What Does the Foxx Phase?

[anotherjim]

Some rough calculation tells me the range of control at the output of Z3 is a total swing of about 1.5v centred on whatever the bias trimmer is set to. I get this from the range of the pedal pot which is 0 to a little less that half 6v - which is halved again by the resistors around Z3. This  should be about the same for pedal sweep or LFO. There isn't a "range" setting, so you have what you have. It's some work to change all of the FETs for a different Vgs, so I'd try the following...

Measure volts to ground on Z3 pin 5. This is the bias you have now, note it so you can go back to it if necessary.
Adjust bias to give 1.5v on Z3 pin 5. This is the centre of the working range (0-3v). The optimum could be anywhere between 0.75v and 2.25v, depends on linearity of the FETs.

A range control could be added, R34 could be a 1M in series with a 1M trimmer, but I guess the designer wanted to keep production setup as simple as possible. If you don't feel the range of sweep is enough, no matter how much you tweak the bias, you could try a lower value for R34. 1M would be the maximum swing The FETs could handle with bias centred at 1.5v - but you would find the extremes of travel have no effect, which would be more noticeable under LFO sweep.

[nickbungus]

Thanks as always Jim.  I did try what you said but I seemed to get the best phasing at the 2.7v mark.  

I also had a dirty experiment with the range mod (simply by  putting another 2M2 in parallel with R34) and you could hear a marked different.  So it would be well worth me implementing this mod fully.

To me it sounds like the Foxx.  Shame I don't have one to compare it to but I do have the Digitech Brian May thing and they are pretty similar.  Actually, mine sounds more like what the recordings sound like to me.

.

I suppose I can call this verified.  I'm sure this can be further tweaked to get it closer to the original or to make it into its own thing.

I've uploaded the pcb etch I used (on page 1).   If anyone makes one please let me know about your results and if you changed anything.

[anotherjim]

Sound the real deal to me -  though I'm not an aficionado, I'm of an age that couldn't help but hear Queen regularly.
How do you plan to box it -  wha pedal shell?. The way the pot is used, it looks like it might be an easy job to have a socket in a normal enclosure to use an separate expression pedal.
Hmmm... that's another thing to watch out for - you can have full pot travel with a manual pot, but it won't be the same in a pedal rack&pinion drive.

[1878]

That sounds bang on !!

The Foxx treadle pedals (old DeArmond stock I think) have a slightly longer throw than Crybaby shells. I have a Foxx Loud Machine & I reckon there's one or two teeth extra. I would second anotherjim regarding boxing it up with the option of an expression pedal. I only really found a use for the treadle when using it as a wah type thing.

Congratulations on cracking it. You've got something to be proud of there.

[nickbungus]

I bought one of these:  http://www.ebay.co.uk/itm/Musical-Electric-Guitar-FX-Tones-Effect-Wah-Wah-Pedal-/180692952764?pt=LH_DefaultDomain_3&hash=item2a1223a6bc for £18.

Its actually not a bad wah - but its a plastic enclosure, but the plan was to try it in that.  But I just don't think I can fit the beast in (which my wife says is usually not a problem).

So, I had been thinking about the expression pedal route.  Unlike you Jim though, I didn't think far enough ahead and hadn't considered the travel in an expression pedal.

When Greg Convington was selling his version, he discarded the manual mode and just had them wired for auto.  That's the way Brian May used his, but to me, it seems a bit wasteful and taking something away.

So, I think I'm going to explore the expression pedal route.  Its the best of both worlds.  Would it be possible to switch between manual and auto by simply detecting whether a jack has been inserted?  If not, keeping the switch wouldn't hurt.  I'm not sure as how to wire it, but that's why god invented Google.

Just another note, my thumb is broken and I can barely hold my pick so please don't judge my playing.  I wanted to re-record this as a comparison, which I recorded with the Digitech Brian May thing, but that's a few weeks away when I can take off this splint.  https://soundcloud.com/nickbungus/queen-medley-with-vocals

[1878]

You would need a switched jack, but yes it's possible to automatically switch to a pedal when it's inserted. Personally, I would have the expression pedal switchable with a footswitch. That way, you could have two different speeds set up & switch between the two, or two different depths, sweep ranges etc...

[anotherjim]

A short travel pedal mechanism might not be so terrible. A log pot can be set up on the gear so that most of the change in resistance is within the travel - since a log pot has one end where there's very little change in resistance per degree of rotation. That would make it tricky to set filter notches versus pedal angle like people do with a Wah - but you can have the manual pot mode for that.
If the pedal travel was really short (about half pot rotation), the pot could be 220k linear and set so the mechanism sweeps it from 0 to about 100k, which is the same as original.

