Need help with pre-out/main-in question

I'm a little confused on the pre-out/main-in thing... I bought a used stereo receiver (NAD 7400) with pre-out/main-in jacks and the factory jumpers are in place. I'm thinking of creating an old-school but high quality 5.1 system by adding a digital surround processor like a used Sony EP9ES and outboard 3-channel amp to make a 5.1 system. Will it be ok to remove the jumpers but leave the "pre-out" jacks open and only use the "main-in' jacks to connect the front L/R output from the processor? Since there's no digital inputs on the NAD, why would you need to pre-out anything? The Sony processor has it's own volume control, as well.

Either I'm missing something or the owner's manual isn't clear enough on this feature. Essentially, I just want to use the power amp part of the NAD while in home theater mode and connect all digital sources to the processor but still use the NAD's pre-amp and volume control for my stereo sources. The diagram in the NAD's owner's manual are from the days of Pro-Logic and it shows the (analog?) processor being connected in a loop to both sets of terminals much like an equalizer would be. That makes sense if you connect a HiFi VCR to the NAD and then need to send the analog output for processing, but what about with digital?

Please advise..
Hi John.

The pre-out on the NAD receiver is for connecting an external amp.

The main-in is for conecting an external source that has its own volume control. Like, some CD players have a volume control.

Unless your receiver has a pass-through where the signal from another receiver (connected to the main-ins) bypasses the preamp section of the NAD and will drive the NAD's amps directly, I would not recommend doing this. I seriously doubt your NAD has this. In fact, I've never heard of it, but that does not mean it ain't out there somewheres.

Most modern receivers are designed to give the option to use the preamp section only and drive external amps. They are not designed to have an external reciever drive their internal amps.

My suggestion is to buy an external amp(s) for the new receiver.
You can't do both (without reconnecting the jumpers).

You can definitely use the amp section of the NAD receiver to drive the front L & R for HT as you state. However, by removing the jumpers you have disconnected the NAD's preamp section from its amp section so you won't be able to use it for your stereo sources. You could route your stereo sources to the Sony and use the NAD as just a 2-channel amp.

The preamp out and main amp in jacks essentially allows an integrated amp to be treated as separates. The jumpers are very short ICs from the preamp to the power amp. NAD is one of the few companies that provide this most desirable feature.
Thanks guys. Now this is making more sense to me. I was afraid of damaging the receiver by taking out the jumpers and not connecting something to the pre-out jacks.

The Sony EP9ES processor I'm considering is an excellent, inexpensive (used) DD decoder but unfortunately does not have analog inputs or a phono stage. It was designed primarily to be connected between your digital sources and receivers with "Dolby Digital-ready" 5.1 analog ins. My other receiver is just such a beast, and I originally bought the NAD just as an upgrade for stereo music in a separate system. Then i got to thinking of making it part of my main surround setup.

The only other way I can see this possibly working with the EP9ES is keeping the jumpers in place and feeding the decoded L/R line-level signal from the processor to one of the tape inputs on the NAD. Otherwise, I'd be into much more money by buying a more full-featured preamp/processor that has all the connections, but then I'd be bypassing the NAD's excellent preamp stage and tuner. I may just use my NAD for good 'ol stereo and enjoy it for what it is. Thanks again for all your feedback..

You can do what you're suggesting by running the L & R analog outputs from the Sony into any of the NAD's inputs. You'll have two volume controls to deal with, but that shouldn't be too bad.