Pt80 Delay Boosting signal issue

[Atodovax]

Hello everyone, i built a Pt80 Delay and when the pedal is engagged the singal is sligthly boosted mostyl there is like a boost in the treble. Is that normal? I built it to play clean with my guitar so i dont want that treble boost. Is there a way to get rid of it?

[antonis]

Without  schematic of your specific build is hard to say..

In general, I'll try to enlarge NFB loop cap of last stage op-amp, IF the "unboosted" level of the rest of frequencies is OK..

There of course are other options for that (e.g. respective cap of initial stage..) but that implies to whole signal path and maybe an overall modification should be needed..

P.S.
<I built it to play clean with my guitar>
No signal passed through a modulation device could be considered "clean" anymore..

[Atodovax]

I used GGG layout, i know but i just wnat to get rid of that treble boost, do you have any idea? i dont understand to what capacitor you are referring

[antonis]

It's the only one 47pF cap (as far as I can see..) and is placed between pin 1 & 2 of TL072 dual op-amp..

[ElectricDruid]

Check the 10K resistor and 15nF capacitor in the input buffer and output mixer amps. It looks to me like it does a pre-emphasis/de-emphasis type of noise reduction, so if there's a mistake in those components, it either will over emphasise or won't correct the pre-emphasis correctly after the delay. Either of these could cause too much treble.

Alternatively, as Antonis said, you could just increase the value of the 47pF cap in the output mixer to damp it down a bit more to taste. But if there's actually something wrong somewhere, I'd start with that.

HTH,
Tom

[Atodovax]

Check the 10K resistor and 15nF capacitor in the input buffer and output mixer amps. It looks to me like it does a pre-emphasis/de-emphasis type of noise reduction, so if there's a mistake in those components, it either will over emphasise or won't correct the pre-emphasis correctly after the delay. Either of these could cause too much treble.

Alternatively, as Antonis said, you could just increase the value of the 47pF cap in the output mixer to damp it down a bit more to taste. But if there's actually something wrong somewhere, I'd start with that.

HTH,
Tom

Thank you very much!! I will try that first in case i did something wrong and them try with the cap in the tl072. I will try both tomorrow and update the changes.!!