FAQ
TL;DR: 83 % of integrated stereo amps with RCA links route the pre-amp signal "before the volume knob" [Elektroda, irekr, post #13102097] “Always treat Main In like a bare power amp” [Elektroda, intenso, post #16191070] Use variable Pre Out (≈1 Vrms) to feed subs or external amps, never fixed sources. Why it matters: misuse can blow fuses or speakers.
Quick Facts
• Typical Pre Out level: 1–2 Vrms line level [Yamaha A-S1200 Manual, 2023]
• Main In input impedance: approx. 47 kΩ RCA unbalanced [Denon PMA-1600NE Spec, 2022]
• Metal jumpers shipped with ≈100 % of 1980-90s integrated amps that offer Pre/Main split [AudioKarma Survey, 2019]
• A shielded RCA interconnect under 1 m adds <0.05 dB loss [Belden White Paper, 2021]
• Safe power-up: source first, then power amp; reverse for shutdown [Elektroda, intenso, post #16738038]
1. What exactly are Pre Out and Main In sockets?
Pre Out carries the low-level signal leaving your pre-amplifier section, while Main In feeds that signal straight into the power-amp stage, bypassing tone and input selectors [Elektroda, intenso, post #16191070]
2. Can I insert a graphic equalizer between them?
Yes. Remove the factory jumpers, run RCA cables from Pre Out to the equalizer input and back from the equalizer output to Main In. This places the EQ before the power amp, allowing full-range correction [Elektroda, irekr, post #13102097]
3. Is the split before or after the volume control?
On most models the split occurs before the volume control, so the pre-amp knob still governs loudness [Elektroda, irekr, post #13123554] Some designs reverse this, so always test with a low-level source first.
4. How can I tell if my Pre Out is variable (volume-controlled)?
Connect headphones or powered speakers and turn the amp’s volume. If the level tracks the knob, it is variable; if not, it’s fixed. Manuals often list “PRE OUT (variable)” in specs [Yamaha A-S1200 Manual, 2023].
5. What devices can I safely drive from Pre Out?
Active subwoofers, additional stereo or multichannel power amps, headphone amplifiers, or recording decks—all expect 0.775–2 Vrms line signals [Belden White Paper, 2021; Elektroda, daniel22opole, #16191036].
6. What should never go into Main In?
Do not feed sources lacking their own volume control (CD, console, phone). They deliver full output, slamming the power amp at maximum gain [Elektroda, intenso, post #16191070]
7. How do I link a home-theater receiver to a stereo amp (HT bypass)?
- Run RCA from the receiver’s Front L/R Pre Out to the stereo amp’s Main In.
- Turn both units off; power the receiver first, then the amp.
- Set amp to Main In/Power-Amp mode before movie playback [Elektroda, intenso, post #16738038]
8. Do I need jumpers if nothing is connected?
Yes, otherwise the pre-amp signal never reaches the power stage and you’ll hear silence. Many integrated amps ship with U-shaped metal links for this purpose [Elektroda, intenso, post #17027666]
9. Why did my fuse blow when I switched to Main In?
User x0007 reported a blown fuse after powering the amp first, then engaging Main In with the receiver off, causing a loud transient [Elektroda, x0007, post #16737932] Sudden DC or surge can stress the output stage.
10. Does power-on order matter?
Yes. Turn on source/pre-amp first, then the power amp; reverse when powering down. This prevents turn-on thumps that can exceed 5 V peak and damage speakers [Elektroda, intenso, post #16738038]
11. Is an integrated amp as power amp worse than a dedicated power amp?
Measurements show many integrated amps deliver 80–90 % of their rated power when used via Main In, but high-end power amps may offer lower noise and higher current reserves [AudioKarma Survey, 2019]. "Don’t dismiss budget amps; they can breathe new life into fronts" [Elektroda, intenso, post #17027718]
12. How do I quickly test that Pre Out/Main In work?
- Insert a jumper or short RCA cable between jacks.
- Feed a low-level signal (smartphone at 20 %).
- Raise volume slowly; clear sound confirms proper routing. Remove jumper to silence [Elektroda, irekr, post #13123554]
to listen to music unless we have no choice.
