Reminder: how to tell current from an amp's specs?

I have a sinking feeling that I've been here before but, as the subject line says, how can I tell an amp's current from its published specs? 




If I can point something else out: Just because your amplifier can drive to 2 Ohms and is able to double power as it does so does not mean its sounding its best when doing so. All amplifiers make higher distortion when driving lower impedances! If you think that distortion is inaudible think again- the increased distortion is audible as increased brightness, harshness and a reduction of detail (distortion obscures detail) because most of that added distortion is unmasked higher ordered harmonics.

Hi Ralph 

I appreciate you pointing this out. It’s very often overlooked in these types of discussions. I have always failed to find the wisdom in designing low impedance/high phase angle (Difficult load) speakers that then require/demand massive amplifiers to drive them. An environment for the appearance of high odd order harmonic distortion. 



The REGA Osiris integrated amp is one of these exceptions. While it is a beefy hi-current and high WPC amp that doesn’t fully double down, it still has LOTS of current because of its high-end build and design. This is provided by those four Sanken output transistors per channel, that insure that no speaker is too hard to drive.

This statement is incorrect. The extra transistors make sure the output section can support the current without damage but if the power transformer lacks the current capacity it really won’t make any difference.


I’m no engineer but it’s still a beefy beast, It’s power supplies are big muthas,

it’s a no compromise, super high performance, 162 W into 8 Ω (250 W, 4 Ω), dual mono amplifier housed in a custom Rega CNC machined aluminium case. It weighs over 54lb.that provides more than enough current to drive the hardest of loads.

The Osiris uses two low noise, purpose designed 400 VA toroidal transformers using high-grade, fully bonded core material. Eight Sanken 200 W output transistors are used in a “triple” high current output stage enabling the Osiris to drive even the most awkward of speaker systems with ease.

@8th-note   how do you know the Thiel's will sound anemic in the bass with tube amps, have you ever tried a high powered tube amp with them? There is a guy running tube research labs gt800 tube amps with apogee full range and he said the bass was way better than any solid state amp that he had tried with them, and the list is long.

I asked Wendell at Magnepan that same question and he said:


"If the amp doubles its power between 8 and 4 ohms you will be fine."  In my experience, the Maggie .7 sounds best with class-A solid-state or a good push-pull tube amp. 



@invalid First, when I took in my Krell for rebuild I hooked up a few integrated amps and receivers that I had on hand just to see how they would sound. It was unmistakable that these amps produced a different frequency response than my Krell. Specifically the bass was reduced in volume and "anemic." I extrapolate that a tube amp would produce the same result.

Second, there is a very good "Thiel Owners" thread on Audiogon where this phenomenon has been discussed. I partly based my statement on real world experience of several Agon members.

Third, I've been to three different audio shows where they had the larger Wilson speakers. In every case they were driven by D'Agostino amps that double their power down to 1 ohm. I've read many times in reviews and forums that the larger Wilsons sound their best with a high current amp. Reviewers have also noted that when they drive a speaker with a difficult impedance curve with a tube amp the bass is often weak. Check out the review of the Octave Audio Jubilee tube amp in the September Stereophile. JV Serinus describes this exact phenomenon with his Alexia II speakers. Then, in the testing section John Atkinson praises the amp for having lots of power into 8 ohms but he doesn't recommend it for use with speakers where the impedance drops below 4 ohms. I've read similar examples dozens of times. Over and over again reviewers state that the tube amps they are reviewing are not appropriate for speakers with difficult impedance loads.

I can't believe there is even a debate about this. It is well known that driving a speaker that has a variable impedance curve that dips below 4 ohms with an amp that cannot produce the appropriate current at the low impedances will change the frequency response of the speaker. It's a well documented fact. If you can produce evidence to the contrary please do so.