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Author Topic: 1 Source 2 Destinations - Impedance Matching?  (Read 3266 times)

Jason Thompson

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1 Source 2 Destinations - Impedance Matching?
« on: February 01, 2011, 10:15:44 am »

I guess we're here now. So here goes.

In the past, I've tried just wiring up a y cable from my main "monitor" outs on the console to 1) the input on the amp that runs the nearfields and 2) the sub. I put a toggle switch on the one that goes to the sub. When the switch was open and the sub would come on, the studio speakers would dim. I guess it's because I was robbing half of the load?

Thanks,

Jason
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John Roberts {JR}

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Re: 1 Source 2 Destinations - Impedance Matching?
« Reply #1 on: February 01, 2011, 10:39:03 am »

You are forming a simple voltage divider between the source (output) impedance of your send, and the input impedance of the two amplifiers.

When both amps are connected you have their input impedance in parallel.

In general the input impedance of the amps should be high (10k ohm) or so, and the source impedance of your console output should be low (600 ohms or less).

This level drop should not be very large (< 1 dB).   If you are experiencing a larger drop in level, you may have unusually low input impedances, unusually high source impedance, or both...

JR
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Jason Thompson

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Re: 1 Source 2 Destinations - Impedance Matching?
« Reply #2 on: February 01, 2011, 11:06:09 am »

Thanks, JR for the quick reply. I was using this method on a different console at the time. I want to do something similar but didn't want the same result. I'll try again and see if it's good.

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John Roberts {JR}

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Re: 1 Source 2 Destinations - Impedance Matching?
« Reply #3 on: February 01, 2011, 12:36:07 pm »

Note: when connecting to two destinations from a single balanced 3 wire send, either of the two destinations could imbalance the balanced output and cause noise.

JR
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Ales Dravinec

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Re: 1 Source 2 Destinations - Impedance Matching?
« Reply #4 on: February 12, 2011, 12:54:15 am »

Note: when connecting to two destinations from a single balanced 3 wire send, either of the two destinations could imbalance the balanced output and cause noise.

JR

Unbalancing the balanced line may also provide for fore mentioned level drop (6dB).
Maybe here's the catch ...
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John Roberts {JR}

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Re: 1 Source 2 Destinations - Impedance Matching?
« Reply #5 on: February 12, 2011, 09:43:12 am »

Unbalancing the balanced line may also provide for fore mentioned level drop (6dB).
Maybe here's the catch ...

The unbalancing I was thinking of was applying a different load impedance to + and - output signal legs, but losing one of two active outputs could result in a drop of 6 dB.

JR
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boggy

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Re: 1 Source 2 Destinations - Impedance Matching?
« Reply #6 on: February 12, 2011, 07:52:44 pm »

The unbalancing I was thinking of was applying a different load impedance to + and - output signal legs, but losing one of two active outputs could result in a drop of 6 dB.

JR
I agree, and, also... one of method for unbalancing balanced lines implies connecting (-) contact go ground on input side, and if existing output isn't truly transformer coupled, but simplest electronically "balanced" (two independent buffer circuits, not something based on G. D. Pontis design described in Hewlett Packard journal, 1980, p.12), there will be 6dB drop of signal level for sure, and one of buffer outputs will be shorted to ground, despite all.
To check this, its needed to test whether pin 3 and pin 1 are shorted on input side.
Some workaround for this problem may be transformer coupled adapter (Lundahl or similar)
More about unbalancing balanced lines and interconnection cables  can be found on Rane Note 101

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