Stax SRD-7

stax_srd7_1

The Stax SRD-7 energizer works differently than a regular Stax amplifier. It requires to be piggy-backed to a standard speaker amplifier, where it takes the current from the speaker amplifier and convert it to the necessary high voltage power for driving Stax Electrostatic headphones. It remains a popular choice among Stax users as a cheaper alternative than a standard electrostatic amplifiers. 2nd hand units sells for roughly $200 and less, and it runs great out of any vintage stereo receivers.

The SRD-7 pictured here is a normal bias version, where both headphone out has the 6-pin normal bias Stax connectors. There are also pro-bias SRD-7s that accomodates the higher bias Pro-version Stax headphones. The unit itself is fairly small, measuring roughly 12cm x 7cm x 20cm, and it easily finds place next to your computer. The front panel has a knob for turning power on and off. When the knob is on the off position, the signal from your speaker amplifier is passed on to the speakers, thus you conveniently can switch between your headphone and speaker set up.

stax_srd7_2

On the back panel, we find two cables as well as four binding posts for connecting your speakers. The black cable is the AC Power cable, where the gray cable goes into your speaker amplifier. Conveniently, Stax included the cabling legend for connecting the SRD-7 to your speaker amplifier. Power consumption is surprisingly low at 0.1w.

stax_srd7_3

Facebooktwitterredditpinterestlinkedinmail

22 Comments

  • Reply February 18, 2010

    manaox

    $200 is running a bit high for the normal bias SRD-7. I sold an SRD-7 Pro at that price (low sell, but still). I wouldn’t pay more then $80.

    • Reply April 24, 2010

      Mike

      I see, thanks for the input manaox. I think you know the Stax 2nd hand market price better than I do.

  • Reply April 24, 2010

    ChaoticAngel

    Mike, Please submit pict for simple set up for this old Stax type (YM-ed)

    T.I.A

    • Reply April 24, 2010

      Mike

      Dude,

      You mean a photograph of a simple set up for an SRD-7?

      • Reply April 24, 2010

        ChaoticAngel

        Yes Sir :), never had chance to see simple(st) set up when I was in Jakarta. I saw (heavy)full set one at Winsome's maybe you can elaborate more how will it works with foobar as my source. (got Little dot DAC on my list).

        • Reply April 24, 2010

          Mike

          It's pretty simple.

          Basically, these SRD boxes need to be paired with a speaker amp (I'm sure you know what a speaker amp is). It can be a small T-amp such as this one from Whiplash: http://www.cryo-parts.com/images/pop_pulse_t-amp_… or it can be a big receiver such as this one from Adcom: http://www.adcom.com/prod/shopdisplayproducts.asp… or an integrated amplifier, or a big tube amp, basically anything that you normally use for driving Speakers. You connect the leads to the speakers terminal and that's how the SRD boxes receive power to drive the electrostatics.

          Using foobar, a simple set up would be: Laptop > USB DAC > Speaker amplifier > SRD 7 > Stax amplifier.

  • Reply April 24, 2010

    ChaoticAngel

    and, what's difference between Normal Bias and Pro-Bias, pardon my stoopidity 🙂

    • Reply April 24, 2010

      Mike

      Basically Stax Electrostatic headphones fall into two categories:
      Normal bias, and Pro bias.

      If you look at the connector for the headphone, it has 6 holes which means it takes headphones that has a 6-pin connector. This is normal bias, and it runs on a 230V bias voltage. The pro system uses a 5-pin system, thus a "pro bias" headphone would have a 5-pin connector, and a "pro bias" amplifier would have a 5-hole connector.

