aion POLYPHEMUS Manual - Page 6

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BUILD NOTES

Vactrol selection

The original Philosopher's Tone was designed around the resistance range and on/off speed of the

VTL5C6 optocouplers. Substitutes such as the VTL5C3 or home-rolled optocouplers do not sound the

same and are not recommended for this particular circuit.

When the Philosopher's Rock and Philosopher's Bass were released, they used the VTL5C9, while at the

same time changing the R7 resistor (the current-limiting resistor for the optocoupler's LED) from 47R to

470R, presumably with the intention of putting the LDR in a similar resistance range as the 5C6.

However, once Xvive began offering a reissue of the VTL5C6, Pigtronix again switched back to the

VTL5C6 for their Philosopher's Tone Micro, the only current-production version of this circuit.

Aion FX carries the

VTL5C6

specifically for use in this circuit, so it's recommended to use this type. We

have not tried the Polyphemus circuit with the VTL5C9 and 470R resistor, but if that's all you can find, it

may work.

Electrolytic capacitor selection

The original Philosopher's Tone used a massive 2,200µF capacitor in the bridge rectifier section. All

subsequent versions instead used two 1,000µF capacitors in parallel, and that's what we've used in our

version. They will perform the same as a single 2,200µF in this application.

For these capacitors (C7 and C8), the PCB layout assumes 8mm diameter, 3.5mm lead spacing, and

15mm maximum height, which is on the low end of the range for capacitors of this value. They only need

to be 10V minimum since they do not see the full 18V supply.

This is also the case for C13, the 470µF filter capacitor that supplies the reference voltage to the

rectifier. The requirements are the same as C7 and C8 except that it needs to be 16V minimum.

If you use the exact parts listed in the Mouser parts spreadsheet for C7, C8 and C14, they'll fit without

any trouble. But if they're ever out of stock (or if you need to order from somewhere other than Mouser)

and you need to source a different type, then be very careful of the dimensions.

C5 capacitor

C5, the coupling capacitor for the effect signal, is 560n (0.56µF), which is a very uncommon value.

The most readily available 560n capacitor is an EPCOS / TDK type from Mouser, part number

871-B32529C564J. The width is not specified in the datasheet, so we initially designed the PCB

assuming 3.5mm, which is the width of similar values from WIMA.

However, they're actually 4.5mm in width, so there's barely enough space to fit between IC2 and C13.

It's recommended to install the IC2 socket first, then fit C5 and C13 together before soldering either of

them so that they can adjust to the position.

You can also use 470n with no real change in behavior, in which case no precautions are needed, since

they're 3.5mm or narrower. The spacing issue will be fixed on subsequent runs, so if it seems like there's

plenty of space then you can disregard this.

POLYPHEMUS OPTICAL COMPRESSOR