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.

 

[Hayabusa]

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:

View attachment 353986 View attachment 353987

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....

View attachment 353990 View attachment 353989

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.

I think I would have risked a direct connection to the 53v supply. There is normally quite some margin and in this case it is 10% off.
What about finding the analog output of the dsp and cut that and make a direct analog input there and use the svs amp like that?

 

[MCH]

I think I would have risked a direct connection to the 53v supply. There is normally quite some margin and in this case it is 10% off.
What about finding the analog output of the dsp and cut that and make a direct analog input there and use the svs amp like that?

Hey @Hayabusa , I opted to step down the voltage because of these reasons:
During my test I observed the that the heat the aiyima A07 max releases starts to increase rapidly above ca. 44V iirc. When it operates with a standard 36V PSU it stays cold. The temperature in normal operation only increases slightly when you increase the voltage until ca. 42-44V but beyond that it starts to increase significantly.
This, together with the intention of leaving the amp behind the sub with very little ventilation and also the fact that the amp has a bunch of electrolytic capacitors rated 50V that would be a bit to their limit and significantly hot, made me decide to step down. And I am happy with it. It has been 9 months now and everything works perfectly fine.

Regarding the DSP, there aren't such analog output signals. The DSP IC outputs a sort of PWM signal that the chip amp takes directly. It would be too cumbersome for me to try to transform that into an analog signal, and possibly only to find out the problem was before or during DSP...

But thanks for the suggestions.

I have now my two subs up and running, one with the mod described here and the second with a reversible mod (in care I want to return it to original state and sell it one day) bypassing all the electronics and using a second aiyima a07 max with it's own PSU and I am super happy with the result, no more rumble and nobody complains about any noise

 

[Hayabusa]

Hey @Hayabusa , I opted to step down the voltage because of these reasons:
During my test I observed the that the heat the aiyima A07 max releases starts to increase rapidly above ca. 44V iirc. When it operates with a standard 36V PSU it stays cold. The temperature in normal operation only increases slightly when you increase the voltage until ca. 42-44V but beyond that it starts to increase significantly.
This, together with the intention of leaving the amp behind the sub with very little ventilation and also the fact that the amp has a bunch of electrolytic capacitors rated 50V that would be a bit to their limit and significantly hot, made me decide to step down. And I am happy with it. It has been 9 months now and everything works perfectly fine.

Regarding the DSP, there aren't such analog output signals. The DSP IC outputs a sort of PWM signal that the chip amp takes directly. It would be too cumbersome for me to try to transform that into an analog signal, and possibly only to find out the problem was before or during DSP...

But thanks for the suggestions.

I have now my two subs up and running, one with the mod described here and the second with a reversible mod (in care I want to return it to original state and sell it one day) bypassing all the electronics and using a second aiyima a07 max with it's own PSU and I am super happy with the result, no more rumble and nobody complains about any noise

It seems you thought this over much better than me!

Well done!

 

[Trdat]

If by noise you mean a low frequency hum, yes these plate amps have this problem and it is very widely known about. SVS sent out two more plate amps and the ones they sent also had the issue.

 

[MCH]

If by noise you mean a low frequency hum, yes these plate amps have this problem and it is very widely known about. SVS sent out two more plate amps and the ones they sent also had the issue.

Exactly my experience. Lucky the people that cannot hear it, but for me, at night, was too distracting.

 

[ZolaIII]

With normal plate amp and no input hum should be very low. When over feed trough low level line as unbalanced RCA it will increase significantly to input SNR (mid 80's for such) so you don't do that and instead feed it to specified input that is enough for it to reach rated max leaving the analog volume pot on 0. This is in the range of 150~200 mV for majority of such (-20 to -23 dB for 2V DAC output) and don't worry decent DAC will still have higher SINAD than what input SNR is rated at. And it's perfectly fine to your hearing sensitivity in such low area (standing or half standing waves) it's meant to cover.

 

[dan_remaincalm]

hey @MCH , thanks for posting. i also have a dual svs sb-1000 setup and the rumble is a bit of an irritation. the weird phase behaviour isn't great either.

i'm driving them with a minidsp flex for room correction and i'm intrigued by the idea of turning them into passive boxes and just doing all of the dsp (crossover/hpf/eq/limiting) and amplification myself - it seems easily reversible, anyway, and i have a spare topping amp here i can play with while i validate it.

i had a go at getting the plate off the back - it looks like it's just held on with the hex screws on the surround, but i couldn't get it detached. is there a trick or is it just brute force? i also thought about pulling the driver out of the front so i can push it through from the hole in the front.

also, in terms of the mod - it's as simple as detaching the old speaker cable from the amp board to the driver and wiring a new speaker cable from the driver to the rear high level ports, right? any idea what the impedance is of that speaker?

any other things to watch out for? cheers!

