Alternate crybaby q mod, and others for high gain (first wah build)

[Liaztraht]

Hello, long time lurker, usually find my answers through the search bar, so never needed to really post lol.

I am thinking of building a crybaby style wah off of the tonepad pcb. Though I am trying to figure out the mods before ordering the board (also waiting on a new drill for pot placement)

Currently, I know the normal adjustable q mod is to swap the 33k resistor in parallel to the inductor with a pot, though I have been looking into the 535q way of taking the resistor in series with the inductor (1.5k i believe) and putting it in series with a 1k pot for the q control. Not entirely sure if it will work better or not. Any experience on this one? This is the first wah I will be doing, and I am still reading and learning the circuit. I have also read through the normal articles I see suggested.

I will be ripping the guts out of a GCB-95F shell, as the stock wah doesn't do well with gain. I will also be swapping the sweep cap for a rotary to select stock, ZW signature, then ranging down to the bass wah.

I have matched up the part numbers from the below schematic from electrosmash, to the tonepad one in their layout pdf for reference, and to make it easier to translate mods to the board. Any other tips to help this work with higher gain amps and lower tunings? i will be ranging from a standard to e standard, doom to death metal. Most google searches were not very helpful.

Thanks!

[Transmogrifox]

The components that directly affect the Q are these:
R1, R2, R7, series resistance of the inductor (built-in and any external you might need) and equivalent impedance looking into the BJT base, which is affected by R4.

R4 affects Q in opposing directions.
>Larger R4 reduces gain, so the wah doesn't sweep as deep.  Higher gain ==> Higher loop gain == Higher Q at the bottom end of the sweep.
-->But, larger R4 increases impedance looking into the BJT base so it increases Q slightly at the higher end of the sweep.

R1:  Larger R1 increases Q, but decreases output level.
R2:  Not a good component for adjusting Q.  Larger R2 will increase Q, but it will screw up the operation of the wah too much in other ways that you will ruin its usefulness before you ever get it high enough to significantly change the Q.
R7:  Typical "Q" mod.  Increasing R7 increases Q, but it's limited by the parallel combination of R1, Q1 base and the other limitation will come from series resistance with the inductor. 
L1:  Has some built-in series winding resistance.  Adding more resistance in series decreases Q, but it also has a shelving filter effect where at a certain frequency you don't attenuate the highs as much.  Increasing resistance series to L1 makes this look more like a sweepable mid-boost.  this will not be very good for high-gain systems.

For use with high-gain distortion you probably want to make the filtering as extreme as possible:
1)  Reduce the value of R2.  This sets something like a wet/dry mix.  Reducing it increases he wet mix, making the highs roll off to a deeper rejection in the stop-band.
2)  Increase the value of C1 to let more low frequency content through.  This will help bring up the bottom if you want some of that dark, thick doom sound.
3)  Now for Q control:
> Change Q1 to a MOSFET or a JFET so the resistance looking into the BJT base is out of the equation.  With a MOSFET you need to tweak with R4 to correct the gain (sweep range) and then mess with R8 to get the bias correct.  With a JFET the bias is more tricky, but depending on the device you might get it to work by putting an LED in series with R4 to get something like a 1.5V drop to work against.
>Increase R1 to something like 200k to 500k and replace R7 with something like 250k to 500k pot.

With R1 change you will lose some output level.  You can restore some gain by making R4 smaller, but this also increases the sweep range so that would need to be compensated somewhere else.  It might be easier to just change the input buffer into a make-up gain stage so you can drive it harder to compensate for the level drop in R1.

The reason to amplify before the wah for make-up gain instead of after is because of noise.  The wah is a filter, so if you amplify first, you get the benefit of filtering off some of the noise added from the make-up gain amplifier.  If you amplify afterward then you insert the full bandwidth of the noise from the make-up gain amplifier directly to the output.  Normally this would not be enough to make an audible difference, but if you're following it with high gain circuits then the difference might become audible.

Ratio of C2 and L1 both have an effect on the Q, but you can only change those with rotary switches.  In the past I have played with replacing L1 with a gyrator, but in this type of circuit the noise in the gyrator is amplified and it would be unworkable with any high-gain pedals.

Fortunately the stock inductor wah is remarkably quiet so it does well with high gain distortion circuits as far as noise is concerned.

