Tube preamp and McCormack DNA-500
Most tube preamps will do a fine job with the DNA-500 - you just have to watch out for the few that won't. Check the output impedance spec of any preamp you are considering - lower is better, at least in this regard. As long as your preamp has an output impedance spec of 800 Ohms or less, you should be fine.
First what have you been using before? In my knowlege there aren't too many tube preamps that are realy good for DNA500 which dictates the limited choice. Manley Shrimp seems to be a great match only if $1k is true for used. Not sure if this one will outperform your current setup if that is what you're aiming for with tubes. |
I also need 2 pairs of preamp outs. Keep in mind that most (though not all) preamps with two sets of output jacks simply jumper them together, at the connectors, just inside of the rear panel. A relatively small number of preamps provide separate buffer stages for the two outputs. That has two implications if you choose a preamp that does not have separate buffer stages for the two outputs: 1)The preamp will see a load impedance that represents the parallel combination of the input impedances of the two devices to which it is connected. The specifications for the DNA-500 indicate that its input impedance is 10K ohms. If the preamp were simultaneously connected to another 10K load, the combined load would be 5K, and you would want to have a preamp with an output impedance of no more than 400 ohms, to maintain the ratio Steve recommended of preamp output impedance to power amp input impedance. If the input impedances of the two loads are not equal to each other, they combine as the reciprocal of the sum of the reciprocals of the individual impedances. If there are exactly two loads present, that is the same as the product of the two values divided by their sum. So 10K in parallel with 25K, for example, would yield a combined impedance of about 7.14K, which would mean that the maximum preamp output impedance that would be consistent with Steve's recommendation would be 800*(7.14/10) = 571 ohms. 2)You could use a y-adapter cable in conjunction with a preamp that just has one set of outputs, and (assuming the cable is good quality, and connections are good), the results (and the required preamp output impedance) would be no different than using a preamp with two sets of outputs which are not separately buffered. Keep in mind, also, that running two sets of cables from the same preamp output buffer stage (whether via a y-adapter or from two sets of jacks that are connected together within the preamp) will double the cable capacitance that the preamp has to drive. If cable capacitance is too high in relation to the preamp output impedance, upper treble rolloff will result. Regards, -- Al |
