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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
rleff
1,065 posts
 
I agree with Philjolet you should try both to see which you prefer.
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.
4est
507 posts
 
Pubul57-
How could the tube life be longer by switching taps. FWIW, I feel all amps should have access to the taps on the outside of the amp.
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.
atmasphere's avatar
atmasphere
11,760 posts
 
The transformer transforms the 4 ohm impedance to the higher impedance that the tubes have to drive. If you load the 4 ohm tap with 6 ohms, the impedance that the tubes see plate to plate will also go up. You will get slightly less power, but the tubes will make less distortion. OTOH, the transformer will not be loaded quite right and so will ring (distort) a bit more. So you get 6 of one/half dozen of the other. It will not hurt the amp.

Bottom line is you just have to try it. I can't think of a good reason to not have the taps available on the outside of the amp. The last thing a manufacturer wants is for the customer to have to open up the unit and mess with it!
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