Is it safe

03-15-12: Wolf_garcia
...you know...now that I think about it, maybe my sister is bipolar.

LOL! so, you get ear-grating, harsh distortion from her??? ;-)

03-15-12: Elizabeth
Thanks for the great clarification Almarg.
And, as usual..LOL! bombaywalla is off the mark
Yeah I like to rub it in too.

LOL, Elizabeth!! not only do you a massive lack of understanding of electronics (as exemplified by your many befuddled posts that litter Audiogon forums attempting to explain a technical subject) but you also have a massive lack of reading comprehension!
re-read my post & re-read Almarg's post.

Thank you everyone and Thank You Almarg for your well explained response. Once again I am amazed by the depth of knowledge and willingness of the members of this site to help each other out.It looks like with the potential to do harm, even in the long term to my equipment I am just going to bite the bullet and get a preamp.

Don't do it unless the vendor's tech expert assures it is OK.

One further thought, adding to my previous post: Noise that may enter the amp via the RCA cable while the XLR input is being listened to will not be rejected by the amp's balanced input circuit, since it will be present on only one of the two signals in the balanced signal pair. That might impact sonics. The amount of noise that is introduced into the RCA input in that situation may be much greater than when the RCA input is being listened to, since the powered down RCA source will presumably have a much higher output impedance than when it is powered up.

Regards,
-- Al

Al's post is nothing if not succinct, detailed, and absolutely reasonable...you know...now that I think about it, maybe my sister is bipolar.

I suspect that what Bombaywalla said will be correct in most and perhaps nearly all cases. But I would not feel 100.0% certain in any given case without analyzing a schematic for both sources, which is unlikely to be available, and/or obtaining clear confirmation that it is ok from the manufacturers of both sources.

I say that in part because bipolar transistors, which might be used in the output stages of the source components, commonly have specified "absolute maximum" reverse breakdown voltages for their base-to-emitter junctions in the area of 5 to 7 volts. A well designed output stage will incorporate diodes or other protection mechanisms to assure that number isn't exceeded, but I would not assume that all designs provide that protection. If the analog output of the sources is specified as 2 volts maximum, presumably on an "rms" basis, that corresponds to 2.8 volts peak, which is still comfortable in relation to 5 volts, but conceivably a significantly higher voltage could be present for a brief amount of time while the component is powering down. I doubt that would cause any immediate damage, but I wouldn't rule out the possibility of effects that are cumulative over time.

Also, some integrated circuit devices that conceivably could be used in the output stages have absolute maximum ratings on the voltage that can be applied to their inputs and outputs that are specified in terms of, and have values close to, the value of the power supply voltage that is applied to the device. When the device is off the power supply voltage is zero, so any significant voltage that is applied will exceed the absolute maximum spec in those cases. While the spec is probably not intended to be applicable to the powered down situation, and from a physical standpoint I doubt that there would be a problem, again I wouldn't be 100% certain.

And of course there is always the possibility of making a mistake and having both components turned on at the same time, which would result in one component having to drive the low output impedance of the other component. Most designs would be unharmed in that situation, but I would be hesitant to assert that all designs would be unharmed.

The bottom line: It would most likely be ok, but it is not good practice, and I personally would not do it.

Regards,
-- Al

Bombaywalla is correct in stating that "the guys here are full of $$$", especially Elizabeth who leaves her gear on all the time, and myself being fabulously wealthy. True, if you're only using one source at a time you're OK...sadly you won't be able to play 2 sources of disparate music at the same time thus robbing you of bewilderingly cacophonous headache inducing events. Otherwise, get a pro audio mixing board and forget about Assumed Diligence.

Wilson667, the guys here are full os s$$$ re. answering your question - it should be OK for you to connect both sources to the Jolida jd502p PROVIDED ONLY ONE SOURCE IS SWITCHED ON AT ANY TIME & THE OTHER SOURCE IS SWITCHED OFF i.e. OFF OFF/COMPLETELY OFF.
The output stage of any component is designed to handle source/sink or push/pull current of fairly large amplitude and the output voltage spec is usually 2V for many line-stage components. So, for an SWITCHED OFF component to see upto 2V on its output stage should be no issue at all - it would be a voltage within spec. Also, there is NO back flow of current into the switched off component because it's off! Current flows only when the 2nd source is powered on & the transistors inside are biased on. When the 2nd source is powered off, the transistors are biased off i.e. they do not draw any current except for some leakage current in the mirco-amps region.
All of this assumes that you will be very diligent in ensuring that only one source is switched/powered on at any one time.

I talked to the tech at Jolida and they said it should not be a problem as long as only one source is operating at a time.However if I understand what Elizabeth is saying the problem is not so much in the amp as it is with the other source receiving a voltage on it's input.I assume that there is nothing in the circuit to prevent a back flow of current through the other source.Wolf_garcia the manual says "Only one input signal should be operating at one time,If both inputs are RECEIVING an input signal, the result will be distorted sound." the way it is worded makes it seem that it would be okay as long as I was only sending one signal at a time.I guess for right now until I know for sure I am not going to blow anything up it will be one source or time to get a preamp that handles more than one source.

Also it says to NOT DO THAT in the 502P owner's manual on page 8, section 1. Distortion will occur. Really...that's what it says.

No, not a good idea at all. Use one or the other, not both.