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

[MCH]

Hi,
I own two SVS SB-1000 subs since a little over one year ago and since day 1 i have been experiencing a constant rumble/noise whenever the sub is on as explained here:

Problem with sub noise

Hello gang, I think I might have a problem with my new sub. But as it is also my first sub I am not sure it is a real problem, so wanted to ask here…. The sub is a SVS SB-1000 (non pro, but new, probably one of the last ones around). The problem is that whenever it is on, I can hear a...

www.audiosciencereview.com

It is present in the two subs i own in different degrees, is very audible, specially at night when watching films, and is there even when nothing is connected but the power cable, what eliminates the possibility of a ground loop.

I contacted SVS and they kindly sent me a new amp plate and even though this new amp had lower noise than the original it replaced, the noise is still there.

Member @connta explained that he had a similar experience with the SVS PB-1000 and even confirmed that all the subs of this model they had in his local shop had the same issue:

Troubleshooting the sub (PB1000) after AVR change

Recently i switched AVRs, went from Onkyo 646 to Denon x4700h, the results are mixed considering the price of Denon but oh well, life goes on. In any case, everything was "fine" with Onkyo, didnt really notice anything out of the ordinary. Switched to Denon and when running Audyssey i noticed...

audiosciencereview.com

This tells me it is a design issue.

As otherwise these subs are ideal for me and to sell them would be a pain in the rear and probably the shipping cost would be as much as i would get for them, i decided to keep them and see what i can do.
My first though was to use a external power amplifier direct to the drive, bypassing all the electronics but leaving the plate there to keep the enclosure sealed. But i need 300 W per channel and even though i still have this alternative on the back of my mind, before doing that i thought that trying to repair it can be a cool project to learn something from, and this is what i am going to try. Any comments or suggestions are welcome!

Two important pieces of data are:
1. the only control that has any effect on the noise is the crossover setting knob of the amp, the higher the crossover frequency, the louder the noise. If set below 60-70Hz there is no noise at all.
2. The volume has no effect on the noise. No matter if you set it to the max or to the min. the noise is the same.

My findings so far:

@trl posted some time ago a nice thread with inside pics and some findings that help me understand how the amp works. I did some measurements and followed traces to confirm and expand some of the information.

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

The amp plate is a fully digital amplifier. The signal flow as is something like this:

line in -> ??? -> (channel R only) AK5358A ADC -> 24 bit 48kHz i2s -> STA309A DSP -> DDX ("direct digital amplification", some sort or PWM signal) -> STA516BE digital amplifier chip -> driver

The fact that the only thing that has some effect on the noise is the crossover frequency and that if set below 60 Hz the noise was gone made me think that the amplifier is capable of outputting a clean signal, so the problem should not be there. The suspects were now the DSP, the ADC or whatever is before the ADC.

But what does not fit is the fact that the volume control has no effect on the noise. The volume pot is a potentiometer that goes from 1 kOhm to 0 Ohm to ground. Initially i was thinking that the volume control was acting somewhere in the amplifier chips or in the DSP, but the traces go all the way to the oposite side of the PCB where input signals are. Unfortunately there are lots of black resin there and i cannot see nor use my multimeter there.

I started to suspect that the problem could be somewhere before the ADC.

I measured the analog input of the ADC (pin 1, R channel, the only connected) with a multimeter with no source connected and i measure a constant 2.4 volts. I don't know if this is normal but it is not what i was expecting. Maybe i am missing something but could this be the source of the noise? Turning the volume control has no effect on that signal, that stays always at 2.4 volts....

With all this information, this is my plan to confirm the hypothesis of the bad analog input signal and at the same time try to solve the issue:
What if i bypass the analog input, remove the ADC chip and input a 24 bit 48kHz i2s signal directly to the DSP chip? If the problem was at the ADC or before, i should have clean output. If not, i will stay as i was, but with a sub with digital input...

What do you guys think? is that 2.4V at the input of the ADC normal? is it worth trying my plan?

 

[MCH]

this is how it looks like:

 

[DVDdoug]

I'd say, "Unusual and unfortunate..."

As you may know, noise is an analog problem and it's obviously coming after the volume control but before the filtering.

The volume pot is a potentiometer that goes from 1 kOhm to 0 Ohm to ground. Initially i was thinking that the volume control was acting somewhere in the amplifier chips or in the DSP

I'm pretty sure that's something controlling the DSP. As you probably know, a normal volume control is higher impedance (usually 10K-100K) and the signal goes through it. There are analog voltage controlled amplifiers but since the thing has DSP they would likely be using the DSP.

I'd be inclined to replace the amplifier (with an external amp or a different plate). But there is probably some custom-unknown DSP "tuning" to optimize frequency response/low-frequency extension.

