While we have published a number of variations on a standard RIAA
preamplifier for magnetic phono cartridges, we have not published a
preamp stage for ceramic phono cartridges. Typically, these were
supplied as turnover cartridges in record changers but there were higher
quality versions such as the Decca Deram. These phono cartridges are
piezoelectric devices which require a very high input impedance.
Similarly, violin pick-ups made by Fishman, Barcus Berry and others are
piezo devices. These two circuits have been requested for a violin
pickup but could equally well suit a ceramic or crystal pickup. The op
amp circuit uses a TL071 connected as a voltage-follower. It can run
from a battery supply of ±9V.
The alternative transistor circuit uses a BC549 connected as an
emitter-follower but with bootstrapping of the input bias network to
provide a high input impedance. Both circuits have input coupling
capacitors but since the transducers are capacitive (ie, piezo) they
could possibly be omitted. Both circuits will probably need to be
followed by further gain, depending on the output level. For a violin
pickup, a parametric equaliser is also recommended, and for this we
would suggest the 3-band parametric equaliser published in the July 1996
issue of SILICON CHIP. With a slight change to the feedback of the first op amp in this circuit, the extra gain required could also be provided.