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In the Forum: Didital Things
In the Thread: Saying goodbye to the digital crossover.
Post Subject: Matching pre to multiple power ampsPosted by KLegind on: 1/30/2010
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 noviygera wrote:
Kris,

thanks. Here's what I have:

>>There is a caveat: The combined input impedance of the power amps must be at least 10 times the output impedance of the preamp. Otherwise the load will kill the sound of your playback.

I use a mixer as a pre-amp and it has two master outputs. (+6db 2V) is a switchable 6db gain for each output. I currently use the 0db setting.quoting specs from the manual:
"
Outputs Level/Minimum Load
MASTER (BAL) 0dBV/600Ω 1V (+6dB 2V)
MASTER (UNBAL) 0dBV/2.2kΩ 1V (+6dB 2V)
"

not sure what "minimum load" means.

and my three amps have the following input impedance:
Jeff Rowland has selectable: 100k, 20k, 600 ohms
Arcam Alpha 5 - "unknown" but can measure

Spectron 1KW - will need to measure

>>BTW - what is your opinion of the delay capabilities of the DBX crossover?
I have not extensively (avoided) used the delay functionality. I had delayed the subs. The function works very well but I am not sure if it screws up the sound out not. I think it's good for subs. I have not used it for mids or highs, I aligned those channels physically.

-Herman


Hi Herman,

Lets say you have three amps 100 K input imp. - that presents a load of ~33 K . The equation is:
R(amps) = 1/(1/amp1)+(1/amp2)+(1/amp N)

So if we have JR=100k and Arcam=47k (might be lower) and Spectron=47k (pure guess work), R_total is 19k
This is fine if you are using the balanced output, but its a stretch with the unbalanced out. As always; listen first.

Now if the arcam or spectron unit is 10k the sound will most likely suffer.

Best
Kris

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