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wmonk
Joined: Sep 15, 2008
Posts: 529
Location: Enschede, the Netherlands
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 Posted: Wed Jun 16, 2010 7:55 am Post subject:
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| jeff-o wrote: |
And don't forget Canada! 
Hey Les, I see a few parts marked "supply dependent" or "choose a value" on the schematic. I used the default values, but how do I go about choosing the right parts in these situations? Got any guidelines (ie. increase for this effect) to help, or am I on my own?
Also, has anyone developed a quick reference to determine which BBD to use to get a certain (stable, noise-free) frequency range? |
I used 3207 and 3208. 3207 gives nice bass guitar sounds, 3208 is lower in frequency.
What I think is that the 3209 will give a nice guitar like range.
R27 and R32 depend on power supply, the standard value is ok for +/- 15V
The filter cap, C7, can be adjusted to get different sounds. I made my cap switchable from 2.2 nF to 15 nF, the latter giving a more bass guitar sound when using with the MN3208.
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Stream Operator
Joined: Oct 13, 2007
Posts: 6221
Location: near Austin, Tx, USA
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| Posted: Wed Jun 16, 2010 9:05 am Post subject:
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Jeff, those are calibrated design values that I have yet to figure out. Good best guess values are labeled on the schematic. For proper tuning the two resistors must be set correctly, and I don't know the exact values. Basically the resistors do voltage to current conversion for the OTAs.
The cap is adjustable to set the sound of the loop. Also larger cap values get rid of that annoying whine that is present on KS7 boards with lower cap values. The whine is due to switching noise of the BBD. I added an extra LPF in the loop, but that may require adjustment also. Basically the design needs more or fancier LPF filtering in the feedback loop to kill the noise. You can double that adjustable cap value since you are looking for a bass guiltar setting.
Sorry but that is the best info I have at this time, will post as I learn more...
Les
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jeff-o
Joined: Jul 19, 2009
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Location: Ontario, Canada
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| Posted: Wed Jun 16, 2010 9:17 am Post subject:
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All excellent info, thanks guys!
The 3209 does indeed give a higher range. I'm looking forward to comparing it to the 3207 and 3208.
Right now I'm running the KS board at +/-9V, supplied by a pair of 9V batteries. Eventually my guitar will be battery-powered so I can avoid using an external +/-15V power supply like the previous version. At least, that's what I'm hoping. If the power draw is too great then I may still need to use an external supply (bleh).
There is indeed some whine when I flip the pots too far to the right. I'll play around with that cap and see if I can eliminate some of that. Ultimately the value I choose will depend on the guitar I make (standard or bass), which will determine which BBDs I use. Maybe I'll make one of each! |
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Stream Operator
Joined: Oct 13, 2007
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Location: near Austin, Tx, USA
Audio files: 267
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| Posted: Wed Jun 16, 2010 7:23 pm Post subject:
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Jeff, although the KS design is a great starting point for your geetar project, it is more complex than you need. It has VCO/VCF LM13700 circuits that are necessary for a modular synthesizer version of the board, but you really don't need all that for your specific project. When you get around to thinking more solidly about your specific project needs, I recommend having a read of the Credit Card Synth thread in the eChucK forum. I'll be working on that in a few months once the KS design stabilizes and gets documented a bit.
Les
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jeff-o
Joined: Jul 19, 2009
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Location: Ontario, Canada
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| Posted: Wed Jun 16, 2010 7:43 pm Post subject:
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No worries! I know the KS11 design is way overkill. However, the VCF and feedback tuning would be nice to keep, as they would allow the musician to "fine tune" the sound of the guitar. Things like string tension and strumming style (finger or pick, for example).
But, that's what I'm experimenting with. What to keep? What isn't needed? Where can I use a single control for all four channels?
Fun times! |
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wmonk
Joined: Sep 15, 2008
Posts: 529
Location: Enschede, the Netherlands
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| Posted: Thu Jun 17, 2010 1:37 am Post subject:
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When you tune the VCOs and VCFs to 1V/Oct, you can build a pot, with wiper to the VCO CV in, and a same thing for the VCF CV in 
And the use the pots of the individual boards for fine tuning the 'strings'
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jeff-o
Joined: Jul 19, 2009
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| Posted: Thu Jun 17, 2010 5:22 am Post subject:
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| wmonk wrote: | When you tune the VCOs and VCFs to 1V/Oct, you can build a pot, with wiper to the VCO CV in, and a same thing for the VCF CV in
And the use the pots of the individual boards for fine tuning the 'strings' |
Well, those questions were sorta rhetorical, but thanks for answering them.
