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Tube Amps, Magnapans and Impedance

I have tubed monoblocks running in class A with the output transformers rated at 8 ohms. They are driving Magnapan 3.7s which are rated at 4 ohms. Before I bought them I called Magnapan to get the frequency curve for their speakers. The engineer advised me that they are nominally rated at 4 ohms, the lowest load they present at their lowest frequency, but the frequency curve was essentially flat at 6-8 ohms throughout the audible range. The curve he faxed was satisfactory and I have been running them this way since new.

The reason for this thread is: A friend brought over his friend for a visit and listen. When the subject of tubes and planars arose and the impedance ’mismatch’ was discussed, he stated I was missing out by not having a 4 ohm amp. I tried to alleviate his concern with the above to no avail. I stipulated that it is good electrical practice to match the load to the amp but in my case a 6-8 ohm load across the band with tubed monoblock running in class A at 8 ohms was not significantly audible if at all to justify altering the transformers. I just didn’t bother after listening.

My question to my fellow audiophiles, particularly those who have tubed amps running at 8 ohms into loads between 6-8 ohms - Magnapans being the best - what are your thoughts on the subject?

In my experience it would take a speaker with a 4 ohm rating in the midrange where the music lives to really affect the performance with an anemic amp. Anemic bass and washed out mids are sure signs of an amp struggling with its load - which I do not have. My Magnapans sing from the very bottom of their range to the top. The human voice is especially seductive.

I think he had a case of ’wish I had a system like this’ blues. I think there is a term for that. Thoughts are appreciated.
keesue

Showing 1 response by erik_squires

erik_squires
16,808 posts
 
I think there are a lot of things besides amp/impedance matching that goes into our enjoyment, or lack of, a combination. The closest I could find were these measurements from Stereophile:

https://www.stereophile.com/content/magnepan-magneplanar-mg36r-loudspeaker-measurements

Speaking only about impedance matching, a speaker like this may have a slightly depressed mid-treble with a high output impedance amplifier. Is that bad? Well, depends on your room a great deal. You might have already tuned the room to compensate by making it less absorptive than you would have otherwise. Another thing to keep in mind is the amplifier’s output impedance. It may very well be complementary to the speaker’s and cancel out, or be a lot less reactive than you think.

With an ESL however, with an impedance curve that goes straight down, a solid state amp can really ensure you aren’t completely missing out on the treble.  My point here is that Maggies and ESLs are different beast and if you are happy don't let impedance curves make you unhappy alone.  ESL's however tend to be really good candidates for SS amps, but yes, there are exceptions.

So, no, changing is not a must. It will probably give you a different presentation and your judgement will tell better than armchair guessing based on the impedance curve of the speaker alone.
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