I'm a huge fan of ear-buds. But I always run it through a pre-amp. Just makes the sound clearer and easier to use. I don't play it much with my acoustic, but you cannot beat the sound quality.
Most 'ear-bud' mics do not do so well being powered directly from the lower-than-optimum mic powering voltages offered from most small flash recorders having mic input powering feature. These typically at 2.5 volts, sometimes as high 5 volts, but most ‘binaurals’ need over 5 volts to really sound good.
Other than choosing a preamplifier solely for having optimum powering for your brand of mic, needing an external preamplifier for satisfactory audio largely depends on your subject recording requirements for having a quiet low noise mic preamp.
Most find current portable deck mic preamps OK for PA amplified pop/rock type venue recording using the low sensitivity mic input setting, but only a few recorders sport mic preamps quiet enough for nature recording purposes. Most deck preamplifiers are lowest noise, and/or crisp/clean sounding only using the Low Sensitivity mic input mode (aka -20 dB)
It may help to know my own DSM mics are fully optimized for low 1.5 to 3 volt powering available directly from most portables. However, my DSM mics also require the deck's mic power current limiting resister be a certain value, and Sony's PCM-D50 /M10 models are the ONLY ones to have gotten this exactly as required for full performance DSM mic operation.
Sony's mic preamplifier is also exceptionally quiet/clean sounding so no external preamp for lowest level nature sounds is required at least when using my brand of mics.
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