Neutron Physical Guitar Synth.

other projects

2010-01-17T01:34:00.001-05:00

I have made a new blog here for other projects such as analog2CV that works through AC coupled D/A converters and whatever else i feel like. it is Neutron-synth

Signal electronics are working!

2010-01-10T23:19:00.001-05:00

I have tested all the parts together and they are working.
I only have one coil untill i settle on the exact configuration i need, but i have tested it on each string and amplifier channel.

I have tried a few different coils including hand wound electromagnets, relays, speaker coils, buzzer and bell coils. so far the bell coil works the best, it is 3 ohms and does not get too hot as long as you do not send it a full level signal for too long (that would never happen) and it imparts the attack of the sound in to the string which is the most important thing.

Unfortunately i dont think you can get these old electromechanical bells anymore.

also the pickup works and i can get the signal in to scope through the fostex VC-8

This is really good progress, and i actually got to hear some sounds :D (i just sent synth pulses from "miniscope" to the string, but it sounded cool. will record some soon.), it is looking good!

Next up will be to create a scope drvice which runs on the Pulsar DSP card. this will do all the hard work generating envelopes and processing the signal to be fed back to the strings

The MIDI part will be done after that. For now i will just use a MIDI keyboard to emulate the guitar keys.

RCA adapter.

2009-12-27T15:20:00.003-05:00

I am using this fostex VC8 as an analog /digital converter and ADAT TX/RX from the Scope card which will do the DSP processing.

I had a few choices.

run it "as is" outside the case with lots more wires all over the place.
Run it in the case with 12 seperate RCA plugs and their wires taking up space inside the case and making a mess.
In the case, Desolder the RCA adapters and run wires directly from the board,
In the case, Make an adapter so i can have only 2 ribbon cables running to the RCA jacks.and the VC8 is untouched so i could use it again.

I chose 4. it is just some 1/8 copper rod cut to length and soldered to the board. It worked out surprisingly well!

Amplifier carrier and Power supply

2009-12-26T23:43:00.001-05:00

Just finished putting this together!
It is a carrier for the amplifiers, and they are easilly swapped out if i happen to blow one (which could happen when testing the string driver coils)

I just need to drill the heatsink and bolt on the chipamps with some nylon screws and mica washers. Each amp has been tested seperately and the circuit of the carrier board has been chacked for shorts and open circuits.

With this i can have neat cabling instead of a mess of in and output wires all over the place.

The board was made with the toner transfer system and is about as big as i ever would want to do again. some places the toner did not stick, and i had to draw the traces in with a sharpie, pretty low tech but it worked.

The heatsink is from heatsinkUSA.com which is a great source for DIYers. i have also used it for my little home theater box here. on [H]ardforums

Input Board

2009-12-05T19:29:00.004-05:00

This is the input board, It has taken me a while to get all the things together which i needed to produce boards

I am using the "Pulsar PCB in a box" which is basically toner transfer from a laser printer, then transferred to the board using a laminator.

It has worked quite well, a couple of traces had to be repaired with a sharpie, but that worked fine.

First the board was designed on the computer.

then printed on special paper

the special paper and the board are run together through the laminator

then another stage with some green foil, which i also forgot to take a picture of.

Then the board was etched with ferric chloride.

The board is translucent white! it looks nice.

Holes were drilled on a Taig Mini lathe

And finally the parts were soldered in.

The LEDs were scavenged from a dead linksys router (for some reason LEDs in a bit of plastic cost almost 10 times as much as LEDs not in a bit of plastic)

All this board does is take the connections from the 13 pin guitar signal and MIDI in and route it to headers. the LEDs for the 13 pin will indicate the positive and negative power supply is working. the LED by the MIDI input is just a MIDI activity indicator.

The power for the 13 pin is needed because the Roland one i am using (and most other hex pickups as far as i know) has the preamp built right in , this power is usually provided by VG99 or whatever you are using the 13 pin system with.

Testing the FSR and spring

2009-11-07T21:18:00.000-05:00

Here is a quick single key for testing.I will try various spring strength and positions for the FSR(force sensitive resistor) to see which gives the widest response.

I will also use this one to test the optical sensors used for keypress and velocity measurement.

So far it is giving about a 2 to 1 response with a fairly weak spring from a bike brake lever.
the wider the response the better, it is more likely i can use the FSR directly with the arduino rather than having to use external circuitry.

It should be ok with 1.25 volts range which would give me 8 bits of resolution out of the 10 bits on the arduino input.

I have completely changed the design of the key since i made that one and the rendering. both parts rotate around the same pivot point. it makes it easier to allign the optical sensors, and makes it more low profile.( it has to fit inside a guitar body.)

