[christopher-h]

I have a DAC-9 and STA-9.  I have been considering getting some KEF LS50’s but have read the Absolute Sound review where the reviewer found the sound of the STA-9 less than satisfactory in that it overemphasized high frequencies.  He reviewed the STA-9 through KEF LS50’s.  In the manufacturers comments Jason indicated that Nuprime confirmed that the STA-9 did not work well with the KEF’s due to an interaction resulting from the addition of even order harmonics in the STA-9 and the KEFs.
Does anyone use the  STA-9 with the KEFs?  What are your impressions?
Jason, what is unique about the KEFs that would cause this?  Would most tube amps have the same problem with the KEFs due to the presence of even order harmonics?  Are there other speakers that might react the same way with the STA-9?  Does the STA-9 through the KEFs tip the sound closer to neutral or too far.  It is not particularly convenient for me to audition my amp with the KEFs but it could be arranged but maybe I would be wasting my time?

Regards Chris

[Wind Chaser]

I have a DAC-9 and STA-9.  I have been considering getting some KEF LS50’s ... It is not particularly convenient for me to audition my amp with the KEFs but it could be arranged but maybe I would be wasting my time?

Chris,

If I was in your position I'd be inclined to try the Kef's. It may or may not turn out to be a waste of time, but at least you will know. What is it about the Kef's you find so appealing?

I've notice they appear on the used market quite often ... perhaps they don't synergize well with other amplifiers? In any case you do have the opportunity to save a few bucks by buying them used, plus they might be broken in. Breaking in new gear takes time and isn't something I particularly enjoy. For that reason alone I'm more inclined to buy used rather than new. But quite often the things I want aren't for sale or rarely do they come up for sale.

[drumnman2]

 I also noted in his review that he said his ls50's have never leaned toward the bright side. I have read quite a few comments from different ppl that feel they can be. And he said he really only noticed it on his ref. recordings. But I'm inclined to go by what Jason says also. I have STA 9 with Sonus Faber Venere 2.0 and 10" subs and think it is wonderful. Smooth, huge soundstage and easy to listen to all day sound, and never ever any irritating brightness. If you're set on ls50's why not try the newer powered one's , same price if you figure in an amp. I just don't like that they don't have an XLR input . I also had a dac 9 which I returned because I decided that it, combined with the STA 9 was a little too warm for me with my speakers. I can't imagine that the 9's combination would be bright on anything but just my ears and opinion.

[jk@home]

I've owned the LS50s for almost 4 years now, they work well in my room. From my limited personal experience, and what I have read on the net, they are finicky when it comes to amps. Not that the Nuprime is not worthy, just not a good match. The first amp I used to drive my KEFs was an Aragon 8008 model, decent amp but didn't work that well either. Plenty of needed weight on the bottom, but the highs were irritating. It's the upper midrange/ lower treble of the KEFs that can be a problem.

The LS50s seem to be rather controversial. They got that "class A" recommendation, but many folks didn't like them when they heard them, for what ever reasons, and made it a point to proclaim that to the world. Stick it in the eye to Stereophile, if you will.  .

I think many owners who did like and buy them are now trading them for the newer powered model, thus the ones on the used market.

I bought mine cause of the decent reviews and more importantly I could get them through my Amazon Store card (free financing). Same way I bought my Nuforce MCP-18, which is used as the preamp to the KEFs.

[slash71]

seems it  sounds good in this video, with st-10 and dac-9
 
https://www.youtube.com/watch?v=OM_s6mR8FRY

[Wind Chaser]

The LS50s seem to be rather controversial. They got that "class A" recommendation, but many folks didn't like them when they heard them, for what ever reasons, and made it a point to proclaim that to the world. Stick it in the eye to Stereophile, if you will.  .

This is why I never take any reviewers or rags opinion too seriously. A great review can be seen as a great *favor* which translates into great sales. But if the opinions of the buying public don't align with the great review, then who's at fault? Any incongruency between the two and I'm more inclined to agree with the buying public.

[John Casler]

As a NuPRIME dealer and associate, I have had several customers/clients/friends use LS-50 systems, with the STA-9 amps.

I think one customer has "stayed" with the LS-50 and thinks it fine in his room, the others have moved on to a couple other speakers with success.

I would probably steer you to a couple other brands (which I won't mention, because I am a dealer for them, as well as KEF)

That particular review was quite surprising  since the descriptions were almost the exact opposite of most other reports, but some times the material, the electronics, the speakers and the room, not to mention the reviewers preferences and hearing ability, don't work as well as something else.

[rustydoglim]

jk@home stated well.  We bought a pair of LS50 in our lab to investigate the issues because until this review, everything else were wonderful. And we have not heard any other problems since.
The review was for the entire system so the reviewer didn't have the option of picking and choosing components.
Regardless, we confirmed that LS50 and STA-9 don't match.  LS50 has too much extended high freq and probably works well with tube, but can become a little irritating for some amps.  ST-10 sounded wonderful with LS50.

*** Keep in mind that the same reviewer reviewed IDA-16 (with LS50) and gave it the best recommendation (which got it the Product of The Year award).  STA-9 was designed to sound a little warmth, so matching it with LS50 probably over emphasised the warmth at high freq.

[kaka89]

I thought "warmth" is more about emphasize mid-range?
Didn't know warmth also emphasize high freq..

[christopher-h]

Hi Jason
You said the STA-9 was designed to sound a little warm.  What did you do with the design?  Was it in increase in the mid-base, a roll off of higher frequencies? Or something else? Did the addition of even-order harmonics achieve this warmth?  What would we actually hear that is different compared to this same amp without the designed in warmth? 
Thanks! Chris

[rustydoglim]

I thought "warmth" is more about emphasize mid-range?
Didn't know warmth also emphasize high freq..

