Possible impedance matching issue with subwoofer?

If you hook the sub up in parallel to the preamp you will go from an output to input impedance ratio of 94 to only 4. I feel that will certainly result in high frequency sparkle loss. You should look into a buffer between the preamp and sub for the line level inputs. The Musical Fidelity X10 v3 has a high input impedance around 400K that will mate well with your amp. I think the ratio would then be about 44:1 and certainly acceptable compared to 4. I am speaking from experience here, not just textbook. I noticed a definate drop in the highs when I hooked up my sub the same way without the buffer. These buffers don't cost that much. Just get one and try it both ways... you will hear a difference.

Koestner, I'm curious as to what preamp you were using. Perhaps it has an output impedance that rises in the upper treble region.

Also, what were the lengths of the cables to both the sub and the power amp, and what was their capacitance per unit length (or alternatively, what was their make and model)? As I mentioned earlier in the thread, the capacitance of the cable from preamp to sub, as well as the capacitance of the cable from preamp to power amp, can roll off the upper treble (as seen by the power amp) if it is high in relation to the preamp's output impedance.

Best regards,
-- Al

Koestner, I have only seen these placed between the preamp and cd or dac. Can it be placed between my preamp and sub amps and work fine?

I assume the second set of preamp outs go into the x10 inputs and then I output to the sub's plate amps right? Is this better or the same as placing the x10 between the cd player and pre? Will my preamps output impedance be lowered by placing the x10 between cd player and preamp? Lowered in the same way as placing it between the pre and subs......

Grannyring, the answers to the four questions in your last post are:

1)Yes
2)Yes
3)Different
4)No

Also, I would be cautious in extrapolating from the results a buffer provides in one system to the results it would provide in another system, unless there is a good understanding of the reasons for the improvements it provided in the first system.

Best regards,
-- Al

First off, I must say that Al definately knows more about electronics/stereos than me from my reading of these forums for so long. So with a bit of confusion I am asking - "Why aren't we seeing this the same way?" This is what I think:

A preamp to amp connection should have an impedance ratio of at least 40:1 from the amps input to the pre out. So if the OP's pre has an output impedance of 5K, and his amp has an input imp of 450K, then his ratio is 90:1

Now if he hooks up the sub using the 2nd line level output on his preamp and the sub has an input inp of only 20K, then the 20K and the 450K are seen to be in parallel by the preamp and thus the preamp is now seeing an input impedance of only 19K, and a ratio of 4.

Won't this cause rolloffs of the frequency lows and highs? It did when I hooked my passive preamp to my amp and sub by splitting the signals, but when I used a buffer to the sub it sounded much better through my mains.

I see this as a necessity for the OP to at least try as a ratio of 4:1 is a serious mismatch compare to his original value of 90.

Al, what are your thoughts here?