Question: Unconventional Sub Hookup

[bcycle]

Hello

I just finished building a DIY sub using a Parts Express SA240 plate amp. It all seems to work well but I have a couple connection questions.

My front end is a Yamaha RXV2500 receiver which has a mono sub output and a preamp out as well an extra line level speaker jacks for "B" speakers. The hitch with the sub output is it seems to send a subwoofer signal only when it's encoded in the source (like Dolby Digital). The receiver also has a feature called "Pure Direct" whereby the audio signal by passes all digital processing. This actually sounds quite good but the receiver send no signal out of the Sub output when in Pure Direct mode.

The SA240 amp has Line level (RCA) inputs and outputs as well as speaker level inputs and outputs.

The Question: Would it be dangerous to use a "Y" adapter (see attached) at the Sub's low level inputs feeding both the Preamp out signal as well as the Sub out signal from the receiver? (The reason I want to do this is so I can enjoy my sub in pure direct mode as well as surround.) Will this introduce some wacky low frequency oscillation that will cause my sub to burst into flames or even worse, damage the amplifier and/or driver? What other negative or positive impact might this have. I'm guessing the pre-outs on the Recvr will bring some signal (below 40hz) into the sub but that would be negligible.

Thankyouverymuch

Greg

 

[j_garcia]

There is no sub in pure direct because bass management is bypassed. That means if there is no ".1" channel, then the sub gets no signal, as you have already discovered - no bass management being part of the point - only what is present in the recording. Using the Y probably will cause you to get some undesirable results in that the pre-outs (which are full range in Pure Direct) are active at the same time as the sub pre-out. I personally would not recommend doing this. If you want to have the sub on, don't use Pure Direct.

 

[bcycle]

Very useful answer, thanks. I forgot to mention that the good folks at Parts Express say I can connect to the high level (speaker) inputs on the amp to hear the sub while in Pure Direct mode (but I need to remember to shut off the B speakers when in Surround mode.. Does that make sense to you?

Thanks Again

Greg

 

[j_garcia]

So did they mean use the B outs to the sub? Yes that should work because the B terminals are often fed a full range signal (no bas management). Not sure what will happen if you forget to turn the B speakers off in surround mode though, probably the same as if using the Y setup.