Powered Speaker Load Spec

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  • Updated 2 years ago
  • (Edited)
On the 6600, what is the lowest load resistance that this output can be driven into?
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Doug - W3UB

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Posted 2 years ago

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Dudley - WA5QPZ, Elmer

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Powered speaker output is a LINE level, intended to connect to input of amplified speaker pair, like powered computer speakers. Connection directly to speakers , there is not enough output there . Hope this helps .
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Neal Pollack, N6YFM

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The speaker output is not, it is really a line level audio output.   It is intended to drive an audio amplifier.
You can use any of;

+  Cheap stereo PC amplified speakers.

+  Studio or Stage "monitor speakers" with built in amplifier (most have this).

+  External DSP unit with speaker amp, like West Mountain ClearDSP, which also has
     a line input, and also helps reduce band noise, and also has speaker amp.

+  An external audio amp of your choice, driving a speaker(s) of your choice.

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Craig Williams

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I guess my new 6400 is broke. I tried 4 different "cheep" PC speakers to the line output. None provided decent output. Would love to know the specks for the line out. In the old component days line out was 1V PP.
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Bill -VA3WTB

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Are these all self powered speakers,,they have to be to work
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Doug - W3UB

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I understand the intention of the port, I would like to know what load resistance it can drive.

In my application I have the 6600 located away from the desk (fan noise of it plus the amp). I don't like the quality of the audio when routed through the Maestro and find that the direct radio output audio quality is better. Using Bose Companion II speakers.

When using a 30 foot shielded audio cable, when the Flex is off (and the powered speakers remain on) the high impedance long cable picks up hum. Placing a pair of 220 ohm (what I had on hand) loads at the 6600 end fixes this.

I would just like to know (there should be specs) what load it can really drive.

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Neal Pollack, N6YFM

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Well, to get the intended line level impedance, you would need to call Flex directly.
That said, it is always in the range of 100 to 600 ohms (outputs).   A bigger problem for you;
it is an unbalanced cable, hence it is an antenna for hum & buzz when open circuit.

ref:  https://en.wikipedia.org/wiki/Line_level

A suggested fix is multiple choice;

1.   Use a small 600:600 line level audio transformer at each end, near the connector, to
make the long cable run a balanced audio cable, which will not pick up the buzz & hum.
ref:  https://www.ebay.com/sch/i.html?&_nkw=600%3A600+transformer&_sacat=0

2.  Use a USB or 12 volt DC powered relay to control AC power to your amplified speakers, so when
the rig shuts off, the speakers do also.  I have not looked, but

3.  Use a programmed USB output cable from the rig to control a tiny relay that applies a 100 ohm
resistor across your powered speaker input line when the rig is off, or better yet, disconnects the signal
wire when the rig is off.

4.  Use Pin #9 on the radio accessory connector to activate a 5 VDC small relay.  This can be a double
poll double throw relay that would disconnect and/or terminate the speaker input signals,  or the
pin 9  output can drive a larger relay controlled by 5 volt logic, to disconnect AC power from the

As you can see, there are many ways to fix this without overloading the line out signal on the Flex rig.
It's not just Flex, any time you have a long unbalanced input wire on an audio amplifier, you will get
noise or hum when it is unterminated by the upstream component being offline.  One reason is that
line level audio outputs may be anywhere from 100 to 600 ohms, BUT, line level audio inputs are
typically 10Kohms in level, hence VERY susceptible to noise, hum, and buzz.

I think the best option here is to either convert to balanced audio line cables or to do one of any
number of relay tricks to effectively terminate the input or the power to the speakers when the
radio is off.   Pin 9 on the radio accessory connector is your friend;  IF the radio is on, that pin
will have a 5 volt DC level on it.  If the radio is off, that pin will also be off.

Also, there is no problem with your 220 ohm termination resistors.  That will not harm
the Flex rig output.