Pass Aleph 3 into 16 ohms

Paul,

Have you tried writing to Nelson Pass over at diyaudio? He answered a couple First Watt F4 questions for me. He seems to still be pretty involved.

David

You will have no problem at all driving a 16 ohm load with this amp.

Hi Paul,

Given that the Aleph 3 is rated at 30W into 8 ohms; that Stereophile's measurements indicate about 32W as the output power corresponding to the onset of clipping with an 8 ohm load; that the amp's output impedance is negligibly small (about 0.1 ohms); and that it is a pure Class A amp; it can be calculated that you will not get more than about 16 watts into a 16 ohm load.

Best regards,
-- Al

That is what I thought, Al. Thanks.

Does that power calculation hold true if the amp is single ended and not push pull? I know it is class A, but it is not a PP design.
I thought the Pass manual said the amp could do the same power into any load (at least for the X series).

Does that power calculation hold true if the amp is single ended and not push pull? I know it is class A, but it is not a PP design.
I thought the Pass manual said the amp could do the same power into any load (at least for the X series).

The amp is spec'd at 30W into 8 ohms, and 60W into 4 and 2 ohms. Stereophile measured a bit more than 32W into 8 ohms, 55W into 4 ohms, and 39W into 2 ohms.

What the manual says is constant is not power delivery, but power draw. See the second paragraph on page 10, which says that "the power draw of this system is constant regardless of the music playing through the amplifier."

From that we can infer that the power draw will be the same with a 16 ohm load as with an 8 ohm load, because if the music waveform is zero volts no current or power will be drawn by either load. Therefore the amp's internal voltage rails, and the amp's output voltage swing capability, will not increase as a result of reduced current demand by the 16 ohm load. That is why I mentioned the fact that the amp is pure Class A.

The low output impedance (typical of solid state amps, of course) means that the amp behaves essentially as a voltage source, within the limits of its current capability. The fact that it can nearly double power into 4 ohms relative to 8 ohms confirms, as might be expected, that its 8 ohm power delivery is limited by voltage swing capability, not by current capability. Its 16 ohm power delivery will be limited by that same voltage swing capability.

Therefore based on P = (Esquared)/R, the maximum power that can be delivered into 16 ohms will be very close to 1/2 of what can be delivered into 8 ohms.

The fact that the amp is single-ended rather than push-pull does not change any of that.

Best regards,
-- Al

Al is right- there is a big difference between power response and voltage response. The manual referred to by 6550c is talking about voltage response, not power response.

Some speakers are designed for voltage response, and some are not. See

http://www.atma-sphere.com/papers/paradigm_paper2.html

for more information.

Now, just because transistor amps cannot make as much power is not a reason to discount 16 ohms! The fact of the matter is that if sound **quality** is your goal all soldid state amplifiers will sound better on 16 ohms as opposed to 8 or 4 ohms, all other things being equal. This is because they will make less of the distortions that the ear finds unpleasant (odd ordered harmonics) since there is decreased current demands in the output section of the amplifier.

Tubes like 16 ohms better as well, although for different reasons- transformer-coupled amps will make slightly more power, less distortion and wider bandwidth because the output transformer becomes more efficient, and OTLs will often make more power, less distortion and less heat with greater tube life.

Anyway you look at it, if you have a given speaker design that can be easily converted to 16 ohms (from the designer's point of view), its a simple way to make the speaker seem as if it is not as harsh and more transparent, both at the same time.