Koss ESP/6A Resto-Modded DJ headphones, with Bass-Beat-Blinking LEDs!

I’m reaching absurd levels of over-the-top with these Koss DJ headphones! LOL

I found these ESP6a’s for cheap and in great condition. Then I gutted them, and modified them in the same manner as my Koss Pro4/AA. It’s kind of a shame to waste good vintage electrostatic headphones, but these are not rare, and they’re not even Koss’s best electrostatic, so I think it’s worth it!

They’re so cool. The cups are much larger than the Pro4/AA or Pro5/LC, and they have flashing red neon bulbs pointing out the front!

The ESP6 is a self-energizing electrostatic headphone, meaning it uses the audio signal itself to generate a high-voltage bias across the membrane, instead of a separate power supply. This is a cheaper, but pretty effective way to do it. There’s a voltage multiplier circuit inside.

Kinda dangerous voltage!

The neon bulbs are used for voltage regulation, and light up when the volume is high enough.

Anyways, all that stuff gets ripped out, and I installed some Peerless 40mm drivers, just like the Pro4/AA I did.

And since the neon bulbs won’t be any use, I replaced them with red LEDs, and created a circuit to blink them on the beat! It’s a 2nd-order Sallen-Key low-pass filter, with a gain of 60. When the audio signal reaches 30mV, the output goes to 1.8V and lights the LED. Gain of 60 was chosen experimentally to flash nicely at normal volume with the Peerless 40mm drivers, which are fairly sensitive. You might like to adjust the gain. I used the calculator here to determine component values. The LED sees about 4mA, which is pretty bright.

The LMV321 is a jelly-bean rail-to-rail, single-supply, low idle current opamp, optimized for battery operation. Only 35uA quiescent per amplifier. It’ll run idle for about 3 months continuous off a CR2032.

Download the LTSpice files here. Also included is the ASY file for the LMV321, and a spice directive. (It’s not the best way to do an assembly, I know.)

Bass Beat Blinker in action. The effect is simple, but surprisingly entertaining!

More details of the in-line assembly.

Here are the EAGLE CAD files, and GERBERS, you can have your own boards made from a house like JLCPCB or PCBWay. Consider it “DON’T CARE WARE”. Do what you want, short of selling them with my logo on it. No support. There are some things I could have done better, feel free to improvise!

Parts: