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In particular I am looking at the JDS Labs Atom and the iFI iCan SE. The iCan outputs a tremendous amount of power, 4 times that of the Atom, enough to drive speakers; But does so less cleanly, at-least according to their self-published numbers. Meanwhile the Atom has a measured noise floor of below -120db (according to audiosciencereview forum) and is incredibly clean and "transparent" for it's price, almost as good as other amps which are 10x more expensive.

Now, the iCan takes 15v DC current at stock (tho it can also take down to 9v) and the Atom takes 16v AC.

Does the difference in working current topology have something to do with the difference in noise levels? Is AC current fundamentally better as a working current when it comes to amplifying audio signal?

I remember Zeos Pantera saying as much during one of his reviews, but then-again he's also fundamentally opposed to actually understanding the science behind audio so as not to "ruin the magic" ...so I take his words with a rather large grain of salt.

Me on the other hand, I love nothing more than to learn new things, so please share your knowledge :)

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The type of current is actually completely irrelevant as all transmitted power is AC. Unless you are driving your amplifier from batteries, everything has to be converted at some point to DC.

The end result all boils down to the amount of power you need to draw from the supply in order to amplify the audio to the level you require.

The main reason why AC is often used is that the power supply inside the amplifier needs to transform the AC into both a positive and negative DC supply. This is because most of the amplifier circuits require both -VE and +VE supplies to drive the amplifier semiconductors and modules. Standard DC supplies generally only have Ground and +VE supplies which isn't that efficient when it comes to amplification. External power supplies generally don't have the ability to generate enough current unless they are extremely beefy, in which case you will need very large gauge power wire to connect to the amplifier unit itself.

It's simpler to house the power supply inside the unit - that way the high-current connections to the amplifier modules can be kept as short as possible and consequently there is very little voltage drop.

Power supplies are generally very good at smoothing and regulating voltages so that you rarely get hum unless you are drawing too much current.

To summarise. Advantages of an internal (AC) supply are:

  • Much higher current availability
  • Shorter distance to high-current components
  • Cheaper to build and all self-contained.
  • Ability to transform AC to both +ve and -ve supplies

I acknowledge that the Atom has an external AC transformer which is quite rare, however the DC conversion is happening on-board the atom. It is evidently easier to do it this way so they don't have to house the transformer inside the case. This will be because of size and design constraints. 16VAC is still easy to get down to +/- 12VDC with some hefty smoothing capacitors and regulators.

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    "External power supplies generally don't have the ability to generate enough current" for amplifiers intended to drive loudspeakers, yes. For headphone amps this is less of an issue. – Hobbes Oct 10 at 14:05
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    It's more a question of design and component costs. DC Wall-warts can be purchased cheaply off the shelf, but it's just inefficient to offload so much current supply to an external device. Sure it's less of an issue for these particular headphone amplifiers, but more generally it's a consideration. – Mark Oct 11 at 5:03
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    They'll use an external transformer partly because it'll be cheaper for them to run this in multiple countries. Requiring a feed of 16V AC means that to swap from a 120V standard mains voltage country to a 240V mains country only the transformer from the wall to the device needs changing, rather than having circuitry in the unit designed to tolerate a wide band of input voltages, or having to hard-lock the device to specific regions. – Trotski94 Oct 14 at 8:20
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Is AC current fundamentally better as a working current when it comes to amplifying audio signal?

No. If anything, using an AC power supply makes it more difficult to have low noise.

The circuits that handle audio are all powered by DC. So any amplifier that has an AC power input has to convert this to DC internally. The AC cabling inside the amplifier that leads to the AC-DC conversion unit (either a transformer or an electronic converter) can act as a transmitter, potentially inducing e.g. a 50/60 Hz hum into the audio path, so you have to put shielding between the AC circuits and the audio path.

A device with a DC input simplifies this by placing the AC-DC conversion outside the enclosure.

On the other hand: by keeping the AC-DC conversion inside the amplifier, using a circuit you've designed yourself, you can exert more control over the quality of the DC conversion.

  • Isn't audio signal intrinsically AC in nature tho. I think the touted reason was that AC current is supposed to make life easier for AB class amps by also going below 0 and make the membrane of the speakers also jump backwards instead of just pushing forward. – Daniel Elefteriadis Oct 11 at 6:25
  • No. Electronics don't work like that. A transistor needs a supply voltage that's higher than the control voltage to work at all; if you were to feed the transistors with AC you'd end up with an output volume that varies between 0 and maximum at a speed of 50/60 Hz. – Hobbes Oct 11 at 7:01
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    @DanielElefteriadis A class A amp is perfectly capable of generating a negative voltage on its output and making the membrane jump backwards. – Tom van der Zanden Oct 11 at 7:16
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    @TomvanderZanden Yep! And to a lesser degree so can the AB class, although not at the full 360 degrees that A-class can. What's interesting is that some newer AB-class amps actually function at A-class capacity when dialed down. It's gotten to the point where some of these AB-class amps are being marketed as "pure A-class" (Aune x7s, I'm looking at you >.>) – Daniel Elefteriadis Oct 11 at 10:08
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    @Mark agreed, and thank you for the valuable input :) – Daniel Elefteriadis Oct 11 at 10:09

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