EH Talking Pedal, possible pot?

[digi2t]

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?

[joegagan]

prr has talked about these. (edit, silly speculation removed)

any way , keep us posted on your experiments!  i wanna see.

[digi2t]

No prob Joe. Just ordered 2. Curiousity has got my cat.... AGAIN!!!

[Ronan]

I know an LDR work around exists, but this is ultimately simpler.

Hope that turns out well, with those noble pots. The loudness tap should be a center tap. Definitely worth trying.

Can you give me any links to the "workaround"? Been searching and keeping my eyes open but can only find stray references. I am interested in simulating the correct pots for the talking pedal using LED/LDR's driven by a microcontroller. I can program the small Atmel ones, and they are cheap, and am a bit stumped on how to program a lookup table. The main advantage being the ability to program different "pot" responses, and just swap in the differently-preprogrammed chip to get the best response (in a talking pedal). If I can get this worked out I have no probs sending out preprogrammed chips at cost for others who are interested. Hopefully an 8-pin DIL uC will do the job. I really like the ehx talking pedal, would be good to ressurect it. I've only heard one clip, but it was good.

[digi2t]

@ Ronan, check your PM's, and your email as well.

As for the programmed chip to simulated pots, totally out of my league. I like it. I'm a total noob at this stuff, but always the willing pupil. If it will fit into my 47 year old brain, I'll take it!

You'll see on the EH schem I sent you, that it seems that the center tap is off set. I don't know if that's actually the case, or just a throw off on the drawing. If I compare this to the Vocalizer, I would be tempted to say that it should be centered, vis a vis the way the Vocalizer's pot uses the center of the sweep on one side of the 22K linear.

I'll know more when I do some testing.

[Ronan]

Dino, thanks very much for the info you sent. Another possible option is using a Morley pedal as a base and making a new card to go between the LED/LDR's. I tried this today and can get around 6K sweep each side of a low resistance to ground of about 600 ohms, just using a slit as seen mounted in the pedal in the pic. There could be an issue with the low resistance to ground not being low enough, and also taking up a bit more sweep range than desired during the low resistance portion, because as the slit passes across the face of the LDR, the reistance does not change. I will try to get this breadboarded during the next week or two and see how it goes. I might not have all the parts, if I don't that will slow me down a bit.

I did a bit of a search on formant frequencies, here's some good links:

http://www.helsinki.fi/speechsciences/projects/vowelcharts/
http://videoweb.nie.edu.sg/phonetic/data/jipa-vowels/index.htm
http://videoweb.nie.edu.sg/phonetic/vowels/measurements.html

Very interesting that different countries with their different accents and languages can have the formants in different positions on the F1/F2 graph. It's possible that a person in a European country would tweak their talking pedal differently to a British person, or American person, and I would tweak mine to the Australian lingo

I had a look at some of the old programming I did with microcontrollers, I would need to do some work to get back up to speed, but believe I can get something up and running if required. One issue I remembered later was that a micro would have to be programmed for a specific LED/LDR pair, as there is a lot of variance between individual LED's and LDR's. Another possibility is using the micro to output a pseudo analog voltage (or current) to drive a transistor ala the markusw "workaround" or the Bassballs circuit, where the transistor does the variable resistance function.

Morley pic1

LED setup pic

[digi2t]

Very interesting that different countries with their different accents and languages can have the formants in different positions on the F1/F2 graph. It's possible that a person in a European country would tweak their talking pedal differently to a British person, or American person, and I would tweak mine to the Australian lingo

I guess there would be one common to both Canadian, and Australian then. eh eh eh eh eh 

Keep me posted on how you make out.

Cheers,
Dino

[Scruffie]

Your pot taper is gunna change with such excessive value faking though surely... might work for, might work against.

I've been in correspondance with the guy that converted the EHX Space Drum to the LM13700, he's just built a Talking pedal without the tap and says it works and sounds great, I beleive he has a youtube video up now too.

[digi2t]

I've been in correspondance with the guy that converted the EHX Space Drum to the LM13700, he's just built a Talking pedal without the tap and says it works and sounds great, I beleive he has a youtube video up now too.

If so, would you happen to have a link?

[Ronan]

Today I had some spare time, breadboarded the circuit and connected up the Morley pedal with 2 LED/LDR's.

Ehtpbb4.wav - 1.44MB

[digi2t]

 

OK, it's on the build list. Sounds like the perfect alter ego to my Vocalizer. Great job Ian. I haven't recieved the dual tapped pot yet, but I'll breadboard as well and try it when it comes in.

Excellent clip. Could you give me the lay of the land insofar as the LED's / LDR's are concerned?

[Ronan]

Just heading off to bed Dino, will post some details tomorrow...

[Ronan]

The pedal has 30mm travel at the toe end. Here's a resistance table I measured off this pedal.
TRAVEL/F1/F2
0mm 6K 960R
5mm 2K 830R
10mm 900R 860R
15mm 600R 960R
20mm 690R 1K4
25mm 1K 2k4
30mm 3K 6K

You can see that's a long way from ideal, but gets some interesting results. I need to do some more tweaking, cut up a new card and see what happens. You can modify the existing card, but if you make another one you can always go back to the first card starting point.

