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Marantz PM6007: Safe to Run 8 Ohm on A and 4 Ohm on B Simultaneously?

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User question

if i connect 8 ohm speakers to network A on my Marantz PM6007 amp and 4 ohm speakers to network B is there a significant risk that I will damage my amp if i run both neworks simultaneously at low to medium volume, playing music that is melodic with a broad frequency range

Artificial Intelligence Response

Direct answer to the question

  • Short answer: Yes—running your 8 Ω pair on network A and a 4 Ω pair on network B at the same time on a Marantz PM6007 is outside the amplifier’s specified A+B limits and carries real risk (over‑current, overheating, protection trips, or long‑term stress), even at “low–medium” volume. (manuals.marantz.com)
  • Key points:
    • With A+B selected the two speaker pairs are driven by the same power stage (same signal on A and B). The PM6007 manual requires 8–16 Ω speakers on each network when A+B is used. A or B alone allows 4–16 Ω. (manuals.marantz.com)
    • 8 Ω in parallel with 4 Ω presents ≈2.67 Ω per channel—below the PM6007’s minimum combined load for A+B. (manuals.marantz.com)

Detailed problem analysis

  • Electrical loading
    • When A and B are on together, both pairs are tied to the same left/right output stages; the manual notes the same signal appears on A and B terminals (functionally a parallel load to the amplifier). (manuals.marantz.com)
    • Parallel impedance: Ztotal = (8 × 4)/(8 + 4) = 32/12 ≈ 2.67 Ω per channel.
    • The PM6007 is specified for:
    • One pair (A or B): 4–16 Ω per speaker.
    • Two pairs (A+B): 8–16 Ω per speaker (so the parallel result stays ≥4 Ω). (manuals.marantz.com)
  • Why “low–medium volume” doesn’t make it safe
    • Current rises as impedance falls (I = V/Z). For the same output voltage that would draw ~1.25 Apeak into 8 Ω, the 2.67 Ω combined load demands ~3.75 Apeak—3× the current. Those transient peaks happen in normal music (bass notes, drum hits) even when average listening seems modest, driving up device temperature and risking protection trips.
  • Real‑world speaker behavior
    • “8 Ω” and “4 Ω” are nominal ratings; actual impedance varies with frequency and can dip below nominal. If the 4 Ω pair dips toward ~3 Ω while the 8 Ω pair dips toward ~6 Ω at the same frequency, the instantaneous parallel load can approach ~2 Ω—well outside spec and harder on the amplifier.
  • Likely outcomes if you try it
    • Best case: the amp runs hot and may intermittently mute or shut down via its protection circuits.
    • Worst case: cumulative thermal/electrical stress shortens component life or causes output‑stage failure.

Current information and trends

  • The PM6007 user guide (current as of its 2020 release and still posted by Marantz) explicitly lists:
    • A or B: 4–16 Ω
    • A+B: 8–16 Ω (per speaker pair)
      This remains the published guidance on Marantz’s manual site today. (manuals.marantz.com)
  • Across modern stereo integrated amplifiers with A/B terminals, the industry norm mirrors this: A+B assumes parallel loading; therefore manufacturers commonly require 8–16 Ω per pair when both sets are active (to keep the combined load ≥4 Ω). The PM6007’s A/B page confirms A and B carry the same program signal from the same amplifier channels. (manuals.marantz.com)

Supporting explanations and details

  • Quick math example
    • Suppose a moderate musical peak produces 10 Vpeak at the speaker terminals:
    • Into 8 Ω: Ipeak = 10/8 = 1.25 A; Pinst ≈ 12.5 W.
    • Into 2.67 Ω: Ipeak = 10/2.67 ≈ 3.75 A; Pinst ≈ 37.5 W drawn from the output stage.
    • Amplifier heating scales roughly with I² in the output devices; the 2.67 Ω case can run ~9× the heat compared to 8 Ω for the same output voltage peak.
  • Why Marantz allows two 8 Ω pairs but not 4 + 8 Ω
    • Two 8 Ω pairs in parallel → 4 Ω (within spec).
    • 8 Ω || 4 Ω → 2.67 Ω (below spec). The manual’s 8–16 Ω per‑pair rule for A+B encodes that constraint. (manuals.marantz.com)

