Cdc, OTL is an acronym for "Output Transformer-Less". It refers only to tube amps, because SS amps don't need an output transformer. The output transformer's role is to impedance-couple the inherently high output impedance of a tube, to the relatively low impedance load of a speaker. If the impedance of a speaker is below the output impedance of the amp, the amp will typically become unstable. OTL amps eliminate the transformer by running a number of output tubes in parallel, thus lowering the output impedance of the amp. This eliminates the output transformers, and any of the negative effects that the transformer may have on the sonic quality, especially at the frequency extremes. But, the additional output tubes in parallel make some problems of their own, notably the fact that they usually end up with a higher output impedance than their transformer-coupled counterparts. This makes them better performers with higher impedance loads like 16 ohm speakers, because of the damping factor.
