Amp & Speaker matching

Looking at the manual, it appears that there is only one output tap, which is stated to be optimized for 5 ohms, consistent with the comment by Rrog.

My GUESS is that using a 16 ohm speaker on an output tap that is optimized to work into a 5 ohm load does not represent a disparity that is large enough to cause amplifier damage, that can result from "inductive kickback" if a reasonable load is not connected to a tube amp that has an output transformer.

However, Hifitime and Ghostrider are correct that power output will be reduced. The amount of reduction will depend on the feedback setting you use and your choice of UL or triode mode (since both of those things affect the amplifier's output impedance), and the impedance of the speaker. On a percentage basis, the worst case reduction will probably occur where output impedance is lowest, which in this case is 1.28 ohms occurring for the maximum feedback and triode mode settings. According to my calculations the corresponding reduction into a 16 ohm load may be as much as approximately 3.75 db. That represents a loss of more than half of the amp's power capability, compared to a 5 ohm load driven with those settings.

Sonics may also be adversely affected by the mismatched loading of both the output transformer and the output tubes. Ringing may occur in the transformer, at least to a small degree, and the distortion performance of the output tubes may not be optimal.

As has been said above, high speaker impedances can certainly be advantageous, but not if the impedance is severely mismatched to what the amplifier is designed to drive.

All of that said, though, touching base with Manley as suggested earlier would certainly seem to be in order.

Regards,
-- Al

Depending on the design - if you don't mind a slight reduction in power, using the output taps lower than the impedance of your speakers can be beneficial in some cases. Presently I prefer the 4 ohm tap over the 8 in my system where the spkrs impedance ranges from 8-10 ohm. The difference is easily heard. I've heard it go both ways w/several different tube amps w/my speakers.

In the case of my current amp, Roger Modjeski/Music Reference, the designer in his own words, "Although higher idling current 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, and allows for more peak current when needed. The only loss is about 20% of the power rating or 1 dB."

The only loss is about 20% of the power rating or 1 dB

Hi Pehare,

That may be true for some of Roger's amps, but it is by no means true as a general rule. As I indicated earlier, the amount of power loss is dependent on the output impedance of the amplifier, on the degree of light loading (i.e., the relation between the impedance of the speaker and the load impedance that the output tap is optimized for), and on other amplifier-dependent variables.

On a percentage basis, the power reduction resulting from light-loading an amplifier having an output impedance of 1 or 2 or 3 ohms or so, such as the Mahi, is likely to be much greater than it would be, for example, with some SET amps that may have output impedances of perhaps 4 to 8 ohms or more.

Best regards,
-- Al

Hi Al,
I agree that the "light loading" principle is likely to yield varied results and is amp dependent. For example my amplifier has an 8 and 16 ohm speaker tap. My speaker is 14 ohm nominal load and 10 ohm minimum. Without question the sound is better at the 16 ohm tap rather than the 8 ohm. Simply put all music reproduction parameters are just better.I understand that the Music Reference amplifiers could be a different situation and thus benefit from the light load appraoch.If there`s loss of power it unnoticeable, the sound is actually more transparent/open, dynamic,with increase scale, fluidity and flow.
Regards,