Tube powered Wah Pedal help

[Casey4s]

I got this bug up my butt to build a tube powered Wah-Wah pedal a couple of days ago and sketched a preliminary schematic yesterday.

I want to see if I can remove all the SS stuff from the signal chain and stil have a good sounding Wah. If it works at all it should sound different to say the least but maybe crappy.

This will be a dual rectifier build, and after the initial start up and testing and tweaking I want to have two 3 to 6 position rotary selector switches to re-voice it. I am curious how the tube rectifier and driver tube sag will affect the voice of the Wah.

This is my sketch,(sorry for the crummy drawng) if anyone has any comments, suggestions, coments, or other input please post.

Thanx...

[Steve Conner]

Since the circuit is Class A, the current draw is constant, so there won't be any sag, and I wouldn't expect the rectifier to make any difference. Apart from that, it should work fine though I'd be tempted to delete R11. That tube works as a cathode follower. The closer the voltage gain of that follower gets to unity, the better the wah will resonate, and all R11 does is reduce the gain.

For similar reasons, you might need to scale all impedances to 10 times what they are in a transistor wah, if you don't get enough resonance.

[Casey4s]

Since the circuit is Class A, the current draw is constant, so there won't be any sag, and I wouldn't expect the rectifier to make any difference. Apart from that, it should work fine though I'd be tempted to delete R11. That tube works as a cathode follower. The closer the voltage gain of that follower gets to unity, the better the wah will resonate, and all R11 does is reduce the gain.

For similar reasons, you might need to scale all impedances to 10 times what they are in a transistor wah, if you don't get enough resonance.

Thanks for the input Steve. I am going to eliminate the hassle of the tube rectifier alltogether and simplify things somewhat. And R11 will probably come out of the circuit too.

Anyone else?

[stokes]

http://www.geofex.com/Article_Folder...h/tube-wah.htm Heres a link to a piece by R.G.Keen on tube wahs.Might be of some help.

[Casey4s]

This is my first revision, eliminating the Tube Rectifier and the resistor from the plate of V2A.

This will look a little bit better when I get my scanner working this is a digital photo of the schematic ...Sorry...

Anyone else...?

[Casey4s]

http://www.geofex.com/Article_Folder...h/tube-wah.htm Heres a link to a piece by R.G.Keen on tube wahs.Might be of some help.

Thank you Mr Stokes, that link is quite interesting.

Keen and I have a very similar design except he uses a MOFSET for the third triode instead of a tube and his power supply is a lot different, it took a few minutes to orient myself to his schematic style. There is indeed a lot of good info there. I wonder if Keen has an emai address publicly available, I would like to ask him some stuff.

[stokes]

Yeah,your first post didnt have the schematic.R.G.Keen posts here from time to time.If you go to the effects section,I recently posted a question about "motor run caps".He responded and I think there is a link to email him on his profile.Or you can go to the main page at geofex.com and see if he has a contact there.Very knowledgeable guy.

[Casey4s]

Yeah,your first post didnt have the schematic.R.G.Keen posts here from time to time.If you go to the effects section,I recently posted a question about "motor run caps".He responded and I think there is a link to email him on his profile.Or you can go to the main page at geofex.com and see if he has a contact there.Very knowledgeable guy.

Thanks again, his email address is understandably restricted, so I sent him a PM.

[Don Moose]

Hey, Casey - may I suggest you get hold of a copy of KiCAD to do your schematics (and layouts). Free tool, works really well on WinXP and linux.

Hope this helps!

[Casey4s]

Thanks Don,

I realize my drawings are a little rough, I'll give the cad a look see.

[Paul P]

I thought your drawing was pretty nice, very clear and neat. I don't think
Don was criticizing your work. I love drawing things by hand. You can do
it anywhere, like sitting on bench in a nice park or in the middle of the woods.

It's when it comes time to make changes or start over that it gets time
consuming and this is where using a drawing program can be a real blessing.
It's also nice to be able to cut and paste bits within and between drawings.

Unfortunately there's always a learning period with new software that can
be painful. I've been using the same program for 18 years now and I wouldn't
want to have to learn a new one. So far I've been lucky with Windows'
backward compatibility as my program hasn't been supported for quite a few
years.

Paul P

[Casey4s]

I thought your drawing was pretty nice, very clear and neat. I don't think
Don was criticizing your work. I love drawing things by hand. You can do
it anywhere, like sitting on bench in a nice park or in the middle of the woods.

It's when it comes time to make changes or start over that it gets time
consuming and this is where using a drawing program can be a real blessing.
It's also nice to be able to cut and paste bits within and between drawings.

Unfortunately there's always a learning period with new software that can
be painful. I've been using the same program for 18 years now and I wouldn't
want to have to learn a new one. So far I've been lucky with Windows'
backward compatibility as my program hasn't been supported for quite a few
years.

Paul P

Well, it is what it is Hahaha,
Everybody is accustomed to CAD schematics, so I realize hand drawn stuff is a little out of kilter now days. I was doing schematis and mechanical drawings for an Engineering Co. as a draftsman 40 years ago (then I was drafted myself )but I am not as practiced as I should be and usually nobody sees my schematics but me. I have just never endevored to learn CAD, I feel more intimate with my designs when I draw by hand, and by the time I learn CAD I'll be dead from old age.

[Don Moose]

Like Paul said, I wasn't criticizing your draftsmanship - it's quite good - but there's a reason it's a dying art. The convenience of automated BOM generation that keeps up with your drawing changes (KiCAD is actually pretty miserable in this regard), netlist/wirelist generation, and tightly integrated layout (even for tag boards, a full-sized plot is a very handy thing) are all pretty compelling.

But hey, if pencils work for you, they work.

[tbryanh]

I'm interested in this vacuum tube wah. Do you have a working unit yet?

[Casey4s]

I'm interested in this vacuum tube wah. Do you have a working unit yet?

It'll be a few weeks before I have it "prototyped", I am still searching for and ordering parts. I am just starting my layout and will make my turret board as soon as I get the layout ready. This is going to take a bit of fabrication to build a chassis box, and a working "Pedal" section. So I am thinking the end of Feb. to have it working and "tweaked".