colorsound wah values?

[Rob Strand]

I posted this in the simulation section,

Thanks.  Looks a lot what I get with the basic circuit.
I've been doing a some sims to try out some mods.

So far I've managed to get a reasonable match to the inductored wah with quite a substantial flattening of the peaks.   I've just did some intuitive tweaks.   Top is the inductored wah and the bottom is the tweaked inductorless circuit.





The circuit has a number of nasties so I'm taking a step back and looking deeper into it.

[mac]

The circuit has a number of nasties so I'm taking a step back and looking deeper into it.

Its simplicity worth the try

mac

[thomasha]

I built that circuit some time ago, but instead of the pot I used a LED LDR pair.
It sounds really nice, not as pronounced as a cry baby, but I could always blame the LED/LDR cause it needs some adapting to find the sweet spot.

good thing that it's a really small circuit, so I could fit it in a 1590a.

[Rob Strand]

its simplicity worth the try

I've played with inductorless wahs in the past and I've always found them weak sounding.   The colorsound seems to get closer to the mark.

There's a lot of interactions going on in the circuit so playing with parts is a bit hit and miss.  I'm sure you have seen that on your simulations.    Luckily I saved the circuit that generated the above plot but in my mind it's still a hack (that's why I didn't post a circuit).   I did some more playing, some things improved, but others got worse.  It's easy to make it worse  .

Anyway, ATM I'm just working through it slowly.   I generated a 6 page document just thinking about the twin-T, which will easily go out to 15 pages and that's before I even consider about turning it into a wah.

[Paul Marossy]

I made a full blown clone of the Colorsound wah shell so I could get an accurate sounding Colorsound inductorless wah pedal, with the cam and all. Did it just for the heck of it. You can see video here if interested

What final values did you end up using?

I've got this schematic which I believe John Lyons drew up based on "nirvanas silence"'s  info in an old thread:



I'm pretty sure the 10nF input and output caps are correct.

The value I still dispute is the 5M7 resistor.

I've looked at a few boards and I see 3M3 in that position more often that not.  I suspect 5M7 is actually a misread 2M7, which is close to 3M3.

The thing about using 3M3 is the biasing tends to suit a generic 2N3904 transistor more than the commonly quoted 2N5088.   More than likely the actual transistors were generic BCxxx types such as those used on the inductored Colorsound Wahs.     Like it could be that the transistor is deliberately biased with a slightly lower VC in order to get more gain out of the stage.

Another missing piece of info is the Wah pot taper.

I know, I'm being a real gravedigger here, but I never got an email notification to your response... I've been revisiting my Colorsound Twin-T wah pedal, and stumbled on this thread doing an internet search for the schematic. Have been modeling a bunch of wah circuits in LTSpice over the last week for fun, and thought it would be interesting to do the Colorsound "inductorless" circuit. So as in my Ebow quest, while I was trying to verify what the actual circuit is I found things that don't make sense. I have never really been satisfied with the sound of mine and have wondered if I did something wrong or if the values I used per these internet schematics were wrong. It appears to me that most of these schematics on the internet are wrong. I found pictures of an original PCB today and drew it up in CAD. While I can't make out all of the resistor values, it seems to me that the 0.015uF and 0.0068uF caps on these schematics need to switch places. I only discovered that today after I traced out the PCB backside vs the components on the top side. I was also looking at it logically, it just didn't seem to me like there would be much change happening between a 0.0022uF cap and .0068uF cap at the output to the pot. When I swapped those two caps this evening it was a MAJOR improvement.

Here are a few other things that in my experience don't really work:

1- 330K input resistor too big. I used 3.3K. Maybe 33K would be OK, but I stuck with the 3.3K
2 - The resistor between base and collector - for the 2N5089 I am using, the 5.7M was just too big. I don't have 3.3M on hand but a 2.2M seems to be good value.
3 - I used 220K series resistor on the output. 100K kills the output just a little too much.
4 - Putting it into a Crybaby type shell. The Colorsound wah uses that interesting linkage system, that according to Gagan, was to produce a log taper response from a linear pot. I don't know if that's true or not but it does get quite a bit of the pot's rotation vs. that rack and pinion arrangement of the Crybaby type shell. That was one reason why I built that one in the YouTube video linked above out of wood and aluminum, so I could reproduce that whole arrangement.
5 - 0.1uF input/output caps are incorrect. Per the pics of the original PCB they are 0.01uF. My personal experience confirms that 0.1uF caps don't work very well.

