I am trying to replicate a synth filter in guitar

[Elmasodoacro]

Hi guys! I'm new here. A good fella and I make some pedals, even though most or the circuit and the building is made by my pal.
Anyway, yesterday I showed him the song Nangs, from Tame Impala, and told him I was obsessed with the filters used on the intro (it is made by a Roland Juno-106 synth) but the only pedal I know which does kinda the same is the Dwarfcraft Happiness but is too far from my price point so I decided to design something with my pal.
We came to the conclusion that it is made by a LFO going into a filter (we are arguing if it si LPF or HPF) but then we don't kno were to go after that. What do you recommend to do?

Thanks in advance!!

[nocentelli]

Sounds like a lowpass or bandpass filter modulated by an LFO.

There are a many different DIY filters and many different DIY LFO circuits to choose from, AND a wide variety of ways to couple a given LFO to a particular filter, so the choices required here could become overwhelming. There is a whole thread on synthy filters for guitar here:

https://www.diystompboxes.com/smfforum/index.php?topic=104178.20

The actual Juno filter uses some (probably extremely expensive) obsolete chips - You could try to replicate it with more easily available parts, but you could probably make something that approaches that sound with any number of circuits. The 9v VCF (Voltage Controlled Filter) schematic posted by Eric Archer does a nice squelchy and resonant LPF, has a mix control and can go into oscillation at maximum resonance:

www.ericarcher.net/wp-content/uploads/2014/07/9v-analog-diy-lpf.pdf

... but it doesn't have the LFO part of the circuit, so you would need to find an LFO that can provide a varying voltage in place of the frequency pot. It also uses a rail-splitter and an opamp that isn't necessarily available everywhere (at least for cheap): I am not certain it will function properly without those parts.

There is an even simpler version of that type of OTA LPF by Escobedo, but again, it only has the filter with a frequency pot, and no LFO.

http://www.jiggawoo.eclipse.co.uk/guitarhq/Circuitsnippets/sk.gif

I made the Archer filter with the intention of mounting it in a wah shell for manual sweeping (and it sounds very good).

I also made a modulated filter from the EHX bassballs pedal (actual two [bandpass?] filters that sweep different frequency ranges to give a "vocal" filter sound, with a mix control between the filters) that has the LFO taken from a tremelo circuit:

Schematic:
https://tinyurl.com/y6oy9b24

(lengthy) Demo video:
https://www.youtube.com/watch?v=GNgquTEslCg

This circuit doesn't really need that TLE rail splitter, and works fine with a 1M||1M voltage divider to provide the 4.5v vref ("Vb"). You could probably try grafting the LFO section from the schematic (right hand circuit) to the Archer filter by connecting the "CV" from the LFO in place of the wiper of the VCF frequency cut-off pot.

[ElectricDruid]

If the sound is made by a Roland Juno106, then it's a lowpass filter, since that's all the Juno had.

Specifically, it had a 4-pole OTA-based filter, so something based on a pair of LM13700s would be very similar in sound. The Juno used a custom quad OTA chip. Nearest thing that exists to that nowadays is the AS13704 quad OTA from Alfa Rpar in Latvia - four 13700-type OTAs in one SOIC package.

The Eric Archer design is a 2-pole state-variable filter, so it's a different design to the Juno's filter, but it will certainly get you into the same territory. The rail splitter isn't essential - there are plenty of 13700 designs that don't use one, but it'd involve some tweaking if you chose to omit it.

If you wanted something similar (2-pole SVF) with a LFO attached, I designed a "FilterFX" pedal which uses a vactrol-controlled filter and can provide LP, HP and BP modes. It gets pretty synthy.

https://electricdruid.net/filterfx-lp-bp-hp-lfo-filter/

The final example is getting pretty close to what you're after, but the Tame Impala song has synth chords through it (err, yeah, it's a synth!) so that sounds a bit different from guitar strumming.

HTH,
Tom

[Elmasodoacro]

Thanks for your answers guys!

I'm definitely going to check that whole thread patiently. But first those options seems really useful too. Maybe we have to do some mods because we want the PCB to fit in a 1590D.

The electric druid sounds really close indeed, and yeah I know it's gonna sounds different because the Juno is a synth lol but I'm gonna give it a try!

[FUZZZZzzzz]

I found this to be a cool filter as well for guitar and bass (and whatnot)



based on the weird sound generator filter by music from outer space.

[FUZZZZzzzz]

discussion here:
http://electro-music.com/forum/topic-47418.html