The Stax Thread III

[Aspirant Audiophile]

It’s interesting how people like the amps correlates with their ‘imperfections’. For instance, the MT has an AC-coupled signal path. The low-end will naturally have a phase shift. When the lows are no longer time-aligned with the highs from the same instrument, it tends to stand out and gives the impression that there is more bass, or more ‘quality bass’, although the amp does not have higher gain in the bass region compared to other frequencies. The same works with the amp’s performance at the top end. A rolled-off top end or increasing low-order harmonic would sound less ‘bright’ or ‘fatiguing’. T2 probably falls into this category. Also the noise floor problem is due to its architecture. Comparing the noise floor, a diy T2 would probably be 10 times noisier (20dB) than a well executed Blue Hawaii (I have no data for BHSE).
I don’t mean to discount any subjective impressions on those amps, or any personal preference. I just want to say, they sound different for a reason. An ideal ‘wire with gain’ amp may be an oversimplification of the engineer’s answer to the complex problem. The ideal amp are ‘all the same’, while the less-than-ideal amps all have their different imperfections that causes them to sound different.

Really, really appreciate builders who offer clear lets-cut-through-the-'impressions' explanations for a layperson. More @simmconn posts, please!

 

[alota]

Really, really appreciate builders who offer clear lets-cut-through-the-'impressions' explanations for a layperson. More @simmconn posts, please!

Indeed!

 

[Bingturong]

So I got a few vintage Stax amps and I was wondering how they might sound with a SR-007, got both an SRA-3S and SRA-12S modified with a pro bias output and my Lambdas sound wonderful on them but I can't help and think maybe to get something a bit more modern like a T1 for the SR-007. Any advice?

 

[padam]

I like the SRA-3S but not with Pro bias. I think the SRM-T1 is not great either (stock or modified), instead I recommend an SRM-717 as the minimum.

 

[bigjako]

At one point, I had a modded 006t and a Mjolnir Carbon at the same time, and the modded 006t worked very well with the SR-007. The Carbon was 'better' yes, but also too solid state for my preference. So I would say that a CCS-modded 006t would work nicely with a SR-007, in the context of your request for good vintage amp pairings.

 

[Bingturong]

I have been considering a CCS modded 006t, but I wonder how that will compare to the SRA-3S or 12S

 

[Chefguru]

At one point, I had a modded 006t and a Mjolnir Carbon at the same time, and the modded 006t worked very well with the SR-007. The Carbon was 'better' yes, but also too solid state for my preference. So I would say that a CCS-modded 006t would work nicely with a SR-007, in the context of your request for good vintage amp pairings.

X2 on this. Essentially a mini-kgst under the hood.

 

[alota]

At one point, I had a modded 006t and a Mjolnir Carbon at the same time, and the modded 006t worked very well with the SR-007. The Carbon was 'better' yes, but also too solid state for my preference. So I would say that a CCS-modded 006t would work nicely with a SR-007, in the context of your request for good vintage amp pairings.

Nice post

 

[kevin gilmore]

the megatron is a dc coupled output. there is a cap between the gain stage and the output stage.
phase is 3 degrees at 20 hz. many servo's in fully dc coupled amplifiers are no better than this.

 

[Schelp san]

It does seem our reviews reached similar conclusions. Few notes:

1) Our MTs are different. Mine has premium parts (e.g. silver wiring in the amp, is two-box… etc) and I’m using in-production tubes. These things may or may not make a sonic difference.

2) The T2 I heard is an original DIY so it had some noise floor issues (I believe this has been solved for) and is known for bringing heavy low end (so even more impressive that I felt the MT had an edge). His is the Soren OG design + recent updates. I don’t believe it has any noise floor issues.

3)I don’t full agree with the MT is a Bentley and T2 is a Ferrari analogy the way he had suggested. They’re both Ferraris.
The MT has very powerful “organic” sound. Iron fist in velvet -esque. The T2 in trade does a better job of swinging between low and high volume passages.
For instances I would argue that if you’re into classic rock (I.e. zeppelin) the megatron may present a more exciting experience to the T2 because of how thick it will convey guitar riffs, along with the ability to crank the volume.

