How do I hook up 2 preamps to one amp

If the stereo preamp has a Home Theather bypass input, you can connect the Krell front LR pre out to that input.

When you are watching movies, switch the stereo preamp to HT bypass mode.

My Bel Canto Pre3 has an input I can configure for that.

As for my Audio Research Reference 5 (PROC mode).

Go to radio shack and buy a double pole double throw switch. Connect each pre to one side of the switch and the amp to the center. By flipping the switch you will alternate between pre A or pre B feeding amp C.

what Elevick said is the answer - both of his posts. I'm not sure what Lexicon you're using but it's likely to be superior to your NAD - even for music, but if you prefer the NAD, then what you do is connect the the speaker outputs (ie Main L/R) from the Lex, to one of the inputs of your NAD. This can be Tape in, or any other unused input. When you watch video you pick set the volume level of the NAD to a level that is easy to remember and repeat - for example - 12:00 position. You calibrate your HT volume levels at this setting, and any time you watch HT, you return the NAD volume to this level. This way the volume control of your Lex will control your HT volumes - and pass through the NAD.

This all assumes your NAD doesn't have HT Passthru. This is the safest, lowest cost, and best sounding of all options for you.

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what Elevick said is the answer - both of his posts.

BDG,

no, he said to run the Lexicon through tape loop which will not work. In fact, I don't really know what that means. How do you "run something through the tape loop"?

What you said will work which is basically what I said.

Perhaps he wants to use the NAD for music because it has a phono section. In that case he could feed the tape out of the NAD to a Lexicon input, the Lexicon preouts to the amp, and use the lexicon to control the volume for everything.

Otherwise I agree just ditch the NAD.

I don't like the idea of a switch either. You need another set of cables and have to build a box to house the switch and connectors unless you want to cut the connectors off the ends of the cables.. It is unnecessarily complicated when there are much easier ways.

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thanks Herman - yes, I re-read his after I posted mine and realized I misunderstood. I agree with you - it won't get to the power amp that way.

The way I described works very well - I used it with a Musical Fidelity Nuvista preamp and a Lexicon pre-pro. It's not as clean as if you have a true HT bypass in your pre - but with a quality preamp you will not notice any difference.