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 Forum index » DIY Hardware and Software » Les Hall's Projects including eChucK
The Karplus Strong eChucK DIY Project
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Inventor
Stream Operator


Joined: Oct 13, 2007
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PostPosted: Thu Sep 03, 2009 1:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

You know, it's funny, those thoughts of yours were the last thoughts I had before deciding to post the diagram as it was. So we're all thinking alike. In my case, my lack of modular synth knowledge led me to question whether the average synth could form appropriate signals, but I guess it can.

If we can eliminate the noise chip and the transmission gate chip, that reduces our chip count from 9 to 7, which is a step in the right direction. I also think I went a bit overboard on all the voltage followers, perhaps that can be done simpler.

Thanks for the suggestions guys, I'll update the diagram and post it for your review.

Les

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Stream Operator


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PostPosted: Thu Sep 03, 2009 4:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK folks, I put in your changes and did some simplifying. The burst is simply an input now, so a modular user could use any desired signal for it. The voltage followers scattered about have been reduced from 8 to 4, removing one quad opamp. They have been replaced by appropriate bias networks. The VCF and VCD inputs now have a bias control such that one need not hook up inputs to them, and can work them from two front panel pots if desired.

This reduces the circuit to just five chips, one of which is just a three-terminal regulator, so only four big chips. The discrete count goes up though. I hope this will fit on the tiny boards proposed, because we just can't get any better than $51 for a set of prototype boards as far as I know.

Please let me know what you think, then I'll start working on a schematic.

Les

p.s. maybe we can add a switch to the Burst input, that way one could produce music using this module alone and no inputs would be required (though highly desired).


KS_BlockDiagram2.jpg
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Revised Karplus-Strong Block Diagram
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Dan Lavin



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PostPosted: Thu Sep 03, 2009 7:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Les, If you can stay with that low of a chip count, i can definitely use the Expresspcb $51 for 3 boards deal. Even with supporting passives, I don't see a problem. -Dan
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Stream Operator


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PostPosted: Thu Sep 03, 2009 8:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Dan, that sounds cool, in fact I changed the DFF into an MN3202 companion Clk/Divider chip which is 8 pins instead of 14. Now we only have two big chips, two little chips, and a 3-terminal regulator. I also added some nice features, outlined below.

Code:
Notes on Karplus-Strong Block Diagram

The board functions as both a modular synthesis module and a stand-alone eChucK module.  This is accomplished with three input jacks for the three modular synthesis mono input jacks as well as a stereo input jack for connecting to the headphones out of a PC.  A shorting switch can be engaged to cause the eChucK right channel to simultaneously control both the VCF and VCD.  Output is a single stereo jack wired with tip and ring shorted together. 

The power supply may be a pair of 9V batteries or +/-12V or +/-15V so the board can be stand-alone or can run from a modular power supply. 

The PWM block converts a PWM signal on eChucK right into a DC level which is then summed into the VCF and VCO signal paths. 

There are two features that permit operation of the board with no input connections.  The Stim switch provides a front panel control which when pressed will cause a burst to occur manually.  Also two Bias adjust potentiometer circuits allow the user to dial in the VCF and VCD inputs if desired.  These should be adjusted to zero position when driving the inputs through the jacks. 



KS_BlockDiagram3.jpg
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The third revision, this one looks pretty good I hope
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DGTom



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PostPosted: Fri Sep 04, 2009 7:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Shocked Wow!! I get distracted by other things & look what happens! I will need to go back & read thru again but this is looking amazing!

As a modular guy, the seperate boards is a massive bonus, I would be looking at 2-4 K-S modules minimum & a pair of boolean sequencers dueling it out would be a dream come true Very Happy

Love the addition of CV & external excitation (if I understand correctally?) can't wait to see this project develop, sign me up for the first run of boards!
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Stream Operator


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PostPosted: Fri Sep 04, 2009 10:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Why, that's great news, DGTom! Thanks to everyone's help this project is starting to shape up. Should be a pair of nifty little boards, I hope. Of course we don't have a working prototype of KS yet, so please be advised that there is plenty of work to do.

At the present time, the latest is that this morning I began the schematic capture and layout. I made a part for the 1/8" audio jacks and we need five of them. Well, don't you know it they are too big and won't fit on the prototype board. So the lesson learned is that for cost and software reasons we will have to at least do the prototype with Jacks and Pots and Switch on a panel-mount thingie. I'm open to suggestions on how to proceed with that.

Les

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Stream Operator


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PostPosted: Sat Sep 05, 2009 12:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Since my last post I have completed a schematic and board placement for the Karplus-Strong board. Please see below for screenshots. Oh, i forgot to put a copyright on the schematic: schematic is copyright 2009 Les Hall.

I just have one question at this time: What is the pinout on the three pin Molex power connector?

Since the prototypes will be only $51, I feel no need to breadboard the circuit. Please let me know of any issues or questions you may have. Thanks.

