Skiraly017 figured out that you can affect the amount of treble roll-off by switching out a couple of caps.
Here's where this all started - Delay roll off Part 1.
The values used in today's testing were 0.0018uF, 0.0022uF and 0.0027uF.
I had some free time today so I decided to experiment some more. I found the easiest way to look at things was this. Think of the 0.0027uF in the upper position as the cap that sets/affects the amount of treble that gets rolled off on the first
repeat. However much treble you decide to roll off here will only increase in the repeats that follow. The 0.0027uF in the lower position affects the amount of treble rolled off in subsequent repeats. That being said, here's what I found -
The lowest value in the upper position that I found useable without producing any undesireable side effects was a 0.0018uF. When I dropped below that, the limitations of the PT2399 started to show. If you want the absolute cleanest sound delay available from the circuit, the 0.0018uF's in both positions is the way to go. The treble roll off is slight but noticeable in the initial and subsequent repeats but may be too clean or not "analog" enough for some. Personally I like it.
I think the best way to approach this is to install sockets on the PCB for the upper and lower cap positions, gather up two each of the values from 0.0018uF to 0.0027uF and start swapping. Try setting the upper position/initial repeat sound first. Start with the 0.0018uF, hit a note or chord and listen to that first repeat only. If you want to hear the biggest difference, replace it with a 0.0027uF and play the note/chorg again. Notice how much treble rolls off that first repeat. Once you get that where you want it, go through the same process with the lower cap. The lower value the cap in the lower position, the less treble roll off over the greater length of time. The higher the value, the faster the treble will roll off with each repeat. The ideal test situation would be to have two delay pedals side by side, one stock and one with socketed caps. In lieu of that I would strongly recommend a capacitor substitution box
(last item on the page). For $16.99 you can't go wrong and it would undoubtedly come in handy for other projects. A possibly cool mod to the delay would be installing two switches...one that would allow you to set the roll off for the initial repeat and the other to set the roll off for subsequent repeats. I hope this helps out and if I was unclear during any part of this post please do not hesitate to ask questions.
Now on to figuring out how kill the switch pop in the delay!
After playing with the treble roll off some more, my suggestion would be this. Replace the upper 0.0027uf with a DPDT on/on toggle with a 0.0018uF on one side and a 0.0027uF on the other. Replace the lower 0.0027uF with a 0.0022uF. To my ears this gives you the ability to switch between very nice clean(er) analog sounding repeats (0.0018uf + 0.0022uF) and darker sounding repeats (0.0027uF + 0.0022uF) where the treble rolls off quicker. The easiest way to hear the difference is to set the Delay and Blend all the way up and set the Repeats to the maximum before oscillation kicks in.