A/V Receiver Impedance Selector Switch

[paveldeg]

Nothing has changed is latest gen amp sections of D&M AVRs in terms oh how the impedance switch works. I also have direct access to the head of engineering Denon Japan and he has confirmed my findings. Be careful what you read on forums from end users that don't have the knowledge on amplifier design.

OK, thanks. I'm just shocked that "head of engineering Denon Japan" basically confirmed that they screwed up their design, instead of keeping power same across all impedances they reduced output power for 4 ohm loads. So much for Japan engineering I guess, hope they proud of it.

 

[gene]

OK, thanks. I'm just shocked that "head of engineering Denon Japan" basically confirmed that they screwed up their design, instead of keeping power same across all impedances they reduced output power for 4 ohm loads. So much for Japan engineering I guess, hope they proud of it.

The switch is there for one reason only, UL certification for 4 ohms with all channels driven. All Japanese AV receivers function similarly. One Yamaha i measured in the past did deliver same power in 4 ohms in low setting as 8 ohms in high setting but again it's limiting your power. Yamaha already has a lot of nannies built in to ensure the amp doesn't fail without having to step down the voltage via the switch.

 

[everettT]

So, any actual technical explanation from you including schematics, besides insulting everybody who is so "mistaken" from your point of view?
I do trust Gene's measurement, but they are mostly for Yamahas, and speaking from common sense perspective - cutting output power for 4 ohm loads does not make much technical sense, the power should be same as for 8 ohms to avoid overheating, so voltage can be limited, but since amperage is higher for 4 ohms loads output power should stay same.
If it's not the case with Yamahas it's just means poor design, nothing else, it's unlikely to be same for all other AVRs.

This horse has been beaten so much I'm shocked manufacturers still offer it. If you wanna limit your amplifier section, go for it, most just purchase an appropriate product.

 

[Trebdp83]

 

[PENG]

"When using 4 ohm speakers you draw twice the current from the amp. Voltage times ampere are watt and at 4 ohm you will only need half the voltage to produce the same watt as compared to double the voltage using 8 ohm speakers. When the voltage is dropped from the power supply when selecting a 4 ohm setting it has to drop to half voltage to produce the same watt from a 4 ohm speaker as in a 8 ohm setting using 8 ohm speakers, but it is only reduced some 35% so it will be more power available in the 4 ohm setting when using 4 ohm speakers. When using 6 ohm speakers in the 4 ohm setting it will produce the same watt as in 8 ohm setting and 8 ohm speakers.

That does not sound logical! If you reduce the voltage by 35%, you will get less current and therefore less "power" whether the load impedance is 8 ohms or 4 ohms.

So in reality the only important thing that change with the speaker impedance setting are how the protection circuit operates

."

That could be the case, but in the case of your AVR-X3700H, it is obvious that impedance setting of 4 ohms will limit current, and power naturally, again regardless of 8 or 4 ohms.

Denon x3700H Impedance Setting - Different Impedance...

www.avsforum.com

Those guys seemed to know their math, but also seemed like they are a little confused, making it hard to follow their thoughts.

So essentially in Denons switching to 4 ohm stops protection triggering too early, and allows thus producing more power for 4 ohm speakers.

Again, that could be possible in theory, but bench tests after bench tests show that it is not the case, so setting to 4 ohms will limit "power" severely, but if you don't need that much power then of course you will be fine, or more than fine, using the low setting.

If you are experiencing performance issues in your specific use case, then I would suggest you investigate further, as there could be other reasons. To be clear, if the poorer performance you mentioned, such as weaker bass, was due to protection triggering too early, then you will know because Denon's protection scheme will trip the unit, not just limiting the current and continue to operate that way. Some recent Onkyo models might (not 100% sure) in fact do what you described but certainly not Denon's X3700H.

 

[TLS Guy]

The switch is there for one reason only, UL certification for 4 ohms with all channels driven. All Japanese AV receivers function similarly. One Yamaha i measured in the past did deliver same power in 4 ohms in low setting as 8 ohms in high setting but again it's limiting your power. Yamaha already has a lot of nannies built in to ensure the amp doesn't fail without having to step down the voltage via the switch.

Gene, you need one more line on the questionnaire: - I don't have an impedance selector switch and don't need one.

This whole issue is just testimony to the idiocy of the multichannel receiver concept. Not surprising that Denon/Marantz may be on the "chopping block".

 

[PENG]

This horse has been beaten so much I'm shocked manufacturers still offer it. If you wanna limit your amplifier section, go for it, most just purchase an appropriate product.

He has a point (you are being fair, that the horse isn't completely dead as it was still sort of still moving a little while the beating continues), just that it is not the case with his X3700H. ASR's recent test on an Onkyo (iirc only, could have been a Pioneer clone) might do something like how described about the "protection" though there has not been enough info to really confirm that, but it could have been something similar though not the same.