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


I recently acquired an old Grundig Majestic console radio/turntable. It's an all tube mono amp with - as best I can tell so far - three speakers. With its FM section it's a surprisingly nice sounding amp, in a sort of lush tubey sort of way. It does have an unused input, but of course it's also mono. Is it possible to take the two channels out of, say, a DAC, and blend them down into a mono input? I'd love to be able to play streaming music or computer files through it.

Regards,
grimace
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.
Yes, can be simple as using 2 resistors, along with with more
advanced ways of doing that.

Google "stereo to mono mixer".
Actually a simple "Y" adapter will do.
Mofimadness, yeah, you're right - I was just overthinking it. No matter what, he can't hurt anything by trying that.
"Is it possible to take the two channels out of, say, a DAC, and blend them down into a mono input? I'd love to be able to play streaming music or computer files through it."

Your playback software should have a mono option. If not, try Clementine music player. I know that player has it.
I agree with Joey's first post, but not his second. And this is the first time I can ever recall not agreeing with Mofi.

If ZD's good suggestion proves to not be applicable, perhaps because one of your sources is not computer-based, a y-adapter will probably work, but IMO it is very poor practice that, depending on the output impedance and other characteristics of the DAC, could eventually lead to its premature failure. Especially if that output impedance is particularly low, and if the DAC's output circuit is not robustly designed in terms of short-circuit protection.

Consider, for example, the situation in which you are playing a recording in which high volume transients are produced by an instrument that is off to the side, which are therefore primarily in one channel, and occur at times when little or no sound is coming from the other channel. You will then have one channel of the DAC trying to produce 0 volts, and the other channel trying to produce a relatively large voltage, the result being that the two interconnected channels will fight each other. Resulting in turn in an abnormally large amount of current having to be supplied by one channel, as it tries to drive a load impedance corresponding to the perhaps very low output impedance of the other channel.

As I say, it will probably work ok in most cases, for a while at least, but at best it is poor practice, and at worst (depending on the specific DAC design) it may result in premature failure.

My recommendation: If ZD's suggestion doesn't apply, either implement a two-resistor DIY summing arrangement, as Joey suggested, or visit the B&H Photo Video website and select and order a simple line-level mixer.

Regards,
-- Al
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
Right you are Al, your original post wasn't up yet when I made mine. As for sound quality loss from a Y-adaptor, with the Grundig being the final link would that really be of much concern?
"
09-22-15: Mofimadness
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?"

If the OP uses software to convert stereo to mono, there is no hook up question. The same exact signal goes to the R & L channels. If actual components like a source or preamp has the ability co convert the signal to mono, its the same thing, as well. If you just have 1 mono amp, all you need to do is plug one of the channels into the amp. You don't need to combine the two.
09-22-15: Zd542
"If the OP uses software to convert stereo to mono, there is no hook up question."

Yes, there is a hook up question. Just because the signal is converted from stereo to mono "at the source", how would the OP get that from his DAC to the Grundig? You never addressed that in your original comment.
At the risk of sounding wishy-washy, Almarg is right - it's better to work into a load for any output - otherwise, you're basically shorting the left and right channels to each other.
"Yes, there is a hook up question. Just because the signal is converted from stereo to mono "at the source", how would the OP get that from his DAC to the Grundig? You never addressed that in your original comment.
Mofimadness (Threads | Answers | "

"It does have an unused input, but of course it's also mono.his Thread)"

Where am I going wrong? Why can't the OP just use the input?