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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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jeff-o



Joined: Jul 19, 2009
Posts: 97
Location: Ontario, Canada

PostPosted: Fri Aug 13, 2010 9:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

OCV varies from 0.167V to -0.163V.
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Stream Operator


Joined: Oct 13, 2007
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PostPosted: Sat Aug 14, 2010 2:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Sigh, I can't even make that measurement because my voltmeter is broken...

Fortunately other stuff is going very well so I'm quite happy these days, but progress on em projects has come to a standstill until after the festival. BTW, Kevin, deadline for Lunetta workshop signup is tomorrow...

Les

p.s. I'll be bringing about 25 KS11 boards to the festival if anyone wants one.

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jeff-o



Joined: Jul 19, 2009
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Location: Ontario, Canada

PostPosted: Sat Aug 14, 2010 7:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
Sigh, I can't even make that measurement because my voltmeter is broken...


Sucks!!! Is it something you can fix yourself, or do you need a new one? I suppose you could use your scope for measurements in the meantime...
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Stream Operator


Joined: Oct 13, 2007
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PostPosted: Sun Aug 15, 2010 4:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, the good news is that I've made an effort to stop certain expensive habits like alcohol and cigarettes, so if this keeps up like it has been I'll be able to afford to replace the voltmeter and put more funds into this hobby. But until after em10 nothing is going to happen. I guess it's good to have a little down time occasionally...

Les

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kkissinger



Joined: Mar 28, 2006
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Location: Kansas City, Mo USA
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PostPosted: Mon Aug 16, 2010 7:51 am    Post subject: Reply with quote  Mark this post and the followings unread

jeff-o wrote:
OCV varies from 0.167V to -0.163V.


Thank you for this info.

Your measurements narrows my investigation to the expo converter -- much appreciated.

Since I was out on a campout and, then, had a house full of people yesterday I have not had a chance to revisit this. Hope to have some time in the next couple of days, though.

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Inventor
Stream Operator


Joined: Oct 13, 2007
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Audio files: 258

PostPosted: Sat Aug 21, 2010 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, since I'm taking a break from music for a while, I've thought about it and decided to donate the Karplus Strong design to the electro-music.community. The prior arrangement was that I would do most of the work in exchange for half of the profits if there are any to be had. That would have been cool to pay for parts and stuff on future projects, and then maybe those projects would yield rewards, and then over the years I figured I'd be able to have a decent music setup. That was the plan anyway.

What throws a kink in the works, however, is that I won't be working on this stuff for a while and I don't want to let people down. Scroll up and you'll see the trouble Kevin is having and I really can't help much which sucks. So anyway, if any one person or group of people would like to carry the torch on this project, I'd be happy to pm the design files their way. Just let me know by pm because that way i'll get an email notification to check your message. Or you can email to my inbox which I'm checking every day or two: inventor-66@comcast.net thanks.

Les

p.s. I also have parts and boards and a breadboard of the expo converter to send out to the next "keeper" of the KS design...

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kkissinger



Joined: Mar 28, 2006
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PostPosted: Sat Aug 21, 2010 4:48 pm    Post subject: My Karplus Strong Modules is up and running! Reply with quote  Mark this post and the followings unread

Well, it turns out that I did not fry my BBD chip. The culprit was that I fried one of the zener diodes (the one that connects to ground). It was pulling the feedback signal so low that the only thing that made it through was the stim signal.

Additionally, I had to replace Q2 (the PNP transistor for the VCO's expo converter). I am now getting a good voltage swing from Q2 as a result.

The module sounds great! I have to mess with some resistor values to sweep the VCO through a larger range. I will share the results when I determine good values.

Well, one advantage to my little "trial by fire" is that I think I know every part in the circuit!


