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...

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/013.jpg?t=1201064150

[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_Folders/tube-wah/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...?

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/005.jpg?t=1201147437

[Casey4s]

http://www.geofex.com/Article_Folders/tube-wah/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 (http://www.lis.inpg.fr/realise_au_lis/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".

[tbryanh]

Sounds cool. You might consider taking an off-the-shelf expression pedal and bolting a sealed chassis to the side or end of it. Then drill a hole for the wires to travel between them. Expression pedals can be purchased with only a pot inside, no other circuitry.

[Casey4s]

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.

No sweat, I wasn't offended... you are not the first person to suggest I go CAD, but most of the time I am the only one looking at my drawings. At this point in my life I think I am just going to stay PAD (Pencil Aided Drafting).

[Casey4s]

R.G. Keen emiled me and suggested some changes to by initial design which are incorporated in this version of the schematic. (Rev 2) I discovered the power transfomer I intend to use has no CT, so I changed to a full wave bridge rectifier too.

I am ordering the parts from AES and Weber this evening or tomorrow and will make the turret board over the next couple of days.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/006.jpg?t=1201655982


And my layout sheet.


http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/003.jpg?t=1201656388


Any last minute comments before I get the soldering iron out?

[Paul P]

I'm looking forward to your report on how it works and sounds once you're
done.

One little thing, I believe the 'recommended' way to wire the AC line-in
is to have the fuse come before the switch.

Paul P

[Casey4s]

I'm looking forward to your report on how it works and sounds once you're
done.

One little thing, I believe the 'recommended' way to wire the AC line-in
is to have the fuse come before the switch.

Paul P

Thanks for the input Paul,

You're right, but I never would have actually built it that way, I just messed up the drawing when I redrew the power supply.

I am also going to parallel the two sections of V2, but decided not to redraw the schematic to reflect that.

[sportster4eva]

The only thing that I had noticed is where V2 grid gets it's reference from, through R15 tied to V1b cathode. That looks like it will bias the grid positively compared to it's (v2's) cathode? In your schematic it shows V2 having only a 1.8k cathode resistor, and no plate resistor. Is that intentional? I may be way off here, but that just struck me odd. Can you or another of our bottleheads clarify this?

[Casey4s]

The only thing that I had noticed is where V2 grid gets it's reference from, through R15 tied to V1b cathode. That looks like it will bias the grid positively compared to it's (v2's) cathode? In your schematic it shows V2 having only a 1.8k cathode resistor, and no plate resistor. Is that intentional? I may be way off here, but that just struck me odd. Can you or another of our bottleheads clarify this?

Thanks for the well thought out input and question. This one I had to think over a little bit :confused: I talked (eMail) to R.G. Keen and this is his suggestion to refrence the signal from the cathode of the cathode follower (V1B) as shown. so at this point I am going to run with it as is and see what happens.

And no, I don't intend to use a plate load resistor for V2. I had originally put one on the plate (was R7) but it was not needed so I deleted it.

Thanks again...

[Casey4s]

I got mos of my parts together and started assembling the "Guts" of this thing a day or so ago.

First I had to build a chassis box

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/005-1.jpg

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/012.jpg

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/015.jpg

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/026.jpg

[Casey4s]

I started putting my turret board together waiting on the rest of my parts, and the full wave bridge rectifier.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/005-2.jpg

Then I started the Mechanical assembly, cutting all the holes and mounting tha big components.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/004.jpg


There was no way to make this small, so I went the other direction and just went BIG with everyting, it may not be pretty when it's all done but it should at least be a conversation piece...


http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/Aoo6.jpg

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/Ao12.jpg


http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/Ao15.jpg

[Paul P]

I like that brake of yours. Must come in real handy.

I have a question or two. Is that a rotary switch you've got there
beside the big capacitor ? What does it do ? Your schematic shows
a wah pot, which I presume will be a pedal of some sort. Have you
decided how you're going to do that ?

I'm looking forward to hearing about what it sounds like. I've been
wanting a wah pedal and it would be neat to build one.

Paul P

[Casey4s]

I like that brake of yours. Must come in real handy.

I have a question or two. Is that a rotary switch you've got there
beside the big capacitor ? What does it do ? Your schematic shows
a wah pot, which I presume will be a pedal of some sort. Have you
decided how you're going to do that ?

I'm looking forward to hearing about what it sounds like. I've been
wanting a wah pedal and it would be neat to build one.