Case Modding

2009-10-17T21:16:00.000-04:00

Well i managed to get the PC part in to a case now.
I bought a 2u rack mount box from ebay (very reasonable and quite nicely made)
The rear panel is from an old Pentium 3 server case. it took a bit of hacking up to make it fit properly.

Still some work to do, a front panel power switch and connect the power cord from the brick to the receptacle on the back.

There is quite a bit of space there, maybe enough for a mic preamp and a power amplifier.

But i dont need it for the project that is for another day.

New PSU for computer, measured wattege.

2009-10-13T21:09:00.001-04:00

I got a DC-DC converter and power brick for the mini ITX.mini box now the only fan is the intel CPU fan which runs very slowly and barely makes a noise.(you have to put your ear next to it and only if no other computers are on) i have run it 24 hours without any sign of a problem.

The Total maximum power consumption under load gets barely over 60 Watts.
When running the Pulsar card DSP almost fully loaded and a few meters on the display moving. the total power (meassured with kill-a-watt at the plug) is 36 Watts.
(thats for the motherboard, CPU, PSU inneficiency, Pulsar card, and SSD) not bad! i will be happy to run this in a case with no external fan, just the CPU fan and the ventilation holes that are in the case.

The computer will live in one of these.
Inexpensive Antek DIY Project cases
The analog parts will go on the matching 1U case.

its been a while

2009-10-11T23:38:00.003-04:00

I am waiting for a few bits i need to make a key and pressure work, meanwhile programming the new arduino mega. nothing very interesting to show a picture of though.

Layout changes.

2009-09-21T22:14:00.001-04:00

I have made some changes To the layout.
The main reason behind this is because i was worried about having the amplifier power supply coming over a cable, If one rail was to become disconnected or short it is possible all the amplifiers could blow, or at least all stop working at the same time.

This way, if there is a bad connection it is between a speaker output and a "speaker" (the string drivers are not much different from a speaker, basically a coil.) and the amplifier chips have short circuit and open circuit protection. even if one blows, it is relatively easy to change a single one out rather than the whole lot of them.

The disadvantage is that there are now 3 cables, the speakon, the roland GK, and MIDI. before it was just MIDI and 2 nice light ADAT optical cables.also i dont think the speakon is really very optimal for real stage use because the guitar will be firmly attached to the controller box. However I doubt that *I* would ever be going on stage with this contraption!.

An advantage, though is that i do not have to cram so much stuff in the guitar, and the guitar will be lighter.

In other news, 3 of the amplifiers are completed and tested. (and the amplifier power supply) they worked right away, the boards are quite easy to build up.

For the power supply i found a nice torroidal transformer inside some horrible slimline "home theater in a box" which someone had thrown out.It has 13-0-13 secondaries which after rectification give +-17.5 volts.which is very nice for these amplifiers. they can produce 15 watts from that.

Also i found a server case which is almost suitable. It is aluminum, but way too long, i will have to do some modifications. mainly to make the hole on the correct place for the riser card, shorten the case to about half its length, and make a front panel..

How do i put this in laymans terms now? well i cant :D sorry hack a day internet sensation guidelines!

Key sensor circuit board

2009-09-20T01:40:00.002-04:00

I have been working on the circuit board for the key sensors.
Iam using "expresspcb" I do not know if i will use their service yet, but probably will due to lazyness :)

For the mechanical part of the keys i plan to build 1 key myself till it is right, then have the set laser or water cut.

Dont know about electronics? check out "hack a day" or "instructables" to see what people have done. Electronics has never been easier than it is now.

Key Assembly

2009-09-18T16:38:00.004-04:00

Here is a rendering of the keys, you can see where the circuitboard holds all the optical and pressure sensors on one plane, which makes it easier to build.

The first optical sensor detects when a key has been pressed, and the second on is for measuring the velocity. the key then "bottoms out" on the first part of the stroke so you can feel it. you can then press down further to get "poly aftertouch" from the Force sensitive resistors under the main spring. It is not going to output "poly aftertouch" though each will be assigned a different MIDI CC, since it will be playing a custom DSP circuit it makes it more versatile, (each key could control something for that string, or all strings).

anyways, the main thing about this is that you can press the key through another 25mm or so after a note is played, so you can feel by the position what is going on, it is really hard to judge what you are doing with synth keyboard type aftertouch where you press down and do not really feel anything.

It will also be able to generate "pushes" on the string depending on how fast you are moving the key up or down, this will (hopefully) allow a controlled bowing of the string like a violin or other bowed instrument.

For people who dont know what this is all about. this is a "keyboard" but each key will "pluck" a guitar string electronically after you press a key there is additional movement to control the sound.

New Pulsar card. other stuff.

