My quest to eliminate the noise/rumble of my SVS SB-1000

[MCH]

My initial question having read through this, is whether or not this is a mains hum issue being at 50-60Hz range. I am less tech savvy with powered things, so I could be all wet, but I don't see that in the THD sweep. I'm guessing that is not an issue.

A friend of mine has the older ported non-DSP version, and to my knowledge, no issues like this.

No idea, some members here have reported the same issue while others don't have it, maybe there are good and bad batches.I tested a total of 4 plate amps and all 4 showed the issue, at different levels.
I would love to be able to bypass the DSP to see if it is an amp problem or a DSP problem, but i didn't manage. The amp is full digital and i could not think on any way to test it bypassing the DSP section.
Anyways, not a problem for me anymore.

Hi,
I was thinking on going a bit further with this project and i would like to ask for comments or advice on my plan.
As i mentioned, i have now running my two SVS subs as passive powered by Aiyima A07 max. However the original plate amp remains in place, unused, but intact.
I was thinking on ways to reduce a bit the clutter what basically means to try to get rid of the power bricks that feed the amps and i thought, why not repurposing the PSU of the original SVS plate amp that is there doing nothing? my reasoning is the following:
- The plate amp is rated 300 watts RMS, 700+ watts peak power, that means that its PSU must be more than enough to power one aiyima each
- The PSU is nicely placed inside the sub, with a nice means socket, a power button (that i will not use as i use a master/slave power strip but nevertheless is nice to have), and heatsinked to the thick metallic plate itself.
- I still have two unused terminals for the high level in/outs that i could use to bring the DC power out to the aiyima without having to dig a hole.

What is the problem then? according to @trl the PSU supplies 53VDC, and this is a bit too much for the aiyima, i would need to bring down the voltage to 48VDC.
I have no experience with high power step down converters, so i was wondering if what i want to do is even possible or recommended. I understand that the step down converter will dissipate some power, but i only need to decrease the voltage by 5% (5 VDC), i am guessing it should be feasible (?). There is space enough to heat sink it to the back plate, unless the converter is very big. Any recommendations for 300W (at least) converters that can do such conversion? if the output is less than 48V is also ok, currently i am running the aiyimas with 36V. Does all this make sense at all? am i missing something? Thanks for any comments.

PSU and output connector (the one to the left is the one delivering 53VDC.

View attachment 350248 View attachment 350250

Regarding the buck converter idea to re-purpose the power supply bringing down its 53 Volts to 48 or less: I have been trying hard to find a DIY buck converter project that can handle these voltages and power, this would allow me to build a PCB that adapts to the space available and the existing holes of the plate amp. I could find a few of well documented projects online, but none can reach >40 volts.
What i did find is this aliexpress module that fits the bill, and there is a review in youtube where the power and thermals are tested.

https://www.aliexpress.com/item/1005005450194755.html

It could be that the voltage doesn't reach 48V when i feed only 53V, but i will be happy with anything around 40V.
The module has a fan that is always on, that is a clear no go, but i plan to use a normally closed thermal switch that enables it only when the temperature reaches, say, 70°C. Stepping down 53 to say 45V and with the usual very low Watts that it normally uses, i don't think it will ever get anywhere close to that.
I also tried to see if it was possible to modify the PSU to provide less voltage, as itt has a buck converter IC, but I didn't see anything obvious like a variable resistor and my knowledge doesn't allow me to go much deeper. That would be an ideal solution.

 

[MCH]

Curious development.

As explained above, i want to repurpose the PSU of the sub to power the external amplifier i use now. TThe PSU outputs 53VDC so i needed to buy the buck converted linked in the previous post to bring down the voltage to 48VDC.

There were a couple of issues that i needed to solve:
The PSU also outputs +7V and -7V to power the DSP board and receives back 4.6V trigger from it (used to bring the unit to standby and also for the signal sense function). And the DSP board needs to be plugged for the PSU to work. It took me a while to figure out how to fool the PSU. I needed to create a "dummy load" (a resistor between the +7 and -7V supply to the DSP board) and i needed to bypass the trigger input that the board uses when the signal sense is on. As without the board i didn't have 4.6V available and for some reason i dont understand a voltage divider from the +7V pin didn't work, i needed to bypass the trigger input shorting a switch transistor.

Here the result, ready to be tested: DSP/Amp board removed and buck converter occupying the place. The thick aluminum plate will now be the heatsink of the buck instead of the amplifier (not yet fixed in place and connector holes not sealed yet):

Well, i plug everything, connect the external amp but leave the electronics sitting on top of the sub. Everything works fine, i can't be more happy....

... until my 10 year old arrives and says "Papi, what is this noise, it is very annoying"

???!! I can't hear anything

switched off the PSU, noise is gone (????!!!!!)

Fired the UMIK, what the hell is this??

PSU off:

PSU on:

What is that thing?
was it always there?
will my kid hear it when i seal the sub again?
and even worse, why can't i hear it if it's only 12 kHz?

On a serious note, while studying the PSU i measured the switching frequency at 27.8 kHz. I believe that i can modify the frequency changing the value of a capacitor connected to the tl494 PWM controller on board, but i dont get how can that 12 kHz peak be related to the switching frequency.

What else can be causing the noise? As you can see, the board is completely covered in white woo. I cannot describe how the noise is, because i cannot hear it....

(PS: yes, i know i can buy a power brick, in fact i already have one. I do this for fun and learning and because i find neat to eliminate the brick and repurpose the original PSU that sits perfectly fine inside the sub)

 

[MCH]

ok, seems that when i close the sub, my kid cannot hear anymore the 12 kHz tone from the PSU. That is great news after all the time i dedicated to the project. I am very curious now and i will try to see if the plate amp that i still have intact is also noisy. It is clear these plate amps are made to a cost, i would not be surprised if it does emit it.

Time to seal the connectors holes and wrap up:

I used 2K glue in generous amounts and in the areas where the heatsink of the buck converter goes, instead of glue i put some heat transfer tape:

Illy coffee cans are a great source of aluminum plates of the right thickness for a job like this. Thicker than a coke can but thin enough to cut easily with a Dremel.
Aluminum recipients for food contact come coated, but the layer is usually single digit microns thin, so i don't think it hinders much the heat transfer. If it was something more critical the best would be to sand it, but for this project i don't think it is necessary at all. I put some heat transfer tape as well on the heat sink of the buck converter.

And there you go. L is the power to the external amp and right is the input for the driver. Now i just need to clean it a bit and label it properly, not that i get confused one day....

I left the fan of the buck converter unplugged for now. I have been playing music yesterday all day and it didn't get even warm. The plan is, if i find it necessary, to put a 70°C normally open termal switch so that it starts working if the temperature is reached. But i am pretty confident that it is never going to happen, as it is stepping only from 53 to 48V.