Les


KS_Board1.jpg
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Karplus-Strong Board Placement
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KS_Schematic1.jpg
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Karplus-Strong Schematic
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wmonk



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PostPosted: Sat Sep 05, 2009 1:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Why a 3-pin and not a 4-pin? Most modular guys here use the 4-pin molex 0.156" spacing. Layout: +/0/0/-.

I think it's a better practice to breadboard the circuit before ordering a prototype board. You can easily adjust resistor and capacitors to get the best results. And there is no need to spend the money twice (if there is something wrong with the circuit)
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Stream Operator


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PostPosted: Sat Sep 05, 2009 1:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sure, I'm easy going. What you say makes good sense wmonk, thanks for the suggestion and the information. Next I need to work out the component values...

Les

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PostPosted: Sun Sep 06, 2009 8:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

if there is room for a 4 pin .156 I'd go with that... but tbh I'm moving away from them, IMO they are a massive PITA. They are big & 9 times out of 10 a struggle to wrestle with, especially on dense boards, even on Blacet PCBs you are almost always trying to turn your wrist at wierd angles in an attempt not to bend decoupling caps.

making a .156 -> .100 cable to hook up to your existing power distro is trivial & .100 hardware is soooo cheap. All my DIY / perf boards use .100 so I'm just making .100 distro boards that hang off the .156 distros.

.100 are stilled keyed, I just don't see the sense in using these bulky 'legacy' connectors on smaller & denser boards.

With regards to boardmounted jacks / pots / switches, I say leave em off! keep it uber modular so people can have maximum flexbility in how they put these together, a row of headers, 3 pin for pots, 2 pin for I/O would be best - sorry I suck at reading board layouts, you may have done this already Very Happy

Looking good so far tho! I'm really excited by this project, scraped my plans to purchase a BBD module for K-S & having a total re-think about my VCO plans!!
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Stream Operator


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PostPosted: Mon Sep 07, 2009 2:41 am    Post subject: Reply with quote  Mark this post and the followings unread

DGTom, that is nice commentary, thanks. I'll stick with the 0.100" connector that I have, though there is actually room on the board for both connectors if need be. I could even double-footprint them if you like.

I'm happy to hear that you are looking at this board from the perspective of equipping your modular with a rockin' Karplus-Strong orchestra. Way cool. I can't wait to hear one of your audio files with these, though there is a monstrous amount of work to be done before that happens. Thanks for the preorder too, that will help get the ball rolling.

I had a conversation with wmonk and Blue_Hell in the chatroom and they offered over half a dozen suggestions for the board which I implemented. Most notably the rebiasing stage from the VCO to the MN3102 chip is replaced by a transistor buffer at Jan's suggestion. Overall I think I'm ready to prototype but I have to wait until payday to order parts.

I've decided to form a compromise on the theme of parts aligned to the panel. The three pots and the switch are positioned along the long edge of the board for direct panel attachment, and the jacks are done with a wiring harness. That way we get the best of both worlds.

So things are on delay until I can order parts but hey, whatcha gonna do? It's only a week or so delay.

Les

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PostPosted: Sun Sep 13, 2009 6:07 am    Post subject: Reply with quote  Mark this post and the followings unread

I put in all the suggestions made so far except the exponential VCO/VCF feature, there just isn't time or room for that in the first version. Below you will find an updated schematic with component values, text notes, and some other changes like the level shifter that Jan suggested.

Here is a digikey/smallbear order that I have prepared. Am I missing anything from the orders?

Les


Quote:
DigiKey Order for KS and BS prototypes

2 switches
heat shrink
wire
LM13700
TL074
LM7805
CD4017
10 k Pots, right angle
100 k Pots, right angle
10 uF caps
0.1 uF caps
100 kOhm resistors
10 kOhm resistors
1 kOhm resistors
5.6 kOhm resistors
30 kOhm resistors
200 Ohm resistors
2 kOhm resistors
20 kOhm resistors
5.1 kOhm resistors
4 pin molex
0.05 uF caps
1u caps
2.2 u caps
9V battery holders
spst momentary switch, right angle
4V7 zeners
2n2222 transistors


SmallBear Electronics
MN3102 Driver
MN3207 BBD



KS_Schematic2.jpg
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Updated Schematic
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KS_Schematic2.jpg



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wmonk



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PostPosted: Sun Sep 13, 2009 6:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Where is the 4017 in the schematics? I thought you replaced it with a 4040?
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Uncle Krunkus
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PostPosted: Sun Sep 13, 2009 6:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks good Les.
So does a Karplus-Strong work on the idea of making a BBD howl in a controlled kind of way?
My experiments sure have pumped out some cool howling sounds, and I know about the need to "kick" it into action.

