Plus one for Elektrosluch! It's a simple clean headphone preamp and can be built from the available schematics.
The cheapest option, if you have a mic preamp (in your recorder or mixer) is to simply solder a cable to a leaded inductor with ferrite core (for example ).
Anything around 15-30mH will work. Get a few different values and experiment.
I also got some very interesting results with winding my own air core inductor coils. All you need is enamel coated copper wire. This supplier in the UK has a great selection of different gauges:
Greetings from Westmeath!
David
