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Old 1st October 2003, 12:49 AM   #1
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Default Dual outputs for Balanced Line Stage Preamp

What would be the consequences on performance of the Balanced Line Stage Preamp if one were to run two sets of outputs in parallel? Say, one to a main power amp like the ZenV4, and a second to a powered subwoofer. The article says that the preamp can drive low impedance loads (like 600 ohm) with no decrement in performance, except gain. Can one infer that (given most components input impedance) one could therefore drive two devices in parallel, as described above? I have two outputs on my old Jung modified Dyna Pat-5, and it seems to work driving the amp/powered subwoofer configuration. I would like to scrap the Pat 5 and do the same trick with the BLS, when it is done.

Also, what if the main amp were run balanced (e.g., the Pass A-75). Could one simultaneously drive the subamp in unbalanced mode somehow?

Larry Wright
Seattle area
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Old 1st October 2003, 01:44 AM   #2
lgreen is offline lgreen  United States
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Default dont see why not

I don't see any problem with driving two balanced outs. The impedance will be lower but the circuit should handle it. I'm putting two balanced AND two unbalanced outputs on mine, but since its not yet done, I have nothing to report. While I don't intend to run them all simultaneously I suppose I could.

Also, I don't see anything wrong with driving balanced out and an unbalanced out, note that the balanced will be twice the amplitude as the unbalanced so your downstream stuff will have to compensate. Also depending on how you wire your unbalanced (taking the plus or minus output at the center pin and ground at the outer contact), it may be 180 degrees out of phase with your balanced, so check this to ensure its in-phase.
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Old 1st October 2003, 10:33 PM   #3
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Thank you, lgreen; your response is spot on for the questions I posed. I will plan for dual outputs and connect accordingly. Especially interesting was your point that an unbalanced output in parallel with a balanced one would have half the output of the latter. This makes some intuitive sense to my unschooled brain, but I never would have been able to reason out this fact for myself. Merci Beaucoup.

Larry Wright
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Old 2nd October 2003, 02:02 AM   #4
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balanced and SE load in parallel - wouldn´t this cause an asymteric load on the positive and negative outputs? and so degenerate the balanced signal that way amplitude of these is different value?
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Old 2nd October 2003, 02:32 PM   #5
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I was thinking the same thing. Maybe it would be best to add a load resistor on the unused line in an attempt to keep the impedance balanced on both phases?
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Old 2nd October 2003, 06:34 PM   #6
jam is offline jam  United States
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How about buffering one set of outputs- to the subwoofer, minimal sonic damage.

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Jam
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Old 2nd October 2003, 07:36 PM   #7
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Quote:
Originally posted by jam
How about buffering one set of outputs- to the subwoofer, minimal sonic damage.

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Jam
Good idea.
If you're going that far, why not put the crossover in the preamp too.
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