Thru Hole Version of Improved PT2399 Delay PCB Available Now

Check out earlier posts to learn more about this device and see and hear demos. I can’t say enough about how happy I am with this design! The only surface mount part is the MAX 7401 IC which is a SOIC8 and easy to solder.

Go to the link below to download the express pcb file. You can use this, modify it and have the board produced quickly by at a reasonable cost. Check out there site for more detail if you are not familiar with the service

link to zip file with schematic and layout info:

Here is a picture of the layout to scale:

analog_delay_PCBThe Board Layout can easily be altered add PCB Jacks, or resize, etc. Currently it is sized to fit in a 1590B type stomp box.


PT2399 Design Updates

I have produced a PCB and built a new delay using the PCB and the original schematic. The results are gratifying. I did make a couple of minor adjustments.  The board is designed to fit in a 1590b stomp box. It draws 20mA so it works pretty well on a 9V battery.

R12 – changed from 33K to 39K

R2- changed from 56K to 47K

c19- changed from 2000pF to 2200pF

c16- from 247pF to 300pF

PCB Picture:

Video Demo Here:

Updated Schematic:

Alternate Analog Filter for PT2399 Delay

I am using a MAX7401 switchcap filter in my simple delay pedal, but this chip is expensive and not a common junk box part people have on hand. So here is an alterante choice – its only four pole (not 8 pole like the MAX7401) but it should work fine. I use an OPA1652 op amp but others could be used. The op amp needs to be rail to rail because of the 5 volt supply used. A TL072 will not work! I think using the PT2399 for the 1/2 supply ref and sharing the 5Volt supply is a good idea with regard to digital noise.


Filter Plot:

How to Significantly Improve a Simple PT2399 Delay Circuit

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

moonchild solo


Picture of Prototype:

Sound Sample: