JMI Vox - Grey Wah c. 1967

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
sinner
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Post by sinner »

Can you also confirm the wiring diagram while we at it? :)

http://www.turretboard.org/?p=30

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deltafred
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Post by deltafred »

It's an age thing, I know another guy with a 40 year old Wha pedal that he has had form new.

I will hang on to it for a bit longer and do you a full drawing of the board, that bit is easy.

I don't mind pulling the transistors out to measure them and I was going to measure the resistance and inductance of the inductor anyway.

Inductor 297mH - measured on a cheap DMM model no VC9808+ make unknown.
DC resistance 16.6 ohms (measured on 2 different DMMs).

I'll email you a zip of all the photos I take. It might not be immediately as I am away quite a bit in the near future.
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Post by deltafred »

sinner wrote:Can you also confirm the wiring diagram while we at it? :)

http://www.turretboard.org/?p=30
Yep, will do when I get chance.

Both Q1 and Q2 hfe around 410 measured on 2 different crappy little DMMs. This varies with temperature so no point being too precise.
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Post by sinner »

410hfe? twice as much as I was thinking... thanks :)

Also thanks for the rest, I had two another 300mH readings from my website visitors, but never the resistance...

You don't have to draw new template with board dimensions, I already did it, just look on it (it's on my website) and check against yours :)

Cheers
Pawel

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Post by deltafred »

sinner wrote:Can you also confirm the wiring diagram while we at it? :)

http://www.turretboard.org/?p=30
There is a missing link under the perf board. I have shown it above the resistors for clarity.
VOX Grey link.jpg
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Post by deltafred »

Sinner

A very minor point.
The row of component holes are 0.5" apart not 0.45" as you have them. (I said it was a minor point).

The board is mounted by 2 self tapping screws (1/2" x 1/8" approx), on 2 paxolin tube spacers 1/4" long.
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Post by sinner »

Got the jumper fixed

http://www.turretboard.org/?p=30

I had it there in first version, but I've screwed making revision :oops:

Thanks a lot

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Post by Rjcastro76 »

Would 2 500mh inductors in parallel be similar to one 250 mh inductor? I understand the would have to be somewhat separated to shield the magnetic field....

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Post by sinner »

Rjcastro76 wrote:Would 2 500mh inductors in parallel be similar to one 250 mh inductor? I understand the would have to be somewhat separated to shield the magnetic field....
May be similar, but not exactly the same thing. Grey Wah Wah inductor use smaller diameter coil and different wire diameter. Inductor resistance will be off

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Post by Rjcastro76 »

Ok, I guess I'll try to get a 250mh one. Also, on turretboard.org, are both layouts for the grey wah correct? If not, which is? The top, or bottom one? Thanks

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Post by sinner »

Rjcastro76 wrote:Ok, I guess I'll try to get a 250mh one. Also, on turretboard.org, are both layouts for the grey wah correct? If not, which is? The top, or bottom one? Thanks

AFAIK they are correct. True to the schematic at least

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Post by Lucifer »

Hey Sinner - is that really you in the photo ?

Wow, you never told us you were so handsome !
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Post by sinner »

Dude, its Andy Pipkin ;-)

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Post by Lucifer »

I know, dude !

But if it was you, you'd still be a gorgeous bastard !
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Post by sinner »

Yeah, I know ;-)

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Post by PurpleOhmAudio »

deltafred wrote:
sinner wrote:Can you also confirm the wiring diagram while we at it? :)

http://www.turretboard.org/?p=30
There is a missing link under the perf board. I have shown it above the resistors for clarity.
The attachment VOX Grey link.jpg is no longer available
Hi, sorry to drag this old thread up but does anyone know the actual board dimensions in these old Grey Wahs?

As deltafred mentions the component holes are 0.5" apart, and the tube spacers paxolin, so I presume the board will be, and looks to be just 1mm thick.

I have a few of the same enclosures from the corresponding volume pedals, one with the Vox logo on the casting, one is plain without logo but has the exact casting marks and imperfections etc,so in theory from the same place...