 

[MCH]

hey @MCH , thanks for posting. i also have a dual svs sb-1000 setup and the rumble is a bit of an irritation. the weird phase behaviour isn't great either.

i'm driving them with a minidsp flex for room correction and i'm intrigued by the idea of turning them into passive boxes and just doing all of the dsp (crossover/hpf/eq/limiting) and amplification myself - it seems easily reversible, anyway, and i have a spare topping amp here i can play with while i validate it.

i had a go at getting the plate off the back - it looks like it's just held on with the hex screws on the surround, but i couldn't get it detached. is there a trick or is it just brute force? i also thought about pulling the driver out of the front so i can push it through from the hole in the front.

also, in terms of the mod - it's as simple as detaching the old speaker cable from the amp board to the driver and wiring a new speaker cable from the driver to the rear high level ports, right? any idea what the impedance is of that speaker?

any other things to watch out for? cheers!

hey,
no, don't pull the driver, you need to take the plate off the back. The first time is a bit difficult because the foam that seals the opening has been there under pressure for a long time and holds the plate very well, but pull and it will come out sooner or later.
once the plate comes out it is very simple to completely detach it, there are only two cables, the one of the driver and the one for the led. You just need to disconnect them from the plate. If i remember correctly they might have one drop of glue on the connector, but it is that sort of glue that you can peel easily.

Then yes, i think the easiest and most convenient way, that allows to keep the sub sealed and makes the mod reversible, is to use the high level ports to connect an external amp.
I believe @trl measured at least the resistance of the driver in his review. You can have a look in the link below:

SVS SB-1000 - inside pics, personal thoughts

Just got few days ago my second SVS SB-1000 and I thought it would be nice to see what's inside the box and "how it works". This one is the black-ash (MDF with sort of melamine foil on the outside) and the "old one" is a black-gloss (MDF with veneer glossy on the outside). The MDF cabinet...

www.audiosciencereview.com

There isnt much more to it. I posted what the original DSP does, up there in the comments, you'll see there is a very sharp dip, read the comments as someone explains why the dip is there.
I still use my two units and i am very happy with the result, i don't push them hard though. After the summer i will move to a much larger place and lets see what happens there....
Good luck and don't hesitate to ask whatever questions that you might have.

 

[dan_remaincalm]

yeah, these are being used in a 3.5m x 4m room, i need bass extension but not tons of raw power.
thanks for the help!

 

[DWPress]

I've got one of these but it's closer to the listening position than my big 18" sub so is padded down in room EQ quite a bit. During sweeps I hear it's growly distortion but with music it's fine even at high levels because the big sub is doing most of the work, they do balance each other nicely on opposite corners of a 16x24' room with DSP. I measure a couple of deep dips in my sub at the baffle, not much to do but turn up the volume a bit more and chop off the peaks in a room curve further down the signal chain.

 

[dan_remaincalm]

actually ... the thought crossed my mind that i could wire the old SVS processed amp outputs to the high-level output sockets, and wire the speaker to the high-level input sockets.

then i can revert it to the original active sub mode by bridging the outputs and inputs, or as a passive sub by hooking an external amp up to the input sockets. hmm.

 

[olymind1]

If by noise you mean a low frequency hum, yes these plate amps have this problem and it is very widely known about. SVS sent out two more plate amps and the ones they sent also had the issue.

Only SB-1000 Classic's problem, or Pro models also affected?

 

[Trdat]

Only SB-1000 Classic's problem, or Pro models also affected?

Not sure to be honest, and not sure if the higher models are using the same plate amp. Either way, I have been suffering from this problem for nearly 10 years, every time I hear a loud hissing noise I'm trying to figure out from where its coming from till I realize it's the SVS plate amp. This has spurred me to be a big believer in XLR cables over RCA and also ensuring the tech I purchase does not have any inherent hiss or hum from the design itself. I have to manually switch the amps on and off throughout the day.

 

[ZolaIII]

Not sure to be honest, and not sure if the higher models are using the same plate amp. Either way, I have been suffering from this problem for nearly 10 years, every time I hear a loud hissing noise I'm trying to figure out from where its coming from till I realize it's the SVS plate amp. This has spurred me to be a big believer in XLR cables over RCA and also ensuring the tech I purchase does not have any inherent hiss or hum from the design itself. I have to manually switch the amps on and off throughout the day.

It's same plate amp they added preamp stage to later offering. Sub's don't hiss they hum but... average plate amp is SNR and SINAD of mid 80 dB so if you don't stand really close to it it should be fine (nor does noise increase with frequency meter. If you picked up ground loop you will know and hear it and there balanced connection helps so does optical and galvaniic isolation. I don't care and you can't pull dead silent cable (XLR 124 dB SNR) beyond line and amplifier limit (SNR and SINAD). Even to mid field with low environmental noise (controled environment) mentioned hum static noise is not a problem and definitely not there when reproducing (playing). There are high quality unbalanced lines with SNR of 110 dB and even such power amplifiers but really you don't need more than 90 dB SINAD to mid sensitive speakers (which home HiFi ones are). Having dead silent PA with 100+ dB sensitive speakers is possible but a bit sick thing to do. If there is inherent loop problem in internal wiring that's hard to isolate and ground but that is actually design (engineering) problem basically. For known example I will use Kali original LP series which they addressed mostly (just to average level) with second iteration of same products. When you add things like analog end with passive resistor high pass filter it will effect the SNR negative but in deacent design even so only on it's own end. That's the difference between SB/PB old (which had one) and Pro series (ADC, DSP and DAC but nothing staggering still).

