Re: Questions on impedance matching


Ted Rook
 

My understanding of tube amps with output transformers is that the transformer is designed
with care so that the output impedance is as low as possible for the same reason that this is
desired in solid state amplifiers, to minimize frequency response errors that arise due to the
varying value of load impedance found in common dynamic loudspeakers. The output
transformer cannot achieve the very low values of impedance common with solid state
amplifiers and values seem to vary considerably from design to design. Here is an example
of a main-stream tube amplifier whose output impedances were measured for review

https://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measure
ments

The values found are a long way from the values that would be needed to "match" the load
impedance presented by the loudspeaker and I believe this is normal for tube amplifiers.

Ted

On 13 Feb 2018 at 16:30, esmondpitt wrote:

It's been stated a few times here that audio power amplifiers do not impedance-match. This
is true of solid-state amplifiers, but valve (tube) amplifiers impedance-match from the valve to
the output transformer primary and again from the secondary to the speaker load.

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