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Subwoofer pulsing/heartbeat issue! (1 Viewer)

Ab1979

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Oct 26, 2020
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Alfredo
Hi guys! I have tried everything I tell ya, everything! So I have a 5.1 home theater. I have my 5 speakers connected to an onkyo receiver with no issues. However, I have a passive dvc subwoofer (4ohms per coil) connected to a 2 channel d class amp...therein comes my misery :(

My home theater was working great. I had the amp in mono bridge mode and only connected it to the sub. I connected the amp to the receiver via the red and white rca inputs on the amp to the onkyo sub pre out. Again, it was working great for some time.

I recently connected a 4K hdmi extender from a new Tv to the receiver and again, all was working well. Recently, the subwoofer began making what I can only describe as a fast heart beat sound and nothing else. I disconnected everything from the amp and after checking the sub wiring (I have it series wired for an 8ohm set up) eventually determined that the heartbeat sound only happens when the bridge is plugged into the amp. The amp is rated at 8ohm and 275 watts in bridge mode. The sub is series wired mode is rated at 8ohm and like 250 watts tolerant. Here’s the set up I had when the sub was working great:

12FA7C1E-6CC3-4D2D-A36A-C1B106D357BB.jpeg




Dip switch 3 is down because that’s mono mode since I’m only using the 2 channel class d amp for my sub. I was recently trying to figure out what could be wrong and I flipped around the Y rca cable and plugged it into both rca sub pre outs on the onkyo and into the White rca input in the amp and boom it was working again. I go upstairs happy as hell in my home theater and I’m about to watch avatar and switching over to DD+ mode and that heartbeat noice starts again ...now I’m down to just a 5 speaker system and I lost the .1 sub ...please help!!!

I even plugged in the 3 prong power cable of the amp into its own separate outlet with gfi and everything and the heartbeat remains. I know it’s something with the wiring from the sub to the amp but I just can’t figure it out. Any help is appreciated!!!

The only other wiring option for the sub I have would result in 2ohms and I don’t know if the amp can handle that. I was thinking out trying to connect to the amp via the amps optical input, but not sure that makes a difference since again the thumping fast heartbeat sound happens when nothing else but the bridge is plugged into the amp.
 

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Dave Upton

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Hi Alfredo,

Does this sound happen when the receiver is disconnected? I'm not quite clear if you are saying you only hear it when the amp is connected to the Onkyo.

Does running the amp in mono vs bridged mono made make any difference?
 

Ab1979

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Oct 26, 2020
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Alfredo
It only happens when the red and black wires from the sub are connected to the truaudio amp in any mode ...bridged or mono. I called truaudio and they suggested bypassing bridge mode and just connecting to either all right channel or all left channel. I did that and it seemed to work for a while. I then called the subwoofer manufacturer and they suggested just connecting to one terminal of the dvc so I did. So now technically the subwoofer is putting out 4ohms at 100 watts. Again it’s still not consistently working well ...it still make a popping and buzzing noise. At this point, I’m not sure what else to do
 

Simon-Hans

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The Netherlands
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Simon-Hans Niemann
Hi Alfredo,

Sounds like you amp is some how becomming instable (or goes into protect mode, like Dave said).
The recommended load of your amp is 8 Ohm. Then I would stick to that. Don't go lower (2 or 4 iso 8) because that can cause an amp to become instable. Not many amps are disigned for 2 Ohm's.
Do you have the wiring correct: Take care the you don't connect the two coils in parallell, since then you have a 2 Ohm load. The two coils should be connected in series. Did you check the (DC) resistance of your sub (to check the load, exclude a shortcut)?
What happens when you connect a pair of normal full range speaker to your amp?
On your pictures, you have the amp running in stereo mode.

Some other recommendations.
- if you have the ability connecting it optically, I would do that (no grounding issues expected)!
- If you have the possibility to run your amp with 2 x 4 Ohms (stereo) might also be something to try. You have dcv sub.

groetjes, Simon-Hans
 
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