For the pot I used, I don't remember a specific model number but it's a blue plastic Bourns sealed 100K linear pot. Seems to be quite at home in my DIY replica shell.

I've been having trouble trying to model the full circuit in LTSpice... I can really only sim the filter section (probably my own ignorance), but it was pretty obvious when I swapped those caps in the program that it would be an improvement - and it turned out to be matched by real world results. These are my preliminary findings, I may still tweak something. I'm going to use it the AM while doing my normal routine and see how it fares. It's now competing directly with my 60s Italian Vox wah with the original red Fasel inductor. That is my most vocal wah pedal. 

[Rob Strand]

You might want to checkout this thread.   The idea was how to stretch an inductorless wah towards an inductored wah response,

https://www.diystompboxes.com/smfforum/index.php?topic=121430.0

Somewhere in the thread I point out a few issues with these wahs.  Some very subtle things can affect the response.  (From say reply #25 and a few after.)

[mac]

The links to the images I posted are all broken. They were stored in the old Gallery.

mac

[Paul Marossy]

OK here's an update. Never mind what I said about the schematics being wrong... I made an error reading the numbers on one of the caps in low quality pictures and confused myself.  Also what I thought would sound good using test set up turned out to not be good when using it with a guitar. 

However, there does appear to be differences between units, some use a 0.0068uF cap and some use a 0.0047uF cap. I have discovered that the circuit is VERY dependent on what transistor is used. With the 2N5089 I don't even need a feedback resistor but if I use lower gain ones it is absolutely required. Some transistors won't work at all, and others will be OK. I settled on a "C489" that I scavenged out of something, with a 0.0047uF & 0.0022uF cap. Kept the 0.015uF cap. I made drawing of the only PCB pictures on the net that are clear enough to use. It can be found here: http://www.diyguitarist.net/PDF_Files/ColorSound%20Twin-T%20Wah%20PCB.pdf

So here's a couple of things that perplex me. It sounds really great with a clean guitar. Super for funky stuff - but as soon as I use something with a lot of distortion the wah effect disappears. I can't have hardly any input resistance or the wah effect goes bye bye. 330K seems to the correct value for the input resistor according to things I've read in my research, but it flat out does not work for me. Needs to be more like 3.3K-4.7K and that's as high as I can go. Weird. I don't understand either of those things.

[Rob Strand]

So here's a couple of things that perplex me. It sounds really great with a clean guitar. Super for funky stuff - but as soon as I use something with a lot of distortion the wah effect disappears. I can't have hardly any input resistance or the wah effect goes bye bye.

The circuit produces the wah characteristic via feedback.   When you clip the wah transistor stage the feedback will be lost (... the feedback will be lost ... might be a song there) and the wah characteristic is corrupted.    I suspect adding some AC coupled clipper diodes to the input might help stop the clipping.   Probably need to graft that on carefully so as not to stuff up the wah.

330K seems to the correct value for the input resistor according to things I've read in my research, but it flat out does not work for me. Needs to be more like 3.3K-4.7K and that's as high as I can go. Weird. I don't understand either of those thing

If the circuit driving it has a level/volume pot then that resistance will add to the resistance that's there.    I suspect a value of 3k3 to 4k7 without any source resistance is going to be too low.

Given the idea of the high input impedance of the circuit is not to load the pickup you might get better consistency with a buffer feeding the wah stage.   

The more I looked into the circuit it became obvious it was sensitive to components.

I haven't looked at it since back then so I've forgotten a lot of the finer details.

[mac]

So here's a couple of things that perplex me. It sounds really great with a clean guitar. Super for funky stuff - but as soon as I use something with a lot of distortion the wah effect disappears.

Strange.
I have built an envelope filter with this circuit and into a Dist+ or direct to a cranked amp sounds really good.

In my simulations I added a direct coupled buffer. The feedback filter and output taken from the second emitter. It does not change too much the filter sweep but it might prevent loading of the "working" transistor.

mac

[Paul Marossy]

So here's a couple of things that perplex me. It sounds really great with a clean guitar. Super for funky stuff - but as soon as I use something with a lot of distortion the wah effect disappears. I can't have hardly any input resistance or the wah effect goes bye bye.

