Building a Tremolo / Chorus multi-effect?

[sorby69]

Hi folks,
I've been dabbling with a few simple tremolo and chorus circuits (EA & One Chip) on a breadboard and got thinking that it'd be fun to build a general-purpose modulation pedal with a switch to select whether I'm modulating volume (Tremolo) or pitch (Chorus). The underlying modulation circuit (and speed & depth pots) would be common to both, but they would be driving one of two different effect circuits (Tremolo or Chorus).

• Does such a circuit exist?
• Is there a verified/go-to modulation circuit I can use as a basis for exploring this idea further?
• Or am I on a Fool's Errand?

Thanks!
Rob

[Ben N]

In theory, a single LFO could be made to control either or both of a trem and chorus/vibrato. But IIRC, Mark Hammer long ago pointed out that the LFO waveforms that work well for one effect don't necessarily work well for another, which is probably why you don't see this kind of thing in commercial analog pedals. Maybe the answer is to build around a multi-waveshape LFO, like Electric Druid's STOMPLFO/TAPLFO chips. Add presets via a PIC or Arduino, so you don't have to twiddle knobs & switches every time you switch effects, and you may be on to something.

[sorby69]

Thanks Ben - some useful advice there. Those STOMPLFO/TAPLFO look incredibly useful & versatile - but I'm concerned about the 40ms minimum, as I understand chorus may be expected to work from around 25ms? Either way, I can see loads of uses for those chips, so I'll order some.

I'm a coder with a few years of tinkering with Arduino & Teensy under my belt, so I'm liking your MCU suggestion!

Thanks again
R

[Mark Hammer]

Thanks for the nod, Ben.  Insomuch as many popular tremolos AND chorus pedals have both relied on triangle LFOs, I suspect a common modulation source would be fine.  If the goal was vibrato+chorus, like a CE-1, then different weaveforms might be in order.  Sorby69 might, in the end, ponder whether the triangle waveform is to his/her tastes, but certainly, much like 50,000,000 Elvis fans, tens of thousands of satisfied pedal consumers can't be wrong.

As for whether the suggested combo pedal is a "good idea", there are currently many inexpensive digital modulation multi-FX on the market.  I even have one (Donner "Alchemy"; identical to NUX Mod-Core, but minus the USB port) that has some very nice sounds.  I bought mine 2nd hand for $25, and I'm sure there are plenty of others available new for similar prices.  I guess the question is whether what the OP seeks would have the sorts of features/mods that are not available, digitally, and would only be available with an analog DIY project. 

One of the considerations in going after a common-LFO modulation project is whether there is any context in which one would like to use both effects, and whether they would benefit from having individual LFOs, as opposed to a shared one.  Not that a one-at-a-time-shared-LFO build is in any sense "wrong".  It's more a matter of the builder immediately thinking "Geez, I wish it could...".

Ben's suggestion of an Electric Druid tap-tempo-capable LFO chip is a good one, since it will offer many more modulation forms for your adulation, plus tap tempo (not to mention convenience!).  Not being a gigging musician, I don't have much personal use for tap tempo, but the OP might find it handy.

I find PT2399-based chorus to be less than optimal.  I mean, yes, they CAN get chorus-ey with some modulation, but never get really "swirly", which would require shaving off 10-20msec from its minimum delay time.  Although, if one is after a Pat Metheny type of chorus that bumps the delay time well above 20msec, the PT2399 can do the job.  One thing I will note is that the amount of modulation required to yield a satisfying throb with a tremolo, is likely to produce an annoying and severe pitch-wobble when modulating a delay chip in that range.  That can be "cured" by simply downscaling the LFO output range for chorus, in the switching.

[sorby69]

Thanks Mark! (and thanks for all the other useful info I've silently gleaned from you and others these past few months)

While my ears did prick up at Ben's MCU suggestions, this build will be for a non-gigging traditionalist friend of mine who won't entertain digital, plus I think I'll benefit more from spending more time learning about discrete components and circuits etc.