I definitely won't need the expo converter for the VCF, since I won't be changing that dynamically. The CV input to the VCF can probably be a simple pot. I'll still need one VCF per string though, I have a feeling that each one will need a slightly different frequency especially if I need a different BBD for each string.
I will need the expo converter for the VCO, though. The finger position on the fretboard will be connected here, and my sensor is linear. To avoid confusing guitarists who are used to the frets getting closer together as you get closer to the bridge, the expo converter will be needed to correct for that. Then again, I've not learned to actually play guitar yet - could a feature of the laser guitar be that the "frets" are equally spaced?
(As a side note, the laser guitar will play like a fretless guitar...)
I'll have a common stim source for all the strings (either a simple one-shot, or a more complicated noise generator). The length of the stim will be tunable from 1-10ms (ish). With each "pluck" of the laser an analog switch will open for the corresponding KS circuit, delivering that stim.
One thing I want to avoid is overloading the guitar with controls. Sure, I could make every pot for every string available, but it would end up looking like a control knob forest! So, one other decision will be to determine what controls stay internal and adjusted only during serious tuning, and which will be available externally.
One last "killer feature" that I may or may not be able to implement this time around is to replace all the pots with digital potentiometers, allowing the musician to save "presets" to memory. They would simply need to scroll to a certain preset, hit "tune," and all the string tunings, string tension and stim lengths would be automatically set. Shiny. |
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wmonk
Joined: Sep 15, 2008
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| Posted: Thu Jun 17, 2010 7:50 am Post subject:
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| jeff-o wrote: | I will need the expo converter for the VCO, though. The finger position on the fretboard will be connected here, and my sensor is linear. To avoid confusing guitarists who are used to the frets getting closer together as you get closer to the bridge, the expo converter will be needed to correct for that. Then again, I've not learned to actually play guitar yet - could a feature of the laser guitar be that the "frets" are equally spaced?
(As a side note, the laser guitar will play like a fretless guitar...)
I'll have a common stim source for all the strings (either a simple one-shot, or a more complicated noise generator). The length of the stim will be tunable from 1-10ms (ish). With each "pluck" of the laser an analog switch will open for the corresponding KS circuit, delivering that stim.
One thing I want to avoid is overloading the guitar with controls. Sure, I could make every pot for every string available, but it would end up looking like a control knob forest! So, one other decision will be to determine what controls stay internal and adjusted only during serious tuning, and which will be available externally.
One last "killer feature" that I may or may not be able to implement this time around is to replace all the pots with digital potentiometers, allowing the musician to save "presets" to memory. They would simply need to scroll to a certain preset, hit "tune," and all the string tunings, string tension and stim lengths would be automatically set. Shiny. |
Then I would suggest to use trimpots for the VCOs, and tune them, like a guitar, a fourth apart. That would be 0.416 Volts when using 1V/Oct. 
For the spacing on the fretboard, on normal guitars it would be almost "double exponential". No idea how to do it exactly like a real guitar, but what does that matter? With the expo converter it will be playable for everyone
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jeff-o
Joined: Jul 19, 2009
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| Posted: Thu Jun 17, 2010 9:22 am Post subject:
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| wmonk wrote: | Then I would suggest to use trimpots for the VCOs, and tune them, like a guitar, a fourth apart. That would be 0.416 Volts when using 1V/Oct.
For the spacing on the fretboard, on normal guitars it would be almost "double exponential". No idea how to do it exactly like a real guitar, but what does that matter? With the expo converter it will be playable for everyone |
I shall burn that number into my memory.
Double Expo, eh? Also good to know. My goal isn't to exactly replicate a guitar, anyway. Otherwise, what would be the point? Just pick up a real guitar! Hopefully it'll be playable with minimal learning curve for guitarists, while having enough features unique from real guitars that it can stand on its own as a distinct instrument rather than a flashy gimmick.
