Amazon Headphones & Amplifier

Amazon has a pair of very inexpensive on the ear headphones that I thought would be perfect for a variety of low fidelity uses where I did not want to bother with in the ear/earbud type transducers.  Also, it provides a good balance of noise blocking, comfort and bass response.  These headphones, sold under their ‘Basics’ label are very inexpensive and highly regarded (what ever that means) by the Amazon customers that evaluated them.  They can be found at: https://www.amazon.com/AmazonBasics-Lightweight-On-Ear-Headphones-Black/dp/B00NBEWB4U  And they have an average rating of 4.3 of 5.0.

Also, I wanted to build a simple, optimized amplifier to drive these headphones for a variety of uses from Arduino projects (Mozzi based music synthesizer to amateur radio applications), but their specifications were not readily available.  In this post we will describe the headphones and then the amplifier used to drive them.

The over the ear headphones have a diaphragm size of 36 mm and an impedance of approximately 32 Ohms.  By using a simple flat plate coupler and an inexpensive sound pressure meter (not well calibrated, but probably close) the sensitivity was measured as 72mv at 1 KHz to generate 94 dB SPL.  This should be checked, but is directionally correct.

 

The schematic shows the use of two unity gain, low voltage followers as drivers.  One is a virtual ground, the other is a unity gain follower.

 

Here is what the circuit looks like functioning as a follower after the Teensy 3.2 that I am using to run some Mozzi sound synthesis routines.  The circuit, using TLV2462 Op Amps (really great low voltage op amps), can generate almost 1.2 VRMS which generates almost 116 dB SPL with these headphones, which is plenty loud off of a 5 volt supply!  Note that I put the headphones in parallel, so it is 16 ohms and the output is current limited.

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