Spencerleehorton

Vox wah wah mods
« on: January 23, 2019, 03:12:39 PM »
Been looking for some info on vox wah wah mods and most of them mention the same tweaks.
I used to have an old vox wah wah some years ago which along with a fuzz face I made both sounded amazing.
Real vocal quality and a very accurate Hendrix sound into a plexi Marshall.
I had both stolen from me which was absolutely devistating!!
I have just got around to taking another look into modding the stock vox 847 wah to hopefully sound just as amazing as my old stolen one.

I’ve just seen a nice video featuring Dave weyer , who modded jimis wahs at Woodstock.

I don’t know if the circuit is much different from the stock but I can see it uses old resistors and what look like polystyrene caps?

Would basically like to build this version if I can get the info?

Can anyone help please?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


Re: Vox wah wah mods
« Reply #1 on: January 23, 2019, 05:16:30 PM »
I dont have the vox version , but I have modded a couple of Dunlop units , some of the basic mods are having the possibillity to switch inductor or adding an extra tapping ,making the series capacitor switchable so you can tune the range the filter opperates over , you can go from throaty midrangey sounds to higher frequencies that only effect the harmonics , Ive tried winding my own toroid coil as well , a small bobbin was made from bamboo to allow it to be passed through the centre of the toroid ,took time and patience but works ok , I get the impression the fasel inductor kinda saturates compared to the stock kind so adds a sprinkle of distortion into the mix .

True bypass mods as well might be worth a look .

Gus


Spencerleehorton

Re: Vox wah wah mods
« Reply #3 on: January 23, 2019, 07:10:37 PM »
That’s it gus!!

https://youtu.be/B_mc6ztVkDY

What are those caps?

I’m pretty sure I can work out the circuit from the other video as it shows the underneath.

I have a few different inductors to try want to try and get it as close as possible to that sound.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Vox wah wah mods
« Reply #4 on: January 24, 2019, 08:58:10 AM »
made some progress, my inductors are 600mH and 655mH, i have two Vox wahs i'm experimenting on.
Ive changed the 1.5k to 2k, 33k to 39k, 470R to 390R, everything else is the same and it does sound better.
Im interested in trying a 500mH inductor or 530mH as per the Hendrix version (Dave Weyer version)

If anyone could look at these photos and see if they know if the caps are polystyrene or polypropylene?
I think i can work out the resistor values by the colour codes and there is a picture of the back of the circuit.

will try and make up a pcb and go from there.

website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Vox wah wah mods
« Reply #5 on: January 24, 2019, 09:18:01 AM »
Looks like polystyrene caps to me with carbon resistors, also seems to be an extra 1k attached, anyone have any preference for transistors?

will see how it sounds compared with more modern values? the main difference is the 530mH inductor, it must sweep a bit lower in the mid range and the polystyrene caps must sound much better than the film ones.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Vox wah wah mods
« Reply #6 on: January 24, 2019, 09:59:31 AM »
Pretty sure the extra 1k is on the output before it goes to Jack, DW on the video mentions it interfaces better with the fuzz face? Any theories on this?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Vox wah wah mods
« Reply #7 on: January 24, 2019, 04:09:41 PM »
This is the best mod page I’ve seen so far

http://www003.upp.so-net.ne.jp/kazuhee/ewahmod1R.htm

website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Re: Vox wah wah mods
« Reply #8 on: January 24, 2019, 07:29:04 PM »
I fitted a fasel red to a jim dunlop , gravely at the top end, throaty growl in the mids , the smaller cores I think are favourable if you want some distortion thrown in ,where the standard issue part generally are clean sounding .
I kept one Jim dunlop standard just as a benchmark ,then from some of the parts from a Dime bag wah that broke ,I added the cap switch ,5 positions  , the vocal quality that the wah imparts  changes as you change the range , the lower range the dime bag sub board gives me is actually more like bass wah , 

I think Zappa used the wah pedal circuit  as a volume boost distortion  on the solos ,even when he wasnt using the foot control to wah , it was set at a particular point and the whole thing  resonated ,feeding back on itself , Hendrix used it in a similar way ,its a bit like the filter on an analog synth when it starts to osscilate , the tortured strangled sounds like an  iron works   or a train wreck  ,the sounds of bombs exploding and machine gun fire .

Spencerleehorton

Re: Vox wah wah mods
« Reply #9 on: January 25, 2019, 10:11:49 AM »
Today’s tests have ended up not being good.
I changed the 0.01uf caps for a cheap polycarbonate type and the 0.22uf I changed for some polystyrene caps I found.
In the heel position I just get feedback!!!

I changed the 0.22uf back to film type and feedback is gone.

Looking back at the design and type of caps, they should have been the other way round!

0.01uf - polystyrene
0.22uf - polycarbonate or film

I also have changed the 4.7uf to 4uf, I’m going to try 10uf here as well, as I can see on the vintage circuit it uses 10uf.

Resistor wise I lowered the 39k to 22k and the vocal quality of the wah is lost, just ends up being quite a mellow effect, will put a 50k pot here and have a twiddle!

Will try and try again until I find what I’m looking for.

I’ve ordered some other transistors to try to get more mid range, bc109 and 2n5172, I’m also going to try 2n3904 and bc549.

