High Tech Electric Guitar. High School Senior Project

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quote: "If its line, wouldn't I be able to run it almosy directly into a tube?"

The problem is cable capacitance and cable triboelectric noise---not the end of the world, but with FETs you can put the part right with the pickups in the same fashion as the cheap electret mics. Run a hot and a ground and have a pullup resistor at your box.

Also I want to add my voice to those urging you to follow your vision on this and not be discouraged. I am sure you are going to do great things and our purpose is just to see that you get some results for this initial effort.

I worked on a astronomical detector system for four years of 60-70+ hour weeks before the system power was ever turned on. When asked how long it would be to completion at any particular point, I was usually only able to see about two weeks of work ahead for the last year or so! I barely kept my job. But when things actually all did get brought up, it only was about a week to debug and my design was vindicated.
 
The thing about piezo transducers is that they really want to see a high impedance, yes, but they also really, really like tubes. Or rather, tubes like them better than FETs do. See, FETs generate a lot more distortion when fed by a high impedance than by a low one, whereas tubes don't. My friend Brad Sarno sells a thing which he calls the Black Box -- basically a 12AU7 buffer, designed to go between a pedal steel guitar and the solid-state amplifier pedal players often like to play through.

Well, one night we tried it on a piezo pickup, and the difference was like night and day. For the first time, the piezo sounded like a real musical instrument rather than like plastic. The player was going into the same (solid-state) guitar amp as before, but interposing Brad's buffer stage between the instrument (which happened to be an oud) and the amp. Several folks, including a completely non-audio-savvy audience member, remarked that when he used the box, it sounded real.

So I recommend sticking with tubes as your input stages, with nice big grid resistors. Not sure you can find a high-quality 1:1 transformer designed to work into 1M or more, but more power to you if you can. I'd try unbalanced 12AU7s first.

Peace,
Paul
 
I think i'm going to stick just with tubes for now, If I have problems then I'll jump to FETs but hopefully the pickups will sound just fine on the 12AU7s.
 
Paul S. is of course right---tubes are essentially constant input capacitance whereas JFETs are showing a significant change with drain-gate voltage (see another thread where that distortion mechanism for bifet opamp followers was discussed---I forget where). Also at low frequencies and very high Z's the leakage current dependency on drain-gate voltage will start to produce additional distortion. Note that the Miller effect also exacerbates the variable Cdg effect, but you can get only a unity contribution by having the drain go to the input of an inverting feedback amp so that the drain voltage doesn't move with the signal.

There are ways to further reduce this effect significantly. In a follower the gate-source capacitance is more-or-less bootstrapped out unless the load gets really heavy. The drain can be bootstrapped to the source as well and again more-or-less eliminate the effect---this requires at least one more transistor. As long as the source capacitance is a good deal larger than the typical C's in the device the tendency to a net negative input impedance and consequent oscillations is avoided.

Samuel, as far as the importance and what constitutes "high", look at the circuit as a whole. If I am concerned abut a 1nF transducer and am seeing a 1pF variation with signal in my FET stage, that would give an indication I'm getting into trouble. I will probably have a d.c. bias R at the gate so its value will begin to limit the effects of the variable C at low frequencies.
 
Hope you guys didn't miss me too much...
anyway I've started getting in some of the parts for this project. today the piezo ghost pickups came. I plugged them into the clean output stages of my guitar amp (a home brew12ax7 6sn7 300b). It sounded wonderful. I didn't even tune the guitar and it was just... astounding. It gave the sound this rich warm reality. It is most comparable to an accustic. Also it sounded just fine into the tubes w/o tranies or anything. more playing to comem and finaly some progress.
I dont know how I lived without these...*

*almost. they are really good at what they do. I havn't yet tried them at other things but i'm looking foreward to it.

and yes, beautifully HEXAPHONIC!
 
I've been thinking, I need to get power from the powersupply to the preamp.
(seperate cases, etc) Anyone have any ideas on doing this? I'm thinking about those heavy duty plugs that push in and spin to lock
here their site is odd and I cant link to the exact page but it is model number 2311
I need to safely connect 2 B+s, 2 heaters and ground
I was thinking of useing 2 of those; one for the 2 B+ voltages, and 1 ground, and the other for the 2 heaters and 1 ground.
any ideas?
 
Not sure if I was linked to where you wanted. Might be worth checking the RS Components catalogue or the Farnell catalogue for a range of connectors. Find the manufacturer code and go from there. Onwards, onwards...... :thumb:
 
I'm trying to find a schematic for an infinite sustain. anyone know of anything?
 
I think you're referring to something like the Fernandez sustainer?
If so, some info about it is on this thread.

http://www.groupdiy.com/index.php?topic=6763

And check the us patent office website (more info in thread).


-mike
 
well, in the mad rush that was ap testing I jumped right into this project. I did finish 99% within the time limit.
the guitar is wired with the hexaphonic pickup, the cabling is done and I built the preamp. It is a handwired 8 channel tube preamp. 6 channels of 12au7 (moded G-9) and 2 12ax7 for the mags (i didn't finish one of those for the demonstration night). I have to say that the hex pickup sounds awsome, just clean and clear and bright. The entire package sounds wonderful. I added 2 indicator tubes em80 (look here) as signal indicators. I couldn't find any good diodes for them so they are just running with an almost streight signal but it is enough to show the presence one easily. I'll post pics or whatever if anyone would like.

Even though the project is 'over' I would still like to keep working on it. I left a lot of room every where for upgrades and additions;
sustainiac
more controls for the mag pickups
computer controls built into the guitar

I havn't been able to setup the midi stuff yet with my time being spent building and sleeping with some microwave dinners in the middle, but hopefully that will come soon too.

thanks to all who helped with ideas and support!
 
Congratulations. You've done something remarkable, and should pat yourself on the back.

Peace,
Paul

P.S. Now that it's done, treat yourself to at least one healthy meal!
 
Thought I'd drop an update on this project just for the fun of it. (its waaaay over due)
Its 99% done. (sucks, i have to finish it one day but things like work keep getting in the way) I finished 7 of the 8 channels. One of the normal pickups isn't wired (the 6 for each string are wired though) Also, at the last minute I added a pair of indicator (nixie) tubes which aren't perfectly wired (i couldn't find good diodes) but still look very cool and do function! The guitar itself is functional and I do play it quite often. I want to lower the strings a little bit, which is hard because of the mods I had to do. I'll try and post some pics in the next few days.
I love the sound of the pickups on this thing, having them directly into the tube preamp just makes this guitar sing!
 
Just read this thread tonight - dude you you are crazy and obviously very very focused, well done. I feel very old and slow right now...

Would love to see pics,

cheers,
Ruairi
 

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