PT2399 Feedblast Mod?

[thehallofshields]

So I've got a pretty standard PT2399 Delay on Breadboard, and I want to add some crazyness on a momentary switch.

I came across a DIY PT2399 kit from Synthrotek and their mods seem right up my alley.
https://www.youtube.com/watch?v=iCQfKD-kTh4

Here are the instructions for the mods:


Here is the schematic:


The instructions basically say to bypass the Cap on Pin9 with a 200k Resistor (on a momentary switch). The circuit in the video doesn't even use the 200k resistor.

[thehallofshields]

Unfortunately, shorting Pin8 does nothing interesting on my basic PT2399 build. I'm going straight of the Product Datasheet.

[ElectricDruid]

I'm unable to make head nor tail of those instructions, even with the schematic in front of me. Maybe, once I've had enough cups of tea.

Would have been nice if they'd added the mods to the schematic...

[thehallofshields]

I'm unable to make head nor tail of those instructions, even with the schematic in front of me. Maybe, once I've had enough cups of tea.

Would have been nice if they'd added the mods to the schematic...

Circuit Benders right?

Now looking a little closer, their circuit is EXACTLY the design from the Datasheet. So what I have bread-boarded is near identical.

[anotherjim]

Pins 8 & 9 are some low-pass integrator-like function on the record input. Hence the cap, but there is supposed to be a fixed internal 4k7 between those pins too, so I doubt fitting a resistor of >47k would change things much. A momentary short 8 to 9 might just kill recording for the duration? An open circuit could make it gritty/digital? Dunno, haven't tried any of that myself.
I think the other mods we know, but the method seems clunky.

[Mark Hammer]

Rather than "crazy" mods, I prefer things one can use.  And one of those is a "punch-in" function.  In the days of mag tape, higher-quality decks would come with punch-in capability such that you could listen to what was already recorded, hit a button at the right moment, and record sound-on-sound along with what you were listening to.

Delays, whether analog or digital (like the PT2399) normally assume that, if the effect is engaged, whatever hits the input to the pedal will be fed to the delay line and blended back with the dry signal at some desirable level.  Some delays provide a "tails" function such that whatever is currently in the delay path is allowed to spool out until its done, when you hit bypass.   A "punch-in" function complements tails by allowing you to insert new signal into the delay path in an on-demand fashion, using a momentary switch, such that you could add delay to a single note or phrase or whatever you choose, for as long as you hold the momentary switch down.  Lift your foot, and the tails function allows whatever you've put into the delay path to continue, but no delay is added to whatever you play after you lift your foot.

The value of this function is that it doesn't require two separate-and-precise stepping motions.  Lifting your foot is more fluid then stepping a second time, and allows for more precision as well.

What it does require, however, is somewhere to situate a second momentary footswitch, and some reasonable means of electronically defeating input to the delay path via the action of a momentary footswitch. 

So, let's say you had a momentary normally-closed switch.  If you wired it up in parallel with the 3900pf cap to ground in that datasheet schematic, then the input to the PT2399 would normally be shunted to ground.  Step on the switch, and the input now becomes enabled.  Of course, such switches are tricky to find and not cheap.  So we'll assume a normally-open type, readily available from many sources.  If that 15k resistor is turned into something much higher, like 470k or even 1M, then very little makes it to the chip's input.  But allow that momentary switch to strap a 15k resistor in parallel, and bingo-bango you feed signal to the delay.

[BetterOffShred]

Yeah man, the "Punch in" button was suggested to me in the Echo Base thread, and I'm really looking forward to it.  It's neat to be able to inject new little bits in while your repeats are just a smidge from infinite ..  very cool. 

[reddesert]

What it does require, however, is somewhere to situate a second momentary footswitch, and some reasonable means of electronically defeating input to the delay path via the action of a momentary footswitch. 

So, let's say you had a momentary normally-closed switch.  If you wired it up in parallel with the 3900pf cap to ground in that datasheet schematic, then the input to the PT2399 would normally be shunted to ground.  Step on the switch, and the input now becomes enabled.  Of course, such switches are tricky to find and not cheap.

DPDT momentary footswitches are pretty common and not expensive as far as I can tell. That would work for the momentary NC action. I'm not sure how one would arrange for the input-defeat-defeat function that would take it out of punch-in mode and back to normal mode (you could have a third switch that takes the punch-in switch out of the circuit, but that is getting crowded).

[Mark Hammer]

The enabling of a punch-in function likely would require a separate toggle.  The good news is that situating a small toggle is less problematic than installing a separate footswitch which has sufficient space between it and a) the main bypass footswitch and b) the controls.

I have some momentary DPDTs, but find their compulsory hard-click detracts from fluid use. In this application, soft-touch is preferred.  It's the ease of actuation that provides for the precision one wants.

BTW, if you pull a momentary DPDT apart, you'll find that internally they are largely identical to latching footswitches.  The difference is that the little banana-shape rocker contacts inside have a little bend to them that prevents the tiny arms that move the contacts from coming to rest on either side.  The bend pushes them back to where they were.

[ElectricDruid]

I have to say that after having used momentary SPST switches to do the effect in/out bypass switching on the Digidelay project, I'd actually prefer them over switches with a hard click in every situation if I could work out a simple way to do it.

Obviously you can add a flip-flop and some FETs or a uP and a relay or something and *that works*, but it doesn't fit my definition of "simple". That said, in many ways the benefits outweigh the costs. The switches are cheaper and simpler (and I suspect more reliable as a result) and I like the no-click feel much more than a heavy stomp to get some hideous mechanical mechanism to go "CRUNCH" underfoot.

There may come a time where all Druid pedals have soft-touch switching. Jus' warning y'now so y'can get used to the idea...

[thehallofshields]

Rather than "crazy" mods, I prefer things one can use. 

Getting a little bit of messyness and oscillation on a momentary switch seems useful to me. Both the Caroline Meteore & Kilobyte (Analog) and the EQD Avalanche (Digital) have these and the users seem to love them.

[thehallofshields]

As far as the WARP Mod goes; I can confirm that connecting the Signal Input (at the 10k Resistors at Pin 15 and 16) to Pin6 (between the Resistor and Pot) does some interesting stuff to the sound.