[edstrelow]

Quote:

Hi Stax Gurus
I have developed a problem with the left driver of a lambda pro.
There seems to be reduced volume at times which reverts back to normal if I push on the back of the outer cover of the driver or shake my head when listening.
There seems to be a persistant very low volume squeal coming from the driver most of the time when it has normal volume.
I have opened up the drivers to check the wire connections and they all seem good and there does not appear to be any damage or anything out of the ordinary with the driver (the back side only as it appears that I would have to fully remove the earpads to look at front side of the driver)
Does anyone have experience with this type of problem and suggestions for further DIY diagnosis and repair?
Any help would be much appreciated as I am on a tight budget and I love listening to my music.
Thanks

A squeal probably means a short, not necessarily in the drivers but possibly so.   I think you have to get past the earpads to have a proper inspection.

 

[gilency]

I finally agree with Spritzer that the NB Sigma sounds better than the Pro.
Strings and voices sound beautiful, from Bach to Kiri.
Very happy to have both, but liking the normal bias more.
BTW, does anybody have a NB extension cable lying around they would like to sell?

 

[edstrelow]

Quote:

I finally agree with Spritzer that the NB Sigma sounds better than the Pro.
Strings and voices sound beautiful, from Bach to Kiri.
Very happy to have both, but liking the normal bias more.
BTW, does anybody have a NB extension cable lying around they would like to sell?

The original Sigma is a classic, still a worthy phone to have around.  I would compare it to the original Quad speakers, later models have tried to improve on them but the original design had so much merit that people still love them just as they are. 
 
I have three different Sigmas, the normal, low bias, the Sigma Pro and Sigma/404  and don't listen to the low bias one much.  But every time I put them on I  keep thinking "these are a lot better than I remembered."  Sometimes what I hear is bit more sweetness to the sound. 
 
But on balance I still prefer the high bias phones.http://www.head-fi.org/forum/thread/464873/stax-sigmas-compared-low-bias-sigma-pro-and-sigma-404   I made my comparions with dual bias headphone amps.  I see you have a transformer, possibly this changes the sound.
 
Certainly there is more audible ambience with low bias, but I don't think  this is  necessarily accurate.  Having used the dBx dynamic range companders for many years, I can say that any time you compress the dynamics you will probably hear more ambience.  The dBx manuals even pointed this out.  So part of what you get with low bias is more dynamics compared to a comparable high bias phone, which may be good or bad depending on the music.  One day I would like  to get my hands on the original low bias Lambda to see if you can hear this compression/ambience trade-off with these phones.
 
.

 

[John Buchanan]

Got to agree with Ed. It sounds like the sound preference for these sets is (best to worst):
Sigma/404>NB Sigma>Sigma Pro. I have never heard the Sigma Pro however.

 

[edstrelow]

Quote:

Got to agree with Ed. It sounds like the sound preference for these sets is (best to worst):
Sigma/404>NB Sigma>Sigma Pro. I have never heard the Sigma Pro however.

I am not quite saying that.
 
Rather the NB Sigma is just a great phone and stands on its own as a high quality item.   When I sent my last of 2 NB Sigmas for conversion to a Sigma/404,  I immediately located another NB Sigma since I did not want to be without one.
 
It has a sufficiently good frequency range and dynamic capability to be a good general phone, it has an interesting sound signature which enhances many kinds of music and of course it has what I think is an enhanced spatial realism due to the pre-aural driver placement.  Since only the Sigmas and the AKG K1000 have anything like this it is a rare item and once you have the taste  for this type of sound you may very well find yourself dissatisfied with conventional phones, even electrostatics like the 007.  I certainly understand  why you might sell your 007's and keep the Sigmas and some diffuse-field equalized Lambdas.
 
Like just about every phone/speaker/whatever  there is some music that will sound better on it than anything else and some people who will like its sound better than anything else.  As an example, when I was at the Canjam LA last year I had the Sigma pro and Sigma/404 hooked up together to my Stax 717 amp.  Most people preferred the Sigma/404 but one listener said the pro had a better midrange for bringing out vocals.  That was probably true because it also had less bass and treble than the Sigma/404 so if you are looking just for midrange and care less about bass and treble the pro is the way to go.   
 
The NB Sigma is kind of like that too:  Somewhat lacking in deep bass,  rolled off at the top ( but not as bad as the SRM001), but still has a great kick in the bass which makes it a good rock phone.  Its bass boom also seems to bring out the ambience. And I think it  also has  a sweeter sound, possibly due to the low bias operation, or possibly due to the treble roll-off which filters out harshness in the  upper frequencies from cartridge mistracking or digital distortion. .

