The Stax thread - Page 115  

Just remember your low-bias SRD-7 and Lambda Pro earspeakers are not matched... unless your power amp is seriously beefy the results may not be satisfactory. If you're looking at buying something, I'd go above 100wpc, and give strong preference to a differentially balanced circuit topology. There is an Adcom 5800 on AudiogoN right now which would likely do very well. The 5802 eliminates the cooling fans of the 5800, which loudspeaker users found to be a major annoyance. If I ever had to hawk my X250.5 for financial reasons, I would be looking at a 5802, and maybe some old Threshold gear.

Or you could track down a pro-bias SRD-7, and then you can get away with a lot less power.

Then there's always the direct-drive route!

These Stax adapter boxes work with all sorts of power amps. Do you have an old receiver lying around? I would start with something cheap before I bought a special amp just for the phones.

Or get yourself a cheap t-amp. Not sure how well it would power the Pro Stax through a normal bias SRD-7 though. It might be worth trying as I love them with my SR-X.

Thanks for all of the input. I'll have to look in to all of my options a little more. I'm hoping to keep the additional costs as low as possible. Anyway, I really appreciate all of the help and am looking forward to hearing what stax has to offer.

For me the ultimate Stax power source would be something like a Kondo KSL Ongaku... tubes and massive amounts of silver...

You could try K&K Audio on the transformer. They are the US distributor for Lundahl and they are quite helpful with requests. They even have a formum on Audio Asylum.

If you have to build it it is very simple. Justin should be able to sell you one of his always on bias supply's and connectors so you only need some cable and the transformers. Just cobble it together and that's it.

Hmmmm... that's a great idea, to see if Justin would sell me just a bias power supply! Then the rest is really easy - speaker inputs on one side of the transformers, earspeaker outputs on the other... nice WBT binding posts on the input side for the speaker cable of my choice, good internal hook-up wire... get the Stax jacks from Justin... in an ideal world I'd get both normal and pro bias from the box... would have to get a chassis put together of some sort... it's the chassis work I'm really bad with.

I guess alternatively I could simply look at the shematics of a SRD-7/MK2 and duplicate the bias power supply section... or worse, track one down and rip it out! Or... if Justin won't build me a normal-bias supply but WILL do a pro, get the pro from him and strip the normal out of a (plentiful) SRD-6 or 7, since they're not as hard to find or sought after as SRD-7/MK2 or Pros.

Why when I look at the schematics for the various SRD-7s do they look more complex than necessary? My Pro has a pair of resistors soldered to the earspeaker jacks, WTF is that for??

Andrea Ciuffoli's design calls for a pair of Lundahl LL1630 transformers in push/pull configuration (naturally), K&K has them for $120USD each. I wonder what Stax put into their own energisers... and if anyone makes nicer transformers than Lundahl...? Furthermore, is 7.2:1 really the right ratio? Sounds low to me, but what the heck do I know... edit: did some calculations based on ohm's law - with 250WPC into 8 ohms, my X250.5 should be able to swing 44.72V. 44.72V*7.2=321.984V. The SRM-727 swings 450V, so 322V seems inadequate, knowing how much juice the SR-007s like... or am I missing a piece of the puzzle here? I think I want something more like 20:1 - that'd get me 895V or so, which should be PLENTY, with the flexability to use lesser power amplifiers. Heck, I could even go crazy and build multiple ratios in it to suite the driving power amp. I have to imagine that the less of a step up the transformer is doing, the better the sound quality...?

I can't imagine the quality of the parts in the bias supply section is critical, as long as you get that DC230V or DC580V out at the end, it's fine? Or is there noise to worry about?

I typed this once and it disappeared

To make the long story short:

When I first contacted Peter, he told me that it would take 3 months for the amp to get built. It took about 5, but the amp was finished and shipped. When, after a month of waiting, it didn't arrive, we deemed the amp lost. Then, Peter shipped me another amp, not the one that I originally ordered, and one with a few experimental ideas. This amp arrived, but it may have been damaged in transit. It has the following issues: 1) there is a buzzing during certain volume pot positions - most noticeable at the 12:00 position and dropping off at the 5:00 amd 7:00 extremes, and 2) there is a lot of clipping during dynamic passages on certain recordings. Now, I'm not sure if the clipping is due to the amp bringing out the flaws in the recording; that's certainly possible.

Customer service was good, Peter kept me informed of the amp's development, and made the alterations I wanted in the original amp. He took a long time to answer my emails, but that's about the only complaint. He certainly took a massive financial hit shipping me that second amp.

The amp I originally wanted had a permanent bias voltage option, where the headphones would stay biased even when the tube section would turn off. The current amp also has that option, together with balanced inputs, and support for both Pro and Normal bias headphones. It's not a true balanced design, however.

The 404, together with the amp, sounds very much like an electrostatic Grado with soundstage. It is bright, fast, vidid, and impactful, with excellent drive and energy. The foreground is forward while the background is far away. Detail and soundstage are all much better than the 313, and there's no tubbiness or loose upper bass or rolled-off highs that you can expect with a tube amp; the sound is actually closer to a solid-state amp, but with that wonderful long decay that tubes give you. If not for the issues, it would sound good, though too bright for my ears. The brightess, forwardness, clarity, and impact that the amp brings to the table tell me that it has been voiced for the O2 (and Peter does in fact use the O2 as his reference).

I'll be shipping the amp back to Peter to repair at some point; for now I'm too busy with other stuff.