I've some experience with the PT2399 having built DeadAstronaut's excellent Dreamtime Delay pedal, and have decided against a PT2399 solution for my chorus/tremolo build.

Good point about solving the relative modulation scaling needs of each effect in the switching - I'll certainly factor that into my build.

Thanks again - it's much appreciated.
Rob/Sorby69

[eh la bas ma]

I would recommend the PedalPcb Unison with a very simple FV-1 mod. Not for breadboarding, but to build and play with it.

https://www.pedalpcb.com/product/unison/
https://www.musikding.de/Unison-Double-Tracker-kit

This thing is digital and sounds amazingly good. It features 3  modulations ( 2 pitch shifting & delay effects and a chorus & delay effect). With a simple toggle switch connecting FV-1 T0 (pin13) to ground, you can access 3 additionnal effects : reverb & chorus, rev. & flange, rev. & tremolo. You can't easily access all the 7 internal effects, only 3. Here is why :

https://forum.pedalpcb.com/threads/unison-double-tracker-how-to-fully-access-internal-fv1-algorithms.11588/

I would be suspicioius with 6 effects in 1 box, but on this circuit...they all sound very good and the controls allow many possibilities. Good for bass, guitar and other instruments. I lend it recently to a bass player friend (who isn't a big fx user, usually one circuit and that's it) and he is very pleased with it.

[ElectricDruid]

While my ears did prick up at Ben's MCU suggestions, this build will be for a non-gigging traditionalist friend of mine who won't entertain digital, plus I think I'll benefit more from spending more time learning about discrete components and circuits etc.

If I can put in a good word for MCUs, they can do excellent work *outside* the audio path, and like that they don't need to offend even traditionalists. That was the idea of the TAPLFO and STOMPLFO. You can replace the LFO in a modulation pedal (phaser, chorus, tremolo, whatever) and you gain waveforms and features like tap tempo, but you don't have to mess with an analog audio path.

A good example is David Rolo's Twin Peaks tremolo, which is a fender-style harmonic tremolo with vactrols doing the volume control, but a TAPLFO providing the LFO waveforms.

For me, this "best of both worlds" style of pedal building is really where my heart is - all the benefits of analog audio, but with all the clever features and flexibility of digital pedals.

[Processaurus]

Tremolo + Vibrato is a very cool combination.

[Mark Hammer]

Tremolo + Vibrato is a very cool combination.

An interview with John Fogerty indicated that some older Kustom amps would have both of those, and that he was getting someone to make him a custom pedal with tremolo and vibrato.

The "phasefilter" mod for OTA-based phasers accomplishes something sounding sort of like vibrato+tremolo.  Comverting two out of 4 stages to lowpass, instead of allpass, and lifting the dry signal, gets vibrato from the two allpass stages, and the mopdulated corner frequency of the 2 lowpass sections tends to vary the perceived amplitude as mids&highs cut out and come back, yielding something sounding  like tremolo.

[eh la bas ma]

Tremolo + Vibrato is a very cool combination.

An interview with John Fogerty indicated that some older Kustom amps would have both of those, and that he was getting someone to make him a custom pedal with tremolo and vibrato.

The "phasefilter" mod for OTA-based phasers accomplishes something sounding sort of like vibrato+tremolo.  Comverting two out of 4 stages to lowpass, instead of allpass, and lifting the dry signal, gets vibrato from the two allpass stages, and the mopdulated corner frequency of the 2 lowpass sections tends to vary the perceived amplitude as mids&highs cut out and come back, yielding something sounding  like tremolo.

I think the Redshift phaser from Aion ( based on Blackout Effectors Whetstone, itself based on EHX Small Stone) can do it ? There 's a lowpass/highpass switch. Combined with the 2 stages mod and the vibrato mod, it sounds very beautiful and singular.

https://aionfx.com/app/files/docs/redshift_documentation.pdf