Preamp has 1 Center out RCA connector, Amp has 2 for Center input; Connect and Get Hum. Do I need a RCA terminator plug?

[biotech]

I've just hooked up a NHT M6 speaker as a center speaker (not having one before) connected to an Onkyo Integra DHC-60.5 preamp and DTR-9.9 receiver (140 wpc x 7) as amp. Now I have an annoying hum coming from the added center speaker; involving the receiver/amp, with no hum when preamp is off; hum volume increasing with amp output/speaker volume.

The preamp has only 1 Center channel RCA out connector (vs. 2 for all the other preamp outs). The receiver has 2 Center channel RCA-in connectors (like all the other channels), now with one Center connector not connected to anything. Doing what I can (connecting the single preamp Center out wire to 1 of the receiver's 2 Center RCA input connectors), I get the Center channel with good fidelity other than noticeable hum. I've swapped pre-out cables, no change. Will an RCA terminator or grounding/shorting plug (75 Ohm Phono/RCA Terminator Plug?; RCA shorting plug?) set in the unused Center RCA connector fix or help this? Any other suggestions?

 

[BmWr75]

Your preamp with one RCA center out is just as it should be. Not sure why you are using a preamp to feed an A/V receiver???? Your AVR has a multi-channel preamp input per this picture. Run the preamp center out to the AVR multi-channel center in using a single RCA cord. Have no idea if what you are trying to do will work even if hooked up this way.

 

[biotech]

Your preamp with one RCA center out is just as it should be. Not sure why you are using a preamp to feed an A/V receiver???? Your AVR has a multi-channel preamp input per this picture. Run the preamp center out to the AVR multi-channel center in using a single RCA cord. Have no idea if what you are trying to do will work even if hooked up this way.

It's hooked up as you cite, simple enough, but there is some hum when center channel is used. I just swapped in a different amplifier, a Rotel 120 watts x 5 channel unit, and there is no hum from the center channel. The receiver presumably has some problem, has some hum when center channel used, for unknown reason.

Why use a preamp to feed a receiver (with a nearly identical high end preamp section)? I use the dedicated preamp because it has the more capable Audyssey MultEQ XT32 room equalization that I use vs. regular Audyssey MultEQ in the receiver. The DTR-9.9 receiver was Onkyo Integra's top-of-line $2600 product in 2009, has solid 140 watts x 7 channels, with the amp part reviewed as clearly competitive with comparable high end power amps. Other than the center channel, the amp part of the receiver sounds great, such as in stereo can't differentiate it vs. a B&K Reference 200.2 power amp.

 

[Mearle]

So, the issue has all the markings of a bad signal cable open ground, either that or try grounding both preamp and receiver together.

I assume you have isolated and tested both pcs of equipment with the same source and on their own dont produce the hum on their own?