I missed the mark a little on my first attempt, I'm making amends this time around. |
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Airlock
Joined: Apr 06, 2007
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Location: Calabash, NC USA
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| Posted: Thu Jun 17, 2010 2:00 pm Post subject:
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| jeff-o wrote: | | Then again, I've not learned to actually play guitar yet - could a feature of the laser guitar be that the "frets" are equally spaced? |
 Only if your intent is to make something totally foreign to most guitarists, and/or you want less (or more) notes than a standard scale length provides.
| jeff-o wrote: | | (As a side note, the laser guitar will play like a fretless guitar...) |
Fretless basses are great, guitars maybe not so much. I don't want to be a downer but I don't know how playable a fretless guitar would be. I mangle chords out of wack WITH frets, I can't imagine how far off my intonation would be trying to chord a fretless guitar neck, or even play simple melodies for that matter. You might want to check with some guitarist friends on this project. |
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jeff-o
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| Posted: Thu Jun 17, 2010 2:15 pm Post subject:
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| Airlock wrote: | | jeff-o wrote: | | Then again, I've not learned to actually play guitar yet - could a feature of the laser guitar be that the "frets" are equally spaced? |
Only if your intent is to make something totally foreign to most guitarists, and/or you want less (or more) notes than a standard scale length provides.
| jeff-o wrote: | | (As a side note, the laser guitar will play like a fretless guitar...) |
Fretless basses are great, guitars maybe not so much. I don't want to be a downer but I don't know how playable a fretless guitar would be. I mangle chords out of wack WITH frets, I can't imagine how far off my intonation would be trying to chord a fretless guitar neck, or even play simple melodies for that matter. You might want to check with some guitarist friends on this project. |
OK, "exponential" fret spacing it is, then! I could expand the scale past what a typical guitar is capable of, that's just a tweak of a pot away! But I don't think I'll do that - when you cram too many octaves onto a single string it gets very difficult to play.
I read a bit about fretless guitars. The evangelists say that going fretless is "freeing," though they admit that only some chords will work, and there is definitely a learning curve. Since there aren't any frets, you get close and add a bit of vibrato (?) to compensate for slight misses. At least, that's what I read. Another example, instead of bending strings you simply do a slide.
Would it be weird to take a regular guitar and "tune" it to play like a bass? Would that cause troubles for a bassist to adapt to? |
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Airlock
Joined: Apr 06, 2007
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Location: Calabash, NC USA
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| Posted: Thu Jun 17, 2010 4:03 pm Post subject:
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| jeff-o wrote: |
OK, "exponential" fret spacing it is, then! I could expand the scale past what a typical guitar is capable of, that's just a tweak of a pot away! But I don't think I'll do that - when you cram too many octaves onto a single string it gets very difficult to play.
I read a bit about fretless guitars. The evangelists say that going fretless is "freeing," though they admit that only some chords will work, and there is definitely a learning curve. Since there aren't any frets, you get close and add a bit of vibrato (?) to compensate for slight misses. At least, that's what I read. Another example, instead of bending strings you simply do a slide.
Would it be weird to take a regular guitar and "tune" it to play like a bass? Would that cause troubles for a bassist to adapt to? |
The first 4 strings of a 4 string bass are tuned the same as the first 4 strings of a (typical) guitar tuning except it's lower octaves, so there's no difference in the fingering of a scale and so on, but there -is- a big difference in how one plays a heavy bass string as opposed to a thinner guitar string. I don't know if any of that applies for your intents.
I don't know any fretless guitar "evangelists", but I know TONS of guitarists and I don't think one of them would be interested in a fretless anything. Check out the Novak fret system guitars and basses, been around for years and has its advantages over standard practice but you've probably never seen one anywhere...
I really encourage you to discuss this with a guitarist, you might even want to take a couple of lessons and pump the instructor for info if you don't know anyone who plays. I think a project like yours will really benefit from a little more insight into guitar basics. I wish you luck! |
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jeff-o
Joined: Jul 19, 2009
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| Posted: Thu Jun 17, 2010 4:54 pm Post subject:
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One benefit of laser "strings" is that they take no effort at all to play. Of course the technique is different because you can't feel them!
The "fretless" feature is more of a technical requirement rather than a design choice. I basically have to choose between buttons and membrane potentiometers - and pots win for a few reasons.
I do have a few friends who play guitar, I'll pump them for info as well. But what I really need is a friend who plays guitar AND knows electronics! |
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mosc
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| Posted: Thu Jun 17, 2010 5:36 pm Post subject:
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| jeff-o wrote: | | One benefit of laser "strings" is that they take no effort at all to play. Of course the technique is different because you can't feel them! |
I've never heard of laser strings. Do you have any links that might shed some light on the subject?
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jeff-o
Joined: Jul 19, 2009
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| Posted: Thu Jun 17, 2010 5:58 pm Post subject:
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| mosc wrote: | | jeff-o wrote: | | One benefit of laser "strings" is that they take no effort at all to play. Of course the technique is different because you can't feel them! |
I've never heard of laser strings. Do you have any links that might shed some light on the subject?
