Input buffer for a wah wah, why would you want one?

[vanessa]

No, I haven't. Could you trace just the input stage of the Axis circuit?

Fp

I was thinking it may be an issue with that PN2369A in Q1 of the Axis Face rev. 3. There seems to be an issue with that transistor in this circuit. There were several of us that had an issue when lacked an input load on it, meaning it made all sorts of noises if it did not have some sort of input resistor.
I know that this may not seem like a big deal to those that have not built the Axis, but there seems to be bigger fish to fry on this one. The PN2369A is a really cool Si transistor that averages hfe in the range of 70-90 hfe. Perfect for a FF circuit. But it seems to have issues and this may be one of them.

[Fp-www.Tonepad.com]

can you point me to the axis face rev3 schematic (url)

Fp

[formerMember1]

http://fuzzcentral.tripod.com/axisfacesi.html

scroll to bottom of page for schematic,...

[brett]

Hi.
There are some interesting things going on here...

So, Vanessa, if you want a buffer on the front end of your wah, model it after Doug's layout.
If you want an additional gain stage which adds a buffering benefit use FP's.
Do you need to buffer the front end of your wah?
Well, I don't know really. It can't hurt. In this case, I'd say "why not". Spend a quarter and buffer the thing.

Well, actually, I think it can hurt (a bit).  A buffer can change your tone substantially.  In front of a wah, you'll typically get a lot brighter (and I think "thinner" and less attractive) tone.
I like the JFET buffer on the output of my wah, because wahs have high output impedance, and without it I get variable results that depend on what pedal I follow the wah with.  To my way of thinking, it "braces" both the tone and volume of the wah.
About the PN2369A....  Maybe there's some crook ones.  But I've built and sold many fuzzes with Q1=PN2369A and Q2=BD139.  Given that the PN2369A is built for speed, not low noise, it may be important to make Q2 a low hFE transistor.  All my BD139s are in the 130 to 140 region.  I also use a hefty capacitor across the 330/470/1k resistor to dampen high frequency grit and noise.
Oh yeah, the input impedance of a fuzzface or similar with Q1 hFE=60 to 80 is only about 10k ohms.  That's a heavy load for a pickup (which is usually very good) or any other pedal (which may bad).
This is too long a post already, but perhaps one extra comment about the Axis and Ge fuzzes.  One reason why the Axis and silicon transistor fuzzfaces sound different is that the base of Q1 sits 0.7V away from earth.  For a Ge transistor, the difference is only 0.3V.  A Germanium fuzzface therefore starts to clip one side of the signal very early.  This asymetrical clipping seems to be an important part of the fuzzface sound (RG commented on this many moons ago in his "technology of the FF" article.).

Interesting thread...

[Doug_H]

Do you need to buffer the front end of your wah?
Well, I don't know really. It can't hurt. In this case, I'd say "why not". Spend a quarter and buffer the thing.

If you  are going to use a dpdt I would omit the buffer. Buffers in the signal chain just seem to muck too much with rangermaster/fuzzface/other vintage pedals. I'm going to remove the buffer from mine and install a dpdt. Then I'll take down that schem, since I don't really like/use that scheme anymore. Read R.G.'s article for all the wah mods.

Doug

[Steben]

An output buffer is something I hold on the waiting list. It seems to me the wacky wah-before-Fuzz style of setup is most "lush" with a buffer between them. Am I wrong? Since a Fuzz is a real low impedance thing...
I know hendrix placed the wah in front of a fuzz and it is mentioned here there was a buffer used...
Only an output buffer would be nice, since the tone sucking of the wah when on gives the wah its classic warmth too.

[vanessa]

Well I've thought about it and I think I'll pass on the input buffer. I am going to implement a vol/wah (this will be that Frankenstein pedal I'm building for my friend), with a Mosfet Boost in one. I found an old Torchy layout that has a passive output buffer if the boost is off. The way it will be wired is with the wah/boost true-bypassed. You'll be able to turn the wah/volume on-off with a toggle and boost on-off with a toggle. When the boost is off it will act as a passive output buffer, and when the whole thing is bypassed you'll have a direct signal to your fuzz (or what ever). I need to do a post for that Torchy schematic. I have the layout for the Mosfet Boost/Passive Buffer, but I would like to incorporate it into a pcb to save space (I'm also cramming a Ross Comp in there on a separate power supply).