2009-09-18T13:54:00.001-04:00

Thanks to a kind PlanetZ member "Capacitor" I have now got another pulsar card. it was free! he said it was karma for things i have done for the scope community at PlanetZ
And because my card was dead, soniccore also tranfered the keys for free as well.
This one appears to work well, and i will be doing tests this weekend.

I have received some LM1875 circuit boards from Chipamp.com for the string driver amplifiers. they were very generous, I ordered 4 sets of 2 amplifiers + power supply board and ended up getting 10 sets!

The electronics components i was missing for the amplifiers also arrived building the amplifiers has started.

The little switches i had been using are no longer being considered. Each key will consist of 2 opto interrupters and a pressure sensitive resistor for "poly aftertouch" and a bit of mechanical work. (3d model coming soon)

This means i can no longer use the Arduino2009 because it does not have enough inputs, so i have ordered an Arduino "mega" it has a lot more I/O.

Sacrificial Squier.

2009-09-08T18:36:00.004-04:00

I have made a test bed for the string drivers. mostly it used to be a rather bad Squier guitar. funny thing is i could actually correct most of the problems it had with washers on the piece holding the bridge now.

A squier is a cheap version of a fender stratocaster guitar. i cut it up to make a testing platform for the instrument.

RIP Pulsar 1

2009-09-07T22:19:00.000-04:00

Looks like this thing is really kaput. fortunately it looks like i can get another one soon.

Second attempt at ITX + pulsar

2009-09-06T00:34:00.005-04:00

Well i got an intel board this time, it is a DG41MJ
And a E7300 CPU. Of course i saw this SSD on special and bought it as well to see what the fuss is all about.

Everything about the board works great, it boots very fast with the SSD.

Now i find out the pulsar board itself has a problem, when scope tries there is an error, no response from DSP1. well crap, I took it out and wiggled the capacitors and tapped on it a few times and it worked once. so i replaced the power capacitors, still no luck. oh well what the hell, i put it in the freezer for a laugh. well now it is working! but i dont know how long for.

I noticed when it was not working that one of the DSP chips was getting quite hot, and now it is working they are all running cool.

Dont worry i will not be using that ugly old PSU, i intend to get this ATX power adapter with a power brick for nice quiet operation. its a bit lower in the list of priorities though.

Here is a little video of how fast the board boots up with the SSD.

Motherboard options.

2009-08-29T23:40:00.000-04:00

I manged to install windows and scope on the VIA motherboard, then it would no longer even get to the windows loading screen.

I think its just the crappy hard drive i had to use, it doesn't support SATA and i really don't want to buy a new non SATA drive, so ill buy a new motherboard and cheap core2 cpu.

If i get a motherboard with intel chipset and a core2 pentium or low end core 2 duo it should work a lot better with the pulsar card.

I am looking at the "intel BOXDG41MJ" . That name just rolls of the tongue and is easy to remember.

The first victim.

2009-08-29T20:28:00.004-04:00

Here is a MINI ITX i am going to try and run scope on (www.soniccore.com)
I go not have great hopes for it because it has a VIA chipset (its an 800mhz c3!)
if it does not work i will get an intel based one. it just has to have 1 pci slot, and a modest CPU.
the CPU is not actually used for much with scope, all the processing takes place on the card itself.

The card is a first generation pulsar. it has 4 Analog Devices Sharc DSP chips on it, which i hope will be enough for what i am trying to do.

a have 3 of their boards in another computer, and the SDK, so i will be doing most of the "guts" of the circuit in DSP.

Arduino is sending MIDI!

2009-08-29T19:34:00.006-04:00

I managed to program the arduino to measure the velocity of the switches and output MIDI. this will be important for the "keys" on the guitar. It was my first arduino project, arduino is really easy to program and use and there are many examples of code all over the place. And helpful people at the arduino forums.

Neutron Physical Guitar Synth project online.

2009-08-29T18:26:00.007-04:00

This is currently an online notepad for my guitar project.

Guitar project is a rather complicated version of a "sustainer" type guitar.
rather similar to the moog guitar, but with a few major differences.
the biggest one being that the strings can not only be plucked in the usual way, but also played with keys.

The feedback amplifiers are much more powerful than simple opamps used in most sustainers.
there is a 20 watt chipamp for each string.

When played by key The feedback amplifiers elecromagnetically inject a velocity controlled "pluck" signal in to the string itself., and then feedback the signal as required. the feedback signal can also be processed with distortion, "scraping" (like a bow) or other effects.

The attack portion of a sound gives it a great deal of the character, so by varying the waveform injected the guitar should be able to generate some different sounds.

This is really hard to explain in laymans terms, what i am trying to achieve is a guitar instrument that can make new sounds, or a synthesiser which uses the guitar strings as the oscillators.