...Or maybe I'd throw it off the roof or light it of fire!

i measure a constant 2.4 volts. I don't know if this is normal but it is not what i was expecting.

AC or DC?

A lot of ADCs & DACs don't go negative so they are DC biased to handle the AC audio signal. It could be normal for a 5V ADC, biased at about half it's peak-to-peak range.

 

[ppataki]

...Or maybe I'd throw it off the roof or light it of fire!

totally agree with that!

I had two SB-1000s too, sold them then built two Dayton based subs powered by Hypex NC250MPs and they actually beat the shite out of the SVSs..... (actually this is how my DIY journey started, was a real eye-opener)

 

[Chrispy]

Interesting, have never heard this complaint about SVS sub amps that I can think of (out of many posts about these subs), do you have an spl reading to give an idea of the range of this noise, especially as you change the low pass filter setting? This is the older SB1000 rather than Pro model?

 

[MCH]

Interesting, have never heard this complaint about SVS sub amps that I can think of (out of many posts about these subs), do you have an spl reading to give an idea of the range of this noise, especially as you change the low pass filter setting? This is the older SB1000 rather than Pro model?

it is the old model, not the pro. No i don't have any reading of the noise. Could certainly measure it tomorrow if i have the time.

In general, any thoughts about the 2.4V at the input of the ADC?

 

[Chrispy]

it is the old model, not the pro. No i don't have any reading of the noise. Could certainly measure it tomorrow if i have the time.

In general, any thoughts about the 2.4V at the input of the ADC?

No, am just curious about the extent of the noise. No idea on the voltage as you're measuring.

 

[MCH]

I'd say, "Unusual and unfortunate..."

As you may know, noise is an analog problem and it's obviously coming after the volume control but before the filtering.


I'm pretty sure that's something controlling the DSP. As you probably know, a normal volume control is higher impedance (usually 10K-100K) and the signal goes through it. There are analog voltage controlled amplifiers but since the thing has DSP they would likely be using the DSP.

Yes, i also thought that volume control should somehow make it to the dsp, that's why i wrote the 1 kOhm reading, but i am still wondering if there are other possibilities given the fact that the trace seems to go to the inputs...

AC or DC?

A lot of ADCs & DACs don't go negative so they are DC biased to handle the AC audio signal. It could be normal for a 5V ADC, biased at about half it's peak-to-peak range.

Ahhhh ok, missed that from your post. It could perfectly be that. Yes, DC, that makes sense then. Thanks!!

 

[MCH]

ok, i finally found where the volume control goes. it is connected to one of the ADCs of the microcontroller (the 20 pin chip close to the DSP. This microcontroller is obviously wired to the i2c pins of the DSP and runs it). The xover knob goes to another ADC pin of the same chip. This means everything happens in the DSP.

Hmmm hypothesis of the analog input doesn't seem likely now.... :-(

now i wonder if there is a way to bypass the DSP and generate and send a PWM signal directly to the amp chips...

edit: i might try one last thing, that is non destructive, so if it works it works, and if it doesnt, nothing is lost:
There is the possibility that the noise comes from something going wrong during the DSP. The DSP chip has a a register that allows to bypass all the EQ,. Could try and write that register to "bypass" and feed the sub with a signal alredy EQed and with the necessary low pass filter (that i am already doing anyways).

 

[MCH]

edit: i might try one last thing, that is non destructive, so if it works it works, and if it doesnt, nothing is lost:
There is the possibility that the noise comes from something going wrong during the DSP. The DSP chip has a a register that allows to bypass all the EQ,. Could try and write that register to "bypass" and feed the sub with a signal alredy EQed and with the necessary low pass filter (that i am already doing anyways).

It is a miserable day outside, soooo...

I tapped the i2c traces that go from the microcontroller to the DSP chip and connected them to a raspberry pi to see if i could write the register to bypass the DSP

i2c detect to see the devices connected:

wow! i was expecting only 0x40 - the DSP chip, but seems that somehow the microcontroller is showing in many addresses (???)

ok, at least 0x40 is there, lets see what registers it reports:

here i was expecting many more registers not zeroed

Decided to unpower the microcontroller, as it seems it is messing everything up, so i removed resistor 53 that effectively cuts the 3.3V line to its power input:

but it seems that the DSP chip does not want to work standalone:

and well, that's it for this approach i would say. I will keep on trying a few things but my expectations are very low not. I am thinking on buying an amplifier board that can make use of the existing power supply (any suggestions?) and remove the current DSP/amp board. Lets see...

Thanks for your help guys!

PS: hmmmmm...

Hifimediy T3 mono TK2050 amp, Jantzen caps - Hifime Audio

2X300W@4OHM TK2050: TC2000 + STA516

hifimediy.com

 

[JohnBooty]

I own two SVS SB-1000 subs since a little over one year ago and since day 1 i have been experiencing a constant rumble/noise whenever the sub is on as explained here:

Ah, that's frustrating. I've had two SB-1000 since 2017 or so and they've been excellent and problem-free. You deserve better.

I am thinking on buying an amplifier board that can make use of the existing power supply (any suggestions?) and remove the current DSP/amp board. Lets see...

My understanding is that a lot of SVS subs' performance (specifically, bass extension?) is enabled by their DSP programming. Without a DSP assist, I think a 12" driver in a 1' sealed box is going to be kind of anemic. The DSP also keeps the user from doing anything stupid like overloading or bottoming out the driver.

I'd factor DSP into the equation if you're hoping to repurpose the SVS.

Depending on how much you're enjoying the tinkering journey vs. how much you just want a nice functional compact sub, at some point a flat pack DIY subwoofer kit from Parts Express could make more sense.

totally agree with that!

I had two SB-1000s too, sold them then built two Dayton based subs powered by Hypex NC250MPs and they actually beat the shite out of the SVSs..... (actually this is how my DIY journey started, was a real eye-opener)

Your FAST setup looks cool. I've been really pleased with the 2xSB-1000. It's a small room though. In a larger room I could see them running out of steam. Especially for movies. I use mine only for music though. So they great extension down into the 20-30hz range and way more output than I need.

 

[MCH]

My understanding is that a lot of SVS subs' performance (specifically, bass extension?) is enabled by their DSP programming. Without a DSP assist, I think a 12" driver in a 1' sealed box is going to be kind of anemic. The DSP also keeps the user from doing anything stupid like overloading or bottoming out the driver.

I'd factor DSP into the equation if you're hoping to repurpose the SVS.

Thanks John. Yes, i have considered this, but i would definitely trade some bass extension for that rumble. I see all this as a last desperate effort as the resale value might be close to nothing.

Ah, and i think i know what i did wrong when trying to read the i2c line: These subs have auto sense and turn off after some minutes with no signal. I was paying attention to that when doing my tests, but i guess this task is on the microcontroller, so when i powered it down, it could be that all the digital board went off as well, there must be one pin that needs to stay high or something.... I should have cut the i2c lines between the microcontroller and the DSP instead of just power it down.... Well, now i don't fancy to dissasemble everything again, next time will be...

 

[Chrispy]

Thanks John. Yes, i have considered this, but i would definitely trade some bass extension for that rumble. I see all this as a last desperate effort as the resale value might be close to nothing.

Ah, and i think i know what i did wrong when trying to read the i2c line: These subs have auto sense and turn off after some minutes with no signal. I was paying attention to that when doing my tests, but i guess this task is on the microcontroller, so when i powered it down, it could be that all the digital board went off as well, there must be one pin that needs to stay high or something.... I should have cut the i2c lines between the microcontroller and the DSP instead of just power it down.... Well, now i don't fancy to dissasemble everything again, next time will be...

Curious, why didn't you report this as a problem under warranty from the start? Have you tried that route now?

 

[MCH]

Curious, why didn't you report this as a problem under warranty from the start? Have you tried that route now?

I did, and I received a new amp plate free of charge from svs. The new plate reduced but didn't eliminate the issue.
At the time, it was for me it too much of a hurdle to return everything, so decided to set the xover frequency a bit lower until I could not hear the rumble and live with it.
But now I decided to play a bit before taking definitive action

 

[Chrispy]

I did, and I received a new amp plate free of charge from svs. The new plate reduced but didn't eliminate the issue.
At the time, it was for me it too much of a hurdle to return everything, so decided to set the xover frequency a bit lower until I could not hear the rumble and live with it.
But now I decided to play a bit before taking definitive action

It still seems the problem is more likely on your end....

 

[Hayabusa]

Hi,
I own two SVS SB-1000 subs since a little over one year ago and since day 1 i have been experiencing a constant rumble/noise whenever the sub is on as explained here:

Problem with sub noise

Hello gang, I think I might have a problem with my new sub. But as it is also my first sub I am not sure it is a real problem, so wanted to ask here…. The sub is a SVS SB-1000 (non pro, but new, probably one of the last ones around). The problem is that whenever it is on, I can hear a...

www.audiosciencereview.com

It is present in the two subs i own in different degrees, is very audible, specially at night when watching films, and is there even when nothing is connected but the power cable, what eliminates the possibility of a ground loop.

I contacted SVS and they kindly sent me a new amp plate and even though this new amp had lower noise than the original it replaced, the noise is still there.

