And I saw this ebay auction of thought of Keith
http://www.proaudioeurope.com/images/ebay/ebay-25-07-06/Calrec-telefx-2.jpg
Interesting front panel
Telephone Effects Units are basically simple filter sets that can be used to make a voice sound like its coming through a telephone. But they're also very useful for other sources, including music. These units have high and low pass filters of the highest audio quality, with switchable frequencies. Low pass is Flat, 3kHz, 1.5kHz, 750 Hz or 300 Hz. High pass is Flat, 230 Hz, 250 Hz, 900 Hz, 1.8 kHz. It would only take a few simple resistor and capacitor changes to alter these values to more traditional musical filter frequencies. The modules have a built in transformer balanced output (Lundahl LL1517) so the only extra circuitry needed is a power supply (+/-16, and maybe 5v) and XLR connectors from the multipin connectors on the back (mating connectors are readily and cheaply available from any good electonics supplier eg RS, FarnellinOne.