Ethical and legal aspects

  • Operating outside the manufacturer’s specified load can void warranty and, in edge cases with poor ventilation, raise safety concerns. Following the user manual’s impedance limits is the safe, responsible practice. (manuals.marantz.com)

Practical guidelines

  • Safe ways to proceed
    • Use only one pair at a time: either the 8 Ω (A) or the 4 Ω (B). Both are within spec when used alone. (manuals.marantz.com)
    • If you must run two pairs simultaneously, make both pairs 8 Ω (A+B ⇒ 4 Ω total, within spec). (manuals.marantz.com)
    • Use an external speaker selector with impedance protection (prefer autoformer‑based) so the amplifier always “sees” a safe load.
    • Add a small external power amplifier for the second zone; feed it from the PM6007’s record/line output (or a speaker‑to‑line adaptor), so each pair has its own power stage.
  • What to avoid
    • Do not run 8 Ω + 4 Ω directly on A+B.
    • Avoid adding big series power resistors to “fake” higher impedance; they waste power and degrade damping (bass control).

Possible disclaimers or additional notes

  • Your unit’s protection circuitry may prevent catastrophic failure, but repeated over‑current/over‑temperature events still stress components. Designing within spec is the reliable solution. (manuals.marantz.com)
  • Some online advice suggests “low volume is fine.” That contradicts Marantz’s documented A+B impedance requirement and disregards musical peaks and impedance dips; the manual‑based guidance above should be preferred. (manuals.marantz.com)

Suggestions for further research

  • Check the impedance curves of your specific speakers (manufacturer data or independent measurements). If the minimum impedance of either pair is below ~8 Ω, do not parallel it with another pair on the PM6007.
  • If multi‑room/background listening is your goal, compare:
    • Impedance‑protected selector boxes (autoformer types from installer brands).
    • A small separate power amp for the second room/zone.

Brief summary

  • The PM6007 is rated for 4–16 Ω with one pair, but requires 8–16 Ω per pair when A+B are used. An 8 Ω pair in parallel with a 4 Ω pair presents ~2.67 Ω, which violates the A+B requirement and can over‑stress the amplifier even at seemingly modest levels. Use one pair at a time, two 8 Ω pairs for A+B, or add proper impedance management or a second amplifier. (manuals.marantz.com)

User question

If I replace the 4 ohm speakers with speakers sold as having a 4-8 ohm impedance rating, would those allow me to operate both networks simultaneously.

Artificial Intelligence Response

Direct answer to the question

  • No. Replacing the 4 Ω speakers with ones marketed as “4–8 Ω” will not make simultaneous A+B (both networks) operation safe on the PM6007.
  • Key points:
    • On the PM6007, selecting A+B places the two speaker pairs in parallel.
    • Marantz specifies that when A+B is used, each pair must be 8–16 Ω so the amplifier never sees less than 4 Ω.
    • “4–8 Ω” speakers typically behave like a 4–6 Ω load and can dip to ~4 Ω (or lower) at some frequencies, violating the A+B requirement.

Detailed problem analysis

  • What “4–8 Ω” really means:

    • Loudspeaker impedance is frequency-dependent and reactive, not a fixed resistor. A label such as “4–8 Ω” usually indicates a nominal ~6 Ω design whose minimum impedance commonly drops to ~4 Ω in the bass and lower midrange.
    • For amplifier safety you must design to the minimum impedance, not the nominal or the marketing range.

  • Parallel loading on A+B:

    • With A+B selected, the left A and B posts tie together on the left output stage (and similarly for the right), so the loads are in parallel.
    • Using the parallel formula Z_total = (Z1 × Z2)/(Z1 + Z2):
    • 8 Ω (pair A) in parallel with a worst‑case 4 Ω minimum (pair B “4–8 Ω”): Z_total = (8×4)/(8+4) = 2.67 Ω.
    • Even if the “4–8 Ω” pair behaves like 6 Ω at some frequencies: Z_total = (8×6)/(8+6) ≈ 3.43 Ω.
    • Both results are below the PM6007’s allowed minimum of 4 Ω for the combined A+B load, which is why Marantz requires 8–16 Ω per pair when both are active.

