Converting a Microtrack to AA batteries

[Martin Catt]

Just thought I would pass on the information that a Microtrack 24/96 digital audio recorder can successfully be converted to run off three 1.5-volt alkaline batteries. The lithium battery in mine finally gave up the ghost, and M-Audio has raised the price for installing a new lithium battery to $120.00 USD.

The process is pretty simple. The hard part is figuring out how to get the unit open. The case snaps shut. A quick search on the internet will give you instructions on how to crack open the case:

M-Audio micro track battery replacement guide

The intent of the above site is to install a new lithium battery; however, I don't like internal non-user-replaceable rechargeable batteries. I want something where I can swap in a new set of batteries when one set has drained and continue recording.

Anyhow, after opening my unit and doing some testing, it seems that three 1.5 volt cells (for a total of 4.5 volts) will power the unit with no further modifications to the circuitry. I found a plastic battery case for three AA cells, attached it to the back cover of the Microtrack, removed the original lithium battery, and soldered the AA battery pack leads to the circuit pads where the lithium battery had been connected.

Current drain seems to average about 200 milliamps during normal operation, so assuming alkaline AA batteries are rated about 2000 MAH, you should get roughly at least four hours on a fresh set of AA's. I've set my unit up with an external power jack so I can use a larger 3 D-cell pack for longer run times. As an added bonus, the on-screen battery indicator appears to function as well, showing the charge state. I need to run down a few sets of batteries to see how well the indicator tracks charge level. Based on what I'm seeing on my ammeter, there's a pretty steep current drain at startup, but then it levels out at around 200-250 milliamps, depending on what you're doing (phantom power, display backlight, etc).

I haven't tried connecting the unit to a computer through the USB port using disposable batteries, and don't plan on doing so. I download my files off the compact flash card using a card reader.

Anyhow, just thought I would pass the information along.

Martin

[Christopher Drews]

Ugh - I have 4 of these buggers and I know exactly what you are talking about. One unit actually carries a 20 minute charge (although it was one of the first purchased). Usually, I just leave it plugged into a netbook while recording or use a A/C to USB adapter.

Also use this product if I need to run around a bit. Keeps the unit topped off.

Nonetheless, this is useful information.
Thanks,
-C

[Martin Catt]

Chris:
Before the lithium battery finally died (forcing me to open the unit up), I built a six D cell power pack that regulated the nine volts down to five volts and fed it into the USB port of the Microtrack. The disadvantage was that you wasted a lot of power in the regulating circuitry (I used a 3-tab voltage regulator IC) dropping down to 5 volts, and a lot of the power that finally made it into the Microtrack was wasted trying to charge a battery that wouldn't charge.

One option I considered, but didn't explore, was to make an external battery mount that would hold a lithium battery for a cell phone, allowing one to have several batteries charged and swap out batteries as the day went on. I decided to go with the easiest approach and go with AA cells, with an external power jack added as a convenience.

Martin

[Martin Catt]

Here's some pictures showing the finished conversion. The battery case mounts to the back half of the Microtrack case with screws from the inside, and covers several holes I bored through while figuring out how to mount it.

The battery case itself has an extension added to the top to hold the external power jack. Adding the extension (cut from another electronics project box) took more time than anything else.

The last photo shows the unit running on AA cells. Note the charge state indicator in the upper right shows a full charge.

Martin