 

[MCH]

It's same plate amp they added preamp stage to later offering. Sub's don't hiss they hum but... average plate amp is SNR and SINAD of mid 80 dB so if you don't stand really close to it it should be fine (nor does noise increase with frequency meter. If you picked up ground loop you will know and hear it and there balanced connection helps so does optical and galvaniic isolation. I don't care and you can't pull dead silent cable (XLR 124 dB SNR) beyond line and amplifier limit (SNR and SINAD). Even to mid field with low environmental noise (controled environment) mentioned hum static noise is not a problem and definitely not there when reproducing (playing). There are high quality unbalanced lines with SNR of 110 dB and even such power amplifiers but really you don't need more than 90 dB SINAD to mid sensitive speakers (which home HiFi ones are). Having dead silent PA with 100+ dB sensitive speakers is possible but a bit sick thing to do. If there is inherent loop problem in internal wiring that's hard to isolate and ground but that is actually design (engineering) problem basically. For known example I will use Kali original LP series which they addressed mostly (just to average level) with second iteration of same products. When you add things like analog end with passive resistor high pass filter it will effect the SNR negative but in deacent design even so only on it's own end. That's the difference between SB/PB old (which had one) and Pro series (ADC, DSP and DAC but nothing staggering still).

The problem with the hum in these subs is when you use them to watch films, in silent passages you can definitely hear the grgrgrgegegrg and it drives me crazy. Even forusic I could not stand it when nothing was playing.
Ground loops as cause are discarded as the hum stays the same even with the sub completely disconnected.

 

[Trdat]

It's same plate amp they added preamp stage to later offering. Sub's don't hiss they hum but... average plate amp is SNR and SINAD of mid 80 dB so if you don't stand really close to it it should be fine (nor does noise increase with frequency meter. If you picked up ground loop you will know and hear it and there balanced connection helps so does optical and galvaniic isolation. I don't care and you can't pull dead silent cable (XLR 124 dB SNR) beyond line and amplifier limit (SNR and SINAD). Even to mid field with low environmental noise (controled environment) mentioned hum static noise is not a problem and definitely not there when reproducing (playing). There are high quality unbalanced lines with SNR of 110 dB and even such power amplifiers but really you don't need more than 90 dB SINAD to mid sensitive speakers (which home HiFi ones are). Having dead silent PA with 100+ dB sensitive speakers is possible but a bit sick thing to do. If there is inherent loop problem in internal wiring that's hard to isolate and ground but that is actually design (engineering) problem basically. For known example I will use Kali original LP series which they addressed mostly (just to average level) with second iteration of same products. When you add things like analog end with passive resistor high pass filter it will effect the SNR negative but in deacent design even so only on it's own end. That's the difference between SB/PB old (which had one) and Pro series (ADC, DSP and DAC but nothing staggering still).

Apologise, yes I meant hum.

Quite possibly my issue is ground loop because when I move the RCA cable it goes away, however that said one out of my 4 subs regardless of the RCA cables position starts humming after a period of time and is relatively loud, I presume this is the plate amp issue not the ground loop.

Balanced connections would be awesome but the plate amp is an RCA connection. You mention optical or galvanic isolation can you tell me more?

 

[ZolaIII]

Apologise, yes I meant hum.

Quite possibly my issue is ground loop because when I move the RCA cable it goes away, however that said one out of my 4 subs regardless of the RCA cables position starts humming after a period of time and is relatively loud, I presume this is the plate amp issue not the ground loop.

Balanced connections would be awesome but the plate amp is an RCA connection. You mention optical or galvanic isolation can you tell me more?

If it's one out of 4 and developed maybe just contact got lose, you might try to find it and ground it better. Or SPS is going bad and leaking in more for now. Galvanic isolation is very broad term so Google and read. Your problem is internal not input.

Different people have different sensitivity. Let's say self noise as measured close feald to mid field averages to let's say 26 dB for class D cheap still properly done active speakers (1m) and peaking that much in highs, great one's would be 20 dB or less. In bass range you lose more with distance (about 6 dB with every distance doubling in room) and base is midrange (2m) so as really good monitor. If you sit on it you will experience more than humming sound. I can hear static hum from both my sub's and main I just need to be very close to it and I do listening at 3m (little more for sub's). How are you feeding sub's? They are rather sensitive to input level, most being designed to work with 125~250 mV unbalanced input (to 2V DAC -18~-24 dB) and all do SINAD will deep it will still stay above mid 80 dB SNR of amp input line. Finally our threshold is lower in bass range and mid 80 is really more than fine (when it works properly) that's why you don't need better regulated amp in the first place.