Inductorless wah with Inductored wah response - worth pursuing or not?

[Rob Strand]

A week or two ago I was playing around modding the Colorsound inductorless wah.  At the end of this thread I posted the response for a first-pass "hack" at making the inductored wah more inductor like,

https://www.diystompboxes.com/smfforum/index.php?topic=121289.0

Near the end of that thread, mac posted a link another thread showing his simulations of the Coloursound inductorless wah (which are fine),
https://www.diystompboxes.com/smfforum/index.php?topic=99448

As you can see the inductorless wah has quite uneven peaks compared to the inductored wah and they weaken off at the low frequency end.

Today I spent a bit more time playing around with inductorless wah.   I got a bit further.  The response plot below shows the inductorless wah vs the inductored wah.  The yellow text on the plot explains the differences [EDIT: When the pedal is down (HF peaks) the *inductored* wah has the kicked up high frequencies, with the pedal down (LF peaks) the inductorless has the kicked-up high-frequencies  -sorry for the screw-up.]

Click To Enlarge:


This inductorless wah (I've called it V1.4) is looking pretty close to the inductored.   It is by no means optimal I could spend a lot more time on it trying to squeeze the last drops out.   It's a *lot* closer to the inductored wah than the Colorsound inductorless.

Is this worth pursuing?

[deadastronaut]

yes indeed......tunable, would be cool too...

[Mark Hammer]

Perhaps this is one of those things that requires a dual-ganged pot?

[bool]

IIRC you can tweak the response simply by adjusting the 33K resistor value (was it 22k??). I had one of those on my bench in late 80's but obviously can't remember the details ...

[Paul Marossy]

I suppose that would be a way to build a wah pedal without an inductor but the whole reason I made my clone was to get the inductorless sound 

[Rob Strand]

yes indeed......tunable, would be cool too

Tunable in what way?
Like it's pretty pressed even to get it close to an inductored wah.

IRC you can tweak the response simply by adjusting the 33K resistor value (was it 22k??). I had one of those on my bench in late 80's but obviously can't remember the details .

It's the 33k.  That makes it peakier but nowhere near an inductored wah.

Perhaps this is one of those things that requires a dual-ganged pot?

Single ganged.

I suppose that would be a way to build a wah pedal without an inductor but the whole reason I made my clone was to get the inductorless sound 

That's one of the dilemmas.     One goal is to mimic the inductor wah.   Then there's the question, is there something in between the two, or perhaps even different which is better?  (which isn't really answerable.)

Anyway, I'll see if I can put something up so others can play around, even if it's not the final thing.

[Mark Hammer]

How come the Ibanez WH-10 circuit hasn't been mentioned yet?  It's actually pretty tunable, and doesn't sound half bad.

https://www.diystompboxes.com/smfforum/index.php?topic=69992.0

[Rob Strand]

How come the Ibanez WH-10 circuit hasn't been mentioned yet?  It's actually pretty tunable, and doesn't sound half bad.

That one looks pretty good.  It has a single pot and it has the capability of being close to the inductored wah.   (not sure what frequency range it covers but that is just a case of changing caps.)

[thomasha]

mind sharing the schematic? I would be interested in tweaking the circuit I built some time ago.

I have one with transistors and one with an opamp. The opamp version even has a wind sound when I'm not playing.
Here the schematic>

I played some long time ago with ltspice, and can't seem to remember what I was looking for.

My favorite is the transistor based, but it only works on the toe down side. The sound is more like a wow instead of a wah.

[Rob Strand]

mind sharing the schematic? I would be interested in tweaking the circuit I built some time ago.

I'll try to put something up soon.   

My initial goal was to try to answer the question: Can a Twin-T circuit like the Colorsound be tweaked to be more like an inductored wah?   That's looking like a yes.   I'm not trying to build the best inductorless wah (maybe not yet) I'm sticking to the Twin-T with all its issues.

In the early stages of tinkering I often manipulate things at a higher level.  I'll have circuit blocks which aren't directly buildable (normally I would try to removed these or simplify them later).  I have funny valued parts to make it easier to tune when comparing against the inductored wah.  Also I haven't tried to design a finely crafted circuit which optimizes noise and is less susceptible to parts variations.

