oolfur

wow elmo! thats incredible info, thank you SO much!!! now i have a weekend project....

dear list, i have just finished making a touch sensitive keyboard for my electromagnetic instrument, where each of the touch nodes output 5v logic as you touch them. i need these signals to be sent to another module through a cable, to turn things on/off - so rather than using a bulky 30 wire cable to get the control signals where i need them, i thought the 4067 multiplex breakout from sparkfun might come handy :: https://www.sparkfun.com/products/9056 i understand this mux chip can also serve as a demultiplexer, however i dont quite understand how to pack the button states into a single datastream on the keyboard side, and how to unpack them on the other. would i be able to use another 4067 chip in reverse? or do i need an arduino to scan through the inputs at high speeds? here is a diagram of what i need to do: any thoughts would be greatly appreciated!! thank you so much all the best, -úlfur

very cool article... many thanks. since i want to sum, and not mix - are the pots necessary? could i do something like this? thank you so much for the info, im going print it out for future reference!

hey again, i have fixed all switching issues thanks to your help! now i have run into another problem however, and i thought i'd ask the forum and see if anyone has any experience with this sort of thing. so - as previously demonstrated - one of the main features of the instrument will allow you to route any type of audio signal into each and every string. now - for the signal output, i need to sum together all of the 26 strings to a single output. before i buy opamps in bulk - id like to ask the forum about noise accumulation and gainstaging. can i safely sum together 26 pickup coils using TL07x's like this? one opamp on each and every coil operating at unity gain, then all fed into a single unity gain TL071 through 10k resistors... does that make sense? im also wondering if i should sum the coil signals before or after the pre-amp stages... any thoughts would be greatly appreciated!! thanks again, úlfur

thank you - that means a lot - i've put a lot of work into it. to control the switches i am using optocouplers with capacitive touch switch IC's from pcbgadgets.com. the whole electrical interface will be a touch "keyboard" made with copper inlay on the walnut soundboard. there will be superbright LED's just beneath the surface of the walnut, so each note or setting will be indicated as on/off, with glowing amber light coming through the woodgrain. today i will hopefully be sending the last protoboard to the PCB lab, and if it works flawlessly, i will draw the 25 channel PCB's by the end of the week. im planning on having the instruments completed this summer. will keep you posted, and thank you so much for all your help! -úlfur

hmm... and logic 0 (0v) at the input will translate as logic 1 (+5) also? that would be perfect!

A level translator needn't be complicated. This is about as simple as it gets: DC offset won't affect the audio signal as such. As far as the audio signal is concerned it is merely shifted up. Instead of going positive and negative around 0V it will now go "more positive" and "less postive" around a point midway between the two extremes. You will have to remove the offset after you've shifted it before passing the signal on to other processing stages. A series blocking capacitor on the output of the last shifted stage is the simplest way to do it. The value of this cap may have an impact on the signal and is dependent on the impedance of the surrounding circuitry, so leave room for experimentation. Dedicated switching ICs exist, but theyre not easy to come by and usually expensive as well. Don't forget that relays are used all the time for channel switching in guitar amps, mixers and the like, where small signals need to be handled gently to avoid excess noise. Simple techniques exist to minimise switching noise from relays and mechanical switches. thank you for this - this transistor circuit makes it a lot easier for me to deal with the 4066 - i have a lot of transistors laying around. your schematic kinda looks like a transistor "not" gate, - so im wondering.... since im already using a 4049 hex inverter, could i simply supply the inverter with +-5v to get similar results? your help is greatly appreciated! thank you so much!!

curtisa, thank you! that link is very insightful, probably the most helpful reading i have found so far on CMOS audio switching... it looks like the DC offset method would be easiest at this point, not sure how to implement a level translator that swings to negative... how will the offset affect the audio signal output of the CMOS? the reason why im not using relays is im worried about audible clicks - since this will be a high end musical instrument... this is only one of 25 channels that need similar switching. maybe there is a super silent relay IC out there somewhere - do you have any ideas? nope - from there it goes to a VCA, and then to a power amplifier that drives the actuators. it's gonna be hot & heavy! thank you so much for your help, now i'll go back to the lab and experiment...! all the best, úlfur

