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Unbalanced connection - are we Not taking a differential reading?

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Jun 22, 2023
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Hello, and please forgive me for this basic question. The point seemed not to be discussed anywhere.

I was auditioning the Genelec G1-4 speakers, and upon switching from G2 to G3, it got shockingly louder. The rest of the swaps went seamlessly, even when unplugging G4 and switching to those sacred 8361As.

Now as I understand, there’s no intentional sensitivity difference in the entire line - if Genelec took any care, they’d eliminate differences in sensitivity instead. Both G2 and G3 house 50W+50W amps, while the latter supports XLR connections in addition to RCA. The input was balanced XLR terminated in RCA for both of them.

The simple explanation to the volume difference, me thinks, was that the RCA plug was transmitting the full v+v- signal, discarding the ground pin instead of one of the hot pins. The unbalanced-only G2 somehow saw only the v+ signal, while G3 and beyond took (v+ minus v-) and got twice the voltage. That’s a 6dB increase.

But wait, are we not measuring the difference between tip and sleeve in a ‘proper’ un-balanced connection, like, comparing the remote v+ with the remote ground?

It sounds totally insane to me, that the signal were defined as remote v+ against local ground in an unbalanced connection. If the output is floating at 1/2 supply voltage, that will translate into a 6V DC offset at the receiving end! What have I missed?
 

AnalogSteph

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I did some RTFM, and it seems the G2 has a -10 dB input gain option (reminiscent of the 8010A), whereas the G3 and up allow selecting +10 dB instead. You probably did not check these DIP switches? Since base sensitivity is not specified anywhere I can see, there is no implication that it is the same between models to begin with.

I wouldn't rule out that G1 and G2 received some attention in terms of input sensitivity, which tends to be the main annoyance in 8020A and 8010A in particular as it makes them too noisy and too hot at a short distance. (I think the idea was keeping levels consistent in surround setups using speakers of different sizes depending on position.)
 
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