User manual

the Devil Fish. These are the original 1980s design adaptors with a 50/60Hz mains

transformer, rectification (such as with four diodes), capacitor and linear regulator. By

2011 these have been replaced by completely different adaptors with similar names:

PSA-100S, PSA-120S, PSA-220S, PSA-230S and PSA-240S. All these “S” model

adaptors are “switch mode” adaptors, also with proper voltage regulation.

Switch mode adaptors rectify the mains voltage, smooth it with a capacitor, and then

switch it on and off at a rapid rate, such as 50kHz, into a small transformer. The output

of the transformer is rectified and smoothed with a capacitor. An opto-coupler feedback

mechanism controls the switching duty cycle to keep the output voltage close to 9 volts.

Switching power supplies are lighter, more complex, more efficient and (now, not in the

1980s) less expensive to make. The are also a source of electrical noise, since no matter

how well the output is smoothed, the capacitive coupling in the 50kHz transformer,

combined with switching a very high voltage at this frequency (~320 volts for the 240V

model) will couple some 50kHz signal to the device which is being powered. While this

50kHz is inaudible, it might interact with other devices, such as various digital audio

sampling systems to create unwanted audio signals of some kind. In attempt to reduce

this, the “S” models pass the output cable through two toroidal inductors, in a separate

small box, in the middle of the cable.

A further source of interference from these modern adaptors may be that they typically

have substantial capacitors between both the active and neutral mains terminals and the

negative DC output wire. These capacitors may be an attempt to satisfy electromagnetic

interference emission regulations, but they also have the effect of capacitively coupling

the output of the adaptor to mid-way between the active and neutral line. This coupling

may induce hum or high frequency noise from mains switching transients (such as a

fridge turning on or off) into the audio system.

These “S” model adaptors are fine for the Devil Fish, or any other TB-303, since they are

well regulated. However, it is possible that any switching supply might, in some complex

audio setups, cause unwanted sounds. Its not just the device the switching supply is

driving – the capacitively coupled signal may permeate the entire system, and there are

likely to be multiple switching supplies doing the same thing.

In short, the PSA-xx0S models should be fine, but in the unlikely event that there is

unwanted interference in the entire audio system, it might be a good idea to run try to

isolate the cause by running the Devil Fish from batteries.

Beware of other adaptors. Just because an adaptor is labelled as “9 volts 300mA” does

not mean it actually puts out 9 volts when powering the Devil Fish. It may be designed to

put out at least 9 volts under worst-case conditions (usually when warm, which increases

the resistance of the copper windings of the transformer) with a load of 300mA and a

slightly lower than normal mains voltage. But this means that with a good mains voltage

and a lighter load, it will probably put out 10 or 11 volts. If you are going to use

unregulated adaptors (most plain, non-switching, adaptors are unregulated) then it is best

to choose a 9 volt one with a lower rated current than a higher. For instance, the voltage

supplied under a 150 mA load by a “300 mA” adaptor might be an acceptable 9.7 volts,

while with a “1000 mA” adaptor the voltage might be a damaging 11 volts.

In 2012, the great majority of power adaptors are switching adaptors – and these should

all be well-regulated. However, they may cause noise in the whole audio system.