Listening to the Stax SR-009 and Great Headphone Amplifiers

This story originally appeared at

Hearing the SR-009 and seeing all the high-end e-stat amps at RMAF in October gave me the idea that it would be fun to do comparative listening session for a holiday season post. For most here (and that includes me) this stuff is pretty much unobtanium, so I thought a dreamy little vicarious listening session through my words here might fit in nicely with all the other sugar plum fantasies we get to experience this time of year.

My Christmas present to you lucky few who might actually be thinking of getting some SR-009 headphones is just a taste of what you may hear, and a simple starting point for your personal journey into audio ecstasy. (Lucky bastards!)

As I said, the idea started at RMAF when I realized there were four really high-end electrostatic amplifiers that were worthy of pairing with the Stax SR-009 ($5250) electrostatic headphones---a headphone that many consider the world's best, I know I do. The four headphone amps that I brought in for the comparison are: Ray Samuels A-10 Thunderbolt ($6500); Cavalli Audio Liquid Lightning (around $5000, a revised version is expected in April); Woo Audio WES ($4990 base price, upgrades available); and HeadAmp Blue Hawaii SE ($4980, $5980 w/Alps RK-1 pot). Yama's Enterprises loaned me a set of Stax SR-009 ($5250) headphones for the test, but also shipped off the Stax SRM-727II ($2200) and SRM-007tII ($2400) electrostatic headphone amps to use a baseline for testing the above high-end amps.

I also had to figure out what I was going to use as a source, and how to set-up all the equipment in the space available. Physically, that's a lot of big amplifiers, and just getting the signal around to all the amps would be a bit tricky. I contacted Jon Iverson (Stereophile's DAC guru) for a USB DAC recommendation. He really enjoyed the Ayre QB-9 ($2500), and had one on hand that he could send for the review. After playing around with this DAC for a little while now, I can heartily echo his sentiments. This is a very nice DAC, sounding far better than it's price would indicate, IMHO.

The last little bit was getting my hands on some 10 foot balanced and unbalanced interconnects to reach all the amps spread out on my demo room counter. Now, I'm not a cable fanatic, but I do hear subtle differences between cables. A ten foot run of poor cable could certainly color the listening tests. (All you objectivists out there can just put you fingers in your ears and go "la la la la la" for this paragraph, okay?) I've always liked Cardas cables in situations like this. Their cables, it seems to me, always deliver a nice, smooth sound. As most readers know by now, I like things on the smooth side, and I was worried that the speedy nature of the SR-009 headphone might grate on my nerves for the listening tests. I gave my contact at Cardas a call, and asked for ten feet each of the best balanced and unbalanced interconnects they had...not really knowing the current line-up and costs. Two days later I received the long balanced and unbalanced top-of-the-line Cardas Clear interconnects. Valued at $4220 and $3920 respectively! These had better be good...and after playing around with some gear and interconnects I'm very familiar with, I'd say they're damned good...and damned smooth.

So, for those of you following along at home, that's about $45,000+ worth of gear once you throw in my MacBook, Amarra, and some power conditioners. Merry Christmas to me!

Listening Tests
With everything set-up, it's time for the listening tests to begin. Evaluating and describing the differences between headphones is much easier than doing the same for amplifiers. Headphone enthusiasts have long argued whether the source or the headphones are the most important link in the audio reproduction chain, but there's pretty universal agreement that the amp is least important. A decent amp is a decent amp, to a first approximation, and all the amps in this test are quite competent at doing the fundamental job of being a wire with gain.

For the first day of listening tests I decided to simply relax, be non-judgemental, and run my basic test tracks (find information on these tracks here) through each amp listening with the SR-009. First time through my impression was that the amps all sound fairly similar, with one glaring outlier. The one exception was the Stax SRM-727II, which seemed somewhat thick and inarticulate compared with the rest. But first listen is far too early for snap judgements, and I made a second listening round of the amps.

This time differences started to become apparent to me when changing from amp to amp, but again, I resisted coming to any conclusions. Rather than endlessly looping through the entire range of amps, I now began to switch back and forth between two amps listening to differences on a particular track. Once I got familiar with the changes, I would switch one of the amps out and repeat. This proved fairly revealing of the differences between amps, but it was quite time consuming as well.

While I'm very familiar with dynamic headphones, I've not done a lot of listening to the various electro-static headphones and amplifiers available, so I thought it might be a good idea to get some testing advice from a few long-time e-stat enthusiasts I know. With a few PMs and emails and a day's wait, I had some very interesting comments. One common comment was that some electrostatic amplifiers vary significantly in the way they sound between low volume and high volume listening. So I started to add some high volume listening in to my amp testing. Well now! That really began to bring out some changes. Some of the amps did indeed vary quite a bit under those tortuous conditions. I typically listen at a level that's probably lower than most, and I certainly don't recommend high-volume listening, but a good amp should have plenty of headroom to handle dynamic passages without becoming confused. For those of you who might find themselves doing some e-stat amp auditioning in the future, I highly recommend spending some time doing high-volume listening tests. It really is quite revealing.

After a week of listening tests, I did come to some conclusions about the amps. Let's take them one at a time.