Nick - you shall have a PM shortly...

[nickbungus]

Usually, I can find this stuff on Google however limited my knowledge, but I just cannot fathom how to wire an expression pedal jack so that when its inserted, it switches between the expression pedal and R26 (the treadle pot)?



Any suggestions would be welcome, thanks.

[armdnrdy]

Here's a drawing that should help out.

The Foxx treadle pot is connected as a rheostat with lugs 2 & 3 tied together.

The drawing I provided ties the tip and ring together at the jack.

This will enable you to use a standard expression/volume type pedal with a TRS jack/cable.

As anotherjim stated, you'll have to modify the expression pedal with a different pot to get the 100K you need.

EDIT: R28 should be R26. Dim morning light, rough Foxx drawing, and first cup of coffee! 

[nickbungus]

Thanks Armdnrdy, amazing!

That's super clear to me now

Shame that the pinout image is unreadable but I take it this will do the job:  http://www.maplin.co.uk/p/635mm-solder-tag-mounting-stereo-socket-hf92a

[bluebunny]

I take it this will do the job

Yep!

[armdnrdy]

To clarify things even more...

R26 is now an on board control, When a male stereo 1/4" plug is inserted into the expression jack, the contact/switches marked RN, TN, and SN lift off of the ring, tip, and sleeve connections. The external expression treadle pot now makes those connections to the ring, tip, and sleeve.

[armdnrdy]

Looking at the Foxx pedal...the treadle pot is connected lug 3 to ground, lug 1 & 2 connected together to the switch.

[nickbungus]

Looking at the Foxx pedal...the treadle pot is connected lug 3 to ground, lug 1 & 2 connected together to the switch.

Does that still mean that your original wiring diagram is valid or does it change anything Armdnrdy?

[armdnrdy]

No...I have to revise the drawing.

The more I look at the circuit...the more I believe that you should house this in a pedal like the original.

As it stands..if you just put an expression jack to switch in between the onboard control and the pedal...you are going to be left with an onboard sweep control when you switch the toe switch from speed to sweep. (If the expression pedal is not connected)

The way that I see it....you have to purchase a wah type enclosure for the expression pedal. Why not just build this like the original?

[anotherjim]

I don't believe the sweep pedal necessarily has to have a switch. The "Toe" switch can be a toggle switch or latching stomp on the Phaser box. It selects between LFO or Manual pot (the manual works like a "filter matrix" such as on the EM flanger). When you plug an expression pedal in, it switches the manual pot out and you have pedal sweep again like the original. At least that's the way I though this was going?

Armdnrdy's scheme is going to be useful, but you have to know what connections the expression pedal uses.
Need to know the details of the sweep pedal wiring to get into specifics for this. Not all ready made expression pedals  connect pot wiper to jack tip - some it's the ring. You can make that issue irrelevant by simply connecting the phaser "toe" switch to tip AND ring on the jack, and then you've also done the job of connecting one end of the pot to the wiper.

If you're gutting a pedal shell for your own pot and wiring, you can use a mono TS jack, because you only need it to switch between the 2 pot wipers - both pots can remain grounded at one end.

[nickbungus]

Thanks Lads!  I'll go back to the original design then as I seem to be making it more complicated by introducing the expression jack.  The knowledge you guys have conveyed hasn't been wasted though, I've definitely learnt a lot and I'm sure others will benefit too.

I've just gutted that cheap plastic wah shell.  After sizing everything up I think I can squeeze it all in.  Hopefully I'll get another YouTube video posted soon showing the manual mode.

I'm trying to source a proper aluminium wah/expression chassis for long-term use though.

[armdnrdy]

I don't believe the sweep pedal necessarily has to have a switch. It selects between LFO or Manual pot (the manual works like a "filter matrix" such as on the EM flanger).

Not quite correct.

The "toe" switch chooses between manual pedal sweep and LFO speed. Look at the upper part of the toe switch. It connects the treadle pot to the LFO.

This is where the problem is. One would have to redesign the circuit to switch from auto LFO, to manual speed and manual sweep.
There would have to be another switch.

That's why it makes more sense to build this into a pedal enclosure. Nick is a Brian May fan....what would Brain do? 

[nickbungus]

Nick is a Brian May fan....what would Brain do? 

Hmm, I better get my hair permmed, buy some clogs and start ranting on about saving badgers. 

Actually I read somewhere during my research that his Foxx pedal broke at some point and he got it rehoused in a cry baby shell.

[1878]

I can see that happening !! I have a Foxx Loud Machine (volume pedal) & they are as flimsy a pedal as I've seen.

More info on the Foxx.

http://www.brianmayworld.com/PeteCornish.htm