Archive for March, 2020

18
Mar
20

Parabolic Reflector Microphone 2

After creating my first parabolic microphone system (described in this post), I came across a small commercial device which I thought might be worth trying.  It was hard to say if it was really just a toy, but it looked a bit above that, and had some features that made me think it could be a practical device.

This is the box it came in:

and these are the contents of the box.  Clockwise, we see the approximately 20cm parabolic dish, a pair of decent over-ear headphones, the body of the device, and the quite thorough Instruction Manual:

And, when put together, this is what it looks like.  You can see the revolver-style handle; the ‘trigger’ which turns the microphone on; and the two buttons which record and play back the sound picked up by the microphone, which is in the end of the enclosure on the right,  pointing back into the dish.  Along the top is a x8 magnifier, designed, according to the instruction manual, to allow you to see more clearly what is being recorded.  In the base of the handle is a space for a 9v PP3 battery:

It’s not necessary – or, from my point of view, useful – to use the device’s own recording ability, which is only a 12 second burst.  However, you can also see a 3.5mm output socket in the bottom centre of the device.  This can be used with the headphones supplied, to monitor recordings as they’re being made, or to transfer a recording to a computer or external recorder.  More importantly, it can be connected to an external recorder, while the device is activated, allowing recordings of any length to be made.  Monitoring can be done via the external recorder’s system.

I decided to take the device apart and make a few small changes.  There were three reasons for this.  First of all, I wanted to add an option to replace the internal battery with an external socket, as with the other preamps I use while recording; secondly, I wanted to replace the momentary ‘trigger’ switch with a slide switch, which wouldn’t need to be held down all the time I was recording; and thirdly, I needed to replace the knob on the ‘Frequency Controller’ potentiometer – some kind of filter, I presumed, which was designed, according to the instruction manual, to remove unwanted background noises.  This knob was very stiff and well-nigh impossible to turn, not because of the potentiometer itself, but the design of the knob.

So, I decided to open up the device and look inside.  This involved removing half a dozen screws on the opposite side from that pictured above.  The device seemed solidly contructed, and the plastic had a nice feel to it, like a high quality game controller.  This picture shows what was inside.

1 = The small electret microphone element; 2 = the main circuit board with the large record/playback i.c. and the Frequency Controller potentiometer; 3 the switch board with contacts operated by the trigger mechanism; and 4 = the PP3 battery compartment and clip.

The only place which was still firmly connected was the microphone enclosure.  To get the two halves of the body apart I had to saw carefully through the enclosure at the point shown by the arrow.

Fully opened up, this is what the device looked like:

A closer view of the circuit board shows, in the bottom right-hand corner, the two connections, ‘SWITCH’ and ‘GND’ (Ground, or 0v), which I needed to get at.

This view of the other side of the board shows, in the top right-hand corner, where I made connections.  1 = The two switch wires, which went to a new slide switch attached to the upper part of the handle, within easy reach of my thumb; 2 = The ground connection, which went to a new 3.5mm power input socket further up the body of the device, via an LED, which I added to indicate when the device was activated.

In the bottom left-hand corner you can see the ‘Record’ and ‘Play’ buttons, and the LED which indicates when the device is recording to its internal recorder.

I cut the +9v lead from the battery clip to the circuit board and connected both ends to the LED and a new 3.5mm power in socket.  This was a switched type, so that the device would use an internal PP3 battery, unless a plug was inserted in the socket, in which case the internal battery would be disconnected and power would be taken from an external source.  I attached a small square of black velcro to the outside of the device, close to the socket, for this purpose, as I had done on my other recording preamps.

This picture shows the 3 changes I made to the device.  From front to back you can see: the ‘Record’ switch (recording to my external machine, that is, not the device’s internal chip) and indicator LED; the new, easier-to-use Frequency Controller knob; and the 9v external power socket.

As seen in the previous picture, one of my PP3 battery assemblies with integral 3.5mm plug is fixed to the velcro on the side of the device:

These changes should make the device more practical for me to use.  At some time, when circumstances are more favourable, I’ll try it out in the field.




andymurkin

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