The Karplus Strong eChucK DIY Project

Inventor · Posted: Sat Feb 27, 2010 3:55 pm Post subject:

You're welcome Dan, hope the updated schematic helps. I'm also planning to build a system with these boards. It will be a multiple voice system with probably three or four KS boards, each having their own BS board mounted on top. They will be chained together to share a common clock, and I'll make a small mixer board to combine the signals. The system will run on batteries and fit in a small suitcase so I can carry it to events like EM10 for performances. Or at least that's the plan right now, not sure if the concept will evolve.

Les

Inventor · Posted: Sun Feb 28, 2010 3:43 am Post subject:

Hi everyone, please see this thread:

http://electro-music.com/forum/topic-40002.html

for my post of the Shimmering concert performance which included BS/KS sounds. It featured two BS/KS voices running throughout the performance with effects all in software, as well as a lot of the first KS board in action (without a sequencer and with much knob twiddling).

Les

mosc · Posted: Sun Feb 28, 2010 12:02 pm Post subject:

It was a great set, Les. These boards are going to be popular, I would guess.

Inventor · Posted: Sun Feb 28, 2010 12:24 pm Post subject:

Inventor · Posted: Mon Mar 01, 2010 4:46 am Post subject:

Just tonight I finished soldering in all the parts that I ordered and preparing a second order so that I can complete a set of four KS boards. Total cost including shipping, taxes, and higher quality components (like mil-max sockets, etc.) will be around $225 plus the cost of the BBD chips (which I forgot). So it looks like the BOM cost for this board is in the neighborhood of $65. That's for the battery version of the design.

Now that I've done some hands-on and made one board completely, I'm thinking a bit more clearly about offering boards assembled and tested. I'm already building a KS board for each of two friends, so I guess the ball has started rolling anyway. What do you think about this possibility?

Les

Inventor · Posted: Sat Mar 06, 2010 4:10 pm Post subject:

I just helped wmonk populate his KS board in the chatroom. There were many questions and uncertainties, mainly due to silkscreen errors. This makes the first run boards very difficult to build and I want to do something about that. So I thought about it and decided to offer the second run boards at cost and with lower international shipping.

Most of the parts are the same for both boards, so if you haven't built your first run board and you want to avoid the hassle of all the uncertainties, please consider getting a second run board instead. The cost including shipping should be $20 for a second run board. I learned from the first run that shipping internationally is lower than I thought since the board in a padded envelope is so light, so it will be the same price whether you are in the USA or international. The $20 includes shipping.

I have fixed all of the problems, or believe that I have done so on the second run design and I'll be posting pdf files of it soon for your review. Thank you for your understanding and your patience in this matter.

Les

Inventor · Posted: Sat Mar 06, 2010 6:40 pm Post subject:

Tonight in the chatroom we had some fun with the KS board. wmonk successfully built his module and tested it driven by a baby 10 sequencer. He streamed video from his phone to us and we heard the board in action! It was great fun.

One warning, however: the modular power connectors must be installed backward. Again, sorry for any problems that you may have in the build and second run boards will be available at cost to help minimize this problem.

Thank you wmonk!

Les

wmonk · Posted: Sat Mar 06, 2010 6:52 pm Post subject:

Well, this is a fun module guys! Got it working with the help of Les! Very Happy

On my blog you can find the video Les was talking about. A lot of bass is missing because of the phone microphone, but its fun anyway Smile

http://woodymonk.blogspot.com/2010/03/karplus-strong-and-video.html

Cheers,
Woody

Dan Lavin · Posted: Sat Mar 06, 2010 8:57 pm Post subject:

Nice work, Woody! I've got a couple loose ends to tie up on projects then should be able to devote more time to helping everyone out on this.

wmonk · Posted: Mon Mar 08, 2010 4:41 am Post subject:

Thanks Dan!
With a filter its very nice. Can be funky Smile

Will test it with the MN3208 next week. Now used the MN3207.
Calculated the cost of the module, and its about 40 euros including all components and pcb, using cheap alpha potmeters. That's about 55$. That's very good price for what it does Very Happy

Thanks Les!

Inventor · Posted: Mon Mar 15, 2010 4:56 pm Post subject:

You're welcome wmonk and good luck with the build Dan. In fact, Dan has made another contribution to the project in that he got permission from Thomas Henry for us to use an easy expo converter on the two CV inputs.

These expo converters do not require matched transistors so they make for an easy build, though they do have a tempco resistor each. Tempco's are available from DigiKey in surface mount form so there will be a little creative soldering and some epoxy on the transistors and tempcos.

I've also rearranged the schematic and made all changes which was a long list of changes, lol. I figured out from a post by fonik how to print out the silkscreen of the board without the traces, so you can review the placement for correctness if you like. Here are the documents...