Warmth is the result of even order harmonics. But when high freq is emphasised by the speaker, that becomes unintended effect.

[rustydoglim]

Hi Jason
You said the STA-9 was designed to sound a little warm.  What did you do with the design?  Was it in increase in the mid-base, a roll off of higher frequencies? Or something else? Did the addition of even-order harmonics achieve this warmth?  What would we actually hear that is different compared to this same amp without the designed in warmth? 
Thanks! Chris

Keep in mind that this is amp design, not DAC. So we don't put in DSP or EQ.
We rely on the physical characteristic of the components.  The reason some class A amp sounded warmer than others is because of the physical characteristic of the transistor.  Similarly tube amp relies on physical characteristic of tube to alter the sound.
As explained in our amp design article on the website, we created class-A transistor circuit as part of STA-9 preamp stage of the class-d amp (not to confuse this with external preamp) so we are able to tune the sound.  Typically only very high end amp uses custom built transistor circuit (most will just choose very good off-the-shelf opamp).  Since we design our amps in-house, we can do whatever needed to be done.

[Francation]

Jason,

Does the STA-9 (and other STA amps) also have an analog to digital stage? Or is the signal kept entirely analog? I am curious what amp will sound best when used with analog input (turntable).

[kaka89]

Jason,

Does the STA-9 (and other STA amps) also have an analog to digital stage? Or is the signal kept entirely analog? I am curious what amp will sound best when used with analog input (turntable).

I believe STA-9 doesn't have DAC built-in so it must be all analog.
Even DAC-9 is all analog when using analog inputs.

[rustydoglim]

I believe STA-9 doesn't have DAC built-in so it must be all analog.
Even DAC-9 is all analog when using analog inputs.

Correct.  DAC-9, DAC-10/10H, IDA-16, CDP-9 all have analog switch, no ADC.

[dmn]

I tried the DAC-9/ST-9 combo with a vintage pair of KEF 104/2s (restored woofers & tweeters). Am looking for a "tube-like" sound from solid state. Not satisfactory at all. Highs sounded dull, midrange too reserved, and bass almost absent. Even two ST-9s in mono wasn't right. Speakers just lacked that sense of pace and imaging I hear with other preamp/amp combos. Interestingly, an old B&K Reference amp rated at 185W into 4 ohms with a variety of inexpensive solid state preamps sounds best so far, with tremendous pace and imaging with probably as much upper bass output and definition that the bass-shy KEFs can produce. I tried the DAC-9 with various other class A/B vintage amps- better weight than the ST-9, but the turn-on "pop" of the DAC-9 temporarily shut down one channel of the B&K and immediately caused a single channel failure on an old Adcom. End of trials with DAC-9 pending some solution to the "pop". Maybe it's just a case of KEFs liking class A/B & Mosfet amps, or DAC-9 not liking vintage KEFs or vintage amps. Would appreciate any suggestions, since I would really like for the DAC-9, and ST-9 to work.

[in1unison]

@dmn

My experience with DAC 9 / STA 9 combo driving MA GX 200 speakers are about the same as yours. Compressed, lifeless sound, in particular at outer frequency ranges. Using same DAC with ST 10 improved the sound dramatically, to what one can describe as "tube-like", musical, warm and very pleasing to the ear. Therefore, I guess STA 9 is the culprit in the your case too, as far as sound is concerned . I have also paired DAC 9 with Yamaha A-S1100 amplifier and got similar, beautiful sound with that combo. No issues with "poping" sounds, etc.

[dmn]

Thanks for your reply/confirmation that the DAC-9/ST-9 combo isn't a good fit for all speakers. Your positive experience with DAC-9 & STA-10 definitely encourages me to keep/try the DAC-9 with that and other amps. Guess that too much of a good thing (tubey DAC-9 + tubey STA-10) can be a bad thing. Maybe my B&K falls into same category. History with KEF 104/2s is despite the high sensitivity rating (92) and "stable " 4 ohm impedance they really do need lots of current for bass control. Jason assured me earlier that the ST-9 had plenty of zip for the KEFs. When it didn't, I tried 2 in mono configuration, still not good. So not really a question of power I think. I notice that some subwoofer manufacturers use class D amps, whereas others use class A/B especially in their higher end sub amps. Maybe the latter just can provide more current when required for lower frequencies. I am sure others on the Circle will have other opinions. Right now I will see how to avoid that turn on pop. Power comes through a Transparent Audio Reference Power Isolator: very clean, but no way to delay the startup of the amp until after the DAC-9 comes on. What turn-on sequence did you use? Would really like to use the DAC-9 as preamp, so will keep looking for compatible amp for these speakers.

[in1unison]

@ dmn

I have used DAC-9 as DAC only mode, Yamaha used as pre-amp and HF/MF amp, ST-10 driving LF woofers. Also tied other combinations, but have not had any "poping" sounds from DAC-9 (even when used as pre-amp/ DAC).  l have not used any particular power-on sequence either; everything is dead quiet irrespective. Also, I am using stock/ OEM power cables with ferro-choke and only have simple (sacrificial) surge protectors on the power lines.  What is the music source you are playing through DAC? l did find some computers very noisy in particular if used with poorly manufactured USB cables.

[slash71]

my STA-9 (in single stereo) amp drive very well a pair of QUAD S2 speakers,  I don't know if the preamp section powered by HPA-9  change the sonic signature overall , my music game source is almost digital , the kef signature are very strange to understand.. I think the kef are more room acoustics  than other monitor speaker and sound signature went more to upper frequency than low ones ..