2. amps-preamps
  3. 1268945799

Impendance taps setting on a tube amp

I have decided to try out the Rouge Audio Cronus Magnum integrated amp before I upgrade my speakers. Reading a Cronus review, I understand that the amp comes factory wired to the 8 Ohms taps. To switch to the 4 Ohms setting you actually have to remove the cover and fiddle with the wires a little. The 6-Moons reviewer suggested requesting that the amp be wired to match the owner's speakers' impedance to avoid having to do it yourself.

I currently have the Totem Hawks speakers, which have a nominal impedance of 6 ohms. Here's a quote I got from Totem: "The Hawk exhibits a nominal 6 ohm impedance that is very constant throughout the ban. The minimum is 5.2 ohms."

Given this information, what would be the optimal setting: 4 or 8 Ohms? Should I try both and see what works best? That's pretty much what RA recommended, but I wanted to see what others think or perhaps faced a similar dilemma.

Thank you.
actusreus

Showing 3 responses by pubul57

pubul57
3,712 posts
 
If you have enoough power with the 4ohm tap (why you have to listen)I think there is every reason to beleive the amp will be more linear, have lower distortion, and drive the speakers more easily. This concept of "light loading" using the tap lower than the nominal impedance has been discussed my Roger Modjeski of Music Reference in several places. It sure hold true with my Music Reference RM10 and RM9SE amps. An added bonus is that you tube life should be longer.
pubul57
3,712 posts
 
As Roger Modjeski explained it to me, the tubes don't work as hard driving an 8 ohm load from the amp's 4ohm tap as they do from the 8 ohm tap - they last longer because they are not working as hard. You lose 20% of the power with this configuration, so my 160 watt (8 ohm tap into 8 ohm load) Music Reference RM9 feeding my 8 ohm Merlins, only put out 128 watts from the 4 ohm tap into that load. If you google Roger Modjeski and Light Loading, you should find the info, it is also discussed in the 6moons review of the RM10 MKII.
pubul57
3,712 posts
 
From Roger M:

"The RM-10 is very tolerant of short circuits and will not be damaged by them." "The amplifier is flat within 0.1dB and has low distortion of 0.3% when played below clipping on average level material." "At the recommended bias current of 30mA/pair, the idling dissipation is nine watts or 75% of the tubes' rating. I estimate tube life to be 5,000 to 10,000 hours. Although higher idling currents will reduce distortion, it can also be reduced by light loading. Basically, light loading reduces the output current demand on the output tubes, allowing them to be more linear. It also reduces noise, raises damping factor, reduces distortion by 78% and allows for 80% more peak current when needed. The only loss is about 20% of the power rating or 1dB."
More to discover