Credit Card Synth

Inventor

I've been breadboarding some BS and KS circuits lately and I've come up with some minimal circuit implementations that would actually fit on a credit card-sized synth.

This would be an analog implementation. I realize that it could be done in digital using just a PIC and some small external circuitry, so it is not the smallest possible circuit, but it is small for a thru-hole analog version.

Part of the space savings comes from elimination of the LM13700 OTA chip and asosciated discretes, the use of thumbwheel pots, and a fixed song played by the BS circuit. Biased up properly, the whole thing can be run from either a 9V battery or a few 1.5V batteries, or even a solar cell. The output would be an 1/8" jack for output to headphones, computer, or with the right cable/adapter, to a mixer.

I wonder if I should work on such a circuit. Comments?

Les

Dan Lavin · Posted: Tue May 18, 2010 5:41 am Post subject:

Les, as long as you're not diluting your current project /developments, I'd say go for it. Although someone (me, for instance), might not have an application for it, it could encourage further experimentation or inspire another light bulb moment for you or someone else on the forum.

Inventor · Posted: Tue May 18, 2010 7:18 am Post subject:

OK, Dan, I'm actually waiting on others right now for continuation of the KS project and the BS project is awaiting further input from others as well, so I guess I can do this without affecting schedule of BS or KS modular boards.

The block diagram of the circuit that I'm working with goes like this:

555 => 4040 => LogicIC => 555 => BL3102 => BL3207 => opamp => 1/8" jack

with a feedback path from the opamp through a passive RC back to the BL3207. Also there is a small handful of discretes including some thumbwheel pots, R's and C's.

That's all there is to it, 7 chips with most of them being 8 pin DIPs. Actually the first 555 can be eliminated if a 4060 is used instead of a 4040, and the Logic IC can be replaced with resistors if desired, so that reduces the circuit to just 5 chips. Furthermore, only the last 4 chips are required for the KS part of the circuit so that if someone wanted to add KS to say a Lunetta circuit, it would only require 4 8-pin chips.

I'll make time to draw up a schematic later today or tomorrow (or I'll try to anyway).

Les

Inventor · Posted: Tue May 18, 2010 7:49 am Post subject:

Just real quick, here is a preliminary placement of the chips, pots, and jack.

Les

CCS1pcb.pdf

Description:

credit card synth preliminary placement without discretes

Download (listen)

Filename:

CCS1pcb.pdf

Filesize:

13.63 KB

Downloaded:

953 Time(s)

Dan Lavin · Posted: Tue May 18, 2010 10:46 am Post subject:

Hmmmmm.......
So the delay time could be a function of the sequence? That may create some interesting efffects. Or am I reading more into this than you intend?

Inventor · Posted: Tue May 18, 2010 11:40 am Post subject:

Sound · Joined: Jun 06, 2006 Posts: 842 Audio files: 1

Hi Les, I dont understand very well this project, so my first question is: will content this card synth the software of the Boolean Sequencer?

Inventor · Posted: Tue May 18, 2010 4:48 pm Post subject:

droffset · Posted: Tue May 18, 2010 7:19 pm Post subject:

Sorry for being ignorant, but what are the functions of BL3102 and BL3207?

Good choice on 4060, I think this IC is going to be great for small portable thingies.

Inventor · Posted: Tue May 18, 2010 7:36 pm Post subject:

Inventor · Posted: Tue May 18, 2010 7:47 pm Post subject:

Please see this post:

http://www.electro-music.com/forum/post-295938.html#295938

for a radio show on the topic of this thread with over an hour of music made by this circuit.

Les

droffset · Posted: Tue May 18, 2010 8:17 pm Post subject:

Cool I'm starting to listen to it.
So it's like an analog shift register, and it's there to add some reverb?

EDIT
Does it act like a VCA to control decay times?
How is the tomtom sounding one different from the guitar one, which sounds more distorted and complex? Is there filering going on too?

