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[Spann]

Hey guys...

So, I finally managed to finish my first project, a voice changer megaphone (Blogged in the link below). However, I have another board for one upstairs that I would like to build a feedback loop into - do you think it would be as simple as sticking a toggle across the speaker output and the input?

I'm going to be blogging my misadventures here as well:

http://www.electronictorturecommittee.blogspot.com

[crossedout]

hey i'm not sure if you're still working on this project since this post was so long ago but here is pete from casperelectronics schematics for that same megaphone i believe.

he incorporates input, output, feedback loop, pitch (works with feedback) and pitch body contacts.

he also has a wet/dry mod for volume and a schematic for volume increase.

http://casperelectronics.com/finished-pieces/megaphone/cm2/cm2-bending/

hope this helps!

[Spann]

Hey,

I've seen that schematic, but it's actually a different unit to the one I've got. Rather than having the four switches, mine's onl got one three way one.

I'm actually working on another one which I'll hopefully finish in the morning with a 555 input and some other jazz.

I've seen a few different board for these things, and they all seem to be very slightly different - That wet/dry mod does look tasty though.

[adamduke]

Mine is different still...5 switches..seems to be the only type i can find up here in the great white north.  They're all over.. PCB is a small narrow stick like a piece of juicyfruit with a black blob IC.
I added a few bends, changed the mic input for a 1/4" and put it in a box. 

I was trying to figure out a panning knob with the stereo output, but the concept seems lost to me (yet it feels somehow like it should be dirt simple?).  I ended up putting a left & right channel volume control so I can fake it..with two hands unfortunately. 



this was the original version I first made - there are five small silver plastic switches on the opposing side

[Gordonjcp]

Pan pots are simple enough really - wire two 3k3 resistors to the mono output.  Connect the "free" ends of the resistors to the outer terminals of a 10k linear pot, and connect the wiper of the pot to ground.  Now build two buffer amplifiers to isolate the output from the panpot - it's fairly high impedance so the stereo image will be affected by loading from whatever you've plugged it into.  If you're going straight into a high-Z mixer or effects unit input you might get away without the buffers.

How does it work?  Well, with the pot in the middle the signal is effectively passed through two RC dividers giving about  0.7x attenuation.  With the pot at one end, that side is effectively grounded and the other has rather less attenuation.  Draw the circuit out as fixed resistors and apply Ohm's Law if you're interested.

[Spann]

Should anyone be interested, here's what I managed with my second 'phone:

http://www.circuitbenders.co.uk/forum/index.php/topic,1526.0.html

[adamduke]

Nice, Spann - drums through these toys sound excellent!  Hats & snares especially!

thanks for that breakdown, Gordonjcp - I will try this out in short order 

[Ciderfeks]

Hey Adam - what bends did you find on that megaphone? I was working on that very model myself the other day but I fear I may have fried it... They seem kinda fragile. 

[adamduke]

they do seem a little bit fragile sometimes..

I added the standard issue voltage starve, plus I found two bend points that offer different modulations + screaming tones - these can also play over top of the usual microphone use with effects.

here's my soundcloud clips:

http://soundcloud.com/adamduke/bent_rotawk-sample-b

http://soundcloud.com/adamduke/bent_rotawk-sample-c


..if I can read my notes right, the two bends are
a) most bottom left solder joint & most bottom right solder joint
b) 2nd down top left & bottom right again

don't think I have a photo hanging around of the board, sorry.

[Ciderfeks]

Hey nice one cheers for that - didn't think of trying a voltage drop. I'd found a pretty extreme pitch bend before my unit died which I think was on the first of those little components to the right of the black blob - there's a row of five of them (still not very good at identifying surface mount stuff but i guess its a resistor). I was also getting some interesting stuff with a 555 LFO on some of the points but it was whilst doing that that the thing gave up on me.

I'm hoping that maybe I've just blown a replaceable part rather than the blob itself, we'll see.

Some of those tones on your samples are great!

[jamiewoody]

looks cool! i wonder if this is similar to the veleman robot voice changer kit!