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Old January 14th, 2012, 06:44 PM   #1
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Join Date: Jun 2007
Location: Sydney Australia
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DIY portable mic -pre-amp kit

First a background. I wanted to mic my actors for my film using a lav on each actor and some portable recorder. Some scenes had 5-6 people talking.
I first started with iriver ifp recorder with the Giant Squid mics - about 35 bucks per setup. This gave me pre-amp noise as the iriver uses cheap pre-amps. It was recorded as 160kpbs mp3 mono 44.1khz sampling.
Then I tried a bunch of used Sony Hi-MD recorders, about 50-75 each. These default to AGC, and I had to buy a MZ-RH1 (M200 actually) in order to transfer the recording using USB2.0 (the older Hi-MDs come with USB1.1). The pre-amps on the older NetMd and MD were crap.
Now I have the Tascam DR-05, which fixes all the problems related to pre-amps and gives 96khz sampling. However, it is still too big to carry in a pocket.

I found that the biggest problem for human conversational voice is not sampling (44.1khz vs 48khz) or compression (PCM vs 160kbps mono mp3) but pre-amp noise. Resampling can be done easily via command-line using soX.

I also found the form factor of the iriver ifp series to be most convenient for micing actors.

So I looked around for circuits for a simple battery powered electret mono pre-amp for a iriver ifp. BTW the iriver was found to have very low distortion using the line-in setting. AKUSTYK for Praat

I found these DIY battery powered mic pre-amp kits.

Electret Microphone Pre Amp - Cana Kit - 11.95/-

Preamplifiers & Mixers ~ 10/- each

Has anyone used these, any comments ?? BTW I am looking for something to be powered from a 9V or a AA battery, a portable device.
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Old January 14th, 2012, 08:03 PM   #2
Join Date: Jan 2011
Location: Pennsylvania
Posts: 1,340
Re: DIY portable mic -pre-amp kit

Originally Posted by Anmol Mishra
I first started with iriver ifp recorder with the Giant Squid mics - about 35 bucks per setup.
Do you mean to say you can get an iRiver recorder and a GS mic for a total of about $35? If so, where? That seems incredibly low, as the iRivers fetch a handsome price on eBay.

At any rate, the iRiver recorders are interesting. In fact I have several of them, and used to use them frequently. They're not quite SOTA today although the size remains an attractive feature.

Of the three sources you provided, the first and third have no specs, so I would dismiss these.

I am a bit puzzled by the specs on the second source. They say S/N is "> 75 dBA" but that doesn't make sense to me because dBA is an acoustic level. Saying something is "> 75 dBA" means it's a lot louder than normal conversation (which is around 60 dBA). OTOH, specs for a preamp should really state an equivalent input level, or an output level, expressed in mV, Volts, or dBV.

Also, by the time you buy one of these, add a jack for your lav, make room for a 9V battery, put it in a shielded metal box, and strap it to your IFP, the overall rig will be pretty big and ugly.

Furthermore, the gain is set by changing one resistor on the circuit board. So if you're out in the field, and you discover that the mic is clipping, what do you do? Open the metal box (into which you've assembled this circuit board), get out your soldering iron, and change the resistor? That hardly sounds practical for live field recording work.

If you like the DR-05, have you tried a DR-03? They seem fairly similar except the DR-03 is significantly smaller. It's a bit bigger than an iRiver, but it's thinner and fits quite nicely in a pocket.

Last edited by Greg Miller; January 15th, 2012 at 11:21 AM.
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