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Well sure!
http://www.instructables.com/id/The-Prism-A-Laser-Synth-Guitar/
That's my first laser guitar. This time I'm using Les' karplus strong module to generate authentic guitar sounds, among other planned improvements! |
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Airlock
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| Posted: Thu Jun 17, 2010 6:31 pm Post subject:
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| WOW! Cool stuff Jeff-O! |
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jeff-o
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| Posted: Thu Jun 17, 2010 7:35 pm Post subject:
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| Airlock wrote: | | WOW! Cool stuff Jeff-O! |
Thanks! So yeah, picture that guitar making actual guitar sounds and you'll see what my goal is. |
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mosc
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| Posted: Fri Jun 18, 2010 10:22 am Post subject:
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Thanks, Jeff, for posting that link. It explains a lot. A great project. How are you getting the pitch voltage? Is there a sensor on the finger board or are us using some other method?
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jeff-o
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| Posted: Fri Jun 18, 2010 10:59 am Post subject:
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| I used an infrared range finder for the pitch voltage. The model I used has a range of 10 to 80 cm, and outputs a logarithmic analog output voltage between 0 to 5V. Unfortunately, it is only capable of detecting a whole hand rather than individual fingers which limited what I could do with it. |
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mosc
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| Posted: Fri Jun 18, 2010 11:20 am Post subject:
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Thanks. Please keep us informed as you progress... 
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Airlock
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| Posted: Fri Jun 18, 2010 3:45 pm Post subject:
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| jeff-o wrote: | | I used an infrared range finder for the pitch voltage. The model I used has a range of 10 to 80 cm, and outputs a logarithmic analog output voltage between 0 to 5V. Unfortunately, it is only capable of detecting a whole hand rather than individual fingers which limited what I could do with it. |
You know what? Strike everything I've said, as I had no clue what you were up to and nothing I've said applies. Nothing. Man I'm glad this week is over... |
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Stream Operator
Joined: Oct 13, 2007
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Location: near Austin, Tx, USA
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| Posted: Fri Jun 18, 2010 4:39 pm Post subject:
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Isn't there some special tuning for a guitar so you can use a metal tube on your finger to form a few chords? That's basically what you have with the range finder, Jeff. Maybe that's the thing to emulate...
Les
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jeff-o
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| Posted: Sat Jun 19, 2010 7:26 am Post subject:
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| Inventor wrote: | Isn't there some special tuning for a guitar so you can use a metal tube on your finger to form a few chords? That's basically what you have with the range finder, Jeff. Maybe that's the thing to emulate...
Les |
Actually, yes. I think it's called "open tuning" and it does allow you to play some chords by holding all the strings and strumming through. Definitely a possibility for the new guitar, but not for the old one - it could only play one note at a time, and then only while the laser is blocked! A major design flaw for sure. |
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jeff-o
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| Posted: Sat Jun 19, 2010 10:17 pm Post subject:
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More experimenting tonight!
With an mn3209 installed, I'm able to produce clean output (that is, output without audible switching noise and other undesirable stuff) down to about 34hz. Nice! So that'll easily cover the range of a standard bass. I'd need to track down an mn3206 (very hard to get!) to go lower than that. Unless anyone knows of a different way?
The membrane potentiometer works great for controlling the vco. Leaving it "open" plays the lowest note, as expected. You can do slides and hammer-ons. I also noticed that it responds a bit to tapping! Without feeding a stim pulse, pressing on the membrane pot will actually trigger a small output. This was unexpected, but very welcome! I haven't mapped out how its scale compares to that of a real guitar though. I expect I will have to tweak both the range (reduce it) and the linearity.
Also, is there any way to boost the attack of the output? Compared to a real guitar it's missing that "twang" of a string right in the first few milliseconds. Should I tweak my stim source a bit, maybe? Something other than a simple square pulse? |
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jeff-o
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| Posted: Sat Jun 19, 2010 10:30 pm Post subject:
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| Airlock wrote: | | jeff-o wrote: | | I used an infrared range finder for the pitch voltage. The model I used has a range of 10 to 80 cm, and outputs a logarithmic analog output voltage between 0 to 5V. Unfortunately, it is only capable of detecting a whole hand rather than individual fingers which limited what I could do with it. |
You know what? Strike everything I've said, as I had no clue what you were up to and nothing I've said applies. Nothing. Man I'm glad this week is over... |
Haha, no worries! But I do appreciate the advice nonetheless. |
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