[mink70]

Hi everyone--
 
I'm thinking of finding an inexpensive way of entering the land of Stax, and it looks like the older transformer box, SRD-7, happens to be more or less available. I have a newbie question, so apologies in advance. The back of the box appears to have a power cord and another cable, presumably for connecting to a speaker amp. The versions I've seen also seem to have 100V indicated on the back, meaning Japanese voltage. Does that mean I would need a step-down transformer to use one in the US? And, also, why in the world does a transformer box need a power cord?
 
Thinking getting this to use with SR-Lambdas as step one into the Staxosphere. My speaker amp is a Shindo Montille 15 watt tube push-pull design.
 
Thanks for your help!

 

[John Buchanan]

Most versions of the SRD-7 run on any voltage, but they are labelled as such. In this case, I would use a transformer to run it at the correct 100V. Be prepared to be amazed at the sound. The only trouble I have had with using my SRD-7 is that it hums with some amplifiers (Audio Research) and not with others (Studer). Take care with volume (i.e. If you leave the volume up high for speakers and accidentally blast the Lambdas with extreme volume, you may cause damage to the phones).
From memory, the connections to the amplifier are Red = Right (+), Green = Right (-), White = Left (+), Blue = Left (-)

 

[spritzer]

You need the power cord to run the bias supply.  Only the SB units get the bias voltage from the audio signal. 
 
Most of the 100V units will work at any voltage but there are so many versions that I can't say for certain.  Some of the earliest units were 100V only so if you feed them 115V the caps might not like it.  Speaking of caps, it would be a good idea to change the caps in the bias supply since 30 year old electrolytics are well past their prime. 

 

[mink70]

This is an older unit, I'm guessing (photos posted).
 
So then it sounds like a step-down transformer is the way to go? Where, then, does one get such a thing? 
 
And roughly how much power is required of the speaker amp to drive the Lambdas well?
 
Finally, I'm wondering how the SRD-7 box compares sonically with the SRM-1 mk2 solid-state amp. 
 
Thank you again
 

 

[scompton]

I drive my Lambdas with one

 

[John Buchanan]

Saw that one on Ebay. Hopefully the front and rear panels are in good condition, so you can get the cover powder coated for a nice finish. The older versions have the screw terminals on the back for speaker wire. Later versions have larger colour coded terminals.

 

[4eyesnb]

lol, i happen to bought that one for 49.50 GBP, received it 3 days ago, i also bought a $23 220-100v adapter from ebay to use with it.
 
I'm currently using it with my new SR-407 with an old Denon PMA250III as amp source. Sounds great, better than alot of my other headphones, in-ear buds i've owned.
 
btw SR-407 sound very detailed like my etymotic in-earphone,  but with wider sound stage.

 

[scompton]

You're driving an SR-407 with an normal bias, 6 pin SRD-7?  I'm surprised it sounds good.  It can't have much bass.

 

[4eyesnb]

it sound better than all my other headphones such as Senn HD580, 595,  Shure SCL4.
 
The bass is ok, goes deep,  isn't boomy.
 
Anyone compare Pro Stax headphone on Normal bias and Pro bias before? what are your opinions?
 

 

[4eyesnb]

btw, SR-407 is virtually the bigger version of my etymotic ER6, their mid and high clarity are very similar, however the stax has better separation

 

[moodyrn]

Yeah, you are really selling your 407 short with what you have. My very first stax setup was with a normal bias srd7 and a pair lambda pros. I used it until a week or so until my srd7 pro arrived. It was a huge improvement. They really opened up, and everything was much better. Your comment about your 407 sounding like a bigger er6 had me laughing. I use to own er6 and er4, and I owned the 407s for about a year. With the right setup, I would take them over T1, hd800, lcd2. And yes I've heard all of those on several mutli-thousand dollar amps. So you are only getting about half(if that) of what they are capable of.

 

[scompton]

That's what I felt like saying, but I only own normal bias Stax.  I find it hard to believe that they can sound good at under half the bias voltage.

 

[4eyesnb]

initally it sounds bad when i just connect it to my little stereo amplifier directly to SRD-407, i have to turn the amp volume knob over 65% to get decent loudness. I guess it was due to the fact that 230v bias output.
 
however after i did some experiment and using some headphone amps as pre-amp, the sound improved dramatically  

 

 

[moodyrn]

Still not anywhere close to a pro bias box. I tried both with a few amplifiers, and the difference is huge. But you can chose whatever route you want, it's your setup after all.

 

[4eyesnb]

after i tested with a real stax amp SRM-1/MK-2 Pro output,  i still think SRD-7 could still be a good temporary choice provided that you have amp + pre-amp  setup to push in some power.