The circuit produces the wah characteristic via feedback.   When you clip the wah transistor stage the feedback will be lost (... the feedback will be lost ... might be a song there) and the wah characteristic is corrupted.    I suspect adding some AC coupled clipper diodes to the input might help stop the clipping.   Probably need to graft that on carefully so as not to stuff up the wah.

So are you saying that any kind of distortion pedal after this wah circuit will cancel out the effect? My wah pedals are always first in the chain. I'm not getting distortion in the Colorsound circuit. I tried to stick a Stratoblaster between the wah pedal and the distortion pedal and it does not help any. I guess I could try an input and/or output  buffer and see it that helps any.

330K seems to the correct value for the input resistor according to things I've read in my research, but it flat out does not work for me. Needs to be more like 3.3K-4.7K and that's as high as I can go. Weird. I don't understand either of those thing

If the circuit driving it has a level/volume pot then that resistance will add to the resistance that's there.    I suspect a value of 3k3 to 4k7 without any source resistance is going to be too low.

Given the idea of the high input impedance of the circuit is not to load the pickup you might get better consistency with a buffer feeding the wah stage.   

The more I looked into the circuit it became obvious it was sensitive to components.

I haven't looked at it since back then so I've forgotten a lot of the finer details.

I'm using a Strat with Seymour Duncan Antiquity pickups, they are not high output. Guitar is straight into the wah pedal and I have to use that low of an input resistor to get unity gain/very slight boost at the output. Anything larger than that and the output is drastically lower, so much so that it is not usable. I don't get why that is happening. This really is a quirky little circuit.  I feel like I am on the verge of really getting it to work well but it keeps missing the target.   

[Rob Strand]

So are you saying that any kind of distortion pedal after this wah circuit will cancel out the effect? My wah pedals are always first in the chain. I'm not getting distortion in the Colorsound circuit. I tried to stick a Stratoblaster between the wah pedal and the distortion pedal and it does not help any. I guess I could try an input and/or output  buffer and see it that helps any.

I was reading your comments as a distortion pedal before the wah and the high signal level would cause the wah to clip.

However, low impedance loads like some old school distortion pedals after the wah could mess things up as well!   When distorting the impedance of those old pedals can drop further.  I don't know how low the load impedance needs to be to screw up the wah.

If you put a pedal before or after the wah to act as a buffer you need buffered pedals like Boss or Ibanez set to bypass.  Using a Stratoblaster is adding to the complications.

I'm using a Strat with Seymour Duncan Antiquity pickups, they are not high output. Guitar is straight into the wah pedal and I have to use that low of an input resistor to get unity gain/very slight boost at the output. Anything larger than that and the output is drastically lower, so much so that it is not usable. I don't get why that is happening. This really is a quirky little circuit.  I feel like I am on the verge of really getting it to work well but it keeps missing the target.

A buffer before and after the pedal would help reduce some of the effects that have come up here.  However, like you, I found the design of the wah part itself has some quirks.   That's why I left it where it was at the end of that old thread.    The whole motivation for that thread was to see if a simple inductorless wah could get a inductored wah response - which it can,  but there's a few hitches.  The Sallen and Key based circuit posted in that old thread was far less quirky.

[Paul Marossy]

A buffer before and after the pedal would help reduce some of the effects that have come up here.  However, like you, I found the design of the wah part itself has some quirks.   That's why I left it where it was at the end of that old thread.    The whole motivation for that thread was to see if a simple inductorless wah could get a inductored wah response - which it can,  but there's a few hitches.  The Sallen and Key based circuit posted in that old thread was far less quirky.

I've been messing around with this a little more. I've found that it makes a nice little "Q zone" pedal, for that "cawked wah" sound. This circuit seems to depend heavily on the actual transistor used and the taper of the pot. Seems like the best response is with a 100K reverse log pot. That spreads out the response, and it's not all bunched up in the last 20-30 degrees of the pot's rotation. I also changed the 470 ohm resistor before the pot to a 100 ohm resistor, that "opens it up" just a little more at the top end. The one thing I still don't understand is why I can't use the 330K input resistor... I have to use more like 3.3K for it to work with a guitar plugged straight into it. Otherwise the output is too low AND the response is not very good. Strange....