My son David uses the Microvox system, available from the Button Box here in the US. He places the velcro'd mics near the high notes of his English concertina, and says that helps to balance the volume between the quieter high notes and the louder low ones on his Wheatstone. He uses the 9-volt battery driven Microvox and sends the signal into a direct box or straight into the PA amplifier. Take a look at the Button Box web site.

Sandy