Is it possible to down-mix stereo outs to mono amp

Sure, all you need in a Y-adaptor jack or Y-cable. The jack has two RCA jacks at one end (into which the RCA plugs of the stereo cable coming from your source are plugged into) and one RCA plug at the other (which goes into the single input jack on the Grundig). A Y-cable has two plugs on one end (each on it's own cable "leg"), and a single plug on the other.

You can find economy versions of both at any electronics store, and some of the audiophile cable companies offer a primo version of a Y-cable.

Note: Bdp24's comment and mine went up within a few seconds of each other, and his was no doubt written before seeing mine.

Regards,
-- Al

I recant my above "Y" adapter suggestion as per
Al. I never really even considered that a current day DAC
could have such a low output impedance, (and such a poorly
designed power supply section) that would create such a
channel imbalance as to cause the DAC to die prematurely.

Al...ZD's suggestion doesn't address the OP's hook up question. It is software based, BUT, if the source in question can be switched to mono, then would a "Y" adapter work?

The output would then be mono BEFORE it hits the DAC, so the difference in voltage shouldn't be present...correct?

Hi Mofi,

Yes, if the source is switched to mono using a y-adapter would not cause any problems. But in this particular situation, at least, if the source is outputting mono just hooking up one of the outputs should work just as well. (In other situations, where sonics are more critical, there could conceivably be some benefit to summing the two nominally identical signals together).

BTW, the issue I cited with summing a stereo pair of signals together via a y-adapter has no relation to the power supply quality. It just relates to the output impedance of the output stage of the DAC, and to how robustly that output stage is designed. And in most cases it would probably work fine, with no effects on long-term reliability. But as I said, shorting two outputs together is poor practice at best, IMO, and I would expect that with at least a few designs it would eventually cause problems.

Arguably I could be over-reacting a bit, given that many people do that kind of thing without issue, but shorting together two outputs that are producing different signals is offensive to my EE sensibilities :-)

Best regards,
-- Al