[drummer4gc]

I've had good luck adding a 1k pot in series with the inductor as a q adjuster. You can replace a 0-ohm resistor on the stock Cry Baby board wth a trimpot to do this. I like replacing the 33k "q-resistor" with a 100k also, so that you have a maximum sharpness with the trimpot dialed up.

[Danich_ivanov]

Try replacing c1 with something in the range of 100n - 1uf (makes less ice-picky, also increases bass), r1 i would recommend replacing with 100k pot to alter the gain of the wah, and for q/sweep - 100k pot, also try with or without input/output buffers. I did pretty much the same thing last summer, with the exeption that i rebuild my chinese vox wah to clyde mccoy. I tried a bunch of mods and experiments, and found out that unless you want you'r wah to sound very different (which is easy to do), i would recommend leaving all the things as is, but play around with the ones that i mentioned first, also q1 plays a huge role, low gain trannies can screw the whole thing by leaving you with a very narrow range, really high gain ones will make wah ice-picky, i used c828 (which is the one that fulltone uses in their wah), and it worked perfectly, i haven't tried stock msa though.

[Liaztraht]

The components that directly affect the Q are these:
R1, R2, R7, series resistance of the inductor (built-in and any external you might need) and equivalent impedance looking into the BJT base, which is affected by R4.

R4 affects Q in opposing directions.
>Larger R4 reduces gain, so the wah doesn't sweep as deep.  Higher gain ==> Higher loop gain == Higher Q at the bottom end of the sweep.
-->But, larger R4 increases impedance looking into the BJT base so it increases Q slightly at the higher end of the sweep.

R1:  Larger R1 increases Q, but decreases output level.
R2:  Not a good component for adjusting Q.  Larger R2 will increase Q, but it will screw up the operation of the wah too much in other ways that you will ruin its usefulness before you ever get it high enough to significantly change the Q.
R7:  Typical "Q" mod.  Increasing R7 increases Q, but it's limited by the parallel combination of R1, Q1 base and the other limitation will come from series resistance with the inductor. 
L1:  Has some built-in series winding resistance.  Adding more resistance in series decreases Q, but it also has a shelving filter effect where at a certain frequency you don't attenuate the highs as much.  Increasing resistance series to L1 makes this look more like a sweepable mid-boost.  this will not be very good for high-gain systems.

For use with high-gain distortion you probably want to make the filtering as extreme as possible:
1)  Reduce the value of R2.  This sets something like a wet/dry mix.  Reducing it increases he wet mix, making the highs roll off to a deeper rejection in the stop-band.
2)  Increase the value of C1 to let more low frequency content through.  This will help bring up the bottom if you want some of that dark, thick doom sound.
3)  Now for Q control:
> Change Q1 to a MOSFET or a JFET so the resistance looking into the BJT base is out of the equation.  With a MOSFET you need to tweak with R4 to correct the gain (sweep range) and then mess with R8 to get the bias correct.  With a JFET the bias is more tricky, but depending on the device you might get it to work by putting an LED in series with R4 to get something like a 1.5V drop to work against.
>Increase R1 to something like 200k to 500k and replace R7 with something like 250k to 500k pot.

With R1 change you will lose some output level.  You can restore some gain by making R4 smaller, but this also increases the sweep range so that would need to be compensated somewhere else.  It might be easier to just change the input buffer into a make-up gain stage so you can drive it harder to compensate for the level drop in R1.

The reason to amplify before the wah for make-up gain instead of after is because of noise.  The wah is a filter, so if you amplify first, you get the benefit of filtering off some of the noise added from the make-up gain amplifier.  If you amplify afterward then you insert the full bandwidth of the noise from the make-up gain amplifier directly to the output.  Normally this would not be enough to make an audible difference, but if you're following it with high gain circuits then the difference might become audible.

Ratio of C2 and L1 both have an effect on the Q, but you can only change those with rotary switches.  In the past I have played with replacing L1 with a gyrator, but in this type of circuit the noise in the gyrator is amplified and it would be unworkable with any high-gain pedals.

Fortunately the stock inductor wah is remarkably quiet so it does well with high gain distortion circuits as far as noise is concerned.

