The Karplus Strong eChucK DIY Project

Dan Lavin · Posted: Wed Dec 02, 2009 1:56 pm Post subject:

Les,

I think your intuition is correct..64 seconds is a little short. I'd go for the longer 16 minute version. The compromise...does that mean less note variation? If so, I don't think that's a bad thing.

Inventor · Posted: Wed Dec 02, 2009 2:04 pm Post subject:

electri-fire · Posted: Wed Dec 02, 2009 2:28 pm Post subject:

Inventor · Posted: Wed Dec 02, 2009 2:51 pm Post subject:

These are good points Mathe, I can switch it back to 6x8 no problem, just some effort (sigh) but hey it's worth it.

The real problem here is that we are fighting against the board size limit of free EAGLE CAD. Later (some day) I can buy a full version and make bigger boards, but for now we are just making do with what works.

Les

electri-fire · Posted: Wed Dec 02, 2009 3:30 pm Post subject:

Inventor · Posted: Wed Dec 02, 2009 5:54 pm Post subject:

Yes, "Love the constraints" was the advice that and old engineer gave me in my youth. He was right.

Les

Dan Lavin · Posted: Thu Dec 03, 2009 12:41 pm Post subject:

Les,

On a lighter, non-technical side, I put my marketing hat on and came up with some product name suggestions:

For the Bass Guitar:
Karplus Strong = One Mean Bass Guitar! (Kar + Strong, get it?!) Razz

For my planned Chord Guitar:
Karplus Strum

I wanted to use Karplus Strongbad, but I think the fairly stringent copyright/trademark in this country would prevent that.

Maybe others can come up with more amusing or useful names! Very Happy

Inventor · Posted: Thu Dec 03, 2009 12:56 pm Post subject:

You know, it's funny Dan, but I feel that "Karplus Strong" stands alone on it's own merits. Besides the fact that we give credit to the creators of this algorithm, the ring of Strong preceding Karplus is just sweet to my ears. Perhaps we should plan a multi-timbre board with multiple feedback loops that does a chord, would you like that?

Les

Dan Lavin · Posted: Thu Dec 03, 2009 1:45 pm Post subject:

Les,

well you're the boss! You can name these things whatever you like! Very Happy

My idea for the power chord guitar was to use 3 voices with 2 delay triggers so you get a quick 3 note adjustable strum. You tune two of the voices an octave apart with a fifth in the middle, of course. Stand back Angus/Pete/Richie/(insert your favorite guitar hero here)!

If you can do that with one board, that would be great, but I think you need the individual envelopes on each note or it just sounds too much like a synth chord....not that there's anything wrong with that Wink

, but then I don't think you need K-S.

Inventor · Posted: Tue Dec 08, 2009 1:28 am Post subject:

Since we decided to go with 6x8 switches, tonight I made the appropriate changes as shown in the pdf files attached. The board autorouted much more easily and there are eight fewer components - worked out well.

Les

BS10sch.pdf

Description:

BS10 Schematic

Download (listen)

Filename:

BS10sch.pdf

Filesize:

38.34 KB

Downloaded:

346 Time(s)

BS10pcb.pdf

Description:

BS10 Printed Circuit Board

Download (listen)

Filename:

BS10pcb.pdf

Filesize:

85.44 KB

Downloaded:

324 Time(s)

electri-fire · Posted: Tue Dec 08, 2009 5:13 am Post subject:

Dan Lavin · Posted: Tue Dec 08, 2009 3:20 pm Post subject:

Electri-fire,

My power chord guitar would be a subset of Les' creation. I would explore how to do it and publish my results. This would be more of a mod rather than what most people would want.

wmonk · Posted: Tue Dec 08, 2009 4:24 pm Post subject:

When testing the board I'll add a 1V/Oct in. So I can use it with the modular. If you add such a circuit on each board, you can get a power chord by adding 0.583 Volts to another to get the root and the fifth. Smile

Inventor · Posted: Tue Dec 08, 2009 5:17 pm Post subject:

The boards should arrive and get shipped out one week from today (Wed. 12-16-09) or shortly thereafter.

Les

Dan Lavin · Posted: Tue Dec 08, 2009 8:00 pm Post subject:

wmonk,

yes, that is what I had in mind. If we both publish our mods, it will help Les and anybody following the thread. I think these KS modules will have more applications as people work with them. I'm wondering if Les knows what he has unleashed on the world?

I suppose a 1v/octave output could be added to Les' Boolean Sequencer as well to use it with std modular equipment.

Inventor · Posted: Tue Dec 08, 2009 8:16 pm Post subject:

Guys, if you publish your expo mods that would be of great help to us all. I don't know how to do expo, and though I've skimmed a web page on one circuit, I have no really intuitive understanding of how they work. That's a real stumbling block for me.

