[Bingturong]

I just bought a pair of SR-009. When plugged into my T1 (recent serviced by Stax) one side is silent.

Before sending them back, my dealer has asked me to check the bias voltage of the T1. A local electronics engineer is going to help me do this without killing myself.

I have no clue about electronics. Is it sufficient just to put a multimeter across the bias output and earth? Or it life more complicated than that?

TIA

Not exactly, you'll need to measure the bias voltage before the ballast resistor which, if I'm correct, for the SRM-T1 are the two last resistors on the bias section of the board before the bias wire (coloured grey) goes to the output. So you'll need to open it up and measure it from the bottom of the board.

 

[Bingturong]

Though, it doesn't make much sense that if the bias voltage is messed up as for the pro there is only one wire that goes to both headphones. If the bias from the amp is the problem then both channels shouldn't work at all...

 

[martin778]

Exactly this^
Do you have any other Stax headphones to try out? Maybe the cable is messed up somewhere or there is an issue on the source side?

I've bought a small lot of Staxes recently, without knowing what they were. I think it's a SRS3030, SRD7SB+Lambda normal bias and SR001 in-ears albeit with snapped plastic. I've already seen the glue on the panels gone in the lambda's, dangit. Pretty much any lambda or it's derivative I've owned in the past years had that issue - panels coming loose from the metal plate in the earcup.

Does anyone know what kind of load does the SRD7SB (or any other passive energiser) present to the power amplifier? I've looked at the manual but don't really understand how the SRD7SB works, there is no AC cable so how does it keep the bias, a supercap? I assume SB means "Standard Bias"?

 

[Bingturong]

Exactly this^
Do you have any other Stax headphones to try out? Maybe the cable is messed up somewhere or there is an issue on the source side?

I've bought a small lot of Staxes recently, without knowing what they were. I think it's a SRS3030, SRD7SB+Lambda normal bias and SR001 in-ears albeit with snapped plastic. I've already seen the glue on the panels gone in the lambda's, dangit. Pretty much any lambda or it's derivative I've owned in the past years had that issue - panels coming loose from the metal plate in the earcup.

Does anyone know what kind of load does the SRD7SB (or any other passive energiser) present to the power amplifier? I've looked at the manual but don't really understand how the SRD7SB works, there is no AC cable so how does it keep the bias, a supercap? I assume SB means "Standard Bias"?

SB means self-biasing as the adapter uses the signal from whatever speaker amp you're using. The biasing circuit in an SB actually take a signal from the audio path that comes from the transformer and runs it through a voltage multiplier. Compared to a non-sb which takes the bias from the mains and runs that through a voltage multiplier. Downside of the SB is to have a stable bias, it depends on the strength of the music signal. It's not really an issue as the biasing of the headphones themselves is most important at the start and the bias itself takes a negligible amount of current. As for load, it's a bizarrely hard question to answer. Stax has never specified the impedance load but always the wattage. I had no trouble running it out of 4 or 8 or those multiple ohm speaker outputs.

 

[martin778]

Interesting, but how do we know what the bias voltage is, in the end? Are these "SB" adapters all normal/low bias?

 

[Bingturong]

All SB adapters are normal bias only unless you modify it yourself.

 

[timb5881]

I have a pro and a nb bias SRD-7 but never a SB. I have read that the self bias versions have a bit of a problem holding the bias on some music, and it has effect on the sound.

 

[bigjako]

I have a pro and a nb bias SRD-7 but never a SB. I have read that the self bias versions have a bit of a problem holding the bias on some music, and it has effect on the sound.

I have a Pro-modded SRD-7 and a NB-only SRD-7SB and have listened most to the SB. I haven't had any audio issues with either, and have been trying to discern any audio differences between the two, but can't. Selling the 7SB because the pro-modded SRD-7 works for all my Staxen. Paired with a relatively inexpensive but great Emotiva BasX A-100 - it's a killer combo, for me.

 

[bearFNF]

I have had my SRD7SB since the 80's and have never had any issues with it out of several high end and several entry level amps. The only reason it is on a shelf now and not being used is that I had my BHSE built with one NB and one pro socket.

 

[chocolates]

if anyone's interested in picking up an SRD7SB i've got one that i no longer use (since i've got my KGSSHV carbon :v)

 

[mrmarbach]

Do you have any other Stax headphones to try out? Maybe the cable is messed up somewhere or there is an issue on the source side?

I have a pair of 404LE which play purrfectly with the T1.

The dealer suggested that the 009 might be more sensitive to a bias problem.

My electronics guy cancelled, went on holiday. So now I am trying to find a local dealer who will let me plug the 009s into a known good SRM.

 

[Bingturong]

I have a pair of 404LE which play purrfectly with the T1.

The dealer suggested that the 009 might be more sensitive to a bias problem.

My electronics guy cancelled, went on holiday. So now I am trying to find a local dealer who will let me plug the 009s into a known good SRM.

Yeah, I'm certain its the 009? Is it an early model? They were notorious for having imbalance issues.

 

[macdonjh]

I have a Pro-modded SRD-7 and a NB-only SRD-7SB and have listened most to the SB. I haven't had any audio issues with either, and have been trying to discern any audio differences between the two, but can't. Selling the 7SB because the pro-modded SRD-7 works for all my Staxen. Paired with a relatively inexpensive but great Emotiva BasX A-100 - it's a killer combo, for me.

I also have an SRD-7 energizer. I think I have read that some Stax owners have had one output modified to Pro bias level and left the other output at Standard bias. I am quite interested in that. Can this be a DIY project, are the schematics available? I think Mjolnir has offered modded SRD-7 in the past, though I don't see any on his website now.

 

[timb5881]

For anyone interested, there are 3 Stax Sigma headphones for sale on eBay. Prices are steep, but if you are looking! 2 are normal bias and one is pro.

 

[petitpierre]

For anyone interested, there are 3 Stax Sigma headphones for sale on eBay. Prices are steep, but if you are looking! 2 are normal bias and one is pro.

obviously two have been sold since last night but there is still a normal bias at an incredible price!
I paid mine ten times cheaper!
has the seller lost his mind?