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)

Schematic:

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.

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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.

 

 

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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 🙂

 

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Dummy Coils for Dummies

DSC_3247

Yesterday I rolled a dummy coil for my Jazzmaster in an attempt to tame some of the noise the 2 singlecoils pickup.

I followed the guidelines from this very informative article:

https://sites.google.com/site/stringsandfrets/Home/noise-reduction-for-sc-pickups

The principle in short is as follows:

To cancel the noise of your real pickup, connect a dummy coil (without magnets) that senses the same amount of noise, in series out of phase. If you have a dummy that is identical to your real pickup in terms of area and number of turns, the noise cancellation will be optimal. But the increased resistance and the changed inductance will impact and change the tone of your pickup.

One way you can counter that is to create a dummy that is larger than the real pickup and reduce the number of turns. The number of turns needed to sense the same amount of noise is reduced proportionally by the increased area of the coil. I have seen differing versions online of how the relation between number of turns / area is.

Example: increasing the area inside a coil by a factor of ten and decreasing the number of turns in the coil by a factor of ten

VS: increasing the area inside a coil by a factor of ten and decreasing the number of turns in the coil by a factor of 100

The latter was how it was explained in http://www.google.com/patents/US20050204905 which I understood is the patent for the Suhr backplate dummy coil system, so I decided to follow that route  and see how it goes.

My pickups are wound to about 9000 turns. I guesstimated I could fit a dummy coil about twice the area of the real pickup in the cavity under the pickup selector switch. I wound the dummy to 2250 turns with AWG38 wire to reduce the resistance. The finished coil had about 1.5k resistance.

On my Jazzmaster, the upper control plate sported 3 switches, one for series/parallel, one for phase of the neck pickup, one for adding a cap in series to cut lows. I decided to replace the whole wiring, leaving these switches unused (for now..) and replacing the pickup selector toggle switch with a 3p4t rotary switch that allows 4 pickup combinations:

Bridge alone + Dummy

Neck alone + Dummy

Bridge and neck series, no Dummy

Bridge and neck parallel, no Dummy

The only thing you need to check once you have wired everything together is whether in the positions 1 and 2 you have noise cancelling or noise addition. If you have more noise, just flip the leads of the dummy coil around.

Here is my wiring schematic:

Jazzmaster dummyTo my amazement, the dummy coil did indeed cut out most of the annoying noise, at least as much as did the series / parallel positions.

I can finally go crazy and stack multiple fuzzes and distortions together  😀

TWIN PEAKS Tap Tempo Harmonic Tremolo

After a few builds on diystompboxes.com fueled my curiosity about the Harmonic Tremolo used in Fender Brown Face amps (and some others of that era), I did some researches on the web and decided to try my luck at emulating it. Unlike the more common tremolo types, where the volume of the whole signal is modulated, the Harmonic tremolo splits the signal into a bass and a treble part and pans between them. It creates an effect that is a cross between a tremolo, a vibe and a phaser.

After playing around with my initial idea I came up with a very versatile tremolo in (relatively) compact Hammond BB box:

4 Tremolo modes:

  • Black Face (regular volume modulation)
  • Brown Face (modulation between bass and treble, like the Harmonic Vibrato in old Fender Brown Face amps)
  • Bass modulation only, with fix treble
  • Treble modulation only, with fix bass

8 different wave shapes provided by the powerful TAPLFO chip:

Sawtooth, Reversed Sawtooth, Square, Triangle, Sine, Lump, Reverse Lump, Random

Tap Tempo

Controls:
Rate, Division, Tone, Depth, Shape, Shape distortion

Here is a small demo of the different kinds of sounds it is able to produce:

 

A few words about the circuit:

After the Input buffer the signal is split to a LP filter and a HP filter. The Tone knob is able to pan between bass and treble. The signal of each filter goes through an Optocoupler’s LDR and is summed at the output stage (U1B). The output stage has a trimmer that allows to adjust the overall volume.

The Optos are Vactec VTL5C1. One could use others, even home made ones. Anything can be tweaked to work when correctly biased. I chose them over others because they had the best response time with fast square waves.

The optos can be driven either in phase or out of phase. In phase, it produces a “normal” tremolo effect, as both bass and treble are modulated at the same time.
Out of phase, you get the “Harmonic Tremolo” where it pans between the bass and treble signal. I have added 2 additional modes, one with only bass modulation/fixed treble and on with treble modulation/fixed bass.

To switch these modes, I found these very nifty compact 2P4T rotary switches that were a blessing in order to keep this build rather compact while having the rotary switch and pots PCB mounted.

I am using a TAPLFO PIC from Electric Druid, which is a very handy Tap LFO with multiple Waveshapes. Any other common LFO should work the same though. It would allow a much simpler layout an smaller box 😉

The LFO’s PWM signal goes through 2 inverting op amp stages to drive the Optos. The first one has a trimmer connected to the negative input that allows to apply an offset voltage to get the TAPLFO’s signal (0-5V) centered around the half-supply bias voltage.

The 2P4T switch routes the LFO signal to the optos as explained above.

The biasing is easiest like this:

  • Adjust the offset to get the LFO signal centered around the half supply voltage
  • Adjust the 2 Opto’s current with their dedicated trimpot to have the maximum swing without audible ticking.
  • Adjust the volume on the Output stage.

If for example you get too much ticking, reduce the LED’s currents and make up for the volume drop with the volume trimmer.

I found inspiration in 2 circuits on GEEOFEX where R.G. had already laid out how to emulate the sound of the Harmonic Tremolo (or Vibrato as Fender called it)

Here:
http://www.geofex.com/FX_images/FakeFenderVib2.pdf

And especially interresting for me, here:
http://www.geofex.com/FX_images/P90-to-fenderPro.gif

Thanks for all the good people at diystompboxes and other forums who inspired and educate me 🙂