Got them on ebay, one was quite badly butchered (annoying the one with the Vox logo :x ), there was a DIN socket hole in the side (maybe for multi channel volume?] and put a spring and momentary switch inside, very strange....

Was going to build them into clones and get them going again, just need to get a few parts sourced, might even go crazy and goop the board too, might stop the mojo leaking out

On another note, does anyone know if there is a axle tension bar under the treadle on the original 'Grey Wahs', as these volume pedals do not, and seem to rely only on the pot friction, cant find any pictures that show it online, but it looks like originally there was a battery clip which may bolt through to the other side?

Cheers
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Image4468.jpg
Image4465.jpg

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Post by nightraven »

PurpleOhmAudio wrote: On another note, does anyone know if there is a axle tension bar under the treadle on the original 'Grey Wahs', as these volume pedals do not, and seem to rely only on the pot friction, cant find any pictures that show it online, but it looks like originally there was a battery clip which may bolt through to the other side?

Cheers
Yeah, you're quite right, they wedged a battery clip upside down against the 'gear' of the pot assembly, to help keep it in place. Not only do the Selmer and JHS wah pedals from the 1960s seem to have enclosures cast from the same mould as well, they also have this upside-down battery clip thing going on as well.


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Post by modman »

sinner wrote:
06 Mar 2010, 17:40
Here's some info about components used http://wah-wah.co.uk/greyvox.html
Dan N wrote:
08 Mar 2010, 21:19
The Thomas Organ part # for a 250mh inductor is 80-5044-7. Organ Service Corp. ( http://www.organservice.com/ ) have them on their stock list for $8.00. I don't know exactly what OSC stocks, but they replace a brown TDK in a Fasel style package.
I attached archived pdf and xls files to above messages -- both websites are down. You can jump to these posts using the arrows next to the username of the quote.
this one too...
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Post by pacealot »

Sorry for yet another necro-bump, but if anyone is still interested in trying to make a "vintage correct"-style inductor, I found some Plessey 14mm pot cores on the 'Bay which are very similar to the originals ("clover" style, M2-0 ferrite), and I wound one to around 273mH and 16.6Ω (just by coincidence the exact resistance as deltafred's!) using about 410-415 turns or so of 36 AWG magnet wire (I don't have an exact turn count because I overwound at first with 450 winds and the bobbin wouldn't fit in the core, so I pulled off the winds by hand without counting accurately until it fit).

The seller seems to have some pot cores still available if anyone's interested (no affiliation, just a satisfied buyer) — just search for Plessey Telecom pot cores 14mm M2 0 and they should turn up. The bobbins don't come with them, but I just used a normal TDK/Epcos bobbin for 14mm ferrites from Mouser and cut the extra side notches out with a Dremel, and it fits perfectly.

Oh, and very long-time lurker/first-time poster — thanks for all the great info and education over the years....

—Paul

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Post by pacealot »

I breadboarded the circuit with a couple of 2N3707s (around 380-390 hfe) and it sounds fantastic. I did, however, tweak three components from stock to get maximum sweep and a little more low-end, which definitely helps counter the "thin whine" complaint while keeping the distinctive grey character intact. I got very aggressive in lowering the Q1E ("gain/bass") resistor, to the point of landing on 30Ω finally (I even tried it with that resistor shunted, but that just lost a little too much of the character of the circuit). To deal with the awful grating distortion and profuse volume difference that inevitably caused, I upped the input resistor all the way to 240K, which seemed to be a decent compromise between too hot and too noisy (it's surprisingly no worse than the average Clyde-type wah noise-wise, even with all that extra gain on the backend of the circuit). Finally, I raised the input cap to 0.047µF, which is letting in a little bit more low-end as well.

The inductance rose a bit overnight (to almost 300mH!), so to keep the top of the sweep intact, I pulled another handful of winds off (maybe 15-20), and it seems to have now stabilised at around 260mH.

Now to populating the board. The ferrite cores are the only truly "mojo" component, but everything is at least somewhat appropriate for the circuit:
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