A „Vox-Wah“ project, some circuit analysis and measuring results.

[Helmholtz]

Vox Wah OS/158



https://www.voxsupreme.org.uk/vox_wah_wah_pedals_1967.html

Vox Wah OS / 158 uses inductor 0.25H (1/4 H)

Interesting from a historical POV. Seems this version didn't stand the test of time.

The 0.25H inductor with the 10nF cap will shift the frequency range from 440Hz/2.2kHz to 640Hz/3.2kHz.

Also interesting the log pot and the pnp transistors.

[vintagekiki]

Interesting from a historical POV. Seems this version has not stood the test of time.

The 0.25H inductor with the 10nF cap will shift the frequency range from 440Hz/2.2kHz to 640Hz/3.2kHz.

Also interesting the log pot and the pnp transistors.

Frequency range 640Hz / 3.2kHz goes more in HiMid.
Maybe should try how wah “by ear” sounds with a 1H inductor.

[Helmholtz]

Frequency range 640Hz / 3.2kHz goes more in HiMid.
Maybe should try how wah “by ear” sounds with a 1H inductor.

It is easier to vary the feedback capacitor value, as in the Dunlop Cry Baby 535Q.
For me the range from 440Hz to 2.2kHz is optimal to get the Hendrix sound.

[vintagekiki]

It is easier to vary the feedback capacitor value, as in the Dunlop Cry Baby 535Q.
For me the range from 440Hz to 2.2kHz is optimal to get the Hendrix sound.

2.2kHz will be obtained both with 1H and 4.7nF, the only question is how the LC (XL, XC) ratio will affect the sound.

[Helmholtz]

2.2kHz will be obtained both with 1H and 4.7nF, the only question is how the LC (XL, XC) ratio will affect the sound.

A higher L/C ratio means higher impedance and thus especially a higher bass peak. But resonant Q will be lower.
(In simulation the effect on peak height was small but Q dropped from 12 to 8.)
The height of the bass peak strongly depends on the DCR of the inductor.

I have experimented with 0.65H/8.2nF but I think I like the 0.5H/10nF combo best.

[vintagekiki]

Schaller Wau-Wau Yoy-Yoy a dual-inductor wah

https://www.tonehome.de/schaller-electronic/yoi-yoi-bow-wow/

https://www.fingers-welt.de/phpBB/viewtopic.php?f=14&t=9568 ¹⁾

[Helmholtz]

Yes, I remember those. Had Schaller and Höfner wahs in the 70s (couldn't find/afford the real thing).
Never had a use for the second resonance Yoy-Yoy effect.

Looking at the schematics, I think the added gain stage followed by a voltage divider at the output makes no sense.
It might produce a little unpleasant transistor distortion, though.

[Helmholtz]

I played around with the "Q" control of a Dunlop 535Q wah and must say that I found it quite useful to lower the bass peak height and Q, when the wah is connected to an overdrive or distortion pedal.
So the addition of a variable resistance in series with a low DCR inductor like a Dunlop red Fasel seems to be a good idea (much more so than a variable parallel resistance).

Here is an excerpt from the 535Q manual (note recommendations for variable Q settings):

[vintagekiki]

#17
https://music-electronics-forum.com/forum/effectification/guitar-effects/923600-a-%E2%80%9Evox-wah%E2%80%9C-project-some-circuit-analysis-and-measuring-results/page2#post923936

[Helmholtz]

#17
https://music-electronics-forum.com/forum/effectification/guitar-effects/923600-a-%E2%80%9Evox-wah%E2%80%9C-project-some-circuit-analysis-and-measuring-results/page2#post923936

Don't understand what you mean.
I designed some inductors early in my job and know the basics (and a little more).
The Q of the inductor is vastly different from the Q of the resonant circuit:
https://www.gitec-forum-eng.de/wp-co...E_Q-Factor.pdf

My post #68 above is about sound.

[vintagekiki]

My post #68 above is about sound.

Post # 17 is about the Q factor of inductor, which is an integral part of most wah.

[Helmholtz]

Post # 17 is about the Q factor of inductor, which is an integral part of most wah.

As said and explained earlier, the wah sound depends on the Q (width) and the impedance (height) of the resonance as well as the lowest and highest peak frequencies
The Q factor of the inductor is one influence among several others and it strongly depends on frequency.

[vintagekiki]

https://components101.com/articles/how-does-quality-factor-impact-the-performance-of-an-inductor

For the same frequency and the same inductance, the Q factor depends from the resistance. On the influence of resistance to Q factor post # 17

[Helmholtz]

For the same frequency and the same inductance, the Q factor depends from the resistance. On the influence of resistance to Q factor post # 17

I know, but it's not about the Q factor of the inductor but about the the Q of the resonance, which is a different story.
The Q-factor of the inductor, more exactly its ESR has some influence on the resonance Q and impedance, though.

[vintagekiki]

I know, but it's not about the Q factor of the inductor but about the the Q of the resonance, which is a different story.
The Q-factor of the inductor, more exactly its ESR has some influence on the resonance Q and impedance, though.

Sorry, I'm free to ask.
It is known and I know what is the Q factor at inductor.
I don't understand the term "resonance Q" or "Q of the resonance"
ESR at inductor, coming with high frequencies (HF).