That is a nice combo. I had the Mk 60's. Really nice sound. I think you will love it.
26 responses Add your response
I don't agree with the other posters.
The S-30 loves high impedance loads; a minimum of 8 ohms. The power output lessens with lower impedances in Atma-Sphere amps.
I'd check the impedance curve of the De Capo. If it is not ruler flat you could have a problem. Given that and a sensitivity of 92dB, I would not recommend use of this amp for the De Capos.
It is enough power with the DeCapo's sensitivity (92db?), only question is does the DeCapo have a smooth impedance curve which is important with the OTLs, 30 watts should be enough watts though. The M-60s are way more than enough watts with my 89db Merlins (twice the wattage = 3db) (which do have a very smooth impedance curve).
Eyeballing the impedance curve and frequency response curve measured by SoundStage, I think this speaker would work quite well with the S-30. The impedance curve is admirably smooth, and the impedance rise around 2.5 kHz is just about centered on the off-axis dip from the midwoofer beaming. So the interaction with the high output impedance of the S-30 will give about one dB more output in that region, which will not be a problem because the speaker's power response is down several dB in that region already.
Between 70 and 90 Hz, you'll get about 2 dB more output than what SoundStage measured, again as a result of the interaction between the speaker's input impedance and the amplifier's output impedance. In most cases, this will be welcome - if not, stuff some polyfill into the port.
It looks to me like the impedance stays above 6 ohms, and the actual sensitivity is 89 dB/2.83 volts according to SoundStage:
In my opinion, this amp/speaker combination will work fine. The speaker is not within the "ideal" range for that amp, but the impedance curve is benign and zigs where the power response (summed omnidirectional response - not shown but can be guesstimated) zags. I would guess that the midwoofer will begin to exceed its linear excursion limits and start to compress and lose clarity several decibels below the theoretical amplifier clipping threshold of about 103 dB.
I used an S-30 with the deCapo for about 2 years and it worked very well. The deCapo has a wonderful mid band and the S-30 shows that to great effect. But, but, but...
the speaker has no deep bass and is a bit lean up into the mid-bass, Notwithstanding Duke's observation, above, IME the S-30 will do nothing to ameliorate that. The tonal balance of the speaker was pretty consistent with all of the amps I paired it with, but struck me as "even more evident" when paired with the S-30.
I've never used the Speltz autoformers and can't speak to their effect on output power with impedance changes.
However the previous statement "Raising the impedance will also reduce the amplifier's power output" is incorrect with Atma-Sphere amps.
In fact just the opposite is true. The S-30 outputs 45WPC into a 16 ohm load and 60WPC into a 30 ohm load.
I think an amp that might work well if there is a lot of impedance swings in the speaker would be the Pass XA30.5, which also happens to be one of the best amps I've ever heard with my Merlins, although If you believe Ralph Karsten (why woulnd't you?)all amps will work better into flat impedances, the higher the better. I don't if it is always true, but my impression is that speakers with impedance swings are best handled by SS amps.
If memmory serves, I believe that the speaker has a relatively benign impedence curve (I investigated the question when I bought them - more than a few years ago). I suspect that the problem with the S-30 may be more a simple lack of grunt. I'm no headbanger, but as spl went up (to modestly loud levels), the S-30 sounded thinner on bottom with the deCapo.
There were 2 reasons I ultimately sold the amp:
The first was that it worked best with horns (Zingali in my case) and I chose to keep my Cary 300b monos for that application.
The second was that IMHO the deCapos were skillfully designed to present a natural octave to octave balance - the low end limitations were matched with a slightly rolled top. (I always felt that they were a great dynamic alternative to Quads). In the end, those limitations were more than I cared for so I sold both amp and speaker. But the main point is, I don't think any amp is likely to change this basic characteristic of the deCapo.
FWIW, we always get really good feedback from Ref3A owners. This has been true for the last 15 years or so. Customer input agrees with Duke's initial assessments above.
Although the S-30 was really designed for more efficient speakers (it was intended to go after the same market/speaker combos as SETs), it *does* make 30 watts into 8 ohms, which is a lot of power in the SET world. So it gets used on a lot of lower (91-93db) efficiency speakers.
A number of those speakers have less than 'ideal' impedances for the amp, but work great anyway: Merlins and Spendors for example, and the Ref3As. You can always use a set of ZEROs, but another little trick is to run the amp input single-ended and not use the jumpers in the XLRs. This more than doubles the feedback (which reduces the gain) and lets you work with tricker loads.
Funny you should mention the Merlins. I also used my S-30 with the old VSM SE and had an almost identical experience as with the deCapo - the inherent lean quality of the speaker was emphasized. OTOH, I sorta wish I would have waited on the sale of the S-30 until I had my VSMs upgraded (unfortunately the S-30 was gone by then. ) The new VSMs have a significantly richer balance through the mid-bass and I'd love to hear the current VSM/S-30 combo.
Atma, I'd also note that the deCapo/S-30 actually worked well in that the speaker didn't tax the amp beyond its capabilities until somewhat higher spls were required. My observation on the leaness of the deCapo remaining quite evident via the S-30 was more a response to Duke's post implying that the match might mask the issue - in my application it did not.
FWIW, I'm not surprised that you got some great feedback from your customers who used the deCapo/S-30 combo: As I noted it kinda reminded me of Quads and there are many who'd take that as pretty high praise, indeed. Just not my personal cup of tea.
BTW, I expect that most folks who use the amp for its original intended application -SET world -will find few faults. I just walked away guessing that higher output amps -perhaps your 60w monos - would be a better match for the deCapos.