8 ohm amp with 4 ohm switch

natman

New Member
Back in the old days 4 ohm home speakers were common and most amps could handle at least one set of 4 ohm speakers.

Now my HT receiver normally requires 8 ohm speakers, but it has a switch that has to be set to allow use of 4 ohm speakers. How does this switch work? What happens when it is set to 4 ohms?
 
Basically it switches to a lower voltage secondary winding on the power transformer. 8 Ohm loads need more voltage and less current and 4 Ohm loads need less voltage and more current. Keeps the SOA, safe operating area, of the output transistors in check in cost effective designs.

Craig
 
Back in the old days 4 ohm home speakers were common and most amps could handle at least one set of 4 ohm speakers.

Now my HT receiver normally requires 8 ohm speakers, but it has a switch that has to be set to allow use of 4 ohm speakers. How does this switch work? What happens when it is set to 4 ohms?
When you do some looking, most will recommend leaving the switch in the 8ohm position regardless of the nominal impedance of the speakers. Switching just neuters the amp for UL listing.

YMMV
 
I don't know much about HT receivers to know how the switch works, but in an MCS 3125 receiver, the 4/8 ohm switch just changes the sensitivity of the clipping light.
 
When you do some looking, most will recommend leaving the switch in the 8ohm position regardless of the nominal impedance of the speakers. Switching just neuters the amp for UL listing.

YMMV
Well, here's what my Denon manual says, verbatim:
Carry out the following settings when using a speaker with an impedance of 4 – 6
Ω/ohms.
1. Press and hold the main unit’s < and > at the same time for at least 3 seconds.
“zVideo Format <NTSC>” appears on the display.
2. Press [down] on the main unit three times.
“zSp. Impedance <8ohms>” appears on the display.
3. Use < or > on the main unit to select the impedance.
8ohms (Default): Select when the impedance for all of the
connected speakers is 8 Ω/ohms or over.
6ohms: Select when the impedance for any of the
connected speakers is 6 Ω/ohms.
4ohms: Select when the impedance for any of the
connected speakers is 4 Ω/ohms.
4. Press the main unit’s ENTER to complete the setting.
 
Well, here's what my Denon manual says, verbatim:
Carry out the following settings when using a speaker with an impedance of 4 – 6
Ω/ohms.
1. Press and hold the main unit’s < and > at the same time for at least 3 seconds.
“zVideo Format <NTSC>” appears on the display.
2. Press [down] on the main unit three times.
“zSp. Impedance <8ohms>” appears on the display.
3. Use < or > on the main unit to select the impedance.
8ohms (Default): Select when the impedance for all of the
connected speakers is 8 Ω/ohms or over.
6ohms: Select when the impedance for any of the
connected speakers is 6 Ω/ohms.
4ohms: Select when the impedance for any of the
connected speakers is 4 Ω/ohms.
4. Press the main unit’s ENTER to complete the setting.
uhmmm. OK


Have you done a search on this issue to find other opinions than mine? Just type your query into google search w/forum at the end.
 
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