Effects / Pedals

A couple of demos (Dynacord EC280 BBD delay, EHX Y-Triggered Filter)

A couple of demos I did just before selling these 2 beauties that were not getting enough attention from me to justify keeping:

Making the demo for the Y-triggered filter I finally figured out why I was not getting along with it. Unlike regular envelope filters this one seems to have a fixed envelope, that is simple triggered by the attack (hence the name I guess …)

Once you know that it’s actually a lot easier to get good tone out of it.

Ground Control V4 (pimping a DOD FX17)

Long ago I set out to find a way to combine a volume/wah/expression pedal into one single/compact/easy-to-operate pedal…
Oh, and without using rotating pots to control it.

I went through numerous iterations, using LED/LDR’s Morley style, Hall sensor devices, several rocker pedals (including a vintage Colorsound Wah/Fuzz that I had once butchered before these things were considered worth more the stamps used to ship them)

Finally I found that the DOD FX17 had the form factor I was after. I actually sold the first FX17 I had and some years later bought it again, having forgotten why I had sold it. In fact I hated the volume pedal part (noisy 3080) and the switching logic. You cannot switch from Wah to Volume with the foot switch. You can only bypass the wah..
Also it had 2 trimpots that affected at the same time the Wah, the volume and the CV output. So it was impossible to find a setting to make all 3 work as they should.

What I really liked about it is the variable capacitor and oscillator that provided the control voltage. So I decided to keep only that part and to replace all the rest.

The result can be seen here (sorry for the crappy webcam pics …):

The CV signal is optimized through U1a, where you can amplify and offset it.
It then goes to the various control elements.

After trying out several kinds of VCA’s, using LDR’s FET’s etc I ended up using a TDA7052 amplifier. It’s not really made to operate as a VCA but works pretty fine and most importantly, I had some around.
I kept the same wah circuit as the FX17, because I quite liked it. (it’s the same circuit as the FX25 auto wah).
There are also two CV outputs whose voltage can be set independently. (For example, I am using one with 0-5V for the Pitchfork and one with 0-3.3V for FV-1 based pedals).

For switching I am using a HEF4013 (the HEF refers to the model with a built-in schmitt-trigger, good for debouncing the switches a bit)

There are two momentary switches. The original one on the heel and another one I added on the toe side. One switches from Vol to Wah. The other one switches to bypass and engages the CV outputs.

For switching from Vol to Wah I am using a switched dual OP amp NJM2120. I could have gone with Fets but I had these around and they use less components.

The switching part was the most fun as I had not worked with flip flops or logic chips before so that was good learning.
I guess all of the control/switch stuff could have easily been reduced to one microchip but … I have yet to start with that stuff ..

The bypassing of the volume and CV’s works like this:

The CV (0.6-6V)is fed to T1, which is set as a voltage follower. The 2 trimpots optimize the voltage swing to control the gain of the TDA7052 chip (0.4-0.8V). When it is in Vol mode, Q2 is low and T2 is off. When you press the Vol/Wah switch, Q2 goes high and turns on T2, thus presenting the maximum voltage at the common emitter. Any variation of the CV no longer has an effect. At the same time
At the same time Q1 changes state also and switches the NJM2120 chip.

More or less the same principles apply when you press the FX/EXP switch. Vol is bypassed, NJM2120 switched to Vol, T4 and T6 are turned off, allowing for the CV outputs to swing.

The whole thing might not make real sense to everybody as it really is tailored to my particular needs but I am pretty happy with how it works.

Just posting it here in case some of the circuit bits might be of use to someone.

More FV-1 patches

Some new patches I have been working on:

Infinite reverb:
adapted from code available on the SpinSemi site. I added a latching function to latch the infinite mode after pressing the momentary switch just once. The latching switch code is a piece taken from the Tap Tempo code shared by Slacker.

Granular delay with pitch shifter:
delay whose speed is randomly changing and an octave up that can be blended in the feedback path. Pressing the momentary switch sets the feedback to maximum

Particle delay:
This was more of an excercise trying to reproduce one patch in the Red Panda Particle.

