wha model

[Gus]

I have been using LT spice to model some circuits.   One is the wha in my section of the gallery some values have been changed a little.  I am using a 100K lin pot in the model.    I am using 500 ohm and 99.5k as the end points.   R11 and R12 are the lin pot
C4 should be adjusted to taste
Any interest?  Any one else modeling whas with LT spice?

EDIT correct one
http://www.aronnelson.com/gallery/main.php/v/gus/whaS2.PNG.html?g2_imageViewsIndex=1

EDIT 2 I missed this thread
http://www.diystompboxes.com/smfforum/index.php?topic=88929.0

[joegagan]

is the tapering resistor on the control pot meant to simulate a log taper? if a linear pot could be adpated to work, the world of surplus durable wah pots would open up. there are still tens of thousanads of linear taper military spec pots out there in warehouses.

i spent a few hours at my local surplus place measuring pots with a meter, there are at least 80 bins with up to 3 different values each drawer, so literally hundres of different values, mostly high grade pots from our military industry here ( bombs, nuke devices, satellite, military devices, los alamos, etc)
less than 5 % of all values were anything other than linear.

[Gus]

Wow no other posts except Joe Gagan.

Yes Joe lin pots easier to find and taper with resistors.

Yes  R15 and R14 are tapering resistors if you use both you should get something like a S taper.

R11 and R12 are kind of the pot the wiper is the "center" node. I need to learn how to make a pot in LT spice.  I changed the value on both always = 100K

I posted some good stuff in the schematic.  Note the 10K collector resistor on Q1,  Note the high input resistance of Q2(bootstrapping an EF),  Note the lack of bias mixing 470K resistor.

With the lower output resistance of Q1 gain stage and the higher input resistance of Q2 EF stage you can drive a pot and tapering resistor(s).

Do people just not get the coolness of the wha circuit I shared?

Now if you realy want to have some fun direct connect a EF to Q1 output even lower output resistance allowing lower value tapering resistors.

You can adjust the distortion of the Q1 stage and ...

[Skruffyhound]

Do people just not get the coolness of the wha circuit I shared?

Sorry, it passed me by. I'm taking notice now though. Thanks

[B Tremblay]

Gus did a nice job with his wah circuit.  I tried it when he first shared it and even with sub-standard parts, it sounded really good to me.  I keep meaning to commit it to perf and see if it confirms my suspicion that it is better than my modded V847 and Noomerang wahs.

http://runoffgroove.com/gswah1.mp3
http://runoffgroove.com/gswah2.mp3
http://runoffgroove.com/gswah3.mp3

[PRR]

> Do people just not get the coolness of the wha circuit I shared?

Many folks don't read schematics.

My quick-look saw the classic wah in the LTspice style.

If you are going to load the pot, can't you omit the bootstraping and merge the bias impedance with the loading?

[John Lyons]

Thanks for the work/inspiration Gus! I'll have to play with this
when I get time.

John

[Gus]

PRR yes I guess one could. That circuit is an interesting different take

Adjusting C3 can make a difference in the sim at the lower frequencies  I picked .1uf because of the interaction.  Also disconnecting the EF biasing from the first stage allows the operating points of both stages to be adjusted independently.  One might want to move the collector of Q1 up or down for less or more distortion.  Q2 can be adjusted for better output "headroom".  Wha Pot tapering and the ability to move the stages bias independent are some of the main ideas.

The "classic"  inductor wha uses a 470K to bias the EF.  The EF emitter voltage is  lower than the collector due to Vbe drop and the small voltage drop across the 470K.
The boomerang uses a "disconnected" EF but it used the simple base to collector bias that can have issues.
IIRC The colorsound had a grounded emitter first stage. I am thinking distortion.

What I was trying to convey is the use of a lower output resistance first stage and a higher input resistance EF allowing the use of tapering resistors on a lin pot.  Why worry about the taper just find a good lin pot and adjust it.

Also one can direct couple a EF to the collector of Q1 for even lower output resistance.  Lower output resistance will allow things like a 22K taper resistor with a 100K the load will change but the gain stage with a proper coupling cap should be able to drive it.

The parts of this circuit are nothing new but they are put together in a little different way.   I did not call it a design I called it an Idea

Thanks for the feedback

[Gus]

Adjust R10 and C3 if you build it.  Measure the collector voltage at Q1 and note any tone change.  Also you could remove R15 and make R14 a 33K or what ever taper resistor you want.  EF can oscillate so I think adding the 1K like in the patent is a good idea.

EDIT
Another schematic
Bootstrapped input buffer
Direct coupled EF to gain stage allowing the use of lower value tapering resistors
http://www.aronnelson.com/gallery/main.php/v/gus/wha2.PNG