Paul P


I have two different kinds of inductors for this project. One is a Fasel (red) 500 mH inductor as used in most Dunlop and Vox wah pedals, and the other one is a really small iron core OT that can also be used as an 5oo mH inductor. The rotary switch is so I can go from one to the other and then both in parallel to try to voice the wah a little differently. This was a last minute decision to add this so my schematic does not reflect the modification.

The actual pedal will be seperate and will plug into the guts box via a stereo jack. I have some 2 conductor sheilded cable I am going to use for that. I will use the sheilding as the ground connection between the pot on the pedal and the guts box.

My intent is to make a wood box of sorts to cover the sides of the guts box so it doesn't have that unfinished look to it. I will have to wait until the weather is better to do that though. I can only work for a couple hours at a time because it is so freaknig cold in my garage.

I hope to have this working by this time next week less the actual pedal which I need to wait on weaher for also. I will wire up the pot and plug it in and operate it by hand to trouble shoot the project.

[Casey4s]

I did a little soldering in the past couple of days, this is probably the messiest looking thing I have ever built, I am sorta embarrassed to even show these pics. I am just not good at working in such tight places with tubes stuff, this in itself has proven to be a bit of a challenge.

All I really need is to install 3 jacks, the circuit board, and wire all of that up as well as the step on by-pass switch. I am almost finished with the initial phase of this thing. I have my fingers crossed.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/022208-3.jpg


This view shows the two inductors mounted on a small board and attached to one side of the chassis.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/022208-6.jpg



This view shows the Rectifier baord and all the big AC wiring every where, what a freaking mess. I will be amazed if this does not make noise.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/022208-7.jpg

[Paul P]

This view shows the Rectifier baord and all the big AC wiring every where, what a freaking mess. I will be amazed if this does not make noise.


I've noticed the same thing. Everything's nice and clean on paper then you
add all the wires and it turns into a big mess :).

Sometimes I could make a wire real short but the possibility of re-using
the part in some future project makes me want to leave as much lead length
as I can. Power transformer is bad in this respect.

I don't think your wiring's that bad.

This is like brain surgery. I understand the Japanese were so good at
assembling small stuff because of the women's small hands. I envy
them their small fingers. I have sausages and sometimes there's just
too many of them in the way and I can't see what I'm doing.

Paul P

[CarlZ]

Is it just me or did you take the schematic off of your photobucket? Nothing is displaying for me.

-Carl

Disregard. Everything showed up when the page refreshed after I submitted the reply.

[Casey4s]

Is it just me or did you take the schematic off of your photobucket? Nothing is displaying for me.

-Carl

Disregard. Everything showed up when the page refreshed after I submitted the reply.

Hi Carl,

Thanks for stopping by.

My schematic is not a CAD product but I am usually the only one who has to look at it anyway. :o

[Casey4s]

I've noticed the same thing. Everything's nice and clean on paper then you
add all the wires and it turns into a big mess :).

Sometimes I could make a wire real short but the possibility of re-using
the part in some future project makes me want to leave as much lead length
as I can. Power transformer is bad in this respect.

I don't think your wiring's that bad.

This is like brain surgery. I understand the Japanese were so good at
assembling small stuff because of the women's small hands. I envy
them their small fingers. I have sausages and sometimes there's just
too many of them in the way and I can't see what I'm doing.

Paul P

Yeah I guess it could be neater if I trimmed off some of the excess wire from the Power section but I guess I am insecure and can't bring myself to cut it off. ;) If this thing just doesn't work according to plan I might need to re-use that transformer among other things.:eek:

I wish my hands were a little smaller, the more I stuff in this little box the smaller this box seems to get.


I did plug it in last night and "smoke tested" the power supply and as ugly as it is it worked fine so I do feel a little bit better.

[Casey4s]

This is almost finished all that is left here is installing the jacks, circuit breaker and soldering 4 leads going to the tubes.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/022808-7.jpg


Here it is completed and ready for testing... Still wish I could get this a bit neater :eek: a lot of shielded wire for the input and outputs and the Wah Pot.

http://i238.photobucket.com/albums/ff243/Casey4s/HOLDING/022808-8.jpg

[elecktrokatt]

Casey4s,
This is a cool schem, mebbie I missed it (need coffie), but, what tubes are you using?
I'm currently working on a similar design, implemented with 3, sub-mini "hearing aid" tubes (JAN6418 Pentode).
Ekatt

[Casey4s]

Casey4s,
This is a cool schem, mebbie I missed it (need coffie), but, what tubes are you using?
I'm currently working on a similar design, implemented with 3, sub-mini "hearing aid" tubes (JAN6418 Pentode).
Ekatt

I am using two 6SL7GT octal preamp tubes for this pedal.