Would switching amps make a big difference?


I've been using a Belles 21a tube pre and a pair of PrimaLuna Prologue Sevens with Martin Logan Ethos speakers for the last 6 years and it sounds good. I'm pretty stuck in tube land. But does it get better?

I was wondering if a Raven Osprey Integrated amp or the Lyngdorf TDAI-2170 or another amp, ideally integrated could elevate and sound even more, around same price of $5k - which if I went ahead is about what my current amp setup should bring me.

Then there is the idea of switching to the Martin Logan ESL Impression 11a...

Thoughts? Suggestions?


cdc2

Showing 4 responses by almarg

Most speakers are designed to approach a flat voltage response, not power, and amps to be a voltage source.
Agreed, but of course "most" doesn't mean "all."  It just means a majority.
If the source impedance of the amp is rather high (tubes) then there will be an HF roll off. The performance of a solid state amp might sound subjectively brighter but that’s not because it’s tilting up the highs, but because it’s not rolling them off.
The implication of this statement seems to be that in the case of electrostatic speakers, which are what the thread is addressing, that the tonal balance which results when a solid state amplifier is used is necessarily more correct than the tonal balance that would result with a tube amplifier.  If that is what you are saying I and I believe many others would disagree.  It's worth noting, for example, that the Quad ESL-57, which is revered to this day by many audiophiles, was designed before solid state amplification existed.

Regards,
-- Al
  
At 30 watts of output, the amp will put out that same 30 watts into any freq for an even tonal balance.

@viber6
No, that isn't correct, assuming the amp acts as a voltage source (as almost all solid state amps do, and as some tube amps do to a relatively loose approximation).

In the case of an amp having voltage source characteristics, i.e., very low output impedance, for a given input voltage to the amp it will provide an output **voltage** to the speaker that is essentially the same regardless of frequency, assuming the amp is operated within the limits of its voltage, current, power, and thermal capabilities. And that same voltage will result in more current and consequently more power being delivered into low impedances than into high impedances.

As you are probably aware power delivered into a resistive load equals voltage squared divided by resistance. It's somewhat more complicated than that when capacitive or inductive reactance is involved, but I'm putting that complication aside to try to clarify Ralph's point, which relates to delivery of power (as opposed to voltage) into the speaker. And which relates to frequency response flatness at the output of the speaker, not to frequency response flatness at the output of the amplifier.

Frequency response flatness at the output of the amplifier, on the other hand, is normally defined in terms of how the relation between amplifier output voltage (not power) and amplifier input voltage varies as a function of frequency. That characteristic will indeed be essentially flat in the case of a good quality voltage source amp, as long as the amp is operated within its capabilities. But that is not relevant to the point Ralph was making.

Regards,
-- Al
 
@cdc2

Excellent suggestion by Ralph (Atmasphere).

In the absence of a Zero autoformer, though, I would just say that the amplifier output impedance should be a good deal lower than the numbers I cited for the Prologue Seven, which btw correspond to a damping factor of approximately 1. Beyond that the sonics of the specific amp, and how they would synergize with the sonics of the speaker, would be the predominant consideration.

Very often amplifier output impedances are not specified (although if Stereophile has reviewed the amp the measurements section of the review will provide those numbers), but damping factors often are specified. And as you may be aware damping factor is inversely proportional to output impedance, and corresponds at least theoretically to the load impedance for which a tap is designated divided by the output impedance of that tap. So the output impedance of an 8 ohm tap should approximately correspond to 8 ohms divided by the damping factor; the output impedance of a 4 ohm tap should approximately correspond to 4 ohms divided by the damping factor, etc.

I suspect that a damping factor of at least around 8 or so would be preferable with your speakers, if a Zero is not used.

Manufacturers of tube amps having relatively high damping factors/relatively low output impedances include Music Reference, Audio Research, and McIntosh. I would be careful about preamp-to-amp impedance matching, though. I couldn’t find an output impedance spec for your preamp, but the Music Reference RM-200, which I suspect would be a fine match in other respects, has an input impedance of 30K balanced and 15K unbalanced. That is too low to be optimal with some tube preamps. Contact the preamp manufacturer if in doubt about that.

Good luck. Regards,
-- Al

Like a number of other PrimaLuna amps your Prologue Sevens have a particularly high output impedance. Stereophile measured 2.6 ohms for the 2 ohm tap, 4.5 ohms for the 4 ohm tap, and 8.5 ohms for the 8 ohm tap. The impedance of your speakers, which is similar to the impedance of many Martin Logan speakers, is spec’d at 4 ohms nominal, 0.8 ohms at 20 kHz.

The result of the interaction between those impedances is undoubtedly a considerable amount of rolloff in the upper treble region, regardless of which tap you are using. (The amount of rolloff would be least on the 2 ohm tap, although using that tap with nominally 4 ohm speakers might compromise the maximum power capability and the distortion performance of the amp).

Going to the 11a, btw, would probably be even worse in that respect, as it is spec’d as having an impedance of only 0.6 ohms at 20 kHz.

So yes, changing amps is likely to make a big difference, and probably for the better from a subjective standpoint as well as in terms of accuracy.

Good luck. Regards,
-- Al