EH Talking Pedal, possible pot?

[Ronan]

Some progress, it's working, the pcb is good to go with some minor alterations, but works as is. Just trying to fine tune the card with the windows for the LED/LDR pairs at the moment, to make it match the breadboarded version. I am using LDR's from ebay seller tayda2009, and LED's from an Australian supplier. The original EHx LED's/LDR's are available from www.muzikus.sk in Europe, 0.54 and 1.93 Euro for the LED and LDR. I'm keeping records of pedal position versus resistance to help make the results repeatable.

I now have 3 Morleys of various vintage, including a brand new one! (cost $100 shipped to Aussieland) and the last one cost $50 shipped. It seems they all have exactly the same chassis which is a good thing, it means the PCB should fit all of them except the very early ones with tall chassis.

I am not that happy with the quality of my home etched PCB's, the bare copper areas and traces have pitted areas, I would rather spend the bucks and get them professionally done. If anyone could help with generating gerber files for a single sided PCB, solder mask and no silkscreen, that would be cool! Otherwise I will learn a PCB program again. Might be a good thing to do over the Christmas break.

Barebones test bed:

[Ronan]

All finished! Its a prototype, going to my bro-in-law as a Christmas present. Hopefully he will give me some feedback. I really like the sound, very happy with it. Will get some more PCB's made with minor changes, I'll let you know Dino when I have some in hand. Give me a month or two, its that time of year. But I'll be onto it, I only have the breadboard version to play with, and I want a finished one for myself, yesterday

the pedal

the guts

the circuit

the card

[digi2t]

HOLY SMOKES!!!!  

That is just freakin' awesome. WOW, what a clean build.

I'm scanning Ebay now for old Morley boxes  

This one just leap-frogged over my AP-7 Jet Phaser vero build. Fantastic work Ian!

Please give me more precise info on the LED/LDR combo. If you could shoot me the exact links, that would be great.

I found a fantastic idea for the card here; http://www.diystompboxes.com/smfforum/index.php?topic=36215.40 . Transparency plastic, and a laser printer! Print the card to scale, and then just cut it out with an Xacto. I fell upon this thread by accident, while I was looking for info on the strips used in the Digitech, or older ART X-15, footcontrollers. They use a gradient tinted strip between the LED/LDR to increase/decrease the resistance, and I started wondering if we could do the same somehow. But, I think blacking out the transparency, and then trimming out the slots would be more reliable, since gradient printing would be very printer quality dependant. Like PCB transfers, if we could put out a clean crisp image that one could download, scale, and print, that would make it easy for someone to get decent results. Besides, plastic would be much better than cardboard.

It's going to be a very busy winter....

[Ronan]

Dino you've brought up some good points there. Repeatability of results and the card slots are something to think about. The only repeatable result is by measuring the resistance across each LDR with the circuit powered up, and plotting resistance versus pedal travel. I can supply tables which work, and a builder would have to tune the slots to roughly match the table. I scanned the card I am currently using to give an idea of slots that work, that's the rough "card" pic in the post above. I have 2 other cards in the breadboard version with similar slots. The reason I have long legs on the LED's and LDR's was to allow some room for position adjustments of these components to get it all working. I am thinking of using non-acidic silicone near the heads of the LDR's and LED's to stop them from any further movement once set up correctly. The reason the slots have a rectangle in the middle of one, and at the end of another, is that this rectangle roughly matches the size of the active area of the LDR, and where the rectangle is, is where I wanted minimum resistance. Those slots have been arrived at by trial and error. The actual travel of the card is a very small distance, so the slots are small, and a good hobby knife or scalpel helps a lot. The reason I tried the tayda2009 LDR's is that they have a narrower active area on the face of the LDR, so I was thinking this would make it easier to use than the wide active area of the EHx LDR's, given the small travel of the card. But in practice, it has turned out to be no real advantage that I can tell at this stage, and the EHx LDR's being more sensitive can easily go down to 500 ohms with an LED close by, and the tayda2009 ones only go down to 1k for the same LED intensity. For this circuit, we need around 1K minimum resistance to get full use from the filters. On the original circuit, there are 1K resistors going to the pots, so on the PCB I made, I left these 1K's out, knowing that the LDR's can make up for that 1K, its sort of built-in. It can be difficult to get an LDR resistance to go below 1k is another way to put it, without burning up lots of milliamps in the LED's that is. The Fairchild MV50152 LED's I am using have similar brightness at low current as the Morley LED's, typically they are using around 1.5mA which is a decent brightness at very low current compared to many other LED's. I happen to have around 100 of the Fairchild LED's on hand, and after comparing them to the Morley LED's and finding them to be a suitable replacement I used them.

