untitled Chorus/Vibrato pedal

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asbestosaurus
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Post by asbestosaurus »

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.
chorus vibrato.PNG
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:
M65850P.pdf
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Ben N
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Post by Ben N »

With that short min delay, I would imagine this chip would be ideal for an ADT type effect. Asbesto, does your project do that? Might also work great for flanging.

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Post by asbestosaurus »

Ben N wrote: 24 Jan 2022, 13:15 With that short min delay, I would imagine this chip would be ideal for an ADT type effect. Asbesto, does your project do that? Might also work great for flanging.
Analog Double Tracker?
Automatic Double Tracker?
Not entirely sure what ADT means here but it almost certainly could, with a little tweaking.

In this design the delay time sits around 30ms with the LFO depth at minimum, (entirely shunted to ground potential)
which isn't much better than the 2399.

15ms might be close enough for a flanger with just one chip, i do have a conceptual schem for a 2 delay-chip flanger i may post soon.

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Post by Ben N »

Artificial/Automatic Double Tracking. 25-75 ms with slight modulation of pitch and/or delay time. https://en.wikipedia.org/wiki/Automatic_double_tracking
https://www.youtube.com/watch?v=OIzylCWOG58
https://www.youtube.com/watch?v=-3jTSw0grXg

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Reachahighernoon
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Post by Reachahighernoon »

asbestosaurus wrote: 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.

chorus vibrato.PNG

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:
M65850P.pdf
How would you go about making this into a duo chorus like the Dimension P?

Image

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Post by Andon »

Reachahighernoon wrote: 04 Mar 2022, 11:54 How would you go about making this into a duo chorus like the Dimension P?

Image
The easiest way would be to use a summing amp setup:

Image

Where R is a constant value (15K, 33K, 47K, etc.), although the non-inverting input (+) should be tied to Vref (4.5V) - usually via a resistor - instead of to ground as shown in this picture (convention tells us to use a resistor of the same value as used in the summing amp setup, but whatever's clever). Any single or dual op amp package should work here. Just duplicate M65850P portion of the schematic (adjusting delay time resistors to taste - see the datasheet for references) as many times as you'd like, and make sure your clean signal (top line on the original schematic) also has a resistor of the same value as you chose for the summing amp.

In this case, you could keep the blend circuit if you wanted (though I would/did swap it out for the summing amp setup for ease of use), but I would try it out and see if you needed to adjust resistor values to get parity between both signals.

More reading: The Summing Amplifier

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Post by Andon »

Also just want to add that you can get an easy 1 second of delay out of this chip if you're willing to deal with some noise (on a breadboard at least). Feed pins 13 and 14 into lugs 1 and 3, respectively, of a 1M pot, tie lugs 2 and 3 of the pot together, and inject the LFO into lug 2 of the pot (or disregard the LFO injection if you're not using this chipset as a chorus). Also, I'd go for a much larger pot for feedback than the datasheet recommends if you're looking to use it - currently using a 1M pot in lieu of the recommended 50K pot in the datasheet, with lugs 1 and 2 tied together.

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