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Fosi Audio ZA3 - XLR vs. RCA

Steamrolly

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Jan 28, 2021
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I was trying a comparison between my Fosi Audio ZA3 and SMSL AO200 amps combined with a SMSL DO300 DAC and Totem Skylight speakers. Using a dB meter, I wanted to compare volume variance between the two amps, XLR and RCA inputs and a couple pairs speakers but found something unexpected (to me anyway).

With the ZA3 with the volume set to 12’ O’clock there is a 6 dB (average) difference in volume between XLR and RCA whereas with the SMSL AO200 (with a volume level as close as possible) there is barely a difference (0.2dB) between XLR and RCA.

As I only have the two amps (with XLR) for comparison I am curious if this is, normal between various amps, an issue with the ZA3 or has SMSL compensated for a variance in signal from the DAC (XLR vs RCA) where FOSI has not? In other words, is this normal for the ZA3 or did I receive an amp where the gain is set too high on the XLR output similar to what Amir describes in his review? “Upon testing, I noticed that the gain was substantially increased…”
 
If you have a device that does full differential working on its balanced input and is non-differential on its RCA input, then normally you would expect the balanced line to produce more output from a source that has a fully differential output on its XLRs and normal single ended working on its RCAs. If you don't get a difference, it might be that the gain is deliberately matched so that there is no difference in output levels, or it could be that something isn't actually differential when it should be.
 
My first thought was that SMSL has deliberately matched the gain and Fosi Audio have not but I don't know what the industry standard is (if any) for amplifiers. It was due to @amirm 's comments regarding gain being increased on the initial ZA3 unit he received that made me question if I may have received a similar unit. That said I may have misunderstood his comments; it could be unrelated.
 
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