Whew! Lots of good info! Thanks!
Didn't think of changing out any transistors, will have to breadboard a few and see.
So far (before reading this) I had started blending some different schematics together to create some hybrid ideas.
I had come up with swapping R4 with a lower value, something like 360 (pulled from a wizard wah schem) or even down to 330 from another source. Adjusting R1 to keep the levels similar, or put R4 on a switch for stock/gain and a R1 on a pot for various level adjustments. I also liked the at .1uF as per a BBE schem, but will mess around with higher values there.

Definatly happy with the idea of putting C2 on a rotary to adjust the sweeps frequency, but haven't tried it with R4 at a lower value yet.

And for a q control, I also liked the BBE's schem way of putting R7 in as a pot with the minimum Q resistor in series for a minimum usable q. Though may swap in a 100k instead of the 50k, and have the R7 resistor at 33k instead of 10.

[Liaztraht]

So it does look like the parallel (R7) q is the preferred mod over the series resistor way like the 535q model. It will be easier as I am not working with a crybaby board. Less flying leads cluttering the enclosure.

[Transmogrifox]

So it does look like the parallel (R7) q is the preferred mod over the series resistor way like the 535q model. It will be easier as I am not working with a crybaby board. Less flying leads cluttering the enclosure.

The series vs the parallel is a matter of taste, what you're looking for in the sound.  I'm guessing for high gain & doom or death metal stuff, adjusting Q with the parallel R7 is more likely to get you closer to the sound you want. 

The other mods I recommended make it possible to get higher Q if needed, but it may not be necessary, including the MOSFET/JFET.

Start simple and work your way into more advanced stuff if you find you just can't get what you're looking for.  High gain death and doom metal sounds definitely weren't on the mind of the original wah pedal designers back in the 60's..

[Liaztraht]

No doubt they weren't built with those in mind lol. Doom wise, I was planning on using it as a slow, controllable filter, used much like a slow phase would be, for various parts, and kicking up the sweep range for some metal leads/solos, as I am finally learning the techniques. May make it so I can get a stock wah tone for some occasional funk.

Got my crybaby classic for 30 bucks, but its way to synthlike in the low end with practically no wah under gain. Since its all smd I am ripping it out. Will salvage the inductor though.

[Transmogrifox]

Got my crybaby classic for 30 bucks, but its way to synthlike in the low end with practically no wah under gain. Since its all smd I am ripping it out. Will salvage the inductor though.

Good deal.  The main thing of value is the mechanics and possibly the pot if it's in good shape.

This is such a simple circuit that building from scratch is not a very big deal.  You can build with extra space to be able to easily hack things in that aren't in the stock circuit.

SMD wouldn't be too bad if all you were doing was replacing component values, but if you need to re-route or add stuff in then any flying leads stuff is too fragile to withstand stage shock.

[Liaztraht]

Good deal.  The main thing of value is the mechanics and possibly the pot if it's in good shape.

This is such a simple circuit that building from scratch is not a very big deal.  You can build with extra space to be able to easily hack things in that aren't in the stock circuit.

I may end up building off of vero/stripboard to try and get it a bit more compact. Save a few bucks  as I will also be using it with board mounted pots and sweep caps to have less components hanging around.

[Liaztraht]

Hey Transmogrifox, since you are well versed in wah circuits, with increasing the input cap to .1uF to let more bass in, would swapping R4 for a lower value be redundant? As R4 and R1 both increase gain, I would probably only need to swap one.
I was also reading one wah mod page that said decreasing that R1 resistor can introduce radio interference. Would a 47k be high enough to not need to add a small cap between the base and collectors of the transistors? I get no radio signals at my house (too far out) but everything picks up radio at the bands rehearsal space.

I know I want a bit of bump in the volume, and I am building without the input buffer.. I started modifying a layout from the tagboard effects blog to both fit the fasel, and to keep R7 on the board, but at a lower value running in series with a pot (minimum Q). Also added in the JC/Original Dime Sig style control to adjust top end as needed. And decided on running only two sweep caps on a dpdt. Also saved a version with added 10pF caps on the base and collector of the transistors. Probably sticking with the stock/standard MPSA18.

Waiting on a few more parts to arrive, including vero, as its smaller than the pcb I was looking at.

[Transmogrifox]

RF interference is helped somewhat by the input buffer -- even better if you put the small-valued caps on the input to ground -- probably 100 pF would be better, but 10pF would do something if RFI is >10MHz.  100pF would do something for noise that comes from fluorescent lights and AM radio.

