untitled Chorus/Vibrato pedal
Posted: 13 Jan 2022, 08:58
here's a little design i threw together based on a neat little digital delay chip i found on AliExpress while looking to build a vibrato with a better frequency range than analog can provide.
its a fairly standard chorus/vibrato-with-blend type of deal, nothing super novel or innovative, more a proof of concept than anything. i've just borrowed the LFO from the VB-2 since i wanted a sine wave. and since it also had its own precision Vref supply, which i like, so i could keep it isolated from the audio supply.
the anti-aliasing and reconstruction filters are 3rd order multiple feedback type with a cutoff around 6-7kHz, mostly per the datasheet. i didn't bother with pre/de-emphasis filters since i wanted extra low end sensitivity to use with bass. there's an output gain control for some boost which i find useful in pedals that deal with phasey stuff.
i've confirmed the circuit to work on breadboard, although my vero build is mysteriously haunted (though its only the LFO that doesn't work).
just for fun i used an RGB LED to get colour-changing rate indication.
i used an LT1058 for the audio path since i had some, its like a TL074 with slightly lower noise and current draw, and no phase inversions.
star of the show is the M65850P from mitsubishi, very similar to the faithful PT2399 in many ways but with some fun bonuses:
built-in startup delay (wooo! no burnout); DIP-14 instead of 16; and it can get down to a cool 15ms delay time.
however, the max delay time is only about 200ms so I wouldn't bother to use it for a delay build (2399 is still DIY king here)
like with its cousin the delay time is current controlled (though this chip sinks, rather than sourcing as the 2399 does) and not internally compensated so modulation is very easy to set up, i just split the current supply resistor in half and plugged some AC current in there, instant wobble. there are probably better ways to do it and i'm exploring those for a 2-chip through-zero capable flanger i'm developing, but for now this works.
i've measured the current draw at 20-25 mA. not unexpected for a digital chip.
although its out of production now, they are still available in DIY quantities from resellers, etc. i managed to find a bunch for less than 1 NZD each.
here's the datasheet i used:
its a fairly standard chorus/vibrato-with-blend type of deal, nothing super novel or innovative, more a proof of concept than anything. i've just borrowed the LFO from the VB-2 since i wanted a sine wave. and since it also had its own precision Vref supply, which i like, so i could keep it isolated from the audio supply.
the anti-aliasing and reconstruction filters are 3rd order multiple feedback type with a cutoff around 6-7kHz, mostly per the datasheet. i didn't bother with pre/de-emphasis filters since i wanted extra low end sensitivity to use with bass. there's an output gain control for some boost which i find useful in pedals that deal with phasey stuff.
just for fun i used an RGB LED to get colour-changing rate indication.
i used an LT1058 for the audio path since i had some, its like a TL074 with slightly lower noise and current draw, and no phase inversions.
star of the show is the M65850P from mitsubishi, very similar to the faithful PT2399 in many ways but with some fun bonuses:
built-in startup delay (wooo! no burnout); DIP-14 instead of 16; and it can get down to a cool 15ms delay time.
however, the max delay time is only about 200ms so I wouldn't bother to use it for a delay build (2399 is still DIY king here)
like with its cousin the delay time is current controlled (though this chip sinks, rather than sourcing as the 2399 does) and not internally compensated so modulation is very easy to set up, i just split the current supply resistor in half and plugged some AC current in there, instant wobble. there are probably better ways to do it and i'm exploring those for a 2-chip through-zero capable flanger i'm developing, but for now this works.
i've measured the current draw at 20-25 mA. not unexpected for a digital chip.
although its out of production now, they are still available in DIY quantities from resellers, etc. i managed to find a bunch for less than 1 NZD each.
here's the datasheet i used:
M65850P.pdf- (3.87 MiB) Downloaded 71 times
