2. amps-preamps
  3. 119236-6055

Parasound A21 question - can I use both balanced and unbalanced input on the amp?

In my second system, I would like to double the duties for both HT and music. For preamp, I'm using a Cambridge Audio 851D, which unfortunately doesn't have any HT bypass or even analog inputs.

Originally, I was thinking that I might be able to connect the pre-outs from my AVR to the 851D. And then from 851D to Parasound A21 via balanced/XLR connection. But the problem is that my AVR has only RCA pre-outs and the Cambridge has only digital inputs.

Another option that comes to mind is something like this:
1. Cambridge 851D --> Parasound A21 via balanced/XLR -- for music listening
2. AVR --> Parasound A21 via unbalanced/RCA -- for movies

Is this even possible? Assuming it is, can this cause any potential harm to the amplifier if both balanced and unbalanced inputs are connected to different sources? What should I set the switch (Balanced/Unbalaned) to on the A21?
128x128arafiq
Ag insider logo xs@2x
dbphd
1,628 posts
 
Send an email to richard@parasound.com.  Richard Schram, the CEO, is very helpful and prompt in replying.  

The A 21 is a very nice amp.  I use mine with balanced input from an Oppo 105 to drive a pair of KEF LS50s with excellent results.  The Oppo does double duty as a disc player and processor, and does it well.

Ag insider logo xs@2x
dbphd
1,628 posts
 
BTW:  I'm pretty sure you can connect both balanced and single-ended without problem, but I'm also pretty sure you will need to switch the A 21 input each time you switch from music to movies.  But you really should contact Parasound.

PS:  An obvious solution is to buy an A 31 and sell the AVR.  Bidding ends 1/8 on an A 31 listed at eBay. 
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
I agree with dbphd’s first response, suggesting that you contact Richard, but not with the first part of the second response.

While there may be a few amplifier designs for which that would work, with most designs it would definitely not be a good idea. In many and probably most amplifier designs which provide balanced and unbalanced inputs, one of the two signal pins on the XLR connector is internally connected directly to the signal pin on the RCA connector. When the balanced/unbalanced switch in those cases is set to unbalanced it simply shorts the other signal pin on the XLR connector to ground, so that the amplifier’s input circuit which receives that signal is not left in an unconnected and uncontrolled "floating" state. And when the balanced/unbalanced switch in those cases is set to balanced the switch does nothing.

The fact that the specified input impedance of the A21’s balanced inputs is exactly twice that of its unbalanced inputs reinforces the likelihood that it is designed in that manner. As opposed to having separate input stages for the balanced and unbalanced inputs, with the switch selecting which of those input stages is connected to the rest of the amp (that being what dbphd was apparently envisioning) .

Assuming the design is as I suspect, the result of connecting to both inputs at once would not be harm to the amplifier. But it may very well be harm, eventually if not sooner, to the AVR and/or the 851D, since their outputs would be shorted together. And at best the results would definitely not be optimal sonically.

But contacting Richard, as was suggested, certainly can’t hurt.

Regards,
-- Al

More to discover