seems to be a little dull and I'd like to add a little treble or brightness, if that's possible.

I'd appreciate any suggestions.
Sascha

[Mark Hammer]

Wahs are bandpass filters. So, while you can (and did) shift the range of sweep such that the centre-frequency is higher, content above the centre-frequency is always attenuated. Even with an input buffer to keep more top end, you still won't get it at the output.

The strategy you probably want is something like what folks use for compressors. That is, some of the unaffected signal is blended in with the effect at the output. But that starts to complicate the circuit, and it stops being a GBC95.

One of the old studio post-production tricks was to use a parametric EQ to mimic wah by maxing the boost, and sweeping the resonant frequency manually for a guitar solo. The advantage of this method is that it does not affect the rest of the spectrum, including the top end, while still providing the emphasis that makes a wah a wah. But that's not a GBC95, and often requires a dual-ganged pot.

[Leo_Gnardo]

What Mark said ^^^. Also, the wah circuit input impedance loads down your guitar badly. That's why you put the true bypass switch in, so in bypass the wah circuit does not roll off high frequencies making your tone muddy sounding. What to do when the wah is in use? Buffer amp between the guitar and wah input. For a couple customers I've built copies of the MXR Microamp on a small board and fit it inside the wah chassis. It's surprising how much brighter the tone is, and you can bump the gain up if necessary.

If you want to try the concept before you alter your wah pedal, all you need is any guitar pedal that buffers the signal in bypass mode. That would include any Boss pedal. Chances are good you have at least one, they're very popular. Of course the MXR Microamp is another candidate.

As far as building your own buffer, you could select from a number of designs. Besides Microamp, I favor the Alembic Stratoblaster, just a single FET plus a couple of resistors and caps. To hear examples of how well that works, have a listen to any track on Grateful Dead Europe 72 where Jerry is using his wah pedal. You'll hear the wah passages sound exceptionally clean and clear - that's the Stratoblaster built into his guitar, driving the wah. Yeh it's funny to use an example nearly half a century old (!) "Sugar Magnolia" for instance, the guitar jam starts about 3:35 so you can get a listen to the non wah tone, then he steps on the wah at 5:12. Happy listening, and have fun with your wah.

[ruepselrum]

@Mark: That totally makes sense to me.

@Leo: I'll try the Boss buffer during next week and also have a look at the video and check out the Stratoblaster.

I have to admit that I converted the pedal to true bypass and removed the buffer more for common sense reason rather than really feeling the need to do so. Neither I recognised any signal loss or desintegrity before the conversion nor any improvements afterwards, both variants seem to be fine for me. Therefore I wonder if another buffer could do the trick, but the Boss test will tell...

[nickb]

Just because it's a bipolar transistor doesn't mean it's a low impedance input. An MPSA18 at 0.5mA collector current and at room temperature will have a small signal current gain of over 1000. Used as an emitter follower follower and having a 10K resistor in the emitter means the input impedance at the base is 10 Meg. That in parallel with the bias resistors get you to 0.9 meg ohm. That's better then many tube amps.

Reducing the load impedance reduces the Q of the low pass network formed by the pickup and the capacitance in the circuit. Thus it doesn't exactly attenuate the high frequencies bur rather reduces the height of the peak, like this example where the load is varied from 60k to 1meg. I expect that the audible effect is pretty much the same though.




So, in order to get less LF ( i.e relatively more HF), you could lower the 10nF capacitor on the input. Try starting with 1nF and vary to your taste. If you find you are loosing too much low end add a resistor in parallel with it in the 100K's range to taste.

[ruepselrum]

I finally did some tests and found out that indeed a buffer helps a lot. I some kind of rediscovered my old Boss NS-2, which I kept in its box for years now. This nice pedal not only preserves the highs, but also drastically reduces noise, what I almost forgot over the years. I should mention that I use the advanced method of connecting, i.e. the wah and distortion pedal are put into the reduction loop and the output of NS-2 goes to the amplifier input. Maybe it would be a further improvement to incorporate the amp's effects loop, I'll see.
And I have to admit, that some treble loss was homemade, since I connected three wah pedals in series to compare them. Even when buffered by the Boss NS-2 still a light treble loss occurs when these three pedals are connected in a row.
Gotta get myself a LS-2!

[pdf64]

Just because it's a bipolar transistor doesn't mean it's a low impedance input. An MPSA18 at 0.5mA collector current and at room temperature will have a small signal current gain of over 1000. Used as an emitter follower follower...

I agree these are great transistors for that application; lower noise / current draw (and perhaps a nicer sound) than many opamp types used as buffers.