hey again, for reference, see the two older threads :: so - the design of the new electromagnetic harp has come a long way since my last post - i am almost ready to send PCB drawings to the production plant to finish the first 4 instruments ! one of the new features im super excited about allows you to pass any audio signal through the strings. here is Chet Baker being played through only ONE string! imagine what it will sound like when I hook up the remaining 25 coils…!! https://soundcloud.com/ulfurh/one-string-chet-baker anyway - i have a few problems i'm trying to solve during the weekend, and i thought you guys might be of help so, the first stage of the circuit is a simple guitar preamp / phase flipping circuit that allows me to: • amplify a signal from a single-string pickup (its around 2.5kohms) • flip the phase of the signal using a single switch • bypass the signal from the output, or rather cutting it off using a single switch the reason why i want to be able to flip the phase is that switching between the two different phases makes the string in question settle on a different harmonic (it's just like the two different "harmonic modes" on commercial ebows...) here is my design; (first switch to the right flips the phase, second is the bypass switch) the circuit works great when i do the switching manually with physical spdt switches, however i need to be able to do the switching electronically - preferably using the quad CMOS 4066 switch and the 4049 HEX inverter (so that by default, the switches are ON). so my problem is that if i power the 4066 with a single ended supply (let's say, 0 - 15v) it wont pass any negative voltages through the switches, and effectively clips the negative swing of the input signal off. it sounds pretty nasty, and looks like this on the oscilloscope. appearantly the 4066 can handle dual ended power supplies(let's say -5 to +5), and then it will pass the signal unaltered(no clipping) - but my understanding is that this also means the incoming logic signal has to be pulled to the VSS (-5v) to turn the switches off. so a 0v logic signal will still be seen as "high"... right? i think thats what the datasheet says... 4066 datasheet is here::http://www.ti.com/lit/ds/symlink/cd4066b.pdf maybe all i need is a capacitor between the signal and CMOS, im not sure... there seems to be a plethora of circuits online that use the 4066 in a single ended configuration to switch audio with no problems at all... maybe i can configure the 4049 inverter to swing the logic signal to negative, even though the input logic still is 0v - 5v? maybe you have better ideas on how to approach this? any thoughts on this would be greatly appreciated! thank you ever so much for your input, -úlfur

well, i am mainly focusing on writing music - but i got a generous grant a few weeks ago to further develop my electromagnetic harp. its all open source, and as soon as i have version 1 up and running i will start putting together a neat website for DIYers. what im most excited about these days is finalizing the "string reverb" feature of the new instrument - it involves routing any kind of audio signal directly through the strings via electro-magnetism resulting in a beautiful acoustic sound effect. this could be a great addition to studios armed with plate and spring reverbs... here is an early demonstration of Jónsi's vocals (of sigur rós) actuating the strings of my acoustic guitar :: https://soundcloud.com/ulfurh/vocals-through-kassagitar/s-XNTkY (its a secret soundcloud link, you have to copy paste!) there are more pictures and soundbytes on my website if you are interested, http://ulfurhansson.com thanks for your tips on sitar bridges! maybe distorting the signal being fed through the strings might result in a similar "raspy" "zingy" tone...

yes! what a great idea! a sitar bridge.... any thoughts on a on/off system for sitar bridges? does anything like that exist?

i know this might not be the right place on this forum to post this, but it does touch on the future of electronics in music, and how they might actuate vibrations in a very different way than speakers do. enjoy! more info on my instrument can be found at ulfurhansson.com all the best, úlfur

a simple rectifier or another type of fuzzy harmonic distortion would be a nice option on the preamplifier, to play with different waveshapes driving the strings. the octavia clone seems a little heavy and complex to make 16x... any ideas for an approach on this? also - here is an idea that you might find interesting - i haven't been happy with the acoustic sound levels of previous systems i have made. the best i have so far is very subtle, and im hoping i could at least reach the sound levels of say, an acoustic guitar. as i am getting sleepier while sketching up ideas, i thought maybe physically driving the string bridges would further induce responsiveness through the magnetic actuation coils. does that make sense? then i would have a driver (kinda like a buttkicker) under the bridges, physically vibrating the strings (the sustainiac model c principle). it would be something like this :: string - pickup - preamp - LM1876 output A - driver coil on said string output B - buttkicker under bridge maybe this approach would lead to the buttkicker taking over the nice weird characteristics of the magnetic feedback. any thoughts on this?

at this stage, im actually thinking of running as many as 16x lm386 to preamplify 16 pickups... what is the most economic way of preamplifying a guitar pickup signal? is the LM386 definitely the best way to go? thanks for your interest in this!! i hope the outcome will rock your socks off... (p.s as i am prototyping the LM1876 - and they are quite pricy - will they be destroyed if i run them without any load from time to time? or is that only the case with tube amps?)

hey thanks guys!!! happy to have found this place... @ cycfi i have been reading your webpage all morning! its awesome, never heard of hexaphonic pickups before... sounds like something i should consider for my new instrument. my drivers and pickups are handwoven with a disassembled drill/bobbin. the drivers are NOT "e-core" shaped, since this design seemed to work better with neo-dymium mags on the front. here are some pics :: maybe the elongated design is not optimal, i will have to make further experiments - it seems like some of you guys have A LOT more experience in winding drivers than me... please share your insight if you like! here they are on a grand piano, smaller ones are 220 ohm pickups, longer ones are 8 ohm drivers, clad in some red shrink tubes. later i decided to make the pickups humbucker style, they work even better. - so, since im not that smart in the diy amp department - whats a class D amp?