The Karplus Strong eChucK DIY Project

Dan Lavin · Posted: Mon Jan 18, 2010 7:55 pm Post subject:

I think if you could spell out the cap locations, that would be good enough. I didn't have any resistor problems that I can remember. Well...we'll see when I fire it up....I don't think I had any other problems outside the caps!

Dan Lavin · Posted: Wed Jan 27, 2010 4:00 pm Post subject:

Well, my board is all done with the exception of the board mount pots. They're on backorder with Mouser until sometime next month. Sad

Inventor · Posted: Wed Jan 27, 2010 5:59 pm Post subject:

wmonk · Posted: Wed Feb 03, 2010 3:47 pm Post subject:

Well, I started populating the board today.
A few things: some designators are very difficult to read. Are C14 and R36 overlapping?
Everything is spaced ok, but I think its better to do somewhat bigger pads for the zeners, as those have big leads.
I didn't realise there were some strange component values in the BOM when I ordered parts. Especially the 40k resistor. Never seen that one. Wink

Inventor · Posted: Thu Feb 04, 2010 1:50 am Post subject:

Oh yes, thanks wmonk. C14 and R36 are adjacent and have overlapping reference designators, yes. I will fix the zeners. The 40k value is approximate, use the closest value that you have. Thanks for helping to work out the bugs.

Les

wmonk · Posted: Thu Feb 04, 2010 6:04 am Post subject:

Ok, will change the 40k to 39k. Same for the 5.11k resistor, that can be 5.1k I think? or has it to be that precise?

Inventor · Posted: Thu Feb 04, 2010 6:48 am Post subject:

wmonk · Posted: Thu Feb 04, 2010 9:32 am Post subject:

Reworked the BOM with your notes.
Please download it, and add the capacitor types to the list! Very Happy

20100204-karplus-strong-BOM.txt

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Inventor · Posted: Thu Feb 04, 2010 7:15 pm Post subject:

Here is the BOM that wmonk edited with the capacitor types listed. "electro" means "electrolytic".

Les

20100204=karplus-strong-BOM.txt

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Inventor · Posted: Sat Feb 06, 2010 9:21 pm Post subject:

Oh yes, another note for anyone building the KS board: Leave the LEDs off. They are there for experimenting with a distortion output stage and the resistor values need to be adjusted to make the distortion work properly.

Les

DGTom · Posted: Tue Feb 09, 2010 7:14 am Post subject:

My board arrived this week! Very Happy

I'm waiting on a shipment of IC sockets & LM13700s + I still need to place an order w/ smallbear for the BBD chips but I'll start before they get here.

I'll be building for a modular system, with no bells or whistles, so, no LEDs?

Inventor · Posted: Tue Feb 09, 2010 9:29 am Post subject:

wmonk · Posted: Tue Feb 09, 2010 12:14 pm Post subject:

Updated the BOM.

20100204-karplus-strong-BOM.txt

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Inventor · Posted: Tue Feb 09, 2010 12:39 pm Post subject:

Wow wmonk, I really like what you did with the BOM, thanks!

Les

wmonk · Posted: Tue Feb 09, 2010 1:53 pm Post subject:

Thanks Inventor. I like to have it as clear as possible, so I made it for myself, and everyone who wants it Smile

Dan Lavin · Posted: Thu Feb 25, 2010 9:52 am Post subject:

Les,

I'm still having potentiometer headaches (getting them).
What are you planning to use for R39, R42 and R43?
Distributor and SKU number would be appreciated!
Thanks!

Inventor · Posted: Thu Feb 25, 2010 10:14 am Post subject:

Dan, I couldn't find pots with 0.2" spacing on DigiKey so I just got some Bourns pots with 0.1" spacing and plan to bend the leads.

Les

Inventor · Posted: Fri Feb 26, 2010 3:15 am Post subject:

I spent six hours all night long building and testing my first KS PCB (the parts arrived last night). The good news is that the circuit works great! The bad news is there are a few minor errors that will require correcting for the second run of boards.

The BOM has an error, R43 is a 100k pot, not a 10k pot. This is causing limited gain adjustment so the sustain is affected. I have to run to radio shack and get some 100k pots later today I guess.

Warning: C11 and C18 have reversed reference designators! Put the 0.1uF cap where it says C11 and the 10uF cap where it says C18. This is backwards and must be fixed next spin.

In the photo below, you see the board (sorry for poor lighting and focus) with a small stim board on the left. This is for test purposes and it makes the KS board be a stand-alone system with 1/8" jack output. To test it, I just plugged in a pair of PC speakers and heard glorious noise!

FirstKSPCB.jpg

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PCB proto, first one of mine. Tested and working (mostly).

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electri-fire · Posted: Fri Feb 26, 2010 4:24 am Post subject:

Nice!

In the BOM wmonk updated Tue Feb 09, 2010 the correct value for potmeter R43 ( 100k) was used.

Inventor · Posted: Fri Feb 26, 2010 5:38 am Post subject:

Oh yeah, it's R35 that's incorrect - should be 100k.

Les

Inventor · Posted: Fri Feb 26, 2010 10:07 am Post subject:

I worked with wmonk this morning online while streaming the audio output from the KS board. We tried a few things to get good sound out of it, and ended up shorting four resistors and then the big fix was to reduce the value of the VCF cap by a factor of 10. Then it sounded just like the original breadboarded prototype! Here is a list of all the changes to be put into place for the second spin of the board:

o indicate polarity on electrolytic caps
o fix hole size on 1/8" jack footprint
o bigger zener pads
o fix reference designators (overlaps)
o get correct value of 40k resistor
o C1, C6, C12, and C13 are too close to other parts
o toggle switch is upside down
o add power LED
o C11 and C18 reference designators are backwards
o short 10k resistors on VCO & VCF pot ends
o VCF cap should be 0.0022uf, not 0.022uF
o remove distortion & PWM circuitry, also remove input 1/8" jack
o and the big one: add expo converters!

That's it, several minor changes. There were no cut traces or jumpers at all, thank goodness. My biggest concern was that I might have gotten some of the pinouts incorrect, but they are fine. Overall I'm fairly pleased with this as a first run board. It's a little bit tough to build because of the silkscreen errors, but such things are to be expected.

Next month I'll fill in some missing parts with another DigiKey order and build the remaining three boards. Hopefully wmonk will help out with the expo converter if he gets time, or else I will do that part of it.

Les

Dan Lavin · Posted: Fri Feb 26, 2010 12:58 pm Post subject:

Les,
Can you pls update the schematic, less the expo convertors? I think that will help the rest of us with trouble shooting. Thanks!

Inventor · Posted: Fri Feb 26, 2010 1:43 pm Post subject:

Inventor · Posted: Fri Feb 26, 2010 5:57 pm Post subject:

OK Dan, It only took a few minutes because I only made the changes that are relevant to building the first run boards. I deleted the PWM input circuitry and the distortion feedback, then changed some component values. Note that the four resistors labeled as 0 ohms should be populated with wires. Remember that C11 and C18 have reversed reference designators.

Les

KS8sch.pdf

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Updated Schematic

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Dan Lavin · Posted: Sat Feb 27, 2010 6:44 am Post subject:

Thanks, Les! Yeah, it's simpler now too. My final Bass Guitar project will probably incorporate a separate fuzz and perhaps a chorus, too., But I'd want those on a separate board. Of course, the expo converter will make it less simpler when that's added.