Now that you mention it, the BS board could use a pot in place of each term's summing amp input resistor to weight the bits, creating different notes precisely. There is no room on the board for six pots, but in the future with a larger board, sure.

As to knowing what I have unleashed upon the world, nope! I feel from the level of interest that there is something good going on here but I don't have much experience in this arena so I really don't know the impact. Thanks very much for the compliment though, Dan!

I am now beginning to wonder about future products, though there is plenty of work left on the existing boards. I wonder if we can make other instruments like a flute or a saxophone by using the ChucK STK models and implementing them in analog form. Interesting...

Les

electri-fire · Posted: Wed Dec 09, 2009 4:46 am Post subject:

Not very hard to come up with, but for your convenience:

CV Sum pots.jpg

Description:

Filesize:

266.43 KB

Viewed:

233 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

electri-fire · Posted: Wed Dec 09, 2009 5:13 am Post subject:

Inventor · Posted: Wed Dec 09, 2009 5:39 am Post subject:

Yes, Mathe, for panel mount pots your solution will work nicely. I was thinking of PCB mount pots when I made that statement, but I guess I should be more open minded, heh. Laughing

Les

Inventor · Posted: Wed Dec 09, 2009 5:45 am Post subject:

Oh, and one more thing, if we use an expo converter on the input of the KS board, then there is no need for an expo converter on the output of the BS board (if I understand it correctly). This is because the 1V/octave is linear in the note circle, and the input expo converter will scale the linear output of the BS board into the exponential frequency spread required by the human ear. Does that make sense?

Les

wmonk · Posted: Wed Dec 09, 2009 5:55 am Post subject:

Yes!

And it's better to have an exponential input, as it can except any voltage source and scale it.
(Try to calculate linear-out to exponential-out, that'll produce big voltages, and without a converter on the output of the BS, you can use the output voltage as linear (by bypassing the expo converter of the KS) or exponential input. Smile

In fact, all CV sequencers put out a voltage, and the VCO (voltage controlled oscillators) have the expo-converter.

Inventor · Posted: Thu Dec 10, 2009 11:29 am Post subject:

I have received payment or otherwise reserved nine boards now, so there is only one remaining. So if you would like a board, please send paypal of $21 + shipping ($5 US, $10 International) to lester.hall@comcast.net. If I run into the awkward situation of more than one more order placed, I'll try to make arrangements, with the worst case scenario being that there may be a wait for second run boards.

Thankfully nobody ordered parts kits, as I am just getting started with this and making a perfect kit without reorders would be a bit of a risk. This is because some of the footprints are not fully verified against available parts, meaning some creative soldering may be required in one or two places.

Four of the booards (including the one for myself) are assembled boards, meaning that I will assemble them and figure out the appropriate charge for that service. I figure it will be parts cost x 1.50 + labor at $20 or so an hour. I think that's very fair in that I won't be losing money this time and yet the overall cost will be low for an assembled board. Please let me know if that billing rate is appropriate.

Thanks to everyone who has made suggestions, caught errors, and especially to those making the commitment of buying a board or two. The teamwork and DIY spirit are alive and well at electro-music!

Les

Inventor · Posted: Wed Dec 16, 2009 5:38 pm Post subject:

I just got the bubble mailers today and put together five circuit boards for mailing out to customers - you know who you are! I will mail them tomorrow. Soon I will put together an updated BOM with DigiKey part numbers so you can place an order and get exactly the right parts. I will post that BOM here.

My thanks go out to everyone who helped out on this project so far and in the future, and also to those who placed orders. I'm not making a profit, but the extra 50% you are paying covers my part of the hobby costs so who can ask for more than that on a first run board?

So keep an eye out for the mailbox, you'll be getting your board soon!

Les

Inventor · Posted: Fri Dec 18, 2009 6:04 am Post subject:

I am exhausted, simply exhausted. My car broke down and needed a $440 repair (two fuel pumps) which was a great discount but put a damper on projects. I simply do not have the wherewithal to get to the post office today so it will have to be Monday when I do the mailing, sorry.

Also because of the car repair, I cannot order parts to build Karplus Strong boards until next month's check arrives. So it's an off month for the project in my little corner of the world.

Les

Inventor · Posted: Wed Dec 23, 2009 3:13 am Post subject:

I have good news and bad news, first the bad news:

Well I couldn't get to the post office yesterday because my car is still broken down. After a total of $1200 or so in it, now it won't start at all. The mechanic suggests a relay. sigh. I am going out shopping with Sunshine tomorrow so I'll try again to visit the post office.

The good news is that I received a $1,000 check from my old company for a patent royalty, whew! Now I can upgrade my studio, fix my car, and still have enough left over to buy Karplus Strong parts! woohoo! It's a merry Christmas holiday after all...

Les