Tekton Double Impacts

Hi Charles,

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

Hi Al, 
Well, once you explain it that meticulously it does begin to make considerably more sense.  That RF transformer is doing some serious work 😊

My amazement is the 6SN7  is used in this manner so apparently effectively.  In my pre conditioned mind that tube is thought of as one of the iconic small signal tubes and not a device used to drive speakers (especially of the 4 ohm variety). Again,  fascinating. 
Charles 

@mac48025 ; @klh007 ; @corelli

If I go with the Herbies Audio 'Giant Threaded Stud Glider' product, do you recommend going 1/4" 20 in the 1/2 inch length so that the sliders are flush with the speaker base, or would you go with a slightly longer length to offer up some advantages...like elevation and angling, etc.?

I haven't looked underneath the speakers.... @mac480245: you mention that the bass leaks from the screw holes... if they are open ended I would not want to damage anything with a long screw.

If I do a hybrid approach and use the Soundcity Outrigger that @corelli recommends, do you feel that placing Herbies Giant Fat Gliders (not the screw in type) under the Soundcity auto leveling / rubber feet versions would offer further benefits in isolation / sound quality?

This approach (I think) allows me to easily move the speakers because of the gliders and provide (I think) the additional stability outriggers might bring vs going with the Herbie Threaded Gliders alone.

Thoughts?

Thanks!

Al,

youre a marvel. Thanks yet again for explaining something I couldn't previously conceive in a manner that I understand. 

Charles,

teajay mentioned he is using the holy grail of 6sn7 tubes. Maybe that accounts for him being able to drive the microZOTL to its extreme without any harsh results? Just a thought.

David,

I'm using the 1/4/20 giant gliders with 1 1/2 studs for greater lift off the carpeting and more distance for leveling as my basement floor isnt real level. No issues with the threaded studs entering the speaker cabinet.

david_ten

If you use the studded glider directly to the speaker, agree with mac at 1.5".  If you use the outriggers, the steel is 1/4" and you would need another 1/4" for a brass acorn nut/washer on the top of the outrigger and then another 1/4" to adjust for uneven flooring, then the jam nut---so you will need the 1"  1/4-20 glider.  Also, I opted for the knobs from soundocity--they are only $3 each and look nicer than the acorn nut.
I attached the outriggers with hexhead SS bolts/washers, 1 1/4 length 1/4-20.
Either way ought to work well.  I would keep the speakers vertical.  Not a fan of self leveling footers.  Way to much wobble for me.  I'm a believer in a solid/stable footing for speakers to avoid "micro wobble" induced by the woofers which in my mind might slightly add some element of haze.  But I'll be the first to admit I have not spent hours, days, or weeks comparing all the many options out there.