Transformer wah blues

[gez]

Has anyone EVER managed to get a decent sound from a output transformer used as an inductor in a wah pedal?

Although I have a Cry Baby, I thought I’d play around with some ‘Eagle International LT 700’ transformers on the breadboard.  I measured an inductance of 400mH across the outer lugs of the primary, wired up a typical circuit and, although it works, there’s hardly any wah on the bass strings.

After a couple of days of tweaking and trying out just about everything, I still can’t get much of a wah sound on the lower two strings.  It seems that the resonant peak just isn’t strong enough.  I removed the 33k ‘Q resistor’ and made the feedback cap bigger, which did give a nice (albeit subdued) vocal wah effect in the mid range, but precious little down below.  I even tried wiring up another transformer in series to get 500mH, 600mH and 800mH, which results in a slightly deeper wah effect as the inductance increases, but the lower strings still sound weak.

I even tried bootstrapping the inductor, which (and I don’t know why I expected anything different, but that’s desperation for you!) made things louder, but no better.

So, are there are any tricks that might help kick-start one of these little suckers into life, or has anyone successfully designed something and would be willing to share a schematic?  No suggestions along the lines of  â€˜use a such and such inductor from so and so’ please, that isn’t my question (and I already have a decent wah pedal).

[Pedro Freitas]

See if you can take a reading of the actual inductance and resistance of the winding you are using.
If the inductance is wrong see if you can take the transformer apart and take or add a few turns of wire to the coil.
I've used many gauges of wire to roll may own inductors sucessfully and you can get away with resistances up to +/-100 ohm. The wah effect gets less pronouced with more than that.

[Skreddy]

The stock input cap value of .01 doesn't let a whole lot of bass into the circuit in the first place.  Have you tried using a .1uf input cap instead?  (I use a .224 in my old Thomas Cry Baby, and it's almost too much bass now at the low part of the sweep.  With a high Q setting, it almost wants to feed back.

[Tobias Karlsson]

I've tried a lots of transformers for wha's.
At first I was very happy when I found tranformers that were around 400-500mH. I've now realized that the resistanse VERY often isn't low enough for use ina a wha in those transformers and that will produce a less prominent wha effect :cry:

Tobias Karlsson in Sweden

[Ansil]

I've tried a lots of transformers for wha's.
At first I was very happy when I found tranformers that were around 400-500mH. I've now realized that the resistanse VERY often isn't low enough for use ina a wha in those transformers and that will produce a less prominent wha effect :cry:

Tobias Karlsson in Sweden

that is precisly why i jacked up my q1 gain and dropped the resistor down a nothc. i found using a relay worked great for a inductor.  little 12v ratshack relays. i even leave the magnet in there.

[gez]

The inductance is 400mH and the DC resistance about 75 Ohms.  I don’t think adding any more turns will do anything as increasing the inductance using another transformer of the same type didn’t help.  I’ve tweaked just about everything (including the input cap) and still no joy - looks like these are duds!  Shame really as the upper strings sound good, giving a nice mellow vocal-type wah.  Plenty of other things I can use them for though…

Ansil, nice tip about using relays!  I’ll pick up some shortly and do some experimenting.  

Thanks everyone.

[gez]

i found using a relay worked great for a inductor.  little 12v ratshack relays. i even leave the magnet in there.

Which of these did you use Ansil?

http://www.radioshack.com/category.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F013%5F000&Page=1&find=relay(keyword)

There are about four that are 12V.  Although I won't be ordering from ratshack, it'll give me an idea of what to look for in my suppliers cataloges.  

Do you happen to know the DC resistance of the ones you used?

[Boofhead]

The things you have tried like removing the 33k and making the cap larger are good things to push it closer - as you have found. Try an even larger cap perhaps.

Try placing replacing the 330/470 (whatever) emitter resistor with a 500ohm trim pot. As you decrease the resistance the sound will become more peaky and resonant.  *Warning* if you make the reistance  too small the unit will squeel-so don't adjust it with the amp on full. Also make sure it doesn't oscillate over the whole range of the sweep and repeat the test with your guitar volume off maximum just to be sure.

[gez]

Try an even larger cap perhaps.

Try placing replacing the 330/470 (whatever) emitter resistor with a 500ohm trim pot

I've done both of these things already Boof, no joy I'm afraid.  

Making the cap bigger helps get a better wah sound in the mid-range (albeit muddy), but just ends up shunting all the high end to 'ground' (Q2's emitter).

Changing (removing even!) Q1’s emitter resistor also did nothing.  I’ve even tried subbing in a few different trannies in case gain was the issue…bugger all change!

Thanks for the reply though.  If anyone knows of any transformers/relays that work well and are available in the UK, I’m all ears!