Cube Audio Nenuphar Single Driver Speaker (10 inch) TQWT Enclosure

Chris ( @cal3713 ) thanks for quoting my post from another thread in this one, where it is also relevant as you indicated.

@riaa_award_collectors_on_facebook, keep in mind that the majority of tube-based components having line-level outputs employ coupling capacitors at their outputs, which often cause their output impedance at deep bass frequencies to rise to **much** higher levels than the specified output impedance (which is usually based on a mid-range frequency such as 1 kHz). So in those cases the 10x ratio should be applied to the 20 Hz output impedance, if it is known. (If the component has been reviewed by Stereophile JA’s measurements will indicate that number).

If the 20 Hz output impedance is not known, and there is reason to believe that the tube-based component employs an output coupling capacitor as most of them do, I suggest applying a ratio of 50x to 75x to the specified output impedance. Some here have even suggested 100x.

Also, the minimum recommended load impedance ARC almost invariably recommends for their line stages and preamps is 20K, including for the Ref 10, even though its specified output impedance is 600 ohms balanced and 300 ohms single-ended. And for a few of their designs I’ve seen recommendations of "60K recommended, 20K minimum."

And just to cite one further example, the Herron phono stage which I use has a specified output impedance of 400 ohms, but its manual recommends a minimum load impedance of 50K "for optimum performance."  Although Keith Herron has indicated that 20K would usually be acceptable, in most systems.

Perusing JA’s past measurements of tube-based line-level components will reveal numerous other such examples.

Regards,
-- Al

Thanks Al.  I should have paid more attention in school :)  Somebody gave me that formula and told me the REF 10 and Bakoon would be fine. Thanks for stopping me from blowing up my gear!! LOL

Although I know RIAA's above comment is in jest, just to be clear for future readers... If you don't follow the 1/10th ratio rule, you will not get a flat amplification of the preamp signal with frequency aberrations in the bass response.

Also, it may be possible to modify the amplifier to address this issue (depending on amplifier design). My first watt f4s (simple class A without feedback) have a 47.5k input impedance, but can be modified to have a higher I.I. simply by changing out the resistor on the input.  I was informed that I could use anything up to 250k without changing the operation/sound of the amp. Doing so enabled me to use much smaller output caps on my Don Sachs 6sn7 preamp, and allowed me to afford some top end duelund's that greatly improved the sound. No idea if this is possible on the bakoon... but hopefully useful information regardless.

Having an outstanding tube line pre driving a 10k load is possible. I fact I had Don Sachs configure one output to drive a 10K load and one to drive the normal 100k load. Sounds fantastic!  Just takes a big ass high quality cap.

EnjoyTheMusic has a short news item on Aries Cerat and their new Ianus series of electronics:
www.enjoythemusic.com/news/0720/

Aries Cerat Ianus Series amplifiers is a showcase of the company's unique TriodeFet technology. After years of developing and refining their technologies, they are proud to introduce the TriodeFet technology, and a Series of amplifiers that implements this truly innovative technology. This technology is neither a hybrid topology (in the usual sense of a tube-driving solid-state stage type), nor a solid-state driving tube kind of stage. TriodeFet is a new way of using hollow and solid-state devices. The concept is to have a low voltage / high current active device, which had the linearity of a triode, and at same time would be able to source enough current to drive low impedance loads directly.

The TriodeFet, can be seen as a three terminal active element, just like a MOSFET or a triode. The company's breakthrough is that its transfer curves are identical of a true high quality triode, with the only differentiator from a true triode is that, the Y-axis (current) is in scaled in Amperes and not mA. What this means, is that you can design circuits that were never before possible either by using tubes or transistors. This new active element can be used to develop simple, very linear circuits, which are stable down to very low impedances, while the TriodeFet's inherent linearity is making the use of the problematic negative feedback redundant. New models within the Ianus Series include the Geminae (€110,000) Class A amplifier that produces 130 Watts @ 8 Ohm. Aries Cerat's Essentia (€39,000) is the little brother that produces 40 Watts @ 8 Ohms.