Pre-out / Pre-amp Out Preamplifier Output

What a pre-out is

A pre-out (preamp output) is an analog jack that carries a channel's signal after input selection, processing and volume control but before the receiver's own power amplifier. Feed it to an external power amp and the receiver becomes a preamp. Denon's AVR-X3800H manual says you can use the unit as a preamplifier by connecting an external power amplifier to the PRE OUT connectors. If every speaker is externally amplified, you set Amp Assign to Preamplifier, and the signal path to the internal amplifier can be switched off per channel to reduce interference.

Pre-outs carry processed channels, not raw inputs. The same manual notes that the pre-out signal for Height 1 and Height 2 varies with the combination of height, ceiling or Dolby Atmos Enabled speakers in use, so the layout you configure decides what each jack outputs. Dedicated pre-outs for Zone 2, Zone 3 and height channels are common on modern receivers (Celsus Sound). A pre-out is not a speaker output: it carries volts at line level, while a speaker terminal on the same receiver must swing about 29 V for 105 W into 8 Ω, so a speaker wired to a pre-out jack plays almost nothing.

Voltage levels, with numbers

Consumer line level is nominally -10 dBV, or 0.316 V RMS. Professional line level is +4 dBu, or 1.228 V RMS, which is 11.8 dB higher. The AV pre-outs below are rated well above the consumer reference. Marantz lists the AV 10's rated pre-output as 1.2 V on unbalanced RCA and 2.4 V on balanced XLR. The RCA figure is 11.6 dB above 0.316 V, and the XLR figure is exactly 6 dB above the RCA one. Denon's AVR-X3800H analog section lists a rated output of 1.2 V against a 200 mV input sensitivity. Line outputs are low impedance, typically 100 to 600 Ω, while line inputs are typically 10 kΩ or more, so a pre-out loses almost no voltage into a power amp's input (Wikipedia).

Worked example: gain the external amp needs

The AVR-X3800H's internal amplifiers are rated 105 W per channel into 8 Ω (20 Hz to 20 kHz, 0.08% THD). Power into a load is V²/R, so 105 W into 8 Ω needs √(105 x 8) = 29.0 V RMS at the speaker terminals. From a 1.2 V pre-out, an external amp needs a voltage gain of 29.0 / 1.2 = 24.2, which is 27.7 dB, to match that output. From the AV 10's 2.4 V balanced output it needs 12.1 times, or 21.6 dB. An amp with more gain than the pre-out requires reaches full power before the receiver's volume reaches its top end, which is normal and simply moves the usable volume range lower.

Pre-out vs line-out vs subwoofer out

Pre-out and line-out are confused constantly. Line-out is usually a buffered, fixed-level signal taken before the volume control, so it suits a recorder or an amplifier that has its own volume knob. Pre-out is a variable signal that follows the receiver's master volume, because most power amps are fixed-gain and have no volume control (Boomspeaker). The practical rule: feed a power amp with no volume knob from a pre-out, and leave its input level fixed so the receiver stays the only volume control. A subwoofer output is a separate jack. The Marantz AV 10 gives four independent subwoofer outputs alongside its 17.4-channel pre-outs.

Receivers vs processors: what the specs show

A processor has no power amplifiers, and its audio specs usually show it. Marantz lists the AV 10 at 105 dB signal-to-noise and 0.005% distortion on the analog path, and 110 dB S/N, 110 dB dynamic range and 0.002% distortion on the D/A output. The AVR-X3800H lists 100 dB and 0.008% on analog, and 102 dB S/N, 100 dB dynamic range and 0.008% on D/A. All are Direct mode figures from each maker's manual. Channel counts scale too. Yamaha rates the RX-A6A at 185 W per channel into 8 Ω (1 kHz, one channel driven) and 150 W (20 Hz to 20 kHz, 0.06% THD, two channels driven), with 9.2 amplified channels and 11.2 channels of pre-out; the RX-A8A has 11.2 and 11.2, and the RX-A4A has 7.2 and 7.2. The AV 10 offers 17.4 channels on both RCA and XLR from a 15.4-channel processor. See AVP vs AVR.

When pre-outs earn their keep

Three jobs justify them. The first is power: Celsus Sound notes that even expensive receivers may lack the headroom for demanding speakers, and an external amp supplies it. The second is channel count: a receiver like the RX-A6A can send 11.2 channels of pre-out to separate amplifiers for a 7.1.4 or larger layout even though only 9 channels are amplified inside. The third is multi-room: Yamaha lists Zone 2 and Zone 3 pre-outs on the RX-A6A, with powered zones for Zone 2 and Zone 3 on the same page.

The costs are real. Celsus Sound lists price, extra cables and the chance of added interference as drawbacks, and the feature tends to sit in more expensive models. If you only need more power for one pair of speakers, a stereo power amp on the front pre-outs covers that case. Balanced XLR connections need XLR-equipped pre-outs on both ends; see balanced XLR vs unbalanced RCA. For matching receiver ratings to speaker needs, use the receiver match tool and amplifier power tool, and read the AVR spec guide before paying for pre-outs you will not use.