Lots of great PT2399 designs out there….. I have tried a number different variations and have built what I consider a best performance design, using a compander, elaborate filters, etc. I have been frustrated as many builders out there are – that the PT2399 is so easy to use but that it just goes to crap with longer delay times! So I decided to work and experiment with different approaches to converge on a simple, yet well performing design. I am really happy with what I have come up with.
The design uses a discrete FET input buffer and uses one of the on board op amps as the wet/dry mixer. The dry signal always passes through and the effect is defeated by just opening the connection of the signal input to the delay chip. This allows “tails” or the echos to naturally decay even when the delay is bypassed. There are two features that make this circuit perform really well. One, the cap between pins 9,10 is made much larger than typical in other designs and the data sheet reference design and two, I use a 8 pole switch cap filter IC for the post delay aliasing filter. The larger cap provide significant increase in the delay output but the noise remains at the same level. I then attenuate the output in the wet dry mixer to the normal level this also downward expands the noise. The switch cap filter is really simple, requiring only one capacitor to set the corner freq from 1Hz to 5KHz. It is very easy to implement and has excellent performance. The total circuit rivals the simplest bare bones designs but approaches the performance of the more advanced circuits such as the PT80 delay.
Below are the schematic, a picture of a breadboarded prototype and some example audio of the prototype below, in use.
Updated Version in pedal form
Picture of Prototype: https://circuitsaladdotcom.files.wordpress.com/2012/09/delay_proto.jpg