I live in the UK, so the shipping costs for Jules' PCBs are way too expensive for me!......
So I tried out my own experiments with the OPA1642 and OPA 1641 amps that Jules recommended.... Some project notes here: ?
You can see from those notes that I opted for a single sided output, and a passively balanced second output to help maintain CMRR.
Taking that approach I can see that you could achieve what you want with 4 op-amps ( 2 x OPA1642). Any more than 4 and you are probably going to start running out of phantom power?
I've attached a concept schematic of how I might approach your idea for multi-pattern??
It would require a 3 position? - (centre off)? - single pole switch.?
Top position: Omni? ---? centre position: Cardioid? --- lower position: Figure of 8?
The single sided output idea takes a simpler approach, which would reduce the number of op-amps required, and simplify the switching for the task you have in mind.
I'm not sure Jules' PCBs would be much help here though ? ...
Anyway, just a thought.... :)
On Sat, Apr 9, 2022 at 02:26 PM, <michaeljtbrooks@...> wrote:
Hi All,?
(Mainly FAO Jules, but I thought this discussion would be useful to a others)
What would be the best way of introducing a pattern switch to the rather than extracting two separate signals from the mic?
I totally understand Jules' reasons for pulling two signals from the mic where it's much easier to switch pattern on a desk than to fumble around with the mic. However I'm lacking a polarity inverter (?) in my mixing desk so want to be able to do it in-mic.
I've got this CK12 style edge-terminated capsule from AliExpress:?
I'm using the Dual OPA Alice circuit with DC-DC hex inverter multiplier to provide capsule bias. I'm using Jules' PCBs (, ) from PCB Way
I'd quite like to switch between cardioid, omni and figure-of-8, but without having to generate a negative bias voltage for the rear capsule. Given that there are two dual OPAs in the circuit outputting a fully balanced signal, surely there's a way to mix them in the mic by swapping the outputs of one of them when needed?
i.e. using a double-pole triple-throw switch on the rear capsule OPA balanced output
- Cardioid: rear capsule OPA outputs not connected
- Omni: rear capsule OPA outputs connected to front capsule OPA outputs in phase?
- Figure-of-8: rear capsule OPA outputs connected to front capsule OPA outputs out of phase (swapped over)
Would that work?
Could I get away with a passive resistor-based mixer for the front + rear signals? Or am I going to be looking at adding another op-amp here (do we even have any more current headroom from phantom power)?
Cheers,
Mike
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