The LED's in the Morley (Bad Horsie 1) are both slightly different and are powered from 9V, one with a 6K8 and the other with a 4K7 series resistor. A trimpot to slightly vary the intensity of the LED might be useful for final trimming of the LDR resistance range. I don't think the type of LED/LDR is critical, as long as you can get the LDR down to 1K resistance, in the EH circuit there are 1K series resistors to the pots, which is handy, I left them out, not required with LDR's. Getting a correct response from the LDR's can be a bit fiddly, but not nearly as difficult as I originally imagined. A hobby knife and some patience to cut the card works well. If you cut some part of the window too big you can patch it up with masking tape.

The only changes to the circuit were the cap sizes, I had no 1n8 or 6n8 so used a 1n5/2n2 pair for the F2 filter and 4n7 + 2n2 = 6n9 pairs for F1. 1N914 for the clipping diodes.

[Ronan]

I played around with it some more today. What I like about it most is that instead of just being a couple of vowels like a wah pedal (ooo-aahh), it has several sounds, there is something happening near the toe-down position, another sound in the middle and yet another near the heel-down position. Its just a ton of fun! At this stage its a good bet that it will replace my wah pedal when I get it built. Sounds great set to clean with a favorite distortion pedal in front of it, but the distortion circuit in the pedal itself is quite nice too. Thanks Dino for the inspiration and information to make me give it a try.

[digi2t]

My pleasure Ian. It's just as fun for me, as it is for you.

Well, I had two Crybaby shells left to fill, but I think one is spoken for now. I really don't know much about Morley's, other than the fact that they are optical. So from what I understand, the BH1 has 2 LDR's already in there? If that's the case, maybe I'll just track one down, and save myself some work. If you could post some gut shots of your setup, that would be choice. I think I've listened to your clip around a dozen times now, boy is that pedal ever vocal. Just a bunch of vowels that jump out of that sucker.

As for the caps, don't worry about having to blend caps together to get the right value. It's done stock in the Vocalizer (220pF + 680pF, to get 900pF). But, I did find that ceramic caps sounded sooooo much better here, rather than metals, micas, or polys. Normally, my ears have never picked up a difference in other projects, so I've just stuck to ceramics for size, and cost. In the Vocalizer case, the ceramics give a crisper, cleaner sounding vowel. The other caps sounded kind of dull. Just my impression.

Keep me posted.
Dino

[Ronan]

I'm not sure how I'm going to build this yet, I'm thinking of removing the entire Morley PCB and making a replica of the lower section of the PCB's shape and bolting it to the chassis using the 4 standoffs and nuts like the original. Then use a seperate stomp switch and input/output/DC jacks. The battery compartment can stay and should still be usable. Here's some pics of the setup as it is now.

pic1
pic2
pic3
pic4
pic5
pic6

I won't have time to build for a couple of weeks. In the meantime, I'll get some ceramic caps to try.

[digi2t]

That is just too super cool. Great job Ian. There is a ton of room in those pedals, so I guess the sky's the limit. I only work with vero, but I would follow your mind set, and tailor a vero to fit, and mount the LDR/LED's just as they are there. Then shape some opaque acetate to replace the cardboard.

Thanks for the pics. Let me know if the ceramics make a difference to your ears.

Cheers,
Dino

[Ronan]

Dino, thanks for the heads up on the ceramics, they seem to work fine and are smoother sounding in the filter sections. I was surprised, I bought a heap of them for peanuts.

I've drawn up a pcb and printed it on paper to see if it fits the pedal. Looking good at this stage.



I have some unverified PCB and overlay PDF's but not sure if I can upload them onto this site. Might try to get a prototype PCB done this week. My bro-in-law had a play through the breadboard talking pedal with the Morley footpedal controlling it, he loved it, I'll make him one too, and a spare PCB as well, if all goes well your name will be on it.

[digi2t]

and a spare PCB as well, if all goes well your name will be on it.

wow, thanks man, I don't know what to say. That's really nice. I tried the 100K pot, with the circuit on the breadboard, but it didn't work right. Faking with resistors really doesn't do it. LDR method is the way to go. I'm going to use your method. If there's any way I can repay you for your efforts, let me know, I'll see what I can do.

As for posting projects and info for the forum, contact Aron, and ask him if you can have him open an account for you in the gallery. I have one there, and that's where I store all my projects and info. If you go into the gallery, look for "Dino's Stuff" in the directory, my work to date is there.

Cheers,
Dino

[pinkjimiphoton]

you guys...YOU GUYS...

dammit, another one to add to the list!!!

that sounds great ian!!

but seriously...you guys should try that mouthmeistor dino vero'd up for me...

to me, that's the best of the formant pedals i've built so far...not as good as the ludwig, real close to the korg, and different than the vocalizer..it's nice that you can "tune in" as much formant as you need.

i'll keep watching this thread!