Repair Help: Dayton Audio SA1000 Subwoofer Amp emitting AC Hum - Page 1
Forum section: electronics / repair

author: achugh
author_rank: Contributor
timestamp: December 12, 2024, 02:40:33 am
content: Hi,After almost 3 years from my last repair; seehttps://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 addingEmotive 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 hearing50 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.

author: achugh
author_rank: Contributor
timestamp: December 12, 2024, 03:08:14 am
content: Could my problem be related to these type of main capacitors likevideo 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?

author: achugh
author_rank: Contributor
timestamp: December 14, 2024, 06:18:35 am
content: Looking athttps://youtu.be/f85gbyYTDfo?t=480I 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 selectedhttps://www.digikey.com/en/products/detail/nichicon/LGW2D222MELC45/1966870Nichicon 2200uf 200V 105CThe 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.

author: MathWizard
author_rank: Super Contributor
timestamp: December 14, 2024, 02:33:17 pm
content: 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.

author: achugh
author_rank: Contributor
timestamp: December 15, 2024, 06:01:00 am
content: 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?

author: achugh
author_rank: Contributor
timestamp: December 16, 2024, 04:01:25 am
content: After some good night sleep, it occurred to me I should check the power cables going into my miniDSP and DSPeaker AntiMode 8033. Sure enough, I made the dumb mistake of switching these power connectors. They both use an external transformer based power connectors with identical cables and connector. DSPeaker needed 9V DC and miniDSP needs 12V DC and since I was swapping cables in my cabinet with bunch of cables I accidentally swapped them which caused this new really strong hum.So, if anyone else makes this mistake hopefully an internet search will help them to check that correct power is being sent to your device.Once I corrected my mistake, the loud hum issue is gone. Now I have installed the new RG6 based RCA cables as well and I am back to low or mild hum in my subwoofers. For me switching cables did not make any difference.I do not hear this hum when at normal sound level. I only hear it in the quiet parts of the movie or content at my listening position. This is what I would like to reduce further so that at least at my main listening position I don't hear it.I am waiting for these new power filter caps from Digikey as well as my ESR meter to arrive so that I can check and confirm if these caps can reduce this hum a little bit for me as I have tried lots of things with no success. Things I have tried so far:Newer RG6 based coaxial shielded RCA cables throughout my audio chainEmotive CMX2+ for ground loop and DC voltage issueFMUser Audio IsolatorPanamax M5400-PM Power Line Conditioner Bank 4 and Bank 5I have noticed that I have very low hum if I have no input signal connected to the Dayton Audio SA1000 amp. The moment I connect the input signal wire, the volume of this hum goes up. Without changing the gain on this amplifier, the hum level stays the same as the input audio single goes up and down.

author: achugh
author_rank: Contributor
timestamp: December 26, 2024, 10:46:18 pm
content: I finally got DER DE-5000 meter as well as the new capacitors I ordered from Digikey.I spent some time replacing TWO of the 2200uF 200V from one of the two subwoofer amps I got. The older capacitors I took out I believe are measuring good. Using TL-21 kelvin leads, they measured 2340uF using 120Hz frequency with 0.07 ohms (or 70 milliohms) for the ESR. The new capacitors measured roughly 1900uF using 120Hz frequency with 0.03 ohms (30 miliohms) for the ESR.Since I spent lot of time taking them out due to all the glue and me not doing regular repair job (I didn't know how to take out these large components quickly) that I installed the new capacitors I got from Digikey as the older capacitors have been in use for about 15 years.Changing these capacitors did not make any difference in the slight hum I hear from this speaker.Using aCM-140SPL meter on SLOW, C and 32-80db measuring range, I noticed that when the amp is turned off, I measure 50db on this SPL meter at 1" away from the center of the sub (basically my ambience noise). Now when I turn on the amp, with no audio cable connected to the amp, I measure 60db at 1" away from the center of the sub. Basically, this hum is about 10db in volume. So the amp itself is producing this hum.Now, if I connect the RCA (RG6 shielded cable for subwoofer with RCA connector) audio cable to the LFE input the hum increases slightly more in volume. I did not measure the volume with CM-140.With all this information, is there anything else I can do to figure out what is introducing this hum?

author: AVGresponding
author_rank: Super Contributor
timestamp: December 27, 2024, 08:35:48 am
content: The best way to avoid ground loop hum is to not have a ground loop... have a single grounding point and practice star grounding. This may require some careful planning, depending on how individual components of the system are configured.I note you have several devices with external power supplies. Are these SMPS, or linear? SMPS in particular can cause problems, due to the Y-class caps causing coupling between primary and secondary.