P8200013a.JPG
 Description:
My new Karplus Strong VCO module mounted in the case.
 Filesize:  1.29 MB
 Viewed:  116 Time(s)
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P8200013a.JPG



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Airlock



Joined: Apr 06, 2007
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PostPosted: Sat Aug 21, 2010 4:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow that looks awesome Kevin!
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kkissinger



Joined: Mar 28, 2006
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Location: Kansas City, Mo USA
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PostPosted: Mon Aug 23, 2010 8:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
Scroll up and you'll see the trouble Kevin is having and I really can't help much which sucks. So anyway, if any one person or group of people would like to carry the torch on this project, I'd be happy to pm the design files their way.


With all DIY projects one doesn't have trouble as much as one gains an education. Ironically, had the k/s unit worked perfectly the first time I powered it up it I would have little/no insight into it.

Whenever a module doesn't work to spec, I attempt to assess the situation. What works and what doesn't?

The expo converter is working -- the evidence is that when I connect my keyboard to the k/s's CV input, the pitches are evenly spaced.

The issue, then, is the VCO's sensitivity -- it is not sensitive enough to the input voltage. I am currently scrutinizing the voltage divider -- particularly R11. The datasheet (which specifies a +/- 15v supply) shows a 10K resistor.

http://www.media.mit.edu/resenv/classes/MAS836/ToPost/LM13700.pdf

(ref: figure 18 on page 17 -- "Single Amplifier VCO" -- note that the explanation next to the schematic has a typo -- it references figure 19 instead of 18!) The schematic has a much larger capacitor value which is to be expected -- after all, the k/s vco has to run at 2056x the desired output frequency!)

I am confident that this circuit will work to spec once I tweak a few resistor and perhaps the the C8 capacitor value.

I think this will be useful to to others -- once we establish the part values for 15 volt operation it shouldn't be too hard to interpolate for 12 volt operation.

After this, I want to investigate the low pass filter -- I think that it's cutoff frequency may be a little on the low side. I'll just experiment with its capacitor value.

More later...

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jeff-o



Joined: Jul 19, 2009
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Location: Ontario, Canada

PostPosted: Mon Aug 23, 2010 9:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for your work, Kevin. Sadly I haven't had much time to play with this myself lately, as I am in the midst of renovating my bathroom. It's eating up most of my spare time for one thing, and some of my space as well!

Keep working at it!

And to anyone else who's on the fence about buying one of these boards, worry not! I had both of mine up and running without any issues. Both make guitar noises or plenty of noisy drone, if that's what you're after. There is certainly plenty of fun to be had.
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Stream Operator


Joined: Oct 13, 2007
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Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Fri Sep 17, 2010 4:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, after a brief hiatus away from electro-music, I'm ba-ack! I don't recall if I had posted a photo of my "The Brick" music synthesizer, shown below, which makes BS/KS/KS sounds so here it is.

A breadboarded Boolean Sequencer drives a shorter BBD Karplus Strong board to create the basic sound source, then another long BBD Karplus Strong board acts as a resonator. With this setup I can produce a wide range of sounds in three main regions: Normal, Deep Bass, and Overdrive. Also many adjustments within each region and transitions between regions are possible.

To finance continued developments in the Karplus Strong project, I am offering The Brick for sale. I may not get any takers though because I feel that I must set the price at a fairly hefty $300. It's got about $150 worth of parts in it so that's a 100% markup to cover all the labor in creating a custom design. Also The Brick has somewhat of an electro-music historical significance in that it contains a Boolean Sequencer developed by myself on em, a KS rev 2 board as the audio sound generator, and a KS rev 1 board as the resonator. The Brick also includes an obsolete MN3209 BBD chip to make it extra-unique.

The Brick will get shipped to the first person to send me a private message on electro-music's PM service, followed by PayPal payment to lester.hall@comcast.net.

Also, Doug Slocum has three Karplus Strong bare boards which he can build for you at a fair price, and I have about 20+ bare boards left that can be sold either built by Doug or bare from me. End of shameless commerce discussion...

It's good to be back!

