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Good morning sorry for the long post


I got bitten by the upgrade bug again and have run into an issue I hope someone can help with. I had an opportunity to buy a set of definitive tech. SM350s still in a factory sealed box from a friend who had them in storage for $200. Thinking they would match my BP2002’s in the front (same drivers) I thought they would make great centers.
I replaced my procenter 1000 with one of them and was happy with the improvement. But if one was good then two would be better right???
I was not willing to risk running the 2nd speaker in serial or parallel because the Marantz is only rated for 6 or 8 ohms so I decided to take advantage or the SR6006’s preouts and a separate amp.
After much thought and research I decided to try the Crown XLS1000 pro amp. A trip to a local Guitar Center I discovered they had a sale on the XLS 1500 for $319 plus a 15% off coupon made it too hard to resist I bought 2.
Last night I connected both amps 1 for front mains and the other in bridge mode connected to both SM350 in the center. No small feat to disconnect everything and rewire. Powered up and
I have a ground loop hum from the cable box that was not surprising but easily fixed. I verified this by removing the box and the hum went away. So far so good until I threw a blue ray into the PS3. I have almost no volume.
Center channel has 1500 watt output in bridged mode into 4 ohms and front is 300 watts stereo 8 ohms and I had to bring the volume up to 90 % on the receiver and gain on the amp all the way up to get 60 decibels on my SPL meter. Extreme disappointment and much head scratching ensued.
I swopped out the RCA cables (good quality from monoprice) with no improvement and went to bed thinking the pre out on the receiver did not have enough voltage for the pro amps.
This morning I turned on internet radio and almost got blown over with the output. Hit mute and turned everything down and am very impressed with the sound quality and now at 35 % volume on the receiver and amp gain on less than ½ easily hit 75db. Hum is also gone. Amps are dead quiet. Very confused. ????????????????????????
I went back and tried the cable box and the blue ray and again very little output. The only thing I can find that’s different is the cable box and PS3 are connected using HDMI with the receiver reporting a digital input and the internet radio shows as an analog input. Is this possibly the problem?????
The Marantz manual has very little info about using separate amps and I have gone thru the entire thing several times today and I find it hard to believe this could be the problem. Unfortunately GF using my car today so I can not get more RCA cables to try analog output on the cable box or PS3 but again I find it hard to believe that’s the issue.
Anyone with any experience with this issue ????
 

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I have not experienced this particular issue but do have Crown XLS running my surrounds. Did you re-calibrate the system once everything was connected? I know this may sound off but with running multi-channel on the bluray and cable while the other signal was stereo, at least I imagine it was, it could be in need of some adjustment. Also, did you try splitting the signal from the Marantz into a Y and then going into the XLS for the centers? By doing this you could take mono out of the scenario and run the centers in parallel.
 

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Dale thanks for the response.

I did run the setup last night but I admit I only used 4 measurements instead of the 8, it was late, I was tired and the GF was sleeping. I live in a 900 sq ft studio so I was trying to be considerate. That will teach me :)

My first attempt was with a y splitter and stereo mode for the centers but I changed that as my first trouble shooting attempt.

Internet radio was tried in both stereo and multiple surround formats and they all seemed to give the same output, I was very confused.

Because I did not have my car today I kept trying different things and on my 4th attempt today I believe I got it right.

Still not sure what was causing the problem but after the 4th rewire and complete audisy setup this afternoon everything seems to work. I still have about 6 to 8 decibel drop on the SPL when using the PS3 or the cable box instead of the network connection. I tried some movies and music I have on my server and anything coming over the network still has more output, never noticed that before.

The engineer in me hates not knowing exactly what was wrong but I am happy enough with the sound to have called Guitar center today and reserve a 3rd amp I will pick up tomorrow after work for the surrounds. This is my first time dealing with this store and I can not say enough good things about them, the young kid I dealt with was very knowledgeable and even though the store was crowded spent time with me and did not try to rush me. I will defiantly do more business with them.

I can say the addition of the 2 SM350’s has improved the sound from the center channel. I want to believe the new amp on the fronts is an improvement over the SR6006 but it is too early to say. However I can say the extra power is great to have .I had the time this afternoon to crank it up to insane volume and it literally drove me outside long before I could hear any degradation in the quality. Nearest neighbors are over 100 yards away and I could clearly hear the music from their driveway.

I think this will satisfy the upgrade bug for a while at least, however I have decided I will have a rack setup instead of the shelving unit I have today to make any future work much easier and I am in desperate need of better wire management. I will add a rack mounted power distributor connected to a relay activated by the 12 volt output on the receiver to turn on the amps automatically.

This rant has gone on long enough and we are going to enjoy a movie thanks for the help again.
Last parting question, do you think 2 channels stereo on the centers is a better way to go than the bridged mono sonically?? I may change it back only because I am concerned about getting stupid some day and blowing the SM350s with so much power in bridged mode.
 

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Last parting question, do you think 2 channels stereo on the centers is a better way to go than the bridged mono sonically.
Can’t say for sure if bridging is worse sonically (although I suspect it is), but I can’t see any advantage to do it in your situation. With this amp bridging seems to get way more power at 4- or 8-ohms than the stereo ratings, even after you divide the bridged power between your two center speakers.

But keep in mind that adding a second speaker generating an identical signal from the first is going to get you greater acoustical output – something between 3-6 dB, can’t remember the exact figure. Naturally you’re going to end up turning down your center channel to compensate. So, while your center channel has the potential for quite a bit more power output (watts) in bridged mode, it reality it’ll never get used.

Regards,
Wayne
 

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I would "Y" the center channels before the Crown amp and run in stereo mode. Are you running 1 speaker above and 1 speaker below your screen? I ran a setup years ago with 2 centers off of a QSC amp and loved it.
 

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With the SR6006, you can go into the setup and adjust the audio levels so that all sources are the same volume. Press the "Amp Menu" button on the remote. Then cursor up or down to "Source Level (Audio)" and press "Enter". You can then adjust the level up or down up to 12 dB. This info is in the manual on pages 92 and 96.

Mike
 
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