Hi guys i built the DH Pitch Shifter at General Guitar Gadjets and i get lots of noise when i play chords hard. Except this it works well, i checked all voltages and everything seems ok. I also checked the circuit with the audio probe and i saw that there was noise even at HT8950's output (pin9). Any suggestions?

How about noise coming out of one or both of the opamp stages? Maybe you could dial back the opamp gain a bit?

What kind of "noise" is it? might be overloading, clipping.
Opamp noise isn't dependant on the signal type or level, but clipping or intermodulation artifacts are.

Quote from: Paul Perry (Frostwave)What kind of "noise" is it? might be overloading, clipping.

Highly likely with this chip as there isn't much headroom from 3V!

Whaddaya mean 3V? Looks like it all plugs into 9v... :?

Quote from: smoguzbenjaminWhaddaya mean 3V? Looks like it all plugs into 9v... :?

Take a closer look and you'll see 3.6V zeners providing the bias.  The  HT8950 chip can only handle a ABSOLUTE max of 5.5V.  The recommended range is 2.4 - 4V.

Yeah I think the typical supply is about +/- 3.5 V

i think you should add a compander like it's used in analog delays or the pt80  digital delay, plenty of suitable schematics are around

i think you should add a compander like it's used in analog delays or the pt80  digital delay, plenty of suitable schematics are around

Thank you for responding. I don't know how to describe this sound, but it is really annoying maybe it's clipping because it happens when i hit hard chordsand notes. I checked with the audio probe the output of the first opamp that is feeding the HT8950 with signal and it's crystal clean. The only strange thing that i noticed is that although i use 3.6V zeners for
the power supply i get +/- 4.1V. Do you think the 4.1V makes the chip to work bad? And something else i can't hear any real difference between robot and vibrato mode.