1. I can assure that different tubes, especially in the first two stages of Megatron, can make a very noteworthy difference (I tested 5 different in 1st, 4 different in 2nd stage and 3 in 3rd). Same I experienced in T2 where I tested 6 sets in the input (latest finding: “just get” Siemens CCa, thank you for the follow up costs of visiting you, Rainer ) and 2 in the output. All tubes have their own characteristic, but I would judge some tubes as clearly being better than others, not just different.
2. I could not detect any noise floor on either Megatron or T2 with any of the tested tube sets. Maybe it is possible to measure a noise floor on (my) T2 higher than on Megatron, or maybe somebody with better ears can hear something what I can´t. From what I understand, building a T2 is already a challenge, but for finishing the build without having a noticeable noise floor, the builder has to have the expertise and patience for adjusting the circuit properly (parts and tolerance of certain parts seem to also play a role). Afaik my T2 has no “recent updates”.
3. Depending on tube choice, T2 can sonically be tuned towards Megatron (not so much vice versa, if "less relaxed" tubes are applied on T2). No problem to crank up T2 with 009 or whatever, just maybe not so much with JAN Philips 6922 (which I had in the initially).

 

[simmconn]

I think you're probably right regarding the AC vs DC effect.

With regards to roll-off, I believe this is related to the output. Each lesser amp I've heard for estats seems to have less control over the highs (and lows) due to the challenging voltage swing. For example many people are under the impression that the KGST is a "warmer" amp than something like the Carbon because it uses tubes - but in my experience the Carbon is significantly less piercing. Perhaps someone can shed some light on this? Comparing a solid state ma (carbon is 18-20 ma?) to a tube amp (MT is 27ma?) doesn't really cover the story

I believe the noise floor issue has been solved for T2 with different small signal tubes. In the case of the one I heard, it wasn't. My MT is dead silent.

My observation is that the T2 gives the impression that the highs and lows have bigger db swings than the megatron does. I tend to define this as "dynamics". So at a lower average volume the T2 has more "slam" and tact. Perhaps this is a function of the 500v vs golden reference? The Megatron can be listened to at a louder average volume since the peaks are less prominent.

I have to admit that I don't have much experience with the MT. I built it half-way, listened to it and measured it, and then decided to tear it down. It could be that I didn't get it right to begin with. Another project to revisit for the cold winter nights.
Regarding the T2 noise floor. Its architecture determined that it would be noiser than BH and other Dr. KG amps of similar architecture. A noisy front-end tube can cause annoying audible noise, which would be a 'manufacturing' issue. Solving the latter doesn't necessarily fix the former. The remaining noise may not be easily audible but clearly measurable.
That lead me to a hypothesis of why people feel that some amps are more 'dynamic' than the others. To compare amps, their output levels need to be precisely matched and not rely on perceived loudness. For amps with lower SNR, to retrieve the low level details you would have to crank up the volume, but the large signal is not affected by the poor SNR. In the end, the output is louder and appears to be more 'dynamic'.

 

[Kiats]

Some relaxing Saturday morning listening with the Lambda Nova Signature.

 

[gammi]

Look what parts finally arrived from Sweden after many months of waiting

 

[simmconn]

Look what parts finally arrived from Sweden after many months of waiting

Although not shown in the picture, I assume you also got the barbed retaining ring for the Amphenol connector. Those are hard to come by separately. The connector with the retaining ring sometimes pop up on eBay. Are the Jensen caps for bias supply filtering? That would be super luxurious.

 

[gammi]

Although not shown in the picture, I assume you also got the barbed retaining ring for the Amphenol connector. Those are hard to come by separately. The connector with the retaining ring sometimes pop up on eBay. Are the Jensen caps for bias supply filtering? That would be super luxurious.

Yeah, mine came with the retaining ring. And yup, the caps are just for bias. Pretty excessive but I guess that was the point of this build
May eventually replace the transformer based bias circuit with a DC-DC buck converter but we'll see how this goes first.