AVM Ovation SA 6.2 stereo amplifier Review

With the Red Wolf Audio Alpha 2 Server

I happened onto a file server/streamer at AXPONA this year, the Red Wolf Audio Alpha 2. If you are into extreme file playback you will want to check out this optimized computer playback system complete with high grade component quality outboard power supply, upgraded internal wiring in the server and an optimized version of JRiver’s Media Center. I paired the Alpha 2 with the beguiling Exogal Comet DAC, which creates its own signal based on Exogal’s proprietary algorithm. These two together are stunningly beautiful in my system.

Particularly striking is the depth, detail and dimensionality provided by the Alpha 2.

It amazes me how a digital file playback device can have so much character; after all it is simply rendering zeros and ones. The analog section of a streamer/server is radically important to the overall outcome. [Dan’s note: Unless the unit includes a DAC, it does not have an analog section.] I have heard users of cheap servers suggest there is no sonic difference between a several hundred-dollar server and a several thousand-dollar device like the Alpha 2. My response is, feel free to use whatever cheap gear you wish, you will not get premium sound. You will get mediocre sound, and, despite protestations, the difference sonically is easily heard and requires no blind comparison. The distinction between file playback devices can be on the order of changing out a pair of speakers. I cannot explain all the technical reasons why such a profound difference exists, but I can tell you that it soars past my Law of Efficacy, which requires changes to systems that are profound, immediately discernible and repeatable.

The all important impedance setting

Most solid-state amps can capably drive 4-8 Ohm speakers, but fewer have the current capacity to drive 2-Ohm speakers well or at all without potential damage to the amp or the speakers, especially when played at higher listening levels. This can be a problem when considering matching an amp to speakers having low nominal impedance. I found a beautifully clear and concise explanation of this from a participant on the Audioholics website on the first page of the discussion, “Differences between high current amps and normal ones” (http://forums.audioholics.com/forums/threads/differences-between-high-current-amps-and-normal-ones.40343/):

“A high-current amplifier is simply one in which the power supply and output stage can pass enough current to drive low-impedance loads. The “high-current” label is pretty much a marketing label, it gets tacked onto even entry-level receivers with slightly beefier power supplies than one usually sees at that level, but not much else (there is still only one pair of output transistors per channel, driving low impedance loads with a single pair can push the transistors out of their safe operating area – this is why many receivers have a “4-ohm” mode, it limits the supply rails and engages current limiting in the output stage to keep from blowing outputs.) When an amplifier attempts to swing a given voltage into the load, the load will attempt to draw a certain amount of current, and if the power supply cannot provide it or the output transistors cannot safely pass that current, output either sags (and the amplifier clips, and you can toast your tweeters if the distortion harmonics are strong enough) or you toast outputs (and if the protection circuit doesn’t trip, possibly your woofers as well since up to 30-50VDC could pass through whichever transistor shorted to the speakers.)

To deliver large amounts of current, you need a beefy power supply, multiple output device pairs, and GOOD heat sinking. The amplifier can be class A, AB, B, D, whatever…the physics still apply. Also, you really can’t divorce power in watts from current in amperes, since P = IE (P is power in watts, I is current in amperes, E is potential in volts.) If an amplifier cannot deliver the current a speaker asks for, the power in watts dissipated into the load will not be there either.”

Thanks to B3Nut for that! We see here that the settings on the amplifier for 4 Ohm or 2 Ohm limits the supply rails and engages current limiting in the output stage. The change from 8 Ohms to 4 Ohms, or if possible 2 Ohms, to the supply rails and current limiting is an audible effect with all amplifiers I have used. In fact, the Owner’s Manual for the VAC Phi Two Hundred Stereo Beam Power Amplifier (reviewed) not only discusses the different sound afforded by each set of Impedance output posts, but suggests the owner experiment with bi-wired speakers in using more than one set (i.e. 8 Ohm and 4 Ohm) when connecting the speakers. Sadly, I missed that point when I perused the Manual and never did toy with that feature. Let that stand as an example of why it is important to carefully scrutinize the documents that come with a product. If you don’t pay close enough attention you could miss an important performance tip!

With the Ovation SA 6.2 when I switched, it was nearly on the fly. (I paused the music momentarily; I did not have the Owner’s Manual to assure that true real time switching was acceptable. If you have a question about this please direct it to AVM.) Between the 8 Ohm/4 Ohm/ 2 Ohm settings very different sound palates were presented. With each step down of the Impedance setting the SA 6.2 took on more solidity and fortitude. This was especially critical with the Kingsound King III electrostatic speaker, which like all panel speakers benefits greatly from additional low-end reinforcement. The effect of running the amps on the 2-Ohm setting did not so much extend the bass frequency as strengthen it, allowing it to be used sans subwoofers. The same effect is heard with more efficient speakers as well. The Legacy Audio Whisper DSW Clarity Edition similarly had more drive and presence with the SA 6.2 set to 2-Ohm impedance.

A solid-state alternative

The Impedance setting is a feature that distinguishes the Ovation SA 6.2 from other fine amps. Two favored and distinctly flavored amps from the past come to mind, the Pass Labs X-600.5 Monoblock Amplifiers and the Wells Audio Innamorata, both Class AB. Just as with the SA 6.2 I had a pair of Innamorata, so the comparisons here will be relevant.

Not every amp maker knows how to create a sense of openness, space, headroom and scale – whatever terms you wish to use to describe hugeness – as Pass Labs. Decades of refinement have allowed Pass Labs to be unquestionably one of the amps in the industry that can be purchased with little worry of disappointment. Though the track record is far shorter, the same can be said in terms of sound quality of the Wells Audio amplifiers. As discussed in previous reviews of these manufacturers’ products I would be comfortable building a system with nearly any product they offer. Whereas the Pass Labs hallmark is scale, I would conclude the hallmark of Wells Audio amplification is timbre, or tonality. For a solid-state amp the Wells Audio is rich, really rich.

The AVM Ovation SA 6.2 fits in between these two. The Pass Labs sonic signature is what I would call “airy” in that it trades some density of images in the soundstage for extension and depth of the soundstage. Conversely, the Wells Innamorata does not have the expansiveness, but more robust and colorful imagery. The Ovation SA 6.2 has commendable expansiveness and colorfulness. It is a precision-lover’s amp, much as class D amps, but with no whiteness or sterility.