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Cable conundrum: Parasound A21 with RCA AND XLR

Ok, hope someone can give me a lesson. I recently aquired a Sonic Frontiers Line 2 preamp with both unbalanced and balanced outputs. First I hooked up my Audio Metallurgy GA-0 XLR's to my A21 amp, and I was not pleased with the sound. No depth, soundstage was choked. (gain was adjusted) I then connected my Synergistic Res RCA's to the outputs after disconnecting the XLR's. still not that pleased with what I thought was an upgrade.

In an accidental discovery, I reconnected the XLR's to the preamp WITHOUT ever disconnecting the RCA's. BLAMMO!! What sound I got! almost 5.1-like wide soundstage, reach-in depth, and the detail...let's just say i heard things from my CD's I never heard before.

So...how can this be? Both outputs from the preamp go to both inputs at the amp (balanced and unbalanced). Parasound tells me this is not a detriment to the amp. But I thought you could only use one or the other. Not both at the same time.
Any explanation?
evergrey

Showing 3 responses by almarg

almarg's avatar
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almarg
9,670 posts
 
In what position was the switch on the A21 that selects between the balanced and unbalanced inputs, when you had both sets of cables connected? And in what position was the ground lift/normal switch?

Regards,
-- Al
almarg's avatar
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almarg
9,670 posts
 
EG,

I can't formulate a precise explanation for your findings, but I suspect that if you put the ground lift switch to "normal" you may very well obtain results with only one set of cables connected that are similar to what you have obtained with both connected.

The ground lift switch isolates the ground sleeves of the rca connectors (and possibly also the ground wire on pin 1 of the xlr's) from the amp's chassis. I would only use that position if it is necessary to prevent ground loop hum or buzz. That isolation could conceivably account, in subtle ways related to the grounds, leakage paths, stray capacitances, etc. within the amp, for the sonic effects you observed when only one set of cables was connected.

Having both cable sets connected, while the ground switch is in the lift position, could conceivably alter the paths and impedances through which signal return currents flow, between the input circuits of the amp and the preamp. That in turn could conceivably alter or undo the sonic effects of having the cable grounds isolated from chassis.

That's all conjectural, but I definitely think it is worth reassessing your findings with the ground lift switch set to normal.

Re your question about phasing, I don't see any relevance, because neither the relative phase nor the absolute phase (polarity) of whatever inputs are selected (balanced or unbalanced) would be affected by the presence of the other set of cables.

Regards,
-- Al
almarg's avatar
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almarg
9,670 posts
 
EG, sorry to hear of the left channel problem, which I can't shed any light on.

Re your and MGlenn's observations of improved sound with both sets of cables connected, I suspect that the reason it is not discussed more frequently is that it is specific to your equipment.

I think that MGlenn's observation that significant sound comes through even when unconnected inputs are selected is key. That indicates crosstalk between inputs within the A21, and is most likely an unintended (and non-ideal) characteristic of the design. For whatever reason, though, it apparently happens to be synergistic with the A21's overall sonic characteristics and/or the characteristics of the rest of your systems.

Best regards,
-- Al
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