| Electronics > Repair |
| Repair Help: Dayton Audio SA1000 Subwoofer Amp emitting AC Hum |
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| achugh:
Hi, After almost 3 years from my last repair; see https://www.eevblog.com/forum/repair/help-fixing-and-understanding-a-simple-rc-circuit-from-dayton-audio-sa1000/ one of my SA1000 has developed a noticeable hum in the connected subwoofer speaker. Since I have two of these amplifiers, if I replace the amplifier for the subwoofer, I get a noticeable improvement (much reduced hum sound) in the sound output of this AC hum. Can anyone over here give me some pointers to help troubleshoot and repair this issue? My Right subwoofer has a hum and my left subwoofer is quiet like it should be. My room has single electrical circuit with multiple electrical outlets in the room. The electrical circuit goes from Left to Right side of the room. At the start of the circuit is where I have my Left subwoofer connected which is quiet with no issue. This electrical circuit then goes to the front of my room where I have Panamax M5400-PM power management and line conditioner unit installed. All my home theater electronic devices are connected via this Panamax conditioner. I have an electrical wire going from the HIGH CURRENT (Bank 5) to the right side of my room as a dedicated direct wire to my right subwoofer. This right subwoofer has developed a noticeable hum. The sound level of the hum does change on its own when other devices in my home are turned on or off or randomly as well. Sometimes this hum is loud while at other times it is not that loud but still noticeable. I originally thought that I have developed some kind of group loop issue or DC offset issue. I tried adding Emotive CMX2+ and this has not made any difference. Next I moved the subwoofer electrical wire from High Current Bank 5 to Voltage Regulated + EMI/RF Noise Filtered Bank 4 on my Panamax M5400-PM and that did not make any difference as well. I was thinking maybe my Panamax bank has gone bad or the whole Panamax unit has gone bad. Finally, I changed my Right amp with the Left amp and the hum is immediately reduced (not fully gone but low enough that I can live with). This makes be believe that some component inside Dayton Audio SA1000 of my right amp that was doing some type of line conditioning has gone bad in its power supply. This is now causing my subwoofer to have this AC Hum. Here's the sound I am hearing 50 or 60Hz Group Loop Noise (time marked) as a reference (this is not my video, equipment or room). I can share any pictures as needed. Can someone guide me in fixing this hum as well? Thanks for your help in advance. |
| achugh:
Could my problem be related to these type of main capacitors like video is talking about? My hum is nowhere near as loud as this guy. It does come and go on its own hence I wanted to check here if I should also think about replacing the big capacitors in my amp as well? |
| achugh:
Looking at https://youtu.be/f85gbyYTDfo?t=480 I tested with my multi-meter in beep/continuity mode that the outer ring is beeping with the amplifier chassis so my ground for the input signal seems good. So I don't think I have a grounding issue. This is why any of the ground loop devices are not solving my issue. The power supply portion of the circuit is using TWO 2200uf 200V 85C capacitors to reduce the ripple noise and filter the AC from the transformer. Visually they are looking good. Like the video from my previous post above these power stage capacitors could be the cause of these hums. I have ordered from Digikey the replacement caps. I selected https://www.digikey.com/en/products/detail/nichicon/LGW2D222MELC45/1966870 Nichicon 2200uf 200V 105C The board is currently having 35mm dia x 50mm height for the OEM caps. This new cap matched the dia and is below the height. From the available options, I selected this one as it has the higher ripple current at low frequency. I believe for these power stage caps, higher current is preferred so the subwoofer can be properly energized for sound output. There are caps with lower ripple current as well that match the size and rating. I hope I did not make a mistake in choosing this cap. I will appreciate if someone here can confirm that higher ripple current is the right choice for power stage noise/ripple filtering caps. Thanks in advance for your help. |
| MathWizard:
Do you have a scope tho, I guess you don't have an ESR meter ? I would have tried a few tests, to narrow down the area involved, like the PSU section vs the input section. IDK how much supply ripple it takes to get a noticeable hum on the output. Did it scale with volume changes ? I'd hang on to those old caps, even if they are a bit worn out, you could probably still use them at way lower voltages for something. |
| achugh:
Hi MathWizard, Thank you for responding. I don't have an oscilloscope but I have ordered DER DE 5000 ESR meter with Kelvin Clips. I don't have this ESR meter at the moment but it will be here soon. Yes, I plan to keep these older caps. My audio chain for subwoofer goes like below. AVR => DSPeaker AntiMode 8033 => miniDSP 2x4 HD => Subwoofers. My AVR has only 1 LFE output. AntiMode takes this 1 input from AVR and then gives me 2 outputs. One output with 0 degree phase and the other with 180 degree phase. Both these outputs are going into the 2 inputs of miniDSP which then gives 4 outputs. I am only using 2 outputs out of the 4 available from miniDSP. These outputs from miniDSP are going into the subwoofer amps (Dayton Audio SA1000). My miniDSP unit gives me unbalanced signal. I have lots of cables in my audio cabinet so I thought maybe the cable is picking up some EMI/RF signal as well. I ordered new RG6 coaxial cables with RCA connector as I read that these RCA cables (called shielded cables) work better. I replaced every single cable in my chain with these new RCA cables from Monoprice. The moment I did that, now both subwoofers have a very strong hum in them. Very similar to the hum at time marker 1 minute and 25 second of my 2nd post in this thread which is showing the YouTube video preview. In this person's case the hum is coming with no signal wire connected whereas in my case this new louder hum is only coming when I connected input signal wire for LFE and my miniDSP is turned on as that is what's sending the audio signal to these subwoofer amps. Since replacing the wires caused a deteriorating impact, I replaced all the wires again and put the system back using the wires I removed (older RCA cables). I was hoping that things will go back to the much lower volume hum but now the hum has significantly increased even with older wires. Using a multi-meter set to DC with 200mV range, I noticed that the meter is reading about 3.3mV at the miniDSP output side. Since I put the older cables back which are either not as good shielded or their shield has worn, I noticed that at the subwoofer side, my same meter is reading about 1.3mV. If I put all the newer cables made with RG6, I get 2.5mV of DC value at the subwoofer amp. These mV DC values go up and down making me think this is the AC signal getting read by my meter at DC range since the AC range is not sensitive for such low signal. If I have no signal wire connected to the subwoofer amps, I go back to very low volume hum. Before replacing wires, I would also hear like leaves ruffling instead of the hum occasionally. I don't understand yet where this noise is coming from. Is the only way to understand what is happening is with an oscilloscope? I am thinking maybe my miniDSP has developed some signal leak because of which even if there is no input signal to miniDSP, it is now emitting some ripple current causing this hum. I also switched my subwoofer wires to directly connect to the DSPeaker AntiMode 8033 bypassing miniDSP. This reduced the hum volume. It was higher than before but lower than running the signal via miniDSP. AntiMode is also outputting about 0.5mV DC signal. Since this signal is now roughly 8-10 times less than miniDSP hence the volume of hum on the subwoofers is also less. I do not understand how come both of these devices all of a sudden started to cause hum in my system. Could these devices have their caps failing instead of my amp's on the subwoofer? |
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