Pre-Out Splitting

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How many splits on the pre-out line before any loss of signal quality, poor frequency response or any other ill effects happen??

Here is the situation.... Pre-amp has only 1 pre-out line and want to hook up more than 1 power amp. Specifically 2 amps and 1 powered subwoofer.... so in essence 3 parrallelled connections on the pre-out line. Obviously the source signal level and the output and input impedances are factors so here are some specs:

Pre Amp Output Impedance 1v/10 ohms (distortion .002% 20Hz-20kHz, 1v) Signal to noise 105dB

2 Power Amps EACH having Input Sensitivity 1v impedance 25k ohms
1 Powered subwoofer unfortunately no specs (I'm assuming input impedances are typically high as to not load down)

Would appreciate any comments, thoughts, suggestions etc.
 
Thanks for the response Jan. I am very aware on how to do it and that you can even buy cables that do it... I have split line levels before... Y adapters work well :) how else would you do it? I guess I'm looking for more of a technical response and not "normally 2 or 3 times without problems" . "Normally" yes but based on what? As far as I know its based on source signal level, output/input impedances etc.

Also.... its a pretty simple splitting of the preamp preout into several amplifiers in order to drive several speaker sets...I don't think the single amp would appreciate the 1ohm load ;) so why would I use/need an active crossover? I'm not seperating frequencies or bi-wiring or any of that.
 
Ok then ;) You just didn't specify the use in your first post...

Your preamp will see the connected power amplifiers input impedances as parallel loads. So the more power your preamp can deliver, the less influence ...

However you also have to concider the caps in the input stage on the power amps. These will make a capacitive load that rises with the number of connected amps (parallel caps)

It's hard to predict when your signal will have suffer losses, as many factors are in play (total resistance load and capacitive load)

My best guess is that it mostly depends on the output circuit of your preamp :)
 
Cheers Jan,

It seems instictively right to have less caps in the signal path but ........

In a bi-amped setup, is it better to keep the preamp (output) cap or keep the caps on each power amp?

I ask this because in both cases there would be the same number of caps in each signal path.

Regards,
Martin :)
 
funny, I was thinking about exactly this only yesterday. One concern I had - if you leave only the output coupling cap in the pre and connect both powers amps (minus their coupling caps) to its output are you not effectively directly connecting both power amps to each other? Could that cause problems?
 
Spev :D
My reply was to sonusthree..

To your post I can say, that yes you are connecting both power amps together, which means that the impedance seen from the pre will be lower.... If both power amps has an input impedance of 47K, the resulting impedance will be half 47K....
However a good pre has no problems driving loads down to 1K or lower (my pre can drive 50R)
;)
 
I think in essence I have answered my own question. The source signal level, preamp output impedance/sensitivity, pwr amp input impedance/sensitivity are the major factors here. Oh and I almost forgot... the cabling capacitance factors. Someone on another forum said a good rule of thumb concerning the impedance is as long as the load is 10X that of the output impedance there isn't a prob. So my preamp output impedance is 10ohms and pwr amps input impedance are 25k ohms (so preamp would see 12.5k). Cabling I wouldn't consider a factor cause its quality and the runs are very short. The input impedance of the powered sub I want to add is unknown but I think I will be well within the 10X load factor.
 
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