Les


The Brick.jpg
 Description:
"The Brick" Karplus Strong Music Synthesizer
 Filesize:  1.21 MB
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The Brick.jpg



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Stream Operator


Joined: Oct 13, 2007
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Location: San Antonio, Tx, USA
Audio files: 258

PostPosted: Fri Sep 17, 2010 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://electro-music.com/forum/post-307701.html#307701

is the link to the Karplus Strong design files for anyone to download and do stuff with. Enjoy,

Les

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GodSaveMetal



Joined: Sep 16, 2010
Posts: 3
Location: Perú

PostPosted: Sat Sep 18, 2010 12:39 pm    Post subject: Please post the circuit, layout, pdf and all off the BRICK!!
Subject description: PDF all layout and PCB THE BRICK
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Pleace inventor popst all off the BRICK I`m new and want tho make this fantastic instrument; what is the GIGANT plate in the circuit???
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Stream Operator


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Audio files: 258

PostPosted: Sat Sep 18, 2010 3:29 pm    Post subject: Re: Please post the circuit, layout, pdf and all off the BRICK!!
Subject description: PDF all layout and PCB THE BRICK
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GodSaveMetal wrote:
Pleace inventor popst all off the BRICK I`m new and want tho make this fantastic instrument; what is the GIGANT plate in the circuit???


Hi, well I created The Brick on the fly, just wiring stuff together and following datasheets without schematics, so I really don't have any plans to share with you. The big plate in the middle right is a peice of wood for attaching the small breadboard to the circuit. Best way to get started: read the BS and KS trhreads (like this one)...

Les

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Danno Gee Ray



Joined: Sep 25, 2005
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Location: Telford, PA USA

PostPosted: Sun Sep 19, 2010 7:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Kevin,

Are there any updates on this from your experiments?

When the final information is determined, Would it be possible for someone to update documents for download?

Thanks,

Dan

Last edited by Danno Gee Ray on Sun Sep 19, 2010 7:24 pm; edited 1 time in total
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jeff-o



Joined: Jul 19, 2009
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PostPosted: Sun Sep 19, 2010 9:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
http://electro-music.com/forum/post-307701.html#307701

is the link to the Karplus Strong design files for anyone to download and do stuff with. Enjoy,

Les


Thanks very much!!!
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kkissinger



Joined: Mar 28, 2006
Posts: 1212
Location: Kansas City, Mo USA
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PostPosted: Mon Sep 20, 2010 9:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Danno Gee Ray wrote:
Kevin,

Are there any updates on this from your experiments?

When the final information is determined, Would it be possible for someone to update documents for download?

Thanks,

Dan


Last night I powered the module from a +9/-9 v supply (two 9v batteries!).

THe VCO's range was wider in that the low frequency end was lower. However the tracking wasn't improved.

The issue is that the expo converter is clamping the high and low end... the VCO is capable of a wider range.

There are a couple of things I can do. One is to add an amplifier stage between the expo converter and the VCO. The other is to figure out why the expo converter clamps... there may be a workaround there.

The upshot is, to increase the swing from the expo converter will increase the range for the VCO.

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jeff-o



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PostPosted: Mon Sep 20, 2010 9:15 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm tempted to hook up a function generator to this thing in place of the expo converter and VCO, to determine exactly what kind of range that BBD is capable of! Has anyone tried this?
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kkissinger



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PostPosted: Mon Sep 20, 2010 9:30 am    Post subject: Reply with quote  Mark this post and the followings unread

jeff-o wrote:
I'm tempted to hook up a function generator to this thing in place of the expo converter and VCO, to determine exactly what kind of range that BBD is capable of! Has anyone tried this?


I haven't bypassed the VCO, but I did an experiment wherein I replaced the expo converter's output with a sweepable DC voltage. I was able to get a range right around 3 1/2 octaves -- the VCO's frequency will sweep beyond the BBD's operating range.

