weird stuff with pt2399

[thetragichero]

so i had a hankering to try to add an analog octave sound to the feedback loop of a pt2399 delay. why? i dunno, to see if i could?
so i breadboarded the smalltime delay (http://www.valvewizard.co.uk/smalltime.html) and tried various spots to shoehorn the octave portion of the maestro brassmaster (basically a diode ring into a transformer) with very little satisfactory results
so i thought about pins 9-12 and how there's some internal op amps, etc going on. tried a bunch of combinations but the only pair that really worked was removing the capacitor between pins 9 and 10, putting the input to my octave circuit block on pin 9 and the output on pin 10 (which is weird since that seems to be using the internal op amp backwards). repeats pot has to be increased considerably (i had 100k in there but 1M seems to work) to get more than one repeat, but it works about as well as i intended! since I'm planning to put the octave on a footswitch instead of having an led fit the octave i suppose i will place a resistor in parallel to the repeats pot fur when it is in normal delay mode

anyone else end up with weird tricks for the pt2399?

[vigilante397]

Wait. So like. Dry signal unaffected, delays have an octave?

That's cool.

[BluffChill]

Put simply,

Your dry signal goes into the PT2399 at pin 16, and comes out at pin 15.

The chip does all its wizardry to produce a repeat at pin 12. You can then do some extra filtering on it using the second LPF, which is pins 13 and 14. The signal feeds from pin 12 into pin 13 via a resistor, then there's another resistor and capcitor across pins 12-14 to set the gain and filter (like an inverting op amp). You can now get your nice, filtered signal from pin 14.

It's probably not going to be loud enough to drive the same ring-modulator from a Brassmaster. It will need substantial boosting as the PT2399 only accepts low level signals without distorting.

Oh by the way, I did something very similar a few years ago with the 'Hyper Light Delay' - except it went into an LMC567 based ring mod, so the repeats were robotic and twinkly, and the dry stayed dry.



I didn't use the extra filter on pins 13 and 14, but you get the idea. This circuit wasn't perfect but it sounded cool.

[Kipper4]

I did this to it

https://www.diystompboxes.com/smfforum/index.php?topic=120121.msg1123830#msg1123830

[thetragichero]

huh so that explains why when i tried installing an op amp gain stage before and after my circuit block it sounded worse if anything
i like knowing the "whys/hows" so that my tinkering becomes more informed and less blindly moving components
also glad to hear other folks have had similar ideas

[BluffChill]

huh so that explains why when i tried installing an op amp gain stage before and after my circuit block it sounded worse if anything
i like knowing the "whys/hows" so that my tinkering becomes more informed and less blindly moving components
also glad to hear other folks have had similar ideas

You should decrease the signal before going into a PT2399 - it has very limited headroom. You can raise the gain afterwards.