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Old 13th July 2007, 05:16 AM   #1
Bigred is offline Bigred  Canada
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Default Pre-Out Splitting

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.
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Old 13th July 2007, 06:32 AM   #2
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Shouldn't you use an active crossover ??

Normally you can split the preamp output into two or three without problems - you kan even by cables that do it !
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Old 13th July 2007, 07:34 AM   #3
Bigred is offline Bigred  Canada
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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.
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Old 13th July 2007, 07:45 AM   #4
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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
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Old 13th July 2007, 02:26 PM   #5
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Hi,
Would it sound better if we elimated the input caps on each amp and use only one on the output of the pre-amp itself?

Regards,
Martin
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Old 13th July 2007, 02:33 PM   #6
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I should think so

The pre out cap takes care of the DC, so removing the input DC caps of the power amps meens fewer caps in the signal path
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Old 13th July 2007, 02:46 PM   #7
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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
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Old 13th July 2007, 02:53 PM   #8
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I canīt see any difference, as I don't think it has any influence at what end the cap is fitted

More important is to select a good cap quality
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Old 13th July 2007, 03:20 PM   #9
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OK, I just thought that the pre-amp would 'see' double the capacitance if the two power amp caps were left in place because they are in parallel.

Actually, I dont even know if this matters.

Regards,
Martin
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Old 13th July 2007, 03:24 PM   #10
Spev is offline Spev  United Kingdom
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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?
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