Koss ESP/95x Electrostatic System

I loaned @AllanMarcus two modded Stax amps, one was a SRM-727 with global feedback mod, and the other was a refurbished SRM-T1 with constant current load output mod. It also had a TKD pot in place of the original Alps RK27.

A stock T1 runs about $500-$700 these days, with about $100 parts to replace all the electrolytic caps and do the constant current mod. A stock 727 is over $1000, modifying it to have global feedback is about $1 for 4 resistors. An SRM-717 or modded 727 are probably Stax's best SS amps. I prefer the modded T1 myself.

The Stax amps don't have the voltage output of the Koss energizer, but they have significantly higher current capability. According to an old Kevin Gilmore post, the Koss can output close to 2400 V peak-to-peak, but only has 2 mA standing current per channel. The Stax amps can output close to 1200-1400 V peak-to-peak, but have around 9.6 mA to 14 mA standing current per channel. Note that the voltage outputs assume that the amps can swing all the way to B+ and B-, which isn't quite true, but close enough for comparison purposes. Also note that the difference between 1200 V and 2400 V is 6 dB in output volume, which approximates 2-3 clicks of a typical volume control.

What all these numbers mean is that at the limit the Koss will run into current limiting, especially at high frequencies, which require sufficient current to prevent slew limiting, whereas the Stax amps will voltage limit first. However, since the Koss is rated at 104 dB at 1 kHz with 100 volts input, you are likely to incur hearing damage playing the headphones at such high levels.

 

If anyone wants to make their own adapter cable, thank you Darrin Fong

https://fongaudio.com/koss-esp-950-to-stax-5-pin-adapter-wiring-diagram/

 

My Koss arrived. This wasn't really what I was expecting at all...
The mids and treble are so clean, and presented in a way that I just LOVE. I don't get any sort of fatigue from the treble either!

But the bass is lacking, and the stage feels a little smaller than I expected. That said, I'm super digging these. I'm still getting used to them. It feels like an anti-LCD2C, in a really good way. I love both, and I think they make incredible compliments to each other.

 

Kinda neat video!

 

I felt the same way about the ESP-950’s bass, but found mine to respond fairly well to EQ, in my case using a Schiit Loki. Needed a lot of low-end boost for my preferences, but the result was nice and clean... as opposed to my LCD-2, where touching the bass tone controls at all mutilates the sound quality. My favorite setup for the ESP-950 included a Schiit SYS to allow me to set-and-forget the split volume control and an Eitr (Edit: Loki) for bass boost.

 

You are so used to the recessed tremble and boosted bass of the LCD that the more balanced Koss sounds off. Try with just a little bass boost and slightly refused treble for a few days and let your brain adjust.

Also, how does the Eitr boost bass?

 

Brain malfunction. I should have written Loki, which is what I was thinking of, not Eitr.

 

Too much bass will do that to you!

 

How much heresy would it be to add a hardware EQ to this to boost the bass? Or is my DAC (gamma2) anemic and that's the culprit? Maybe I should just stick with my DT1350s. :/ (Not on the basis of sound quality, but convenience and closed back and I like the bass boost.)

 

I have a Schiit Loki in front of mine rn.

You kinda have to be careful mind - if you over-excursion a stat driver it's easy to damage it, so it's not really a good idea to try to turn them into beats by dre.

 

I use anti-static record sleeves for my baby Stax and K1000. Works like a charm.