The second issue is I'm in the process of setting up some more powerful tools which will let me match the circuits quicker, more accurately, and let me change stuff more easily.   I can tell you now it's a *very* time consuming job tweaking this thing.  The number of variables is high and they are all tied together.

Anyway, that's why I haven't put up a circuit (I'm not holding back on some secret which will let me control the world using a wah pedal).

[Mark Hammer]

How come the Ibanez WH-10 circuit hasn't been mentioned yet?  It's actually pretty tunable, and doesn't sound half bad.

That one looks pretty good.  It has a single pot and it has the capability of being close to the inductored wah.   (not sure what frequency range it covers but that is just a case of changing caps.)

The stock one has a 2-position switch for selecting guitar or bass range.  The switch simply adds 10k resistance to 15k, so I tried replacing it with 10k and a 20k pot to be able to vary the range more.  It works, though whether it adds value to any given user depends on them.

[Rob Strand]

It works, though whether it adds value to any given user depends on them.

I can't imagine the simple switch work as well as changing all the caps but might work good enough.

From what I can see the right-opamp is a variable cap.  The left opamp looks like a band-pass filter and the variable cap is connected to it.  However there seems to be a bit more going on which isn't obvious just by looking at the circuit.   There might be a better way to look at it but off hand I can't see the pattern.

[bool]

IIRC tweaking the colorsound back in days was easy and cheap, changing the 33k resistor to 22k and adding a small (was it 20-30pf) cap to transistor b-c. That made these really nice to use in studio.

I had a Ibanez on the bench for a fix in 90's but most players simply preferred a standard crybaby...

So why won't you just post what you have WRT colorsound mod right now and deal with your time-consuming toolkit later? Seems like a no-brainer to me.

[Rob Strand]

IRC tweaking the colorsound back in days was easy and cheap, changing the 33k resistor to 22k and adding a small (was it 20-30pf) cap to transistor b-c. That made these really nice to use in studio.

The addition of the b-c cap is very interesting.   Yesterday I started to set-up the software tools and when I was verifying that against the circuit I found a disagreement.  I traced the disagreement down to the Cbc cap of the *transistor*.   So it seemed my hand-tuned circuit is in the zone where the Cbc cap might help the response.   The first thing I thought was I can't release a POS circuit that depends on the transistor's Cbc cap.   So that left me with the question can I add a cap somewhere which does the same thing.  That would also let me decrease some of the high resistances in the circuit (which another beef I have about the current circuit).

I had a Ibanez on the bench for a fix in 90's but most players simply preferred a standard crybaby..

Off the shelf it looks good.  I someone spent some time tweaking it, it has could quite possibly be closer to the inductored wah.

So why won't you just post what you have WRT colorsound mod right now and deal with your time-consuming toolkit later? Seems like a no-brainer to me.

Well I've got those tools set-up about 80% of the way.  Now I've realized the ckt is depends on the Cbc of the transistor and I don't want to inflict that on the world just yet.

[Rob Strand]

My favorite is the transistor based, but it only works on the toe down side. The sound is more like a wow instead of a wah.

One of the hardest tasks is to get these things to produce an even output across the pedal range.

[bool]

The Ibanez belonged to a local guitar legend which he preffered over a crybaby but not some other "mojo wah" he had (whichever that was) ... But 99% other guitarists simply wanted a crybaby and didn't want to even hear about anything else.

The modded colorsound was a real winner for studio recording, was much more pleasant than a morley and crybaby. Cheap & cheerful.

Are you absolutely 1000% sure that using "high resistances" is the way to go? My intestines say that tightening the damn thing would be you know the right thing to do ... or not, ha ha.

The c-b (miller) cap if anything would flatten the high freq. peak and so deshrill the tone a bit. You could also poke around that messy output r-c-r netwerk. But man that tweakage was 30 years ago ... I don't remember quite that well anymore.

[Rob Strand]

Are you absolutely 1000% sure that using "high resistances" is the way to go? My intestines say that tightening the damn thing would be you know the right thing to do ... or not, ha ha.

