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Output Impadence for Musical Design SP-2B

I want to know if anyone can tell me the output impadence for the Musical Design SP-2B linestage. I recently purchased this tube preamp used and would like to know the output impadence so that I can have an idea as to which power amps it can work with. I have e-mailed Musical Design but they haven't gotten back to me so I figured I'll throw this question up in the air for someone to help me out with. Thanks
speedracerucr
brokenarrow
3 posts
 
If my (long-term) memory is correct, I think that Musical Concepts/Design was using the 6922 in an SRPP configuration (which would make sense since they advertise the SP-2B as "single-stage no feedback" circuit). Now IF that is still the case, then the output impedance of that circuit is 1/2 of the tube's rp. The rp of a 6922 is around 4-5000 ohms (correct ??), so your answer is 2K to 2.5K. But ***please*** confirm this with Mr. Hillig.
(If my facts & figures are incorrect, anyone feel free to correct me!)
Enjoy your new linestage!
speedracerucr OP
16 posts
 
If that is indeed the case (2-2.5K Ohms for the SP-2B), what input impedance should I look for in an amplifier inorder to avoid the problems associated wtih impedance mismatch? In addition, is it a good or bad idea to mix tube pre with SS power? Thanks.
ocean_7
3 posts
 
The input impedance of the amplifier should be equal to or higher than the output impedance of the preamp. Since paractically it is impossible to match the input and output impedance exactly, all you have to do is to be mindful that the amplifier's input impedance is higher than the output impedance of the preamp. This will be true for both SS and tube amplifiers fed by a tube preamp. So, it really will not be a mismatch to use a SS amp which has a higher imput impedance than the SP-2B.
speedracerucr OP
16 posts
 
Brokenarrow,
You are right on with your description of the SP-2B. Jonh Hillig of Musical Design wrote back with pretty much the same info. Here is his e-mail reply in case anyone else needs the same info:

"The figure is around 2K Ohms. We have used this preamp in a wide range of set-ups including driving two of our own amps at some audio shows. That's a 12k load. It works extremely well with a wide variety of power amps."

Now, that is good and all, but I don't understand how the SP-2B with 2K Ohms output impedance can drive amps with input impedance of 12K ohms. That deosn't fit into the 1:10 minimum ratio that I have been reading about in other posts regarding impedance matching. If anyone else can enlighten me on the matter, it would be much appreciated.
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