Preamp vs Power Amp

A preamplifier selects a source and sets the level. A power amplifier turns that level-set signal into enough current to move a loudspeaker cone. They are consecutive jobs, not alternatives — the same relationship a DAC has with an amplifier.

An integrated amplifier is both, in one chassis. That is all “integrated” means, and it is why the word exists.

What a preamplifier actually does

Three jobs, and only one of them involves making the signal bigger.

• Selection. Choosing which input reaches the output. Cambridge publishes four RCA inputs plus a phono input and a front 3.5 mm aux on the AXA35; that switching is the preamp section doing its most basic job.
• Level. Almost always attenuation rather than gain. A DAC putting out 2.1 V into an amplifier that reaches full output on well under that needs the signal made smaller, not larger, for most of the volume range.
• Gain where a source cannot supply it. This is what a phono stageis: a specialized preamp for the one source that outputs millivolts. Yamaha publishes the A-S501’s phono input at 3.0 mV; Marantz publishes the PM6007’s at 2.2 mV. Both live in the preamp section.

Everything a preamp does happens in the voltage domain, into a high-impedance load. It never has to supply meaningful current, which is why preamps run cool and weigh nothing.

What a power amplifier actually does

It takes a signal of roughly a volt or two and produces one of tens of volts, while supplying the current that a load of a few ohms demands at that voltage. That current requirement is the entire engineering problem, and it is why power amplifiers have large transformers and heatsinks.

A loudspeaker is also not a resistor. It is a motor being pushed by the amplifier and, once moving, generating its own voltage back into it. The amplifier’s ability to absorb that and keep control is what damping factor describes — and it is one of the few power-amp specifications that gets published.

Why anyone splits them into separate boxes

Upgrading one half at a time

The usual argument, and a real one. A power amplifier is a mature technology that changes slowly; a preamplifier accumulates features — streaming, digital inputs, room correction — that date quickly. Splitting them lets you replace the half that has aged.

Getting the small signals away from the big ones

A phono cartridge delivers a couple of millivolts and a power stage swings tens of volts into a few ohms, inside the same box. Separating them removes an entire class of interference problem by geometry rather than by engineering.

Driving something the integrated cannot

If your speakers present a genuinely difficult load, a dedicated power amplifier with a bigger supply is the direct answer.

Why almost nobody should

Two boxes, two power cables, an interconnect between them, and a preamp that must have a low enough output impedance to drive that interconnect into the power amp’s input impedance. Manufacturers publish the second half of that pairing rarely enough that you often cannot check it in advance.

More to the point: the integrated amplifiers we cover already publish damping factors of 100 and 240, distortion figures of 0.019% and 0.08%, and signal-to-noise ratios of 99 and 102 dB. Those numbers do not describe a compromised design that separates would rescue.

The specification that decides whether you can split later

If you might ever add a power amplifier, you need a preamp output — and this is where AV receivers in particular differ sharply from one another. From the specifications we hold:

Marantz publishes a full 7.2 pre-out at a tier where Denon publishes 2.2. That single line in a spec sheet is the difference between a receiver you can grow out of gracefully and one you have to replace. It is covered in detail in our AV receiver roundup.

Volume controls: where the attenuation happens

The preamp’s most-used job is the one people think about least, and modern systems have quietly moved it around.

An analog attenuator — the knob on an integrated amplifier — reduces the signal voltage before the power stage. The digital data is untouched because there is none; everything after the DAC is analog.

A digital volume control reduces the numbers before conversion. Historically this was a real concern, because attenuating in the digital domain discards resolution. In practice, look at the numbers on hi-res audio explained: the converters we cover resolve about 18.5 to 20.6 bits against source material of 16, so there is real headroom to give away before it becomes audible.

What the manufacturers publish about it is instructive. FiiO publishes LO/PO switching on the K11 with each mode remembering its own volume — a genuine convenience that also implies the line output can be fixed. iFi publishes a variable/fixed switch on the ZEN DAC 3. Topping publishes a preamp mode on the E30 II. FiiO publishes three separate output modes on the K7: headphone, speaker preamp, and pure DAC.

The specification to check is whether a fixed output exists. A DAC with only a variable output feeding an integrated amplifier gives you two volume controls in series, and the usual result is a source set too low into an amplifier turned up too far — which is the one arrangement that reliably raises the noise floor. Set the DAC to fixed and use the amplifier’s knob.

What about a DAC as the preamp?

Several DACs we cover publish a preamp mode: the Topping E30 II, the FiiO K11 with LO/PO switching that remembers a separate volume for each, the FiiO K7 with switchable headphone, speaker-preamp and pure-DAC modes, the iFi ZEN DAC 3 with a variable/fixed switch.

For a fully digital system that genuinely can replace a preamplifier — one source, one volume control, straight into a power amplifier. The catch is that it selects between the inputs it has and no others, and it has no phono stage. That trade-off is worked through in DAC vs preamp.

The honest summary

Buy an integrated amplifier. It is the same two circuits in one box, sharing one power supply and one chassis, and the published specifications of the ones we cover are not the specifications of a compromise.

If you buy anything at all with separation in mind, buy it for its pre-outs — because that is the only decision on this page you cannot reverse later.