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Squealing Sound from Mains with intro of new Subs

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I am desperartely seeking help on some system noise I started encountering with the addition of two new SVS SB4000 subwoofers into my system. I replaced two older subwoofers( Elac debut 12 and a Cadence CSX-12). The new SVS subwoofers seem to be injecting a high pitch squealing noise that is coming out of my mains. My system consists of a Decware CSP2+ preamp with two output per channel. My amps are monoblock Melody 845-1 tube units. I have gone through all the possibilities with SVS and they agreed to send me new amps to replace the ones that came with the units. The new amps create the same squealing noise. To give some additional background when I turn the preamp off the noise still is present in the mains. The high pitch squeal is not effected by changes in volume. The sound appears to be emanating from the SVS subwoofers amplifiers. My typical mains are 94db efficient but its still audible in some 86db speakers I own. The Decware CSP2+ preamp has output level controls. One for the left and one for the right channel. It effects both R and Left line level outputs equally. With the preamp turned off when I turn the output levels all the way all the way down the squealing stops in the corresponding channel which seams that the noise may be being shunted to ground....maybe. This points to some possible grounding issue within the preamp...possibly?  However if I plug the mains amps directly into the subs high pass output which removes the preamp from the system I still get the squealing sound. This did not happen with my other subwoofers. The other thought is that is some type of impedance mismatch happening between the tube amps and the solid state amps being on essentially a Y-Splitter at the preamp. I currently put a DSpeaker unit between the subs and the preamp and this essentially blocks the noise however I would prefer not to have this additional A-D-A stage in my system.  I have tried cheater plugs on both units to try to isolate a ground loop to no avail. The SB-4000 subs have DSP and im wondering if this is some unchecked digital noise leaking into the system.

I know this might not be the website forum for this but I am thinking more and more that this is a digital related noise so I thought I might look here for advice. Any thought wisdom or advice from the community would be appreciated. Has anyone come across this phenomenon? I would really like to keep these subs in my system but before I move on I would like to have an idea of what is happening so I can avoid this moving forward. I am happy to provide input and output impedance numbers for the units if somebody feels this might help. Thanks for any help or advice in advanced.
Regards,
Steve C

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I am desperartely seeking help on some system noise I started encountering with the addition of two new SVS SB4000 subwoofers into my system. I replaced two older subwoofers( Elac debut 12 and a Cadence CSX-12). The new SVS subwoofers seem to be injecting a high pitch squealing noise that is coming out of my mains. My system consists of a Decware CSP2+ preamp with two output per channel. My amps are monoblock Melody 845-1 tube units. I have gone through all the possibilities with SVS and they agreed to send me new amps to replace the ones that came with the units. The new amps create the same squealing noise. To give some additional background when I turn the preamp off the noise still is present in the mains. The high pitch squeal is not effected by changes in volume. The sound appears to be emanating from the SVS subwoofers amplifiers. My typical mains are 94db efficient but its still audible in some 86db speakers I own. The Decware CSP2+ preamp has output level controls. One for the left and one for the right channel. It effects both R and Left line level outputs equally. With the preamp turned off when I turn the output levels all the way all the way down the squealing stops in the corresponding channel which seams that the noise may be being shunted to ground....maybe. This points to some possible grounding issue within the preamp...possibly?  However if I plug the mains amps directly into the subs high pass output which removes the preamp from the system I still get the squealing sound. This did not happen with my other subwoofers. The other thought is that is some type of impedance mismatch happening between the tube amps and the solid state amps being on essentially a Y-Splitter at the preamp. I currