i’ve been wrapped up in Jeep repair lately as there’s some sort of issue prevent the beloved XJ from firing up. i have, however, in the meantime had some time to work through my initial modulation tests on this version of the PT2399 circuit and nail down a lot of the bugs.
the initial problems were stabilizing the LFO and purging the noise from the chip. as you well know from the datasheet, the PT2399 has very little storage space. it also makes a lot of racket on the output of pin 14. i was able to use 2nF caps on the input to really filter some of that out and get the thing pretty quiet. the LFO problems were locked down thanks to the EchoBase schematic. the final draft will include an SPDT which will switch between the square and triangle wave. the audio test features only the triangle side of things.
as for the audio, the first part is long delay with light modulation and moderate rate. the second is short delay with slow modulation, and the last is kind of a slap-back delay with faster modulation.
i’m really looking forward to getting this one off the breadboard and into a usable stompbox. thanks to all of those people at DIY Stomp boxes who post information. it’s been a big help.