Mic preamp for dslrs from old camera adapters

 

With the advancement of technology, It’s quite common for perfectly functional equipment to become obsolete, and essentially worthless. As is the case with Standard Definition miniDV cameras. They may work, and the professional ones like the Panasonic AG-DVC30 still look the part, but they have been left behind in history.

Attached to the top of most DVC30’s is a unit with the model number AG Mya30g. Just what is the AG Mya30g? Well it is an audio pre-amplifier, allowing the operator to connect professional XLR microphones to the camera, and to allow control over those Mics. It can supply phantom power to two XLR microphones, and provides you with a range of settings for the audio.

Here you can see all the controls over the audio you get with the preamp, and they are all useable with this easy mod.

These features include:

Mic / Line switching – Line level is useful if you wish to feed the camera with a line level output from a mixer. Mic level is obviously for microphones. The original article I’ve used for reference says that this is the input gain of the interface.

Attenuation switch – Useful for cutting the level from a microphone that is outputting a high audio signal that is clipping at the input. This can happen when recording loud noises, or using very sensitive microphones.

+48v – This switch activates the Phantom Power to the unit. Many microphones require phantom power, and this allows you to activate this power.

CH Select – This switch decides the routing of the microphones. It can be a little confusing, but CH1-2 patches the audio from XLR input 2 through to both output 1 and 2. This is usually used to send the onboard shotgun mic to both channels of the camera. The CH2 option patches XLR input 1 to one output, and Input 2 to the other output. This is the option to use when you want to use 2 different microphones, for example, the shotgun mic, and a lapel microphone.

Output volume knobs – Embedded in one end are two little dials, that allow you to adjust the output level of the module.

Now, you can see there are a lot of features here that are missing from modern stills first DSLRs and Mirrorless cameras.

I had a thought when I came across some of these cameras, what if someone was to figure out how to utilise this old but still valid technology, to allow it to be used with modern cameras?

Well, as it turns out, I wasn’t the first person to have this idea. I came across the blog at monterdiy.net

http://www.monterdiy.net/adapter-panasonic-ag-mya30g-jako-mobilny-przedwzmacniacz/

It’s written in Polish, but thanks to the magic of Google, you can translate it well enough to get the idea of what is going on.

And He’s done a whole lot of investigation, and got a lot of very useful info, like the fact that the preamp module has it’s own inbuilt power regulator that can accept a voltage from 3.6 – 36vdc.

He has even posted the pinout of the connector that is wired to the terminal block is also shown.

Which makes it really easy to wire things up.

Here is my interpretation of the pinout for the connector.

 

You could wire everything to the existing cable, and not even open the box (that’s what I did to test if it would work), but if you want a neater solution, you could do as I did, and slice open the insulation to extract the wires, and connect power and audio to the now much slimmer cables.

Before I got too far into this, I cut the multi pin connector from the cable, and wired iti up to power and half a 3.5mm audio cable.

Choosing how to power the unit was one of my first things to decide on.

Thankfully, with such a wide range of voltage input, things are fairly easy. Pick a battery in the voltage range provided, and see how it goes.

In my initial prototyping, I chose to go with 4x AA rechargable batteries.

They give a nominal voltage of 4.8v, providing a decent amount of room for voltage drop as the batteries depleat.

Once I had wired everything up though, I decided to move to a Sony NP-F550 style battery mount. That allows me to use the same batteries that I have for my LED lights. For a battery mounting plate, I used the top off a cheap battery charger. It holds the batteries firmly enough (but not as sturdy as a more expensive locking unit), and you can buy the entire charger for around $5, versus $20+ for a proper battery mount.

The NP-F550 battery fits really well on the unit. You could get away with the even smaller batteries with ease I imagine

For the connection to the camera, I simply cut a 3.5mm audio cable in half, and used one half, wiring it up to the appropriate wires from the unit.

The biggest issue I have with this unit, is that it’s difficult to adjust the gain on the unit on the fly. The gain controls are so small and hidden away. I guess it means that they won’t be bumped, but it’s still a pain.

Once I had everything wired up and working, I needed a way to mount everything to a camera. I came up with a pretty neat, and basic solution.

Here is a shot of the mounting plate with the 1/4 30 to hotshoe adapter attached.

I cut a square of aluminium I had kicking about, and taped a ¼ 20 hole in the middle of it. For long term use, I think the sheet is a little thin, and the thread might pull out, but for this initial testing, it works great. A small cheese plate from Ebay might work better, and allow more mounting options.

Into the aluminium base, I screwed a ¼ 20 to hotshoe adapter, allowing the whole unit to slot into the hot / cold shoe of you camera.

Everything is held together with hot glue for now. Hotglue sticks well enough for now, and allows me to change things if I desire later. Epoxy, or working out how to screw the components together would likely yield better, more permanent results, but I like to be able to tweak things in the future, so I’m a little hesitant to cover it in epoxy.

The preamp allows me to really turn down the internal preamps and avoid that Canon microphone hiss.

Testing with both my Canon EOS-M, and EOS-650d has yielded impressive results. I can turn the mic inputs in the cameras right down, and use the preamps in the Panasonic unit. This allows me to minimise the effect of the noisy preamps on the recordings.

So, now you can see, I have a great little microphone preamp that was destined for the scrap heap, but is now very useful again, with features often seen in products worth hundreds of dollars.

There are a few features that I may like to add to the unit in the future if I can figure out a way to do them without too much cost or effort.

A way to monitor the audio would be very helpful. As my cameras don’t have audio out, or permanent onscreen audio display, it can be hard to keep an eye on the audio levels you are recording. Splitting the mic output, and sending it to a headphone amp and/or VU meters would give some ability to monitor audio, even if it is only a rough idea.

Another thing that I may investigate is adding a port to the NPF battery sled, allowing me to run other items from the battery – specifically, my EOS-M, who’s batteries are small and run out quickly. This would be fairly easy to do.

Here we have the neat little unit, ready for use!

And that is about it as far as this build goes. I hope you have found this interesting, and if I have left out any details, let me know, or check out http://www.monterdiy.net/adapter-panasonic-ag-mya30g-jako-mobilny-przedwzmacniacz/ to get further details from the source.

 

 

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