Stax Sigma Low Bais and Stax Sigma Pros - Page 24

Weird vocals from my Sigmas

I have a pair of Low Bias Sigmas and I drive them through an SRD-6 adapter. Sounds great with classical - string symphonies etc. are wonderful, but anything with vocals sounds plain weird.

I appreciate that Sigmas have a special kind of midrange magic, but I doubt they are meant to sound like mine... Vocals sound recessed, distant and with a strange echo or reverb-like effect. Almost as if the vocalist was around a corner inside a cave... Any ideas?

Odd because I especially like the Sigmas with vocal music. Certainly all of the Sigma models have a midbass hump which can make music sound distant and they also tend to emphasize ambience.

I listen to mine using an old Stax SRA12s amp so that may make a difference, I don't have an adapter for comparison.

I was just comparing the Sigma low bias and the Sigma/404 the other night on 2 different systems, which however used the same model of cd player, a Sherwood Newcastle. Both systems used similar sounding silver interconnects, the Sigma/404 was being driven by a Stax SRM3 amp, while the low bias Sigma was being driven by the SRA12S. The low bias Sigma sounded a good deal more musical and ambient than the Sigma/404 with the orchestral material I was using.

I should add that the Sigma 404 sounds a whole lot better with a better amp such as the Stax 717. but since the 717 only has pro outputs I can't make a direct comparison of the two Sigmas. And I do recall some occasions of the low bias not doing well with crescendos on highly dynamic material whereas the Sigma/pro/717 combination seems to have no such limitations .

While I find the Sigma/404 to be the best Sigma model, I still like the sound of the original low bias model. I think the SRA12S is a better amp for running the low bias Sigma than the SRM3 is for running the Sigma/404 but I wonder what is the best low bias amp out there because I would like to know if the low bias Sigma "scales up" when it has a better driver.


One further thought, as I listen to my low bias Sigma, is that they certainly have more of the quality you describe when they are not warmed up. Since you are using a self-biased adapter you can't just switch the set on ahead of time before you start listening although you could run the system with music or a few minutes to get it properly warmed up. I find the midbass hump less of a problem as the system warms up. This is true of all the Sigmas, not just the low bias Sigma.

Welcome back.

Any chance you could correct the spelling of Bias on the caption of this thread?

Interesting... I just tried some vocal music from a "cold" start, and it was ok. Last night I listened to about 1 hour of string symphonies at healthy volume before switching to some vocal and I had a hard time accepting the way voices sounded. Today, same vocal music, it was ok from a cold start. Maybe it's just me

Or maybe the self bias circuit is too weak and has problems with air temperature and/or humidity? Dunno... I have had plans to build a nice amp for my Sigmas for some time now - better get my act together. Any good pointers for a good way to make the bias supply? The signal part I have covered pretty well I think.

The SB circuit isn't weak by any means and will keep the phones charged for 10+ minutes with no input if it is functioning correctly. It is however tied to the input voltage and that's why I prefer the AC units.

The bias supply needs to give out +230VDC with next to no current so a voltage doubler works well and that is in fact what Stax used. You can also use a high quality DC-DC converter mated to a small, adjustable DC supply.

OK. Any other ideas why this is happening with my Sigmas? Or do you simply suspect it's me?

The Sigma's aren't for everybody and the midrange on the normal bias unit is very colored to say the least. They were designed for large scale orchestral music after all which they do quite well but vocals aren't one of their strengths.

OK, thanks. I'll experiment some more then. Maybe the amp I'll built will improve the situation, otherwise that amp will of course be able to drive any other stax earspeaker. Or I will have to try to get my hands on a pair of Sigma Pros. Is the difference very large?

The Sigma Pro's are more different then better but the amp has a huge impact on the SR-Sigma. I wasn't much of a fan until I constructed a cable that let me use them on my Blue Hawaii and then I saw the light. The bass got a lot more linear and the sound opened up.

Kind of what I was getting to above. The Sigma/404 was not too impressive witha Stax SRM3 amp but sounds fanatastic with the Stax 717. I guess you could say it "scales up" well both with changes in amps and associated equipment.

I have a regular Sigma pro in my office which sounds very good on another SRM3 amp but it is being fed by a much better cd player set-up than I was using in the comparison above. Sometimes I also suspect that one of my two SRM3's is better than the other.

I found a nice Sigma at one of my neighbors...nice to live at a golf course community and be the youngest male here by over 10 years ( a couple trophy wives are about). Anyway he had them in his garage during a garage sale, but were not for sale...BUT I saw the box in one of those clear rubbermaid storage containers so we talked a bit about them...and they are now mine They are non-pro six spikers and the stuffing is pretty grody and smells of tobacco...even boxed up apparantly for years! Has anyone experimented with different acoustical products...foam, no rez, other speaker stuffing materials and their affects on the sound? Fiberglass might be too itchy

You can certainly try some different damping materials but they aren't all that much fun to work with. You have been warned!! If you do remove the damping be sure to replace all the glue pads both to hold it in place and to prevent any "leaks".

As for the smoke stink... that can be cleaned with the right chemicals. I use automotive interior soap and simply place the wool inside a bag, spray quite a bit of the soap inside and then shut it tight letting the soap do its thing. The material is so fragile that I wouldn't do anything more drastic then this.

ok, better living thru chemicals!

I got a pair of original Sigmas (low bias) in very good state today. What I like most about them is the looks . Honestly, I'm a bit underwhelmed. I was prepared for recessed highs and limited dynamics. I also knew that I couldn't count on deep bass, but the missing of pretty much anything below maybe 70 Hz is hard to take - despite the beautiful mids and the new kind of soundstage. Even plan b is at risk as I fear that the problem with bass persists when transforming the phones into Sigma/303's. Has anyone had success in experimenting with different types of damping material in order to improve low bass response?

What are you driving them with? The amp is the biggest factor here as they need a lot of juice to shine. You could try some other damping materials but avoiding reflections will be tough as most foam materials will bounce some of the sound back.

Another option is that your set isn't up to spec no matter how good they look. The glue that holds the damping material is most likely gone so sound will leak and that kills the bass.