Cascadesphil, thanks for taking the time and sharing your experience. Especially pertanent to me was your description of the amounts of heat being emitted. Well done.
- 333 posts total
- 333 posts total
I’m by no means an expert and cannot speak to class d amps, but old school heavy duty class a amps are made for this sort of load. I drive my Apogees with a Balanced Audio Technology VK-600 with bat pack and couldn’t be happier. Yes, they run hotter than class d (and aren’t nearly as efficient), but everything is a compromise in one way or another. At the end of the day, the quality of the sound and the experience are most important to me.
I went to the Purifi Audio website and found many charts and specifications for their 1ET400A, most of which I did not understand so I could have very well missed something important about relationships between the stats they quoted.
I did see this:
Output Power, Short Term
8ohm, 1% distortion = 227 watts
4ohm, 1% distortion = 450 watts
2ohm, 1% distortion = 450 watts with a footnote stating "Power is limited by overcurrent protection system (OCP) and highly dependent on thermal conditions."
Not sure what the footnote means.
I went to the Spectron website for the Musician III Mk2 and they tell us "The current headroom is primarily limited by the amplifier’s ability to deliver high currents into low impedance loads. There are many well regarded speakers whose impedance dips down, some even lower than 1 ohm. When a musical note is played at frequencies where the impedance dips, the current demands skyrocket. When this happens with amplifiers that do not have large output current capability, they “current clip”. These transients will be both attenuated and quite distorted. Moreover, most other amplifiers only deliver their rated peak current for sometimes a fraction of the time called for by the music. Spectron amplifiers can deliver peak currents of 65 amps, with a staggering peak power of 3500 watts per channel for over 500 msec (!), which allows the amplifier to deliver the full transient (burst of music) without current or voltage “clipping”. ".
Their stats also state 0.3% THD up to 600 watts in 8 ohms. Could not find anything about distortion at 4 or 2 ohms.
Not sure what that does or does not tell us.
It appears the old adage about trying it in your listening room will tell the real story.
In the meantime, quit bashing my low impedance speakers as they sound wonderful to me in my listening room 😍!
Thanks for listening,
I did see this:
Amps goes self into destruct mode if current limiting doesn’t work, no other reason for it to be limited, unless purposely done to sound bad into those low loads?
All amplifiers running 2 ohms continuously will get hot, independent of class. But I have seen that class D modules (Icepower, hypex, purifi) have current limit to protect the module from overcurrent.
As for thermal dissipation, musical signal has peaks, it never has the same power requirements as a full signal sine wave. So the manufacturers add dissipation to the modules in a coherent way for music listening.
If an amp was to be built to run full power sine wave at 2 ohms just for long term measurements, just add a lot of heat sinks and even a fan or two. It would do great on the benchmarks, but would make no sense for customers to pay and lift the extra weight.
As for distortion is simple: along with the Benchmark AHB2, the Purifi module is the lower distortion amplifier in the market, as far as we know (most manufacturers don't publish THD x power graphs, just single number specs).