Many STAX enthusiasts have requested my headphones to use with their STAX amplifier. My headphones are not as sensitive (loud) as STAX (about 6dB lower) but they will still get to levels that are excessively loud with pretty much any Pro-Bias (5 pin)  amp and the right input signal level. Some amps that people have used with good results are: SRM1/MK2, SRM3, SRM-717 & SRA-14S, STAX 353X, Mjolnir Audio Octave 2 / Stax 252, SMR-353x, SRM-006T, Kingsound M3, Stax 252s, KGSSHV, SR-D50, EAH5 as well as my Agave amplifier and more.

The Stax SRM-500T is looking really good right now as far as a value proposition for a new amp, at only  $1220 for a new amp with TWO pro-bias outputs and a split volume knob. 

If you’re like me and you’re looking for your first amp that has good performance but at a low cost, I you could find one that is used on a site like e-bay or other exchange sites. (*Please scroll to the bottom for my video on the new Topping EHA5*) Typical good features to have are one with a Pro-Bias (580V 5-pin) and a Normal-Bias (240V – 6 pin) plug and with a split knob that can adjust the L and R volume separately. Although “Normal-Bias” is no longer really used except for very old STAX headphones. In general, you can’t really go wrong with a large STAX amp such as the SRM1/MK2, or SRM-006T or SRM-3 or 313.  The downsides are that they can be difficult to find, and the unknowns that come with age. Expect to pay between $500 – $800 range for a good used amp. For an SRM1/MK2 or SRM3 I would pay about $450-$550. Something to watch for is that some only take a 100V AC (Japan) and will require a transformer adapter to use in the US, while others have a selection for 100V / 117V / 220V / 240V input. 

I would consider an amplifier such as the SRM252S a lower end amplifier at a lower cost and it will save you on space but roll off significantly in the highs. There are also Stax “energizers” such as the Pro-Bias SRD-7 that use output transformers to drive the headphones and provide the bias needed, but need to be connected to and driven by an actual speaker amplifier source. These will work but less commonly used and may require a more complicated setup. There can be risk damaging the headphones if they are not designed properly. The SRD-7 is most commonly found in the 6 pin “Normal Bias (240VDC)” which will not work. The 5 pin “Pro Bias (580VDC)” is needed for most modern electrostatic headphones.

For your first amp, I personally would not go for a portable amplifier like the D10 because it has to sacrifice some amount of range in order to be compact. Stax has many new amplifiers on their site and I haven’t tried them all, but just as a generalization, any decently sized desktop amp should be fine. Check out headamp.com and you can see the SRM-353X, SRM-500T, as well as the D-50 look interesting. The D-50 has a recessed plug that will work with the HiveX plug design but may not attain 100% insertion. Some very reputable amplifiers, with a wide selection are also made at mjolnir-audio such as the KGSSHV and others. https://mjolnir-audio.com/