That's just how it turned out.

The c-b (miller) cap if anything would flatten the high freq. peak and so deshrill the tone a bit. You could also poke around that messy output r-c-r netwerk. But man that tweakage was 30 years ago ... I don't remember quite that well anymore.

It will do that, although my ckt and the color sound has less highs than an inductored wah.  The treble boost at the output tries to compensate for this.

Anyway here's one version.  It has many evils.  I would not even think of building it.

[mac]

My initial goal was to try to answer the question: Can a Twin-T circuit like the Colorsound be tweaked to be more like an inductored wah?   That's looking like a yes.

When I began tweaking the CIW I thought the answer was no, that is, without adding parts and filters.

These are the mods I tried,





Original values are in blue.

mac

[bool]

I see that there are 2 schools of thought: 1) a mod and 2) a total remodel.

My thoughts on the subject are that the original ckt topology is KISS enough to be well-liked. I'm not really in my "dev mode" these days but for you guys here's my 2c on the subject: Personally I would use a darlington and bias it similarly to what Rob S. did. (to keep MPSA13 biased happy at 9v you would generally use 2x 220k in c-b leg and 150k from b-e; and something like 4k7 in collector load). So I would use a small-ish collector resistor to keep the output impedance low (this could potentially maybe perhaps would be allow to use a general opamp model as an approximation in sim??). Then I would similarly to Rob just use a pre-emphasis hi-boost at the input and not at the output. (this works really well in boosters and small one-transistor instrument recording preamps; I have made many). BUT I would then clamp the darlington hard with small b-e and b-c miller caps for general hygiene and better predictability (also RFI and hiss cleanup).

KISS it guys!

[Rob Strand]

When I began tweaking the CIW I thought the answer was no, that is, without adding parts and filters.

Some of the difficulties I've found are getting all these to align.
- getting enough HF boost without trading it for LF boost
- the flatness of the peaks across the range of the wah pedal
- matching the response at the low frequency end

You can see these effects in the response plot of your circuit.  The HF boost is a bit low and there's some LF lift.  In order to get around some of these effects the circuit needs to be changed somewhat. 

Below I overlayed your circuit (i've called it V1.1), on older form of my circuit (which I've given a version V1.9), and the Vox inductored wah.

For the plot: I've set your R7 value to 33k.   I restricted the range of the wah pot so the lowest peak lines up with the inductored wah.  I've adjusted the overall gain so the lowest frequency peak matched.  Here the HF side is low and the LF side is high; I saw that as a good balance point for fair comparison.

My thoughts on the subject are that the original ckt topology is KISS enough to be well-liked. I'm not really in my "dev mode" these days but for you guys here's my 2c on the subject: Personally I would use a darlington and bias it similarly to what Rob S. did. (to keep MPSA13 biased happy at 9v you would generally use 2x 220k in c-b leg and 150k from b-e; and something like 4k7 in collector load). So I would use a small-ish collector resistor to keep the output impedance low (this could potentially maybe perhaps would be allow to use a general opamp model as an approximation in sim??).

The addition of the buffer instead of a common collector stage is something I did for a reason.  There's two issues with the circuit the first is the lower T-circuit, with the caps in the arms,  puts caps in the feedback path.  This naturally causes a low pass filter (and that's the main reason the colorsound has the post wah treble boost EQ).   When the output is a CE stage, the caps in lower T-circuit load down the output signal and form a low-pass filter.   The two effects act to kill the highs and the addition of the buffer is the strongest remedy against it.   Most people see the Twin-T circuit as a nice symmetric behaving circuit but when you load the output (the base side in this circuit) the behaviour is very different.

Apart from those changes I also have a second EQ circuit at the input and an additional attenuation at the output.  I don't like large amount attenuation at the output but that's how it turned out.  So that, and the best way to place the EQ, are things to fine tune.

The circuit below shows those main points.  As shown, it's probably less abstract and more acceptable to most people than the previous ckt but to me it's just a stepping stone to the final goal (like the previous circuit).    The main point of all this is the Twin-T circuit can be made to work like an inductored wah.