The way I have been making up a card is take out the original one from the Morley pedal and photocopy it, then cut out a new one using that as a template, just for the outside shape, the single screw hole, and the 2 locating slots. So you then have a blank card that can fit into the pedal. Then put the pedal into toe down position and put a dot in front of each LDR (on the card), then do heel down and put the other dot. This gives you 2 dots for each LDR that define the length and position of each slot. Then go from there, draw up some minimal slots, cut them out, and test the resistance at different pedal positions. I have found  plastic credit card to be the stiffest, not that easy to cut, but sturdy. The colour doesn't seem to matter, black, white, reflective, whatever, all that seems to matter is how much the LED can shine directly onto the LDR. Laser printed transparencies may work well too, but I'll leave that for others to experiment with.

I have found that the actual resistances obtained from the LED/LDR pairs aren't that critical, anywhere near the ballpark (using the resistances of the pots on the original schematic) will produce very interesting sounds, more than enough to give a builder lots of enthusiasm to keep at it. I suggest that when you first get a good sound, leave that card alone as a backup reference for a good sound, and make another new card to experiment further, and keep the first card for comparison. The whole thing with language/dielects/accents means that each builder's favorite response from the 2 formants will more than likely be different, same as everything else I guess, wah pedals, amps, guitars etc.

In the top right corner of the schematic I posted is a circuit for the 3 LED's, they are switched on with the footswitch (SW1c). It is a constant current source to keep the 2 main LED's (the LED's driving the LDR's) at the same current even as the battery voltage changes, also the 2 LED's draw only the current of one LED since they are in series. The trimpot is to adjust the current through them. That is the only addition to the original circuit.

Morley LED
Morley LDR
tayda LDR's
Fairchild LED's

[digi2t]

Thanks for the info Ian.

I bought a used Morley for a decent price, and the LDR's are ordered. As for the LED's, I'm going to try socketing what I have on hand for the moment. The shipping from your supplier is just too rich for me. I might just use trimmers to tone down the brightness if need be, and then throw in appropriate resistors once I find what works. I run all my effects strictly from power supplies, so power comsumption isn't critical for me. On the breadboard, I found that a 500K trimmer works well as a dimmer using a bright, water clear red, LED. I shrouded the LED in a piece of heatshrink, and then just trimmed the top off. This helps focus the beam straight ahead, reducing any side lighting. I can go from fairly dim, to full brightness within the 500k range. I just need to be careful not to go too far, or else I'll burn out the LED. I could alway use a limiting resistor here as backup, but in the end, once I figure out what works, I'll hardwire the proper resistors in.

The idea of using a credit card is excellent, apart from the fact that it may perhaps contribute in lowering one debt load at the same time  . In this case, I think I'll sneak one out of the wifey-poo's purse  . Seriously though, you gave me a perfect use for those big-box store gift cards I get at X-mas. Thanks again. I completely get your procedure on marking the ends of travel, and then the arc. Makes great sense. With a little time and trimming, it shouldn't be too hard to get into the sweet spot. As for securing the LED/LDR, you could use this;
http://canada.newark.com/multicomp/led-2f/led-holder-right-angle/dp/97K2851 , or
(if the board permits) one could drill a small hole between the legs, just behind the LED/LDR. Then using a small hot glue gun, quickly shoot a bit of glue into the hole, and then draw out to cover the legs. Once it cools, the glue would secure the legs, being anchored by the blob of glue on the other side of the hole. I normally use hot glue to secure my IC's, and trannies (always socketed), and I've never had a problem. Besides, being very secure, it's also fairly easy to remove if need be.

Sidebar, if you need any RC4136 chips for a Vocalizer build, let me know. I could shoot some over to you in exchage for the board. I have a few I could give away for a good cause  .

Cheers,
Dino

[Ronan]

All good thinking Dino, and good ideas, I think you've got this one worked out. I'll post up some resistance tables in a week or so (going to make another card for more data), and I'll let you know when I have some PCB's ready. The PCB has the provision for a tranny, trimpot and limiting resistor for the LED's, or you can hardwire whatever you want in there, just jumper the holes with wires or standup resistors. I'm thinking of putting in some extra pads connected to the LDR's to allow the soldering in of temporary wires that would be hooked up to a DMM to measure the LDR's resistance during the "cutting of the card" stage. It would make setting up a lot easier. Then take out the wires when done.

[Ronan]

Some files to help build a PCB. If anyone wants pdf's or gerbers send me a pm. Gerbers are unverified, have sent them to seeedstudio today, will know soon if they are OK.





I put in 2 test points TP1 and TP2 and an extra gnd to measure the LDRs' resistance when setting it up.
Edit: the files are supposed to be thumbnails but its all gone tits up

[digi2t]

Very nice work Ian. I would try my hand at a drop in vero version, but I've got the Foxx Guitar Synth on my bench now. Maybe one day.

[Ronan]

No need for a vero Dino, I'm getting 10 PCB's made, I'll send you one when they arrive, hopefully in about 3 weeks. I'll pm you for your address once I have them in hand. I'll have just a few spare PCBs left over if anyone else is interested (at cost plus shipping, they cost $3.40 each), assuming they turn out OK that is.