 

[Keithpgdrb]

Quote:

 
I have three different Sigmas, the normal, low bias and Sigma/404  and don't listen to the low bias one much.  But every time I put them on I  keep thinking "these are a lot better than I remembered."  Sometimes what I hear is bit more sweetness to the sound. 
 
 
 
.
 

what is the difference between normal, and low bias?  I though the normal Was the low bias.
 

 

[edstrelow]

Quote:

what is the difference between normal, and low bias?  I though the normal Was the low bias.
 

You are correct. That was a typo, now corrected.  I was trying to say "normal, low bias, Sigma Pro and Sigma/404"

 

[jaycalgary]

Karlson Stax? Pretty happy I will have Sigma pros soon even though the reviewers speak poorly about them since there is such thing as the Sigma/404. It got me thinking of an old design
for speakers "Karlson Speakers" info and images are on google. I remember years ago just for fun making a TQWP  speaker with just an old ghetto blaster speaker and then added the Karlson
"V" shaped angled box in front. It made unbelivable bass for the size of it. Today just to see how it would sound I cut a pieces of cardboard to the size that would fit in the pads of my Lambda Sigs.
with the Karlson "V' shape cut out. Very raw but gave me an idea how the Lambdas would sound. The Bass had more impact and there was more depth. Do you think this would be a bad Idea
for a design?

 

[gilency]

I really think you will like your Sigma Pro. I certainly enjoy mine.

 

[plaidplatypus]

The Sigma Pro have ever so slightly better mids than the Sigma404 in my opinion.  I owned your Sigma Pro for a couple years, so I've heard it a few times.  The Sigma404 sounds nice but I wonder what other Pro bias Lambda drivers would sound like in the Sigma housing.  LNSigma, Sigma404LIMITED, what hasn't been done yet?  Would an Airbow mated with a Sigma be a Sigbow or an AirSigma?

 

[dyna10x]

Quote:

A squeal probably means a short, not necessarily in the drivers but possibly so.   I think you have to get past the earpads to have a proper inspection.

Thanks edstrelow for the advice.
 I did a search of the thread and found a reference you made to discovering a short from the bias electrode along the outside of the insulation of one of the other wires in a Koss stat phone.
Perhaps this is the problem with my Lambda pro as the wire from the right electrode touches the middle thicker rounded electrode on its pathway to the strain relief (I assume that the middle electrode is the bias voltage connection?). Could it be a source of a short similar to the one you discovered?
Besides this does anyone have an idea why the volume returns to normal by pressing on the back cover of the driver (doesnt need much pressure) or a quick shake of the head?
Any ideas will be greatly appreciated

 

[edstrelow]

Quote:

Thanks edstrelow for the advice.
 I did a search of the thread and found a reference you made to discovering a short from the bias electrode along the outside of the insulation of one of the other wires in a Koss stat phone.
Perhaps this is the problem with my Lambda pro as the wire from the right electrode touches the middle thicker rounded electrode on its pathway to the strain relief (I assume that the middle electrode is the bias voltage connection?). Could it be a source of a short similar to the one you discovered?
Besides this does anyone have an idea why the volume returns to normal by pressing on the back cover of the driver (doesnt need much pressure) or a quick shake of the head?
Any ideas will be greatly appreciated

I am not quite sure what you are seeing with the bias electrode, is it the actual wire or just the outer plastic touching?  If it is  the wire, it sounds like a possible short.  It would seem that you need some kind of repair to get the bias cable away from other cables. 
 
If the bias is shorting that might explain the lowered volume, as it shorts, you may be lowering the bias voltage and presumably the volume would then drop. The head shake could cause the bias cable move away so it no longer shorts.
 
There may be other explanations but at least this is simple and consistent.
 
 
BTW when I had the problem with my Koss 950 phones, I could actually see the short in the dark because there was a trail of sparks running from an electrode on the driver down the outside sheath of the cable.  The fix was to pull the cables away from the electrodes enough to create a bigger air space.

 

[DaveBSC]

I'm considering buying an SRM-1 MK2 C series that is a 100V amp but has been used, supposedly without issue, on 120V US power. The price is good but how concerned should I be about wear on the transformer, caps, regulators, etc?
 
Is it true that a step up/step down transformer ruins the sound quality?

 

[kevin gilmore]

Definitely NOT a good idea to run a 100V amp on 120V.
The power supply voltages would be 20% high, and might
be at the absolute limit of the power supply caps.
 
Depending on age, its simple to re-jumper for 120V.

 

[dyna10x]

I got c series srm1/mk2 without the voltage selector plug. It wassoldered together inside. Spritzer kindly gave me instructions for correct connections for 100 117 240 v but not for 120 which is what you need. The info is in this thread for 120 so if you need it you could search or some kind stax guru can tell you. It is not a difficult job to do