The GUITRUMPOPHONE!

[Ben79]

At the weekend I thought I'd spend some time playing about with Tim Escobedo's Bronx Cheer on breadboard. After some tweaks I ended up with something that sounded nice and brassy, something like a trumpet, and something brash and sax-like with a Green Ringer after it. So I shall be building it and the Green Ringer into a pedal and calling it the Guitrumpophone .

Here's the Bronx Cheer...


Here's my schem...unverified as I still have the circuit on breadboard


And here's a demo...



Doesn't seem to work - here's the link https://soundcloud.com/momsazombie/guitrumpaphone-demo

[gnomethrone]

sounds so good man!
what kind of enclosure you gonna throw it in?

[Ben79]

Yeah, I'm digging it. It's the kind of fuzz sound I've been after, something somewhere between a mild ring mod and an auto filter and a gnarly fuzz.

I'll wait and see what comes up to put it in. Might do something with a momentary to bring in or out the octaviness.

The weird chassis connection came about when i discovered that if I touched that part of the circuit the sound got more fuzzy and interesting with this odd ring mod effect that gave it that trumpety gurgle. I wondered if just the enclosure would have a similar effect to my hand so I tried it and it worked, then for some reason I wondered if a cap between that and the circuit ground would make it better and it did. I have no idea what I'm doing really but I was stoked to have made something I like. Would be interested to hear from the savvy guys what this circuit is doing that yields the ring moddy texture.

[eatyourguitar]

is the chassis connected to only one node and one node only? battery power isolated? jacks plastic? presumably there is some RF getting in through the chassis. diodes do some weird shit with RF. I have had pedals on the breadboard with 2N2222 and 1N4148. a well (poorly?) placed diode will leak more at RF than at guitar level. it is strange. I don't know if that is due to the diodes having low resistance or maybe they build up static with very high impedance until Vf is reached?

thought experiment, maybe these schematics will jump start the conversation? so many things go through my mind. when radio and audio interfere there is something called heterodyning that can create an artifact of audible sidebands. diodes are boring but everything being non-ideal will have inductance, capacitance, and resistance. thats all we need to make the diode do something. my theory is that anything in the very very small capacitance (chassis?) 5pf range will tune radio bands through the diode. 5pf is useless for guitar but perfect for radio.

[Ben79]

Yeah the chassis is connected to that node only. The plastic jack socket grounds are connected to each other, the circuit grounds and the negative battery terminal.

Was chatting to Crochambeau about this who enlightened me to the fact that the enclosure is working, as you say, as an aerial. This makes me wonder how sensitive the circuit will be to other enclosures or whether it might even be picking up something peculiar to the environment I have it in - my bedroom and that's what's giving it this nice layer of modulation. I obviously need to build one into a pedal and see what it does. I've always been intrigued by the idea of taking what's out there in the airwaves and doing something with it to a guitar signal so maybe I can run with this some more but for now I want to make a batch of these.... it will be interesting to see how repeatable it is.

[eatyourguitar]

a simple test is to RC low pass the input and the output at 20KHz. put 1M input pulldown. remove the 22nf, and remove the chassis connection. ground the chassis. see what you get, switch the RC low pass in and out on a DPDT. put a resistor in series to the 22n cap maybe 1K to 10K. I think 10n might work better, the demos is a bit dark. then after all those variables are sorted, try moving the chassis connection back to where it was by the diode. also try a resistor there in series to the chassis. start with 100R and work your way up or down. a switch can jumper the chassis resistor so you can play it around in different locations and check if it is an antenna.