I'm seriously thinking of getting the O2, and if I sell off all the stuff that I don't need and was going to get rid of anyway, I can easily afford one. But, all I'll have to use with it is the 313 until the McAlister gets fixed. Do you think that there's any point in getting the O2 in this setup? The source will be my trusty Rega Planet 2000.

What I'm trying to do sonically is to keep the virtues of the 404, but also get rid of the upper midrange emphasis once and for all, and to add some weight to the bass. The midrange emphasis is driving me nuts on some recordings, where everything is portrayed beautifully except some vocals or instruments, which suddenly sound metallic and artificial. If I can at least equal the performance of the 404 in everything that it does well while not having the flaws, then I'll be happy.

Or is there another way to do it? I'm not going to go vintage, since a) I can't outbid you moneybags anyway, nor do I want to grossly overpay for something anyway, and b) I don't want something that can't be fixed. I'd rather have a warranty, or at least the ability to do paid repair.

I also can't make it to a meet, since I'm too damn busy all the time. So, if I do buy something, I'll be buying blind. Hence the asking for opinions

I was just helped (told) by Kevin Gilmore and figured out a pro and normal bias supply. Below is the pic, the top schematic is the correct one. The supply would have to be fed 330VAC rectified(See the KGBH supply).



Catscratch, the McAllister and Rega are not lo-fi. I would recommend getting the O2; it is considered a top tier phone and one of the cheapest. I am actually upgrading the other direction from you. I am balancing my source, building a balanced amp (KGSS), and finally buying the O2. However, if I had your gear I think I would move to the O2 first. If you like it, you can always upgrade your amp and source .

Thanks for the schematic, but having to build a whole beefy 330VAC power supply isn't in the scope of my simple step-up transformer project.

There are other manufacturers that are better then Lundahl (Tango in Japan springs to mind but they can be very expensive. A good bias design is the always on bias KG came up with a I think Justin used and that could be modified for normal bias. I should have the schematic here somewhere but I'll have to find it.

I haven't looked into the voltage swing that much but the amount of stepping shouldn't change the sound of the transformer unless the core is saturated. Then it will go south very fast. Stax used the cheapest transformers that they could get of reasonable quality because you have to remember that when you are producing something and selling directly (no dealers or distributors) you should sell the product for a minimum of three times the part value to break even and when you add a dealer network this figure rises fast. I recommend that you ask K&K audio if some other Lundahl transformer is better suited for the job since they really know their stuff.

I used the SR-007 with the SRM-313 for nearly two years and was preytty satisfied. They aren't all that fussy about the amp but they really like a lot of power but the 313 as a stop gap is not a bad idea. They will continue to grow with the system when you make improvements. I did just change cables to a cheaper sold direct cable and they improvements are so obvious and big that it's mind blowing and the O2's show this.

Some say that the O2's are bass heavy with midbass emphasis but it's not what I hear. Their fit is very much dependent on the size of the listeners head so different opinions are abound. They have much deeper bass and it's better controlled then the Lambda line. Some of the older Lambdas seem boomy by comparison. The SR-007 is a clear step up in all areas and while the price difference is huge from the 404 they are cheap for what they deliver.

My initial research indicates Tango is out of business? If I'm gonna build this thing, I ain't gonna skimp, period.

What advantages does a "good" bias power supply design have over a crummy one?

The KGSS is swinging 1200V peak to peak, while the SRM-727 is swinging 450V. I think 25:1 is the sweet spot, which will get me SRM-313 levels from a 25wpc power amp running flat out, which leaves something like an Aleph 3 in the running at least... while the X250.5 will produce over 1000V! I guess on the other hand, if it doesn't hurt quality to go higher then why not shoot for an Aleph 3 to be able to put out 450V in reasonable comfort, which would be 30:1...

Didn't know that Tango was out of business. I've seen some newly made amps that had Tango transformers but they could be NOS.

For me a good bias supply is simple and cheap with standard but good parts. I've seen quite a bit of different designs over the years and some are using reversed transformers and various other tricks that are over the top.

I think the higher the ratio the better if the transformers insulation can take it. I doubt that they were designed for this high a voltage but you never know. This box with the new WBT low mass connectors and some nice solid core wire should be awesome. You can get the Stax connectors from Allied and I think Woo Audio also sells their own that look much nicer. Allied is often out of stock because the amp builders are buying the whole stock.

Case work is pretty easy but you need to plan ahead and have things like a drill press, stepped drills and various other drill bits.

I read the specs for the transformer and it should be able to handle the voltage. To reach a higher ratio you could always wire two transformers back to back and get a ratio of 52:1 though that might be a little extreme. I'll see if I can't find the schematic from Gilmore...

Edit: I found the schematic

Here is the bigger version

No more crackling noice

In a review I read that the 202 headphone do tend to cause a sort of crackling noise when you move your head.
Well, mine did this, as well. Quite annoying, to be honest.
This evening I took off the plastic clip that holds the can
and put the tiniest bit of handcream on the plastic pins that form the connection can / headband. Only juuuust enough to put an idea of cream coating on them.

And guess what: NO MORE CRACKLING when I move my head!

My baby's doing great!
While typing these words, Tracy Chapman's "Telling Stories" is playing.
Track #9 "Devotion" amazed me with a nice, deeeep, yet subtle drum and bass guitar as never before.

Me happy!

Can you elaborate on what now needs repair, or is this still from the original list?