Member @connta explained that he had a similar experience with the SVS PB-1000 and even confirmed that all the subs of this model they had in his local shop had the same issue:

Troubleshooting the sub (PB1000) after AVR change

Recently i switched AVRs, went from Onkyo 646 to Denon x4700h, the results are mixed considering the price of Denon but oh well, life goes on. In any case, everything was "fine" with Onkyo, didnt really notice anything out of the ordinary. Switched to Denon and when running Audyssey i noticed...

audiosciencereview.com

This tells me it is a design issue.

As otherwise these subs are ideal for me and to sell them would be a pain in the rear and probably the shipping cost would be as much as i would get for them, i decided to keep them and see what i can do.
My first though was to use a external power amplifier direct to the drive, bypassing all the electronics but leaving the plate there to keep the enclosure sealed. But i need 300 W per channel and even though i still have this alternative on the back of my mind, before doing that i thought that trying to repair it can be a cool project to learn something from, and this is what i am going to try. Any comments or suggestions are welcome!

Two important pieces of data are:
1. the only control that has any effect on the noise is the crossover setting knob of the amp, the higher the crossover frequency, the louder the noise. If set below 60-70Hz there is no noise at all.
2. The volume has no effect on the noise. No matter if you set it to the max or to the min. the noise is the same.

My findings so far:

@trl posted some time ago a nice thread with inside pics and some findings that help me understand how the amp works. I did some measurements and followed traces to confirm and expand some of the information.

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

The amp plate is a fully digital amplifier. The signal flow as is something like this:

line in -> ??? -> (channel R only) AK5358A ADC -> 24 bit 48kHz i2s -> STA309A DSP -> DDX ("direct digital amplification", some sort or PWM signal) -> STA516BE digital amplifier chip -> driver

The fact that the only thing that has some effect on the noise is the crossover frequency and that if set below 60 Hz the noise was gone made me think that the amplifier is capable of outputting a clean signal, so the problem should not be there. The suspects were now the DSP, the ADC or whatever is before the ADC.

But what does not fit is the fact that the volume control has no effect on the noise. The volume pot is a potentiometer that goes from 1 kOhm to 0 Ohm to ground. Initially i was thinking that the volume control was acting somewhere in the amplifier chips or in the DSP, but the traces go all the way to the oposite side of the PCB where input signals are. Unfortunately there are lots of black resin there and i cannot see nor use my multimeter there.

I started to suspect that the problem could be somewhere before the ADC.

I measured the analog input of the ADC (pin 1, R channel, the only connected) with a multimeter with no source connected and i measure a constant 2.4 volts. I don't know if this is normal but it is not what i was expecting. Maybe i am missing something but could this be the source of the noise? Turning the volume control has no effect on that signal, that stays always at 2.4 volts....

With all this information, this is my plan to confirm the hypothesis of the bad analog input signal and at the same time try to solve the issue:
What if i bypass the analog input, remove the ADC chip and input a 24 bit 48kHz i2s signal directly to the DSP chip? If the problem was at the ADC or before, i should have clean output. If not, i will stay as i was, but with a sub with digital input...

What do you guys think? is that 2.4V at the input of the ADC normal? is it worth trying my plan?

the AK5358A ADC has only a single ended power supply and most likely the input and output have a DC offset of Vcc/2 , so 2.4V seems normal

 

[Hayabusa]

the AK5358A ADC has only a single ended power supply and most likely the input and output have a DC offset of Vcc/2 , so 2.4V seems normal

You could check how stable the Vcc of the ADC is ( if you have an oscilloscope )

 

[MCH]

You could check how stable the Vcc of the ADC is ( if you have an oscilloscope )

No I don't have one, but later on I found out (post #9) that both volume and xover controls go directly to the microcontroller and from there to the DSP. That means after the ADC, and that rules out my initial theory that the analog or ADC sections could be causing the issue. But thanks for the suggestion.

 

[Hayabusa]

No I don't have one, but later on I found out (post #9) that both volume and xover controls go directly to the microcontroller and from there to the DSP. That means after the ADC, and that rules out my initial theory that the analog or ADC sections could be causing the issue. But thanks for the suggestion.

You were saying that the crossover settings have an influence on the noise which is done in the DSP . If its not the ADC then it looks like it can only a DSP issue?

 

[MCH]

You were saying that the crossover settings have an influence on the noise which is done in the DSP . If its not the ADC then it looks like it can only a DSP issue?

This is what I believe but of course I can't be sure.
The key is that the volume has no influence on the noise, and the volume happens at the DSP. That rules out, not completely but almost, that the noise comes from before (unless something is clipping badly the input even without signal or something like that)