@basreflex, (or another advanced electronician here),
Could you describe ( or point to a easily understandable explanation of) how the dc/dc converter used in the original circuit works in practice: i never really understood the principle i must confess...
Could you describe ( or point to a easily understandable explanation of) how the dc/dc converter used in the original circuit works in practice: i never really understood the principle i must confess...
below a schematic of a simple well known brand microphone.
the capsule signal goes to a 2sk30R source follower, that drives a BC431C emitter follower to drive a transformer U35 to create the balanced signals. the BC558/2sK30GR form a low noise shunt regulator based on VT multiplication of the fet. the BC 183 oscillator creates a high voltage using transformer U26c. that ac signal is rectified by the BAY45 diode and filtered and applied as DC to the capsule using a 1Gohm resistor. as the suply voltage for the oscillator is stabilized by the shunt regulator, the resulting dc ibas voltage for the capsule is stable.
the capsule signal goes to a 2sk30R source follower, that drives a BC431C emitter follower to drive a transformer U35 to create the balanced signals. the BC558/2sK30GR form a low noise shunt regulator based on VT multiplication of the fet. the BC 183 oscillator creates a high voltage using transformer U26c. that ac signal is rectified by the BAY45 diode and filtered and applied as DC to the capsule using a 1Gohm resistor. as the suply voltage for the oscillator is stabilized by the shunt regulator, the resulting dc ibas voltage for the capsule is stable.
below the low power bias supply design that I did many years ago for a large membrane capacitor mike.
it is a balanced sine oscillator driving a voltage doubler, where the tail current is managed by an opamp integrator comparing the output voltage with a 1.225 reference voltage from the LM4041 . The bias voltage HV can be set to 24V or 76 V, 3.18 times or 10dB sensitivity difference. the opamp is supplied by the node generated by the 4 diode string.
it is a balanced sine oscillator driving a voltage doubler, where the tail current is managed by an opamp integrator comparing the output voltage with a 1.225 reference voltage from the LM4041 . The bias voltage HV can be set to 24V or 76 V, 3.18 times or 10dB sensitivity difference. the opamp is supplied by the node generated by the 4 diode string.
Your design of this bias voltage circuit is really wonderful. What is the VIN input voltage?
I am looking for a complete circuit diagram of a 34mm capsule that can be used. My microphone comes with a 48V phantom power supply. Thank you for your help
For a k87 the obvious circuit is U87 :
http://cdn.recordinghacks.com/images//mic_extras/neumann/U87-schematic.png
http://cdn.recordinghacks.com/images//mic_extras/neumann/U87-schematic.png
the vin comes from the 24V zener limied suppy, generated by the PNP followers driving the output
Very nice circuit Basreflex.
I don't recognize the circuit in post 42, which mic is it please? A Neumann?
I don't recognize the circuit in post 42, which mic is it please? A Neumann?
the pnp emitter followers have 6.8k 48V load resistor in the phantom source.
in my final circuit I used 100uH smd inductors and a TS931 low power opamp.
in my final circuit I used 100uH smd inductors and a TS931 low power opamp.