[pinkjimiphoton]

hey bro, i'd love a board, too if one's available. hopefully soon i'll have a couple bucks!!

[Ronan]

No prob Jimi, consider it done

[pinkjimiphoton]

thanks bro, is paypal ok?

[Ronan]

yeah, paypal is fine. If I can send the PCB as a letter (less than 5mm/0.2" thick), which I think I can, the postage would be $5 or $7 depending on weight.

[Ronan]

PCB's turned up in the mail, they look good at this stage, maybe I'll get one built this weekend...

[Ronan]

The PCB's are verified, work fine! Dino and Jimi your PCB's will be in the mail Monday.

I made up a new card by cutting the existing black card into a V-shape and attaching some white cardboard onto it with masking tape.



A pic of using a thin shaft phillips screwdriver to remove the screw that holds the card into the treadle.



Remove the screw with tweezers, then lift the card off the locating pegs and slide it out the bottom of the pedal. You will definitely need tweezers to replace the card and the screw.



This shows the 3 test point wires attached (the untidy green wires around the IC) to TP1, TP2 and ground.



Meters connected to the test point wires to check the resistance of the LDR's at toe down, center, and heel down.



Aim for 1K resistance with the treadle at center for the TP1 connection, and around
6K to 8K at toe down and heel down. For TP2, you want around 1K at toe down and around 8K at heel down. The values are not critical, anywhere within a stone's throw seems to work fine. If you cut too much out of the card, and the LDR resistance gets too low, just patch it up with some miniature masking tape "bandaids".

In case you are wondering, I had no 10K pot on hand, so I put a switch in for distortion vs clean and put a 10K resistor under the PCB to simulate the pot resistance. If you like using sockets to try different components, put sockets in for the 1n8 and 6n8 capacitors, ceramic vs poly, and slightly different values could be tried. The schematic calls for 5% tolerance, many of my ceramics are nowhere near meeting this tolerance, so I tried to pick and match using one of my meters.

Once again I'm very happy with the sound of this one, it sounds very similar to the clip of the one I posted earlier in this thread.

[digi2t]

Ian.... you rock man!

You OWN this baby dude! Big fat THANKS ahead of time for the boards.

Now if only my 220K resistors would freakin' get here, so I can box the Muttroxx, and verify it once and for all  . I did find the perfect wah casing for it though. I'm really stoked about it....



Lots of room for the all the switches, knobs, lights, effects loop jacks... and my size 11 foot, with room to spare . Maybe I'll stick wheels and a hitch on this sucker as well.

[DavenPaget]

Ian.... you rock man!

You OWN this baby dude! Big fat THANKS ahead of time for the boards.

Now if only my 220K resistors would freakin' get here, so I can box the Muttroxx, and verify it once and for all  . I did find the perfect wah casing for it though. I'm really stoked about it....



Lots of room for the all the switches, knobs, lights, effects loop jacks... and my size 11 foot, with room to spare . Maybe I'll stick wheels and a hitch on this sucker as well.

HOLY $!@# Where did you find it ? IT'S AWESOME ! You could squeeze a Noise gate , distortion , wah and probably lots more .

[digi2t]

I came across one on Ebay, just scouting for a cheap wah case. What was really bugging me was that a Crybaby case would have required an additional box attached for the extra bells and whistles of the Muttroxx. Then... I fell upon this sucker, but not the same one. There was an auction, but I lost out on it, so I did a quick search. Lo and behold, I found another one BIN... cheaper than what the other one went for! Let me tell you, I snapped it up at light speed!

If this thing is as big as it looks, I might even be able to fit the Ludwig Phase II clone inside  . I'm already looking for another one.

Research pays my friends.... research pays most handsomely 

[pinkjimiphoton]

Hi all,

Just thinking out loud here. I came across this dual pot on EBay; http://www.ebay.ca/itm/NOBLE-100K-DUAL-LINEAR-POT-LOUDNESS-TAPPING-/150557282743?pt=LH_DefaultDomain_0&hash=item230de9d1b7

It's a dual 100K, with a center tap. By using resistors to fake the 11K and 7K required by the EH Talking Pedal, would this puppy work? The tap for the 11K is there. What do you think? I know an LDR work around exists, but this is ultimately simpler.

Well, I'm picking up 2, and I'm going to breadboard this question this winter. Even if it doesn't work, they might come in handy for something. Not everyday you see tapped duallys like this.

Any thoughts?

hey dino,
i just discovered tadio shack sells dual ganged 100k pots with a tap...the tap is 15k, and is on each pot.
do you think that would work? should be able to make it think it's a smaller pot, right?

[digi2t]

I already tried the center tap pot idea, but it went down like a shot up kamikaze.

I'm going the LDR route. Lot easier.