OPIC

Op-amp Impedance Converter

FETLESS ELECTRET
LDC CAPSULE
MID/SIDE MIC
MULTI PATTERN
MORE OPTIONS

Overview:
'OPIC' is an acronym for 'Op-amP Impedance Converter'....

'Op-amps' (Operational Amplifiers) have been considered as alternatives to discrete FETs in condenser mic impedance converters for some time, but many op-amps suffer from being too noisy for the task - or they draw too much current to be effectively operated from phantom power - or both!
To date, their use as impedance converters has not been very widespread.
In addition, the requirement for a very high impedance JFET input can limit the available choices.

Texas based hobby mic builder Jules Ryckebusch has identified Texas Instrument's OPA164X series of op-amps as a useful option for this task... They have low noise - very low distortion - and only require around 1.8mA of standing current per amplifier.
Jules has incorporated the OPA1642 into his 'OPA Alice' microphone project, and you can find details of ready built project PCBs using these devices here

At the time of writing, shipping costs make those PCBs very expensive for those outside the USA, so I looked into the possibilty of incorporating the OPA1641 (single amp) and the OPA1642 (dual amp) devices into stripboard layouts, for a selection of different mic options.
The resulting project details are outlined in the attached web pages ...

(Just click on any of the 5 buttons at the top or bottom of this page to access the desired project)

FETLESS ELECTRET
LDC CAPSULE
MID/SIDE MIC
MULTI PATTERN
MORE OPTIONS