  • Why “low volume” is not a guarantee of safety:

    • Music contains transient peaks (10–20 dB above average). Those peaks can demand 3–10× the instantaneous current even when average listening seems modest.
    • Output devices heat with I², so a 2.67–3.43 Ω load can drive current (and thus heat) disproportionately higher than with a compliant 4–8 Ω total load. Protection may trip; repeated events accelerate wear.

  • Practical electrical consequences on the PM6007 output stage:

    • Increased current → higher junction temperature in the output transistors and driver stages.
    • Reduced damping factor due to any protection/limiting that engages, degrading bass control.
    • Potential oscillation margins worsen with more reactive, lower-impedance loads.

Current information and trends

  • Stereo integrated amplifiers like the PM6007 commonly allow 4–16 Ω with one pair active, but require 8–16 Ω per pair when A+B parallels them, ensuring a ≥4 Ω combined load.
  • Many “6 Ω nominal” or “4–8 Ω” consumer speakers routinely dip to ~3.2–4.5 Ω; manufacturers emphasize broad compatibility, but amplifier design limits still apply.
  • AV receivers sometimes include a 4 Ω mode or current limiting; hi‑fi integrateds more often rely on the user adhering to the specified impedance ranges.

Supporting explanations and details

  • Example impedance curve behavior:
    • A ported 2‑way “6 Ω nominal” speaker might show 18–25 Ω peaks at box/driver resonances and a trough near 3.8–4.5 Ω in the upper bass. That trough is where program material can demand substantial current, compounding risk when run in parallel with another pair.
  • Why Marantz’s 8–16 Ω per pair rule for A+B:
    • Two 8 Ω pairs in parallel equal 4 Ω, which the PM6007 is specified to handle. Any pair below 8 Ω risks pulling the total load below 4 Ω.

Ethical and legal aspects

  • Operating outside the stated impedance limits can void warranty coverage and risks damage to the amplifier and possibly the speakers if a failure occurs.
  • Disclosure and adherence to the manual’s specs are part of responsible equipment use and resale.

Practical guidelines

  • Safe ways to achieve two zones/pairs:

    • Use only one pair at a time (A or B), both within 4–16 Ω.
    • Use two pairs that are each nominal 8 Ω when you want A+B; 8 Ω || 8 Ω = 4 Ω meets spec.
    • Add a quality speaker selector with impedance protection (prefer autoformer-based rather than purely resistive) between the amp and multiple pairs; it presents a safe effective load to the PM6007.
    • Use an external power amplifier for the second pair, driven from the PM6007’s pre-out/record output, so each pair has its own power stage.

  • What to avoid:

    • Mixing an 8 Ω pair with any “4–8 Ω” or 4–6 Ω pair on A+B directly.
    • Assuming volume control alone will keep you safe from overload conditions.

  • Verifying your specific case:

    • If you have access to an impedance plot of the proposed “4–8 Ω” speakers, check the minimum magnitude. If the minimum is below ~7–8 Ω, they should not be paralleled directly with another pair on A+B for the PM6007.

Possible disclaimers or additional notes

  • A few specialty speakers marketed as “8 Ω nominal” may still dip near 6 Ω; two such pairs in parallel still meet the letter of the A+B rule but leave less margin than two robust, truly 8 Ω designs. Listening levels and room size still matter.

Suggestions for further research

  • Review the PM6007 user manual section on speaker impedance and A/B operation and the specs sheet for exact impedance requirements.
  • Consult impedance curves from independent measurements (audio magazines or measurement communities) for the specific speaker models you’re considering.
  • If multi-room is a goal, research autoformer-based multi-room speaker selectors (e.g., from Niles, Russound, AudioControl) and two-zone solutions.

Brief summary

  • “4–8 Ω” speakers will not make A+B operation safe on the PM6007. When A+B parallels two pairs, anything less than 8 Ω per pair can pull the combined load below 4 Ω, exceeding the amplifier’s design limits. Use two 8 Ω pairs for A+B, one pair at a time, a proper impedance‑matching selector, or a separate power amp for the second pair.

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