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Sunday, September 1, 2013

••◊ Upgrading the Marantz PMD661 audio recorder

I recently helped out at a shoot at the Del Mar Racetrack.  After getting settled with the cameras in the morning they asked me to go out and record some horse racing audio (crowd, hooves, trumpet...etc).  The problem was that the LED audio level meters were basically invisible in Southern California sun by mid-day.  In a desperate attempt to see the level meters I made a makeshift hood out of gaffers tape, but even that wasn't enough.  Evidently the LED output was designed to satisfy a Japanese engineer's testing on a dimly lit lab bench!

Being an adventurous EE myself, I opened up the unit and found the LEDs in question.  They were just standard surface mount run-of-the-mill 0603 size LEDs.  After a quick search on Digikey I found suitable replacements from Kingbright (754-1547-1-ND, 754-1542-1-ND, 754-1543-1-ND).  I also increased the current drive a bit by swapping out the series resistors.  This modification allowed me to swap out the amber LEDs Marantz chose and replace them with yellow LEDs.  It's much easier to distinguish between red/yellow, than red/amber in high brightness outdoor conditions.

The LED driver is a serial to parallel converter made by JRC (NJU3718A).  The IC can drive up to 5mA per pin when powered at 3.3v.  I thought this might be a bit weak since the LEDs are rated at 20mA...until I actually ran the LEDs at 5mA and burned a hole in my retina!  The new technology high brightness LEDs are pretty insane.  I also increased the drive current to the LEDs surrounding the REC button, since it was hard to tell if I was recording while standing in the sun. 

Here's a picture, post modification, with the LEDs causing lens flare with indoor lighting.

While outdoors the LEDs are finally visible and this is in afternoon sun during a Southern California summer.  I would normally be squinting because it's so bright.

I think we have success.  Now the recorder has the opposite issue.  While indoors it's hard to look at the level meters because they are just too bright!

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