Simple ltc1799 pitch modification of a Korg Electribe and a bit of back story.

The fun bit first:

Now a bit of back story:

I love, love, love using the Linear Technology LTC1799 for clock replacement of things like samplers, drum machines and synthesizers.   It is a small chip that, by outputting square waves at frequencies from 100khz to  33mhz, acts in the same manner as a clock crystal for digital devices.

What makes it interesting for modifying older instruments is that it is resistance controlled and so you can use just a few components to make a really powerful tool.

To use it, I just need a +5v source, a couple resistors or a resistor and a potentiometer, a capacitor and, ideally, a multimeter or a frequency counter to make sure it's outputting the right frequency.

You'll only need to make 3 connections on the device you're modifying- clock, ground, and 5v.


Here's a link to the product page

What makes the ltc1799 interesting from a musical perspective is that modifying clock speed has the effect of modifying sample rate of both playback and recording.  By lowering or raising the sample rate on playback, you end up with a differently pitched sound, one that often has really beautiful lofi artifacting.  On recording, lowering the sample rate reduces the quality of the audio being sampled and introduces (sometimes) pleasant noises.  A neat side effect is that you can store dramatically more samples (at a lower quality) in many sampler than you'd normally be able to.

I've modified many instruments with them, several examples, including other Electribes, can be found on my Youtube page:

Click here for examples.

I've alsowritten a little program for AVR/Arduino that allows for clock rate modification of nearly any digital audio device using a variety of controls, I've got it working with an internal function generator, external audio and a variety of  analog signal sources.  Here's an early demo:

I'll be updating with a better example.


Now on to the Korg ES-1.  It's a sampler with the standard step sequencer that all of the Electribe line uses. They are all simple to operate, easy to understand and are really fun to just mess around with.  Because of the simplicity and hands on nature of these things, I really love adding clock modifications and love playing with the pitch in real time as I play the instrument.
 
To start with, I built this probe tool, below:

This is an old ammeter that I used to house an ltc1799 based signal injector.

Aside from the enclosure and the ltc the parts list is really simple, some batteries, a potentiometer, a 3k resistor and a bnc jack.  It works GREAT.  I clip one lead to ground of the device in question and the other to the clock I want to replace.

I measured, using my multimeter and oscilloscope, the stock clock speed of the Electribe to be 16Mhz or so.   Using my clock generator, I tested the upper and lower ends of the stability, in which midi and audio still consistently work for the ES-1 to be ~29Mhz  on the upper end and ~1.5mhz on the lower end.

This is a huge sweep and I realized that the sound doesn't really change past 2.5mhz, so I set my upper and lower resistance values accordingly

The formula to determine the clock frequency is quite easy:

F=100/R, where R is resistance in Kohms and F is frequency in Mhz.

 So, for a given resistance to determine frequency:

F=100/R

and for a given frequency to determine resistance:

R=100/F

So, for a 2.5Mhz to 29Mhz range,  I would need a minimum resistance of ~3.5Kohm and a max resistance of ~36Kohm.  I decided to use a  100k potentiometer with 47Kohm resistor across the leads.

Since everything tested fine in that range, all that was left was to build up the circuit with the mentioned components:

The pictures below give a bit of detail for the modification:

The underside of the Electribe ES-1, before the modification.

This is the location of the clock crystal that I removed.
Note that I remove the stock crystal rather than leave it in as others do.
I find stability of the system to increase and sound quality to improve.
Also, having 2 devices outputting a clock signal to the same destination is just...ugly.

This is the bottom of the ES-1, with the clock and +5volt wires running out.
Note the ltc1799 module.
  I buy in bulk from a Hong Kong Ebay seller and they're fantastic quality at a cheap price.

A small switch gives the scale of the module. It's about an inch square 

I've added the potentiometer and closed up the device.
Here are a couple angles of the finished work

I'd have loved to use the stock Electribe pot covers,
but they didn't quite fit.

And finally a few images of the finished product

This whole project should only take about an hour or so and
should only cost about $10 in parts.