Pot wise I’ve got two types to try.
« Last Edit: January 25, 2019, 10:31:35 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


Spencerleehorton

Re: Vox wah wah mods
« Reply #10 on: January 25, 2019, 05:23:02 PM »
Apparently the jimi modded version had 2n5089 transistors in it!
So I will try these.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Vox wah wah mods
« Reply #11 on: January 26, 2019, 07:50:09 AM »
Question:

Is it possible that by changing to different transistors in this circuit it would make the sound have more mid range ?

I thought this was just a capacitors job?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

midwayfair

Re: Vox wah wah mods
« Reply #12 on: January 26, 2019, 12:28:50 PM »
Question:

Is it possible that by changing to different transistors in this circuit it would make the sound have more mid range ?

I thought this was just a capacitors job?

There's nothing about how the transistors are used here that might affect the sound in a meaningful way. If they're way out of spec you might get low output or bad biasing or something, but overwhelmingly the sound of a wah is controlled by the tone circuit, the pot taper and how much it's allowed to sweep, and the inductor. I'm not even convinced that two inductors of reasonable quality with the same measured values would sound appreciably different.
I'm Jon. Myself's music and things I make: jonpattonmusic.com. My band: www.midwayfair.org. [Disclaimer: PCBs of guitar pedals I've designed are sold by Madbean, 1776 Effects, and JMK PCBs.]

Spencerleehorton

Re: Vox wah wah mods
« Reply #13 on: January 26, 2019, 03:47:52 PM »
That’s good to know as in my mind they wouldn’t have an effect on the tone just the amount of boost.

I will experiment with several different caps of different types on a lorlin, as it seems the 530mh is the sweet spot for the middle of the range of sweep ( given that using the stock values) and if having a 615mh as I have, I could hopefully then approximate the same middle point by use of the correct cap to get the same point as the 530mh inductor.
Other resistors which make some difference to the Q and gain I will use trimmers or pots.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Vox wah wah mods
« Reply #14 on: January 27, 2019, 08:20:11 AM »
I’ve tried the 2N5089 in there and there is a big drop in volume when the wah is on.
2N5089 hfe is 400
MPS-A12 hfe is 580
So maybe this is why I get a volume drop?

On checking another data sheet it says that the MPSA12 has 20,000 hfe!!

If this is the case, I don’t see a alternate?


Changing the 0.01uf caps to polystyrene really makes a big difference and changing the 0.01uf to 0.015uf connected to inductor is much better.
I’ve experimented with changing the 4uf cap to 10uf tank but haven’t come to any conclusion yet.

Have also tried 100k as the first resistor rather than the stock 68k, seems to sound better but will use a pot here so I can hear clearly what sounds better, might use a lorlin or a switch here if there are several settings which sound good.

I see my error here, I was meant to change the 33k resistor in parallel on inductor to 100k!! This may be why I have the volume drop!!!

Will try a 2k pot with 1k in series for the 1.5k resistor on the other side of the base of Q1, so I should be able to dial 1k-3k range.

I have a Dunlop hot potz 100k and another pot which I don’t know the name of but it’s cracking so I’ll think I’ll get another hot potz.
« Last Edit: January 27, 2019, 11:12:39 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: Vox wah wah mods
« Reply #15 on: January 28, 2019, 06:39:16 AM »
So from my experimenting so far i have concluded that the biggest different is the 0.01uf capacitors to polystyrene
C4 0.01uf which you change to about 0.012uf or 12nf-16nf depending on inductor
C1 to 0.01 (10nf) polystyrene
if you have a 530mH inductor you probably want to try 12nf for C4 and if you have a 615mH inductor try somewhere in that range, i put 2 x 6800pf in parallel with another 600pf to give me 14nf and it sounded pretty good.

Ive changed the R12 parallel resistor to 100k and it seems very nice, very vocal sounding.
R5 i've changed from 470R to 390R
R3 i've changed from 1.5k to 2k
C2 4uf cap i've put back the 4.7uf electrolytic
and i've kept in the 2N5089 transistors, I had one round the wrong way!!! sounds much better now!!!

everything else is stock as per the attached schematic.

my wah now sounds very close to how i remember my stolen wah sounding, very happy now.

Schematic

https://elektrotanya.com/PREVIEWS/63463243/23432455/vox/vox_v846_wah_1967_sch.pdf_1.png
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

CJ

Re: Vox wah wah mods
« Reply #16 on: January 28, 2019, 06:47:56 AM »
flip the leads on the pot and you can play Voodoo Chile backwards, which should cause a spiritual awakening of some sort,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Whoops

Re: Vox wah wah mods
« Reply #17 on: February 07, 2019, 06:20:37 PM »
There's a lot of info on Vox wah wah mods and vintage wahs on these 2 forums:

http://www.freestompboxes.org/

https://www.diystompboxes.com/smfforum/index.php

Those 2 places are dedicated to guitar pedal diy builds,
I think you will get a lot of info there fro your wah


scott2000

Re: Vox wah wah mods
« Reply #18 on: February 07, 2019, 06:45:35 PM »
I think this site is by a member here too......

Actually Has the Plunkett wah patent at the bottom......Pretty cool site....

http://www.muzique.com/schem/index.html



 

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