Inventor · Posted: Tue May 18, 2010 9:05 pm Post subject:

droffset, here is the wikipedia page on Karplus Strong:

http://en.wikipedia.org/wiki/Karplus-Strong_string_synthesis

The first illustration shows a block diagram of the KS circuit, which is a feedback loop with a summing amp, a delay line and a filter. You apply a stim pulse and round and round the signal goes, making a percussion or guitar-ish sound. By varying the filter and delay line and loop gain of the summing amp, we can adjust the sound.

Generally longer delays and lower frequency cutoff of the filter create more string-like sounds and shorter delays with higher frequencies create more percussive sounds. Also if you turn up the loop gain you get loud sounds such as what you can hear in the show from time to time.

I think it's an amazing algorithm and it really makes a lot of great sounds with lots of possibilities. Thank you Karplus and Strong!

Les

Inventor · Posted: Wed May 19, 2010 6:17 am Post subject:

This morning I got up early and completed the schematic capture and layout of the credit card synth, attached. It routes well and all the circuitry fits on the board without much room to spare.

I'm not completely sure if the schematic is 100% correct in that I have not breadboarded this exact circuit yet. I'll order parts this week so I can build the breadboard next week. Also I would like to add some sort of compression so that loud feedback squeals do not blast our ears as on the current design.

Les

CCS1sch.pdf

Description:

Credit Card Synth Schematic

Download (listen)

Filename:

CCS1sch.pdf

Filesize:

21.86 KB

Downloaded:

853 Time(s)

CCS1pcb.pdf

Description:

Credit Card Synth PCB

Download (listen)

Filename:

CCS1pcb.pdf

Filesize:

23.34 KB

Downloaded:

711 Time(s)

electri-fire · Posted: Wed May 19, 2010 10:36 am Post subject:

electri-fire · Posted: Wed May 19, 2010 1:15 pm Post subject:

electri-fire · Posted: Wed May 19, 2010 1:51 pm Post subject:

Les, you already had an idea about a compressor , but this is what I meant. It may change the sound as well, clipping the signal asymmetrically with loud sounds. I tend to quite like that usually.

simple dirty compressor.png

Description:

Filesize:

23.02 KB

Viewed:

635 Time(s)

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

Inventor · Posted: Wed May 19, 2010 2:08 pm Post subject:

Yes, Mathe, I got what you meant from your previous description. Sounds like a cool idea but there are some mechanical issues. It requires hand assembly and bending of wires and heat shrink or other optical isolation. It's a cool way to go for onesie-twosies, but I tend to design for production.

I was thinking of a diode and resistor in feedback or something, not sure... Or a clamp at the bias of the MN3207, that would do it, just like on the modular KS board.

Well, more thought is needed and we can use such a circuit in our workshop, but for this board I'm not sure if it will be appropriate. Please do keep those ideas flowing, though, my friend!

Les

Sound · Joined: Jun 06, 2006 Posts: 842 Audio files: 1

A Ok, I'm interested in this project, so I'm ordering those chips. Ill breadboard it.

About the compressor maybe a ready build Vactrol?

Sound · Joined: Jun 06, 2006 Posts: 842 Audio files: 1

OK,

Which are the prefixes of 4070N and 4060 ? HEF4070BP, 74HC4060N?
Where I can found BL2102 and BL3207?

Very Happy

Inventor · Posted: Thu May 20, 2010 8:48 am Post subject:

Yes Sound, that is very similar to what I was thinking. With a zener diode implementation you would connect the two diodes in series, and with a diode or LED implementation you would connect the two diodes in parallel. I don't have much of an idea what the resistor value should be.

Les

Sound · Joined: Jun 06, 2006 Posts: 842 Audio files: 1

Inventor · Posted: Thu May 20, 2010 8:50 am Post subject:

Sound · Joined: Jun 06, 2006 Posts: 842 Audio files: 1

electri-fire · Posted: Thu May 20, 2010 10:19 am Post subject: