I'm happy with dkfan9's explanation that setting impedance to "6 ohm min" will protect your amplifier.
Well, I do not see a problem with 4 ohm front L/R speakers with the UK/European version of the RX-V681. Set it to 6 Ohms. The power supply will not allow the stated output when all channels are driven. The Amp could run hotter. Protection may kick in. Use it with care.
How your speaker combination will sound is a different question.
From the RX-V681 manual:
Caution
• Under its default settings, the unit is configured for 8-ohm speakers. When connecting 6-ohm speakers, set the unit’s speaker impedance to “6 Ω MIN”. In this case, you can also use 4-ohm speakers as the front speakers
[RX-V681]
(1 kHz, 0.9% THD, 8 Ω)
Front L/R ............................................................................... 125 W/ch
Center ................................................................................... 125 W/ch
Surround L/R ........................................................................ 125 W/ch
Surround Back L/R ............................................................... 125 W/ch
(1 kHz, 0.9% THD, 4 Ω)
Front L/R [U.K. and Europe models].................................... 150 W/ch
[RX-V681]
Front L/R............................................................................ 150 W/ch
Center ................................................................................ 150 W/ch
Surround L/R ..................................................................... 150 W/ch
Surround Back L/R ............................................................ 150 W/ch
• Dynamic Power (IHF)
Front L/R (8/6/4/2 Ω) ............................................130/170/195/240
How your speaker combination will sound is a different question.
From the RX-V681 manual:
Caution
• Under its default settings, the unit is configured for 8-ohm speakers. When connecting 6-ohm speakers, set the unit’s speaker impedance to “6 Ω MIN”. In this case, you can also use 4-ohm speakers as the front speakers
[RX-V681]
(1 kHz, 0.9% THD, 8 Ω)
Front L/R ............................................................................... 125 W/ch
Center ................................................................................... 125 W/ch
Surround L/R ........................................................................ 125 W/ch
Surround Back L/R ............................................................... 125 W/ch
(1 kHz, 0.9% THD, 4 Ω)
Front L/R [U.K. and Europe models].................................... 150 W/ch
[RX-V681]
Front L/R............................................................................ 150 W/ch
Center ................................................................................ 150 W/ch
Surround L/R ..................................................................... 150 W/ch
Surround Back L/R ............................................................ 150 W/ch
• Dynamic Power (IHF)
Front L/R (8/6/4/2 Ω) ............................................130/170/195/240
Last edited:
Review with measurements: https://audio-com-pl.translate.goog...l=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
Service manual: https://www.hifiengine.com/manual_library/yamaha/rx-v681.shtml