# Hiring somebody to draw a stereo headphone amplifier circuit

Oct 14, 2016
6
Hello,

I'm looking for somebody knowledgeable who can draw a working circuit meeting certain requirements, a low-noise, high adjustable gain, portable battery-powered microphone amplifier with stereo input (two mics) and headphones output with a maximum sound level limiter.

Any electronic part can be used, as long as it is relatively common, has good performance and is one of the best for its price range in terms of quality, noise etc.
Each single part (mic, transistor, IC, etc.) should ideally cost within $20 (except headphones, since I already have them or would change them from time to time), unless something really superior is found at a slightly higher price, for example$25.

Requirements:
- low noise (as low as reasonably possible, so no place for LM386 and the like)
- high sensibility
- high, adjustable gain (as high as possible within this price range and without decreasing sound quality too much)
- sound level limiter (to prevent hearing damage when gain is set high but microphones bump into something)
- portable (weighing less than 2.2 lbs/1kg)
- battery powered (possibly something rechargeable such as 1.2v AA or 3.7v 18650 Lithium)
- two microphones input, each having as output one headphone channel
- pickup frequency range 50-18000 Hz (mostly would be wild animal calls and insect songs)
- reliable in high humidity (possibly rainproof microphones since they'd be exposed while the other parts would be within a plastic box)
- working at a wide temperature range (-20/+45°C or -4/+113°F)
- reasonable working time, like 24h for each freshly recharged battery/set of batteries
- edit: as a forum member rightfully pointed out, an on/off low frequency cutoff swith would be nice to be included

Let me know how much are you asking for this, I need just a working circuit drawing and will buy parts and assemble it by myself, thank you.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,508
You've left out one important detail, do you want the microphones to be at all directional?

Also, what are you thinking of paying? Does something in the range of a couple of hundred dollars seem like what you're expecting?

Are you expecting a PCB design?

Your going to get pretty ordinary microphones for the budget you've set.

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