      For example this KGSS has a 5-pin "pro bias" connector: http://headfonia.com/wp-content/uploads/2010/

      and this SRM1Mk2 amplifier takes both pro and normal bias: http://headfonia.com/wp-content/uploads/2009/

      And from the SR-404, SR404LE, and Lambda Pro review:

      The Pro model requires a higher bias voltage of 580 volts, compared to the 230 volts normal bias non-Pro models. (It is important to note that the Pro and non-Pro models are non-interchangeable. The non-Pro models come with 6 pins on their plugs, so you won’t make the mistake of plugging them into Pro amplifiers which comes with only 5 pin connectors. The connectors simply won’t fit. However, you can accidentally plug in a 5-pin Pro model into a non-Pro amplifier. The resulting sound will be very low in volume, and it’s not recommended because damage may occur when you try to turn up the volume excessively.

      On a side note, the Stax electrets use 5 pins connector but they must not be mixed with the Stax Electrostatic amps.
      http://headfonia.com/wp-content/uploads/2010/

      • Reply April 24, 2010

        ChaoticAngel

        Gotcha, will it provide effect to the sound quality? which one is better in all aspects?

        thank you most kindly!

        • Reply April 24, 2010

          Mike

          I don't think you totally understand the concept here.

          You can't really choose one bias over the other. Some headphones come in normal bias (i.e SR-Lambda). Some headphones come in pro-bias (i.e SR-404 is Pro. There is no SR-404 normal bias). It's the way the headphones are designed. Even in the case of the SR-Lambda and SR-Lambda Pro, they actually sound quite different from each other. So it's a case of choosing the headphone you want.

          Cheers.

  • Reply May 2, 2010

    ChaoticAngel

    Hello Mike,

    Question, do you need and electricity adapter (e.g 220V to 110V) or this thing can runs on both 110V & 220V?

    • Reply May 3, 2010

      Mike

      Hi Ted,
      If you look at the backpanel picture, it says that the input voltage is 100-240V. So, no, I don't think you'd need a step up/down. 🙂

      • Reply May 3, 2010

        ChaoticAngel

        Thanks Mike, can't wait to hook up on my musical stat.

  • Reply August 17, 2010

    Lawrence

    Has anyone tried this at 240V? Just wondering if you have to open it up and change any switches or can it run off any voltage in thre range without any changes?

    Thanks, Lawrence

    • Reply August 17, 2010

      Mike

      I actually used it at 240V. It looks like there is nothing to change if you want to use it at 110V, since the voltage indicator says 110V – 240V

  • Reply January 22, 2011

    Brian Beattie

    I have had these SRD-7s for many years. I just bought a Denon 1911 7.1 receiver. Can the headphones be connected to the 6/7 speaker terminals (normally for side speakers in a 7.1 setup) on the receiver?

    Many thanks,
    Brian

    • Reply January 22, 2011

      Mike

      Hi Brian,You mean the SRD7 connected to the 6/7 outputs?

      • Reply January 22, 2011

        Brian Beattie

        That's what I meant, but I don't think it makes sense because the other speakers will still be heard. There are different 'zone' setups for the Denon receiver – I probably have to get into a separate zone to hear the headphones only???

        • Reply January 22, 2011

          Mike

          I'm trying to understand the situation better here..If you plug the SRD7 to the rear or side channel output, won't that give you the processed surround signal out to the headphones?

          • Reply January 22, 2011

            Brian Beattie

            Denon receivers are very difficult to setup. I'm asking the same question on the AVS forum for Denon 1911 receivers. I'm pretty sure it has something to do with a Zone 2 amp setup on the receiver.

            • Reply January 22, 2011

              Mike

              If you want to still hook it up to the Denon, use the output for the main speakers. Then you can hook the speakers to the SRD7 rear panel. The switch at the front switches between the headphone and the speakers.

  • Reply July 5, 2018

    Jim

    The SRD-7 actually gets its power from an AC outlet, and its audio feed from
    a speaker amplifier. The Stax electret headphones (I use an SRS-44 system)
    are permanently electrostatically charged so that they don’t need a power source.
    The SRD-4 adaptor has no bias. It merely sends the audio signal from a
    power amplifier to the SR-40 electret headphones.

    When used. with an excellent source and amplifier these older Stax systems
    can sound quite good, offering much more transparency than any dynamic
    headphone at several times the price the old Stax systems are selling for.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.