Then, put a 470pF from output to ground and then a 100 ohm feeding from there to the output jack so RF can't get from the output side and feed back in.  Do this only if you have RF problems at your rehearsal location.

Swapping R4 for a lower value would not be redundant.  If anything it would be complementary.

R4 increases total gain, but also increases the loop gain of the feedback network when the pot is maximized.  Reducing R4 simultaneously increases the output of the wah circuit while also making the sweep range wider (sweeps to a lower frequency).  At the same time it also decreases input impedance looking into the BJT base, so it makes the 3dB cut-off of the input increase and decreases gain on the front end (but less so than the gain increase you get from decreasing it).

Increasing input capacitor 0.1uF just lets more of the original low frequency content through the filter, beefing up the bottom end.

Decreasing R1 decreases Q.

Hopefully by now you're starting to see that every part in the wah circuit affects everything.  If you change one thing, you change everything.

RG Keen put together a lot of good info on these kind of wah circuits.  Use this as your guide with the understanding that each thing that is presented as doing one thing does something to everything.  The reason it's stated to do one thing is because it mostly the one thing and not as much of the other things.

Using a breadboard and RG's Technology of Wah Pedals page you can mess around with things until you get what you're looking for.  This is such an ear thing that learning about how wah pedals work is only the first step toward getting a sound you want.

I do think the way things are so interactive in a wah pedal is one of the reasons these types of circuits do things to music that sound so good to us humans.

[Liaztraht]

Thank you very much again!
I have been reading RG Keen's work (about 20 times through lol) as well as a few other of the usual wah mod pages. Though in Keen's info, some things have caught my eye, and are throwing me further into the realm of wah tweaking. Though those being some of the inductorless variants, as well as op amp based wahs. Honestly, I will have to buy another used crybaby to build another wah at this rate.
Waiting on a handful of pnps to bread board a WH10 as well. That one seems promising for some use with gain.
Maybe go for a double wah!

[Transmogrifox]

Morley also publishes schematics of their legacy wah pedals.  You might find some inspiration also by looking at some of their designs.

Your idea of a double wah made me think of the Morley contour wahs, because they are like having a double wah where one is fixed using a pot and the other moves with the pedal.

[Liaztraht]

I meant it as a 2 in 1 on a switch. Have looked at a morely one, but I believe it was an optical wah.

I do have a vintage power fuzz wah that needs some work. That got me interested in wahs more so than an old weeping demon I used to have.

[Transmogrifox]

Have looked at a morely one, but I believe it was an optical wah.

The optical part is just the control part.  Any of those circuits can be adapted to use a standard pot.  They're based on one kind of active filter or another, giving a certain kind of contour and response characteristic to the pedal.

For example, the Bad Horsie is a standard Vox/Crybaby style wah that uses an LDR to do what the pot does.  A musician can feel the difference in the optical control just like one can feel the difference between pot taper styles, but a listener would be less likely to hear any distinct difference unless it inspired the musician to play differently.

If any of the Morley circuits have an interesting sound to you, then you can get some ideas from looking at their circuits.  If not then disregard.

FWIW the weeping demon is a state variable filter with optical control.  It has a great deal of versatility but it's not a replacement for a Vox or Crybaby style circuit...it's just something a little bit different.  In my opinion, good for what it does, but it's not compatible with a lot of styles that have been built upon the Vox/Crybaby sound.  The other thing is it's so tweakable I think it turns off a lot of guitar players because it has the power to create an infinite number of useless sounds and a few good sounds.

If you aren't particularly inspired by the WD then you know of one circuit you don't want to emulate

[Liaztraht]

Well, for now I ended up really liking the WH 10 circuit and built one of those, though modded it for a frequency adjustment (10k pot in series with the guitar/bass switch). So it has some fine tuning for down tuned music. Got a 50k pot off mouser and modified it to accept the gear.

I stuck my cry baby classic board in a bag, and will be looking for a used GCB 95 to mod the board on with the fasel and everything I learned. Still fine tuning on the breadboard.

Drilled the pots a little too close for knobs, so I will swap the switch and range pot and slap some knobs on tomorrow when they arrive. Also need zip ties to tidy up. Still had room for the battery door too!