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jeff-o



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PostPosted: Mon Sep 20, 2010 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

kkissinger wrote:
jeff-o wrote:
I'm tempted to hook up a function generator to this thing in place of the expo converter and VCO, to determine exactly what kind of range that BBD is capable of! Has anyone tried this?


I haven't bypassed the VCO, but I did an experiment wherein I replaced the expo converter's output with a sweepable DC voltage. I was able to get a range right around 3 1/2 octaves -- the VCO's frequency will sweep beyond the BBD's operating range.


That makes sense, that's about the range specified in the BBD's datasheet.
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Stream Operator


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PostPosted: Mon Sep 20, 2010 6:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Guys, it's really great to see you exploring the circuit and sharing results here. So far everything observed appears to be correct as I recall the details. You are now exploring into areas of the circuit that I had estimated yet not characterized at all. Please continue with your efforts and posts as I find them quite enjoyable to read.

Les

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kkissinger



Joined: Mar 28, 2006
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PostPosted: Mon Sep 20, 2010 7:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Inventor wrote:
Guys, it's really great to see you exploring the circuit and sharing results here. So far everything observed appears to be correct as I recall the details. You are now exploring into areas of the circuit that I had estimated yet not characterized at all. Please continue with your efforts and posts as I find them quite enjoyable to read.

Les


Thank you, Les. I will publish any new findings. The module and its sounds are very nice... once it is tracking it will be awesome!!

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kkissinger



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PostPosted: Mon Sep 27, 2010 7:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have done some more testing and cross-posted the results and request for help to the transistor matching forum:

http://electro-music.com/forum/post-308662.html#308662

It appears that Q2's range is limited -- particularly at high base current it still pulls the voltage down to -8.21 (through R27). Different values for R27 changes the overall frequency of the VCO but the range stays the same.

Any suggestions anyone?

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GodSaveMetal



Joined: Sep 16, 2010
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Location: Perú

PostPosted: Wed Sep 29, 2010 12:03 pm    Post subject:  Ks and BS
Subject description: what is this?
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Dear inventor I'm the new in this adventure; plese can you explain what is the KS and BS modules?; how I get a sound with it?? I have a electric guitar, can I conect to the Synth? where??? please be patient with me; I want to do this it´s great; in PERÚ I found all the components, I have a skill in electronics, I´ve made guitar effects like pedals and mod´s for this effects!!! and I love the fantastic sound of synth!!!! please help me!!!!!!
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kkissinger



Joined: Mar 28, 2006
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PostPosted: Thu Sep 30, 2010 9:38 pm    Post subject: A breakthrough! Reply with quote  Mark this post and the followings unread

It turns out that Q2 is reversed on the schematic -- the collector should connect to GND and he emitter should connect to R27.

I have been experimenting with some different resistor values. At the moment I am using a 3.9K resistor for R27 and a 10K resistor for R26.

Thus, I am getting pretty good 1v/8ve tracking in the bass. the top 1 1/2 octaves tracks at progressively less pitch change per step.

This could be due to the increased current flow at high voltages since Q1 and Q2 are quite sensitive to temperature variations and, since the expo converter is on a breadboard, I don't have the transistors and the tempco sinked together.

Another issue that I must check is the linear response of the VCO -- perhaps it looses sensitivity at higher frequencies. Again, the swing is huge... from 1200Khz to 1Mhz. (yes, you read that correctly, 1 Megahertz!) Of course, at the low frequencies the BBD is at the edge of its capability. About A440 is the best good note from the BBD -- above that it is at the edge of its range.

My hunch is that the expo converter and VCO track 1v/octave in the low range -- much of it the REAL LOW range where perfect tracking isn't as important. I have to find a way to displace the oscillator's frequency such that I'm working on the lower end of the expo converter. I'll try different values for C8 (for starters) and may place an op-amp pair between the expo converter and the VCO to displace the voltage coming off of the expo converter.

Stay tuned... Wink

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