erik2a3
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Good morning, raduscha
That 2.7k resistor on the input to them12AU7 is in a position thatmis sometimes referred to as a 'grid stop' or grid suppressor resistor. These are also sometimes used in the output stage. Common values are in the range of say 1k to 10k ohms or so. There usual function is totally unrelated to gain issues. They are are used to help sort of 'calm' a circuit that may otherwise exhibit high frequency parasitic oscillation. Almost all of my amps use them. My Moth Audio si2a3, which we purchsed in the form of a chassis, schematic, and box of parts, uses just such a resistor on the input stage. In this case it's a common carbon comp resistor where the one on the mini torii is a metal film.
In any event, the output impedance of your DAC is a little high-ish, but not extraordinarily so. The 100k of the mini torii should be well within a suitable range for it in terms of impedance matching. Fireblade is right, however, that the higher gain 12At7 can effect this to an extent, but you aren't using that tube. An impedance buffer could be used, I suppose, and you might try it for curiosity, but you may or may not be interested in adding additional circuitry.
Truly, the common cure for this situation are the in-line attenuators I mentioned above. I am very picky about what I hear in terms of wanting good detail with requisite bite to the music, and I did not find the attenuators to roll off high frequencie, to cause noise, or anything else. They just bumped the signal down a bit.
Another part of this we haven't talked about yet has to do with the sensitivity of your speakers. Sensitivity and efficiency are not the same thing thing, which is why an input voltage spec in the range of a bit over two volts (sensitivity) is listed in conjunction with the efficiency rating (dBs with 1 watt at a meter). Based on your description, your speakers likely have a very simple, low order crossover, such as a 6dB per octave slope, which in a two way system consists of only two elements: a capacitor in the high pass to the tweeter and an inductor in the low pass to the woofer/mid bass driver. If this is the case, a low order network like this presents a low insertion loss to the signal from the amplifier, which means that things will get loud more quickly than they would with a more complex network. More sensitive still, are single driver, crossoverless systems like Lowthers, Fostex, etc. the MT sounds beautiful with our 15 ohm crossoverless lowthers, but the mini torii is a better match for the equally efficient Klipsch La Scalas -- an extremely fine match, actually, and I spent a long time listening to this combination yesterday. I also tried a 12at7 as the driver, and in our second listening space it proved to offer some real excitement. The 12au7 is far better for headphones, however....
Please let us know how things progress!
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