power supply ideas for EPFM kits?

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power supply ideas for EPFM kits?

Post by tfrank8 »

I just received the Ultra Fuzz and Envelope Follower kit and I'm so excited to build them! I am curious if it is possible to use a 9770U power supply with some kind of conversion to run a pedalboard with multiple EPFM projects? Or should I just buy some kind of commercially available power supply? I don't want to use batteries
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Re: power supply ideas for EPFM kits?

Post by PAiA-Scott »

We still have the kit for project 13, the Bipolar AC Adapter:


It outputs positive and negative DC supplies at 8v each, perfect for the CA-6 Ultra-Fuzz and the CA-25 Envelope Follower projects associated with the book Electronic Projects for Musicians, by Craig Anderton.

In the book, Craig gives a mini-course about electronics with construction details for the projects in the series. Chapter Five is titled Powering the Projects with examples for power switching and use with nine-volt batteries. Chapter Eleven shows ways bypass switching can be added to the projects -- Chapter Fifteen is the one for the Electronic Footswitch project, a dc voltage controlled signal router (effectively a remote-controlled DPDT switch).

There are lots of photos showing possibilities for housing or containing the kits, and the rack-chassis with sub-sections shown is not so different than the FR-7 Fractional Rack-mount Chassis on the PAiA website:

FR-7 (shown with options for FR-PWP and a 9770 series supply mounted inside)


The 9770 Series power supplies are all variations of the same printed-circuit-board and it would not be difficult to modify it to work to provide eight volt supplies for use as a substitute for the CA-13. If you ordered the 9770R-12, it would just be a matter of obtaining positive and negative eight volt regulators to use as substitutes for the twelve volt ones (http://www.mouser.com, 7808 and 7908 (TO-220 versions)).

When combining lots of effects to work from one supply, there can be conflicts. If an effect divides a single polarity dc supply to appear to the electronics as dual polarities, the 'ground' of the effect can be at a potential that's half the voltage of the power source, or, at zero with the minus pole of the single polarity power source expected to 'float' and work as the negative potential of a dual-polarity, powered circuit. By themselves, either of these would be OK, but connected with another device using a different power scheme the conflict could arise and the simplest solution would be to use a separate power source for each scheme, dual / split.

Then, just to be sure...

The CA-25 Envelope Follower project is not like effects units called Envelope Followers which work like a sort of auto-wah (actually an Envelope Follower / Filter combination). It is more for deriving control action, dependent upon the input signal amplitude dynamics. It has a CV (control voltage) output and variable resistance nodes. In the EPFM book, there are examples for using its CV output to vary parameters on the Phase-Shifter and the variable resistances as substitutes for potentiometers in the Super Tone Control (filter) and Ring Modulator (ring tone) projects. Added as a link between the guitar,or some other audio signal, and the 9730 VCF you'd get amplitude-envelope-driven-lowpass, bandpass, or highpass (or combinations of), filtering or 'wah'. A VCA or voltage-controlled-amplifier can be used with the E.F. for volume related manipulation, ie compressor/sustain, downward expansion (noise reduction).
Scott Lee
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