Passive mixer for two CD changers

Well, lucky me, I now own TWO 300-disc CD changers (Pioneer PD-F1007 and PD-F1009). Great units. But I have only one "CD" input on my pre-amp.

I would like to mix the two outputs with a passive circuit. Pity I have no schematic for the CD changers.

Would simply having say, 4.7k resistors in series with each output do it? Or do I need some kind of load resistor forming a "Y"?

(I don't lose sleep over signal losses over 16kHz.)

Any guidance appreciated.

Any ideas where to find free service manuals?

Check the owner's manuals, you may be able to daisy chain the changers digitally. Some used to allow that so one was the master and others fed their signal to it.

You'd be better off just using a DPDT switch in a project box. Combining the signals using a series resistor should work, but expect some signal loss. I'd use 10-20K in each line.

If your preamp has a digital input and an analog input you can feed one to each. You may find digital has priority, so turn off the one connected there when not using it. I use SPDIF for my CD player and optical for my computer on the CD input of my preamp, works great as long as the CD is turned off when I want to listen to the computer.
Bob Ellis - thanks for good suggestions. Sad to say, it looks like the PD-F1007 won't have a "relationship" (master/slave) with the more basic PD-F1009 that only has some kind of Pioneer/amp control input, not the more elaborate slave connections. Sure would be great.

Other suggestions have draw backs.

I suppose, if I can assess the high frequency loss, then I don't need to fret about hypothetical distortion and other losses (other than just uncolored broadband signal strength)?
Thanks for replies. Tried it. Yes, half volume with an insignificant drop at 20 kHz due to long cables. But not a practical solution for a lazy listener without a remote control in their little hand.

Soooo, today's main question is now this: if I made a little op-amp mixer run by, say, a 9v battery (or other suggestions) without a power switch, how long would that battery last?

.... and what is this year's favorite cheap op-amp for line-level levels?

Define cheap? Under a buck there's the TL082 or NE5532 for a few bucks OPA2134, and the sky is the limit. You're only going to be using a dual (or two if you worry about absolute phase). Given the source, I don't think that the high speed parts "better" than the OPA2134 are worth it. Of course I could be wrong.

Plan on about 10 mA draw from a dual opamp, your battery will last about 2 days Battery Capacity Use a very low current opamp and you can get longer life, but if you insist on batteries, there is a power switch in your future.

Got a left over AC wall wart? Rod Elliot has a project that will get you a dual supply from a single wall wart. He has boards available and will provide a parts list. The original version should suffice if you are comfortable building on perf board.
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