Reverse delay:
Based on a piece of code from the Spinsemi forum
The ticking is a bit annoying …

“Jonny Greenwood” effect:
This code was shared by Slacker and tries to emulate the MAX/MSP patch Greenwood uses on some songs. I did not change much in this. I think I added a feedback path but that did not do much …

Aliaser + delay and feedback:
Simple aliaser with a delay and feedback path to coax out some flangey glitches.

Molecular Disruption Device – Spin Semi FV-1 based multi-effect

This circuit is built around the Spin Semi FV-1 DSP chip.

This (too long) demo shows some programs I have been working on:

Most of the effects were created with the great SpinCad software created by Digital Larry. Some are parts of available code stitched together (still have a lot to learn in that respect)


Apart from the circuitry supporting the FV-1 chip, you can see an input buffer and a mixing stage mixing the buffered direct signal with the output of the FV-1. The hardware mixing works fine in most cases and avoids dedicating one of the 3 pots controlling the FV-1 parameters. Sadly with some programs where the signal coming from the FV-1 is too similar to the direct signal, there is some phasing effect because of the very slight latency introduced by the DSP.
I also added a hardware feedback path that takes the right output of the FV-1 and feeds it back to the right input through a pot.

The 8 programs loaded in the external EEPROM are selected with an 8 position rotary switch and a network of diode logic.

The POT0 input on the FV-1 is connected to either a pot or the jack for external expression input. A momentary switch is also inserted to this input. A 4 position rotary selects between the use of the pot or expression input each time with the option to have the momentary switch going high or low.

I added the momentary switch mainly to use it for an infinite reverb effect (freeze) and also for tap tempo.

There is a 3 pin connector on the PCB to allow programming the EEPROM in circuit.


Testing some Spin Semi FV-1 patches created in Spincad

Inspired by the Red Panda Particle I recently acquired, I have been spending some time trying to learn how to create effects with the Spin Semi FV-1 chip. As I am absolutely new to programming, finding about Spincad was a real blessing. Basically you get a graphical interface and a program that converts the building blocks, connections and settings you configure to FV-1 code.

This is just a short test of some patches I have been working on. Still need a lot of work but it’s quite fun.

Bipolar Bear Dual Overdrive

The Bipolar Bear is a dual overdrive with on one side (South Pole) an overdrive derived from an OD820 with Mosfets in the clipping section and a mids control inspired by a modification Mark Hammer posted about the Shin-Ei FY-2. The South Pole side runs on +9V/-9V using a charge pump and its drive knob can go from full overdrive to clean boost (using a dual pot).

On the other side (North Pole), a distortion derived from all kinds of Mu-Amp circuits, mainly BSIABII but with bits from the OKKO Diablo, Dirty little secret and probably others. It also has a mids control (that I snatched from GrindCustoms’ Ultrastoner because I thought it worked particularly well) alongside the usual BMP tone control.

Giant Hogweed – Fuzz / Octave UP / Octave Down

This is a bit of a Frankenstein consisting of the Octave UP circuit borrowed from the FOXX Tone Machine, the Octave down from Joe Davisson’s Shocktave. Both are fed into a Roger Mayer Mongoose. The name came from listening to a lot of early Genesis stuff while breadboarding this…

The artwork was made with a nice drawing from my lovely wife 🙂

I stumbled upon the Mongoose by coincidence and decided giving it a try. Turns out it’s a GREAT distortion. It has some similarities with a RAT but has a gain stage before the LM308 which gives it a lot more oomph. It has great sustain and can cover quite a lot of distortion territory. Somewhere between a Fuzz, a distortion and even overdrive on milder settings.



Liquid Mercury – Tap Tempo Phaser

Liquid Mercury Phaser combines an 8 stage analog optical phaser with a digital microchip (Electric Druid’s TAPLFO) providing modulation with multiple wave shapes and a tap tempo function.

The phaser circuit is derived from the Mutron Phasor II, adapted to operate with 9V supply and augmented with 2 additional non-swept phasing stages.

The phaser was built in in two different versions. One with identical phase capacitors, for a classic phasing and one with staggered capacitors as found in the Uni-Vibe phasers. The second one has a less pronounced phasing effect but a swirlier sound.

I could not really decide which one I like best so I will keep both on my pedalboard 🙂