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Stream Operator


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PostPosted: Sun Sep 13, 2009 6:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Andy, I've put a lot of work into it already. Karplus Strong is this really simple digital algorithm for making string and percussion sounds. I'm implementing it in analog form. The basis of KS is a summing amp with a delay line and a filter in the feedback loop. Adjust the loop gain properly, set up the filter and delay line characteristics, and hit the stim input to get a guitar or sitar or percussion kind of sound.

Most definitely if you've been playing with flangers using BBD's and such, it would be quite easy to hook up a feedback loop that sets up a KS type oscillation.

By the way, where is the thread on your BBD project, I'd like to read up on it.

Les

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Stream Operator


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PostPosted: Sun Sep 13, 2009 7:00 am    Post subject: Reply with quote  Mark this post and the followings unread

That's weird, I replied to you wmonk, but the post got lost. Either that or i hit the wrong button. Anyway, you're right it's a 4040 not a 4017, thanks. I'd hate to have to place another order so soon.

Les

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PostPosted: Sun Sep 13, 2009 1:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

With a little time on my hands I decided to work a bit on the Boolean Sequencing board. It's the new version that does only Boolean Sequencing, nothing else. I'm not too sure if folks will be happy with the way that I'm generating CV, but I think it will be OK. There's not much room on the little 2.5" x 3.8" board. It can be wired up to a Karplus-Strong board directly, all you need is a clock source at 4Hz or so.

Comments welcome as always.

Les


BS_Schematic1a.jpg
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Counter and LEDIL Sections
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BS_Schematic1a.jpg



BS_Schematic1b.jpg
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Output Section with pulse generator
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PostPosted: Sun Sep 13, 2009 3:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Am I wrong or are the LEDs in the LEDILs reversed?
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PostPosted: Sun Sep 13, 2009 3:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
Am I wrong or are the LEDs in the LEDILs reversed?


I *think* they're OK. There are six AND gates feeding into one OR gate. The AND gates go low if any output is low, so that's good. Then if all inputs are high or open, the AND gate goes high. The diodes are reversed to do the OR function so that if any input is one the output goes to a low value of one. Any more outputs going high drives up this voltage to create a CV. Then a comparator circuit picks up the rising edges and creates a narrow pulse. Am I correct?

Les

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loss1234



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PostPosted: Mon Sep 14, 2009 5:39 am    Post subject: Reply with quote  Mark this post and the followings unread

not sure why BUT I CAN NOT read any of the values on your schemeatics for resitors, caps,etc

I tried ONSCREEN and printed.

a shame as i really really want to try this KS circuit.

thanks so much

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loss1234



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PostPosted: Mon Sep 14, 2009 5:45 am    Post subject: Reply with quote  Mark this post and the followings unread

also...i noticed in your block diagram that you have echuck inputs...however i see your sequencer scheamtic. so my question is, can i do this entirely in the analog domain or does ECHUCK need to be part of the setup?

thanks so much

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PostPosted: Mon Sep 14, 2009 2:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

loss1234, I am quite happy that you plan to breadboard the KS circuit, hopefully together we can get it to work. Below are four close-ups of the schematic which should give you a clear indication of component values. Any questions, just post.

Regarding the eChucK component, I found that the board would not fit so I removed that feature. Now it's strictly a modular or perhaps stackable board. The VCO and VCD inputs can be left unconnected and just set by their potentiometers. The BS and KS boards are designed to work together but you can actually just drive a narrow pulse train into the KS stim input and adjust the pots to get different sounds for test purposes. Also there is a switch on the stim input which is intended to allow stand-alone operation for test, just hit the switch to get a burst of sound from the KS circuit.

Hope that helps.

Les


KS_Schematic3a.jpg
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upper left detail of KS schematic
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KS_Schematic3b.jpg
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upper right section of KS schematic
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KS_Schematic3c.jpg
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lower left section of KS Schematic
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KS_Schematic3c.jpg



KS_Schematic3d.jpg
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lower right section of KS schematic
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loss1234



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PostPosted: Mon Sep 14, 2009 4:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok

i think the only thing i am stuck on (still cant read) are the BBD chip and BBD clock chip PIN NUMBERS

other than that, i can read it all! I have been spending the last 2 weeks on nothing buy BBD circuits so this will fit right in.

I had been using a 4046 for voltage control, but this method makes more sense to me.

thanks!

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PostPosted: Mon Sep 14, 2009 5:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok dan, I made an extreme close-up of the BBD section for you. There are no pin numbers but the pins are sort of labeled. Sorry, I don't know how to make proper library parts yet so the text is like all over there or something, but you should be able to make it out. Best of luck to ya!

Les


KS_Schematic3e.jpg
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extreme close-up of KS BBD circuit
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PostPosted: Tue Sep 15, 2009 4:07 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks a bunch


one question I have...i notice you are only plugging into the OX pin1 on the mn3201....is this because you are driving the chip in a special way? (with a current...etc)

i have never seen OX 2 AND 3 LEFT OPEN.

looks like a good setup though

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