The 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.
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.
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$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.
I see, thanks for the input manaox. I think you know the Stax 2nd hand market price better than I do.
Mike, Please submit pict for simple set up for this old Stax type (YM-ed)
T.I.A
Dude,
You mean a photograph of a simple set up for an SRD-7?
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).
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_150.jpg, or it can be a big receiver such as this one from Adcom: http://www.adcom.com/prod/shopdisplayproducts.asp?prodid=1155, 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.
and, what’s difference between Normal Bias and Pro-Bias, pardon my stoopidity
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://www.headfonia.com/wp-content/uploads/2010/04/headamp_kgss_2.jpg
and this SRM1Mk2 amplifier takes both pro and normal bias:
http://www.headfonia.com/wp-content/uploads/2009/10/stax_srm001mk2_2.jpg
And from the SR-404, SR404LE, and Lambda Pro review:
On a side note, the Stax electrets use 5 pins connector but they must not be mixed with the Stax Electrostatic amps.
http://www.headfonia.com/wp-content/uploads/2010/03/stax_sr34_7.jpg
Gotcha, will it provide effect to the sound quality? which one is better in all aspects?
thank you most kindly!
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.
Hello Mike,
Question, do you need and electricity adapter (e.g 220V to 110V) or this thing can runs on both 110V & 220V?
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.
Thanks Mike, can’t wait to hook up on my musical stat.