Tekton Double Impacts

Your question is of course a logical and very valid one. After thinking about it a little, I believe I can explain how the 1 watt MicroZOTL amp can drive the DI to levels in the vicinity of 100 db at the listening position.

Three things need to be considered: Output impedance, current capability, and power capability.

I’ll mention first that the amp is rated, somewhat counter-intuitively for a tube amp, to be able to deliver more power into 4 ohms (1 watt) than into a higher impedance (0.5 watts into 14 ohms). And its output impedance is specified as a usefully low 2 ohms. How is that possible with a 6SN7, which like just about any small signal tube operates under relatively high voltage/low current/high impedance conditions? The key to the answer is that the ZOTL amps are not true OTLs in the traditional sense. As I know you’ll recall from discussions in other threads here, between the output tube and the output terminals of the amp is a transformer that operates at RF (not audio) frequencies, as well as some solid state switching devices. That circuit converts the high voltage/low current/high impedance condition under which the tube operates to a much lower voltage/higher current/lower impedance condition, while presumably being efficient enough to not sacrifice a significant amount of power in the process. (For a resistive load power = voltage x current, and when a transformer transforms voltage and current the product of the two cannot increase, since it is a passive device).

So that takes care of output impedance and current capability. Regarding the 1 watt power capability of the amp:

The speaker is rated to produce an SPL of 98.82 db at 1 meter for an input of 2.83 volts. Let’s call it 99 db. 2.83 volts into 4 ohms corresponds to 2 watts. So the 99 db becomes 96 db for a 1 watt input. Assuming that falls off with increasing distance at a rate of 6 db per doubling of distance, which is typical for non-planar speakers, at a typical listening distance of say 10 or 12 feet the 96 db would be reduced to about 86 db. If both of the speakers that are present are supplied with 1 watt, the overall acoustic power that is radiated into the room would increase by 3 db, relative to the output of a single speaker, but the increase would approach 6 db if the listener is approximately centered. That brings us to 92 db. “Room gain,” i.e., the effects of reflected energy in the room, would conceivably add something like 3 db or so. That brings us to 95 db. And probably another few db would be added as a result of some combination of dynamic headroom, conservatism in the 1 watt spec, and a small amount of clipping that would not be perceivable as such. Voila!

Best regards,

-- Al