Pitch Pirate Deluxe a bit dark at some settings

[nonost]

Hi. I built a Pitch Pirate Deluxe time ago. It works great but I've always wondered if there's an easy way of brighten the sound a bit, since I find some settings a bit in the dark side. The wet signal is somewhat muddy with the vibrato.

Here schematic:

https://www.diystompboxes.com/smfforum/index.php?topic=88109.0

I thought about the 100nf cap at the output. I should reduce the bass content, but it would affect both wet and dry signal...

Cheers!

[Rob Strand]

I'm using Bluebunny's schematic at the end.

If you change the 2x1nF caps C2 and C3 on pins 15/16 and pin 13/14 to say 680pF (ceramics) it should brighten the sound a bit.

For more bass increase on both wet and dry paths increase C1 to say 22nF or 33nF

You can experiment with the bass and filter caps.

The 100nF probably isn't doing much in comparison.

There's a few odd things about that circuit:

To me it looks like the dry signal path is affected by the filtering parts from C1 through to C2.

It also looks like the dry signal on pin 15 the has the wrong phase to be blending with delayed output.
That's going to do some weird stuff like cancelling the low-end.

That being the case you need a lot of re-jigging to correct the design.   Sometimes these things are what that are.

You can see in this schematic the output is blended but the Dry signal is tapped off before the filtering; starting at the 0.1uF at the output of the first opamp.

https://i.pinimg.com/originals/a9/07/e9/a907e91822529692b024d92e968aee7a.png

[anotherjim]

It's the PT2399 datasheet example multiple feedback filter with one cap removed both for the input and output. That leaves a redundant resistor really, and it may as well be x1 input R, x1 feedback R and x1 feedback C. For guitar FX, this simplified filtering is all that's needed as the sampling rate of the chip is very fast -  unless for very long delay times when the filters would need larger caps anyway (and would then be too dark for taste).
Notice the input opamp is a comparator fuzz & will be banging out square waves 0v to about 7.5v off a 9v supply (why not run it at 5v?) I see no instruction to tie off the unused half of the 358. TL072 is an odd choice for the LFO.

I think of one way some settings could cause unexpected filtering...
The delay signal could be inverted with respect to the input by the opamp in pins 13 & 14. Now with a squared-up input signal, the delay input is a very consistent sound. When it is mixed in the blend, at some delay times the input and output signals are so similar you get a phase cancellation. This is not an issue with normal clean or character delays (some distortion in the delay only) since the signal always varies over time and differs in character from the delayed signal so the blend never produces any unnatural cancellations.
This might be a little better if the dry side of the blend was fed from the output of the 358 so it isn't filtered but it would be too loud for the blend without more changes.

[Andon]

TL072 is an odd choice for the LFO.

Just curious on your thoughts about the TL072 being an odd choice for the LFO, as I tend to see it utilized a lot for that purpose? Do you mean that something like a TL062 would be better since it draws less power and would introduce less noise, or do you think a different family of IC would be better suited?

Also, for the comparator, you mention powering it at 5V so that it will sit closer to the 5V on the PT2399, correct?

[anotherjim]

The issue with TL072 in this role is the supply current - because IC2b switching states (the square wave output) is too fast and more likely to cause ticking in the audio. TL062 is both less hungry and slower.

The LM358 probably would better match the PT2399 if it ran off 5v. That said, if its output exceeds 5v it shouldn't damage the delay chip - the excess voltage will just be absorbed by the resistors into pin16.

[nonost]

I've been reading quite a bit about the PT2399. Pretty interesting stuff.

The deluxe version of the Pitch Pirate can be used it as a vibrato and delay on their own, as well as delayed-vibrato. It is in the vibrato-only when it sounds a bit dark. It helps the lofiness I guess...In this "mode" you need all the wet signal. At 50%-50% there's a good chorus.

I found the schematic in the other forum. I've attached it here. If that's not ok, please let me know and I will sort it out.

In the delay-only you don't have such a problem because the signal is usually at least 50%-50%, and even though the repeats are warm and not as bright as the dry signal, I really like that being that way. Darker repeats sounds great to me.

I'm going to try a reverse log for the Speed pot. The rest is great.

The cap at pins 13-14 filters the output quite a bit. Lower values make the repeats sound really good but with the PT2399 noise we all know about. As you increase the value, the noise fades away but the sound is not as good. That's for long repeats, at short delays there's no problem. I'm going to use the DPDT switch for this pins: no cap (that works great for the only vibrato mode and shorts delays), 1nf (stock value) and 2nf (for the last part of the time pot). At 2nf the sound detrimental is obvious.

Thank you both for your help!

[duck_arse]

that "circuit diagram" has some sort of error around C5. the whole diagram needs to be straightened out.