Les

KS10Silk.pdf

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KS10 Silkscreen pdf file

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KS10sch.pdf

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kS10 Schematic pdf file

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Dan Lavin · Posted: Mon Mar 15, 2010 6:40 pm Post subject:

Les,

Just one suggestion on the expo transistor pairs. I would put them so that the flat faces are touching each other (move them closer together than you show them). Then, they should be epoxied together with the temp compensation resistor riding over the top of them like a hat. It makes the silk screen a little tough, but you can scootch the resistor letter towards one hole or the other.

Dan Lavin · Posted: Mon Mar 15, 2010 6:47 pm Post subject:

Just a note to everyone on Thomas' permission to use this expo convertor:

It is found in the "Making Music with the 3080 OTA" book, which is available from Magic Smoke. I highly recommend everyone buying a copy. Lessons on the3080 can be applied to the 13700. Thomas credits Terry Mikulic in his article "Exponential Converters," in Electronotes Volume 5, Number 37, March 30, 1975 , pp2-4. This is Thomas' adaptation of his idea.

Inventor · Posted: Mon Mar 15, 2010 10:27 pm Post subject:

I have creditied Terry Mikulic on the schematic and Thomas Henry as well. I moved the transistors so that they are almost touching, leaving space for the tempco resistors to be epoxied in between (with a piece of metal preferably).

I also double-footprinted the front panel potentiometers, though I remain a bit concerned about some of the hole sizes. Let me know if you have any additional suggestions before we send out the board.

And thanks for all your help as well Dan.

Les

Inventor · Posted: Mon Mar 15, 2010 10:58 pm Post subject:

I also double-footprinted the tempco as either a thru-hole resistor or two 1k 0805 surface mount resistors in series. This way the 0805 tempcos use the pcb as a heat sink and a dab of epoxy between the transistors will thermally connect things nicely. Plus this way there is no need for creating sculptures in air of the 0805 parts from DigiKey or your other supplier.

Les

Inventor · Posted: Sun Mar 21, 2010 2:32 pm Post subject:

In the chatroom just now, wmonk has convinced me to create a KS Buddy module, a module that does lots of waveshaping and etc for KS so you can get the most use out of it. Here's some of the features:

Variable Pulse Width One-shot
Noise Source
External Noise Input
Sine Source
Pulse Attack/Release Envelope
BS stim test connection
Whatever else you want to add, it's a kitchen sink module

So ideas and suggestions are welcome as always.

Les

Dan Lavin · Posted: Wed Mar 31, 2010 6:51 am Post subject:

Les,
I received the following pots yesterday from Mouser:
313-1530F-100K
Taiwan Alpha Panel Mount Potentiometers
Audio Knurled 100K

These will fit into the K-S mounting holes for the controls without bending the terminals. THey're audio taper and not linear, but for the prototype, will work just fine.

wmonk · Posted: Wed Mar 31, 2010 7:08 am Post subject:

Agree. In fact, all 16mm pcb mount Alpha pots fit on the board. Smile

Inventor · Posted: Wed Mar 31, 2010 9:07 am Post subject:

Dan, there are several instances on the board where the silkscreen is not very readable. Also please note: the power supply connectors are on bakward, doh! I've got the parts now to build the remaining three KS first run boards, should build them within a few days. The silkscreen seems to be just fine on the second run design, which is nearly ready to go.

Les

Dan Lavin · Posted: Wed Mar 31, 2010 10:03 am Post subject:

Les, yeah I know about the silkscreen, thanks. I plan to green line the schematic vs what I have placed on the board as a final check to be safe. I should be able to start evaluating/experimenting within a week and will let you know any ideas I come up with, but I think Woody has a good list already.

I think a small triangle wave LFO would be good for the buddy module for vibrato. You'll need one pot for rate and one for modulation amount to the vco.

jeff-o · Joined: Jul 19, 2009 Posts: 97 Location: Ontario, Canada

Well, I'm glad I checked in when I did! Glad to see the second batch of KS boards are being made soon. Count me in for one when they're available.

Inventor · Posted: Sat Apr 10, 2010 6:36 am Post subject:

jeff-o · Joined: Jul 19, 2009 Posts: 97 Location: Ontario, Canada

Hey, if you like I can finance the next round of boards. Just send me the gerber and drill files and I'll send 'em off to the board house. I use Gold Phoenix, they've always made good stuff for me. Let me know if you're interested.

Wow, the range of sounds is impressive! Bass is still my goal, but I may include a high/low tuner switch in my final plans.

Inventor · Posted: Sat Apr 10, 2010 7:36 am Post subject:

Inventor · Posted: Sat Apr 10, 2010 8:59 am Post subject:

I've completed the KS10 design and I'm ready to generate the output files for jeff-o to have the second run of boards made. Please have a look at these pdf files and let me know if there are any problems or changes. Thanks.

Les

Edit - fixed the schematic (properly I hope this time)!

KS10bSilk.pdf

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KS10 silk

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KS10bsch.pdf

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KS10 schematic - fixed the multipage error

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