How to split pre out to connect power amp and sub

I am going to be purchasing a preamp (CJ Premier 10) with one pair of outputs. If I have two active subwoofers that I can connect mono (one run to each), am I okay splitting the signal at the Premier 10 with y-adapters at each terminal, one in each pair (channel) going to amplifier, and the other going to a [powered] subwoofer? Will this result in a signal quality loss? Can I split again to make it a three way split? Thanks for your help!

Solst1ce -- As I indicated above, whether or not doing that results in sonic degradation would depend on whether the combined input impedances of the sub and the power amp (and the third device, if you choose to split three ways) remains much larger than the output impedance of the preamp.

Also, keep in mind that the cable capacitance which the preamp would have to drive is the sum of the capacitances of the two (or three) cables that would be connected to each channel. That could become a significant factor if preamp output impedance is high and cable capacitance per unit length is high (e.g., 100 picofarads per foot) and cable lengths are long (e.g. 20 feet each). So I would suggest using low capacitance cables (e.g., less than 40 or 50 pf/ft, especially if the run lengths are long). Otherwise, upper treble rolloff may result.

In your case, I suspect that you'll be ok in all of these respects. I found the following statement at the CJ website about the Premier 10:

The audio circuit of the Premier Ten consists of a single triode amplifier direct coupled to a triode cathode follower. The low output impedance of the cathode follower permits the use of the Premier Ten with highly capacitive amplifier interconnect cables without attenuation of the high frequency information.

BTW, to calculate the combined impedance of three loads in parallel, calculate the combined impedance of two of them as I described above (product divided by sum), then calculate the product divided by the sum of that result with the third impedance. Or, alternatively, the impedance of the parallel combination of three loads is the reciprocal of the sum of the reciprocals of the three input impedances.

Regards,
-- Al

Hello Almarg,

Thanks for the reply !

Gosh ! Though I knew tube amps should never be run without speakers, I must say I didn't even think about this issue !! Damn..

Is it not enough to run the sub or is it not considered as a speaker ? If that's the case, how do you normally use the preout then ?

I'm even more confused now..

Yes, my sub has separate left and right channel inputs.

I'll look into the non-inductive resistor you mentionned.

Resistor :

I googled your advice and I came upon a picture of the resistor. I would never thought it was that complicated just to give more punch to the Shanling...

How do you plug these things ? Do you need wire and does it fit in just like that ?

Sorry if my questions sound dumb, but it's getting way above my head !

Is it not enough to run the sub or is it not considered as a speaker ? If that's the case, how do you normally use the preout then ?

What is important to avoid the possibility of damage that I described is that the speaker outputs of the MC-30 (which are the outputs of its power amplifier section) should be connected to a load that is in the range of typical speaker impedances, such as 8 ohms. Whether or not a sub or anything else is connected to the outputs of the preamp section of the MC-30 is not relevant to that issue.

I suppose it's possible that the MC-30 has some special provisions in its design to avoid the possibility of damage if its pre-outs are connected to a separate power amplifier and its own power amplifier outputs are left unconnected. But I definitely would not count on it without seeing some clear indication in some literature that that is the case. Add the resistors, and you'll have no problem!

As far as the sonic effects of sending the pre-out signals to both the sub and the separate power amp are concerned, unfortunately the MC-30 has a fairly high output impedance of between 1,000 and 1,300 ohms (1K to 1.3K), as indicated in this review:

http://stereophile.com/integratedamps/308shan/index4.html

But fortunately the Prima Luna Prologue Five has a very high input impedance of 100K, which is a negligible load in relation to the 1K output impedance of the pre-outs. The input impedance of the sub doesn't appear to be specified, looking at its description on the ScanDyna website, but I suspect that you'll be fine because the very high input impedance of the Prima Luna means that from an impedance standpoint the pre-outs are essentially just driving the sub.

You might want to email ScanDyna, though, and ask them what the sub's input impedance is. I would say that if the answer is 20K or more, you'll be fine, and even 10K might be acceptable sonically.

In view of the high output impedance of the MC-30, though, do try to minimize cable length and cable capacitance, or upper treble rolloff may result. That applies to both connections, the one to the sub and the one to the power amp. High capacitance on the interconnects to the sub will affect the signals to the main power amp just as much as high capacitance on the interconnects to the main power amp.

Based on a quick calculation I just did, I would say that if your interconnect cables are of average capacitance (say 30 to 50 picofarads per foot), try to keep the total length of the runs to the power amp and the sub to less than about 15 or 20 feet (for example, 6 feet to power amp, 10 feet to sub, for each channel). If the runs will be longer than that, get interconnect cables that have especially low capacitance, such as these from Blue Jeans:

http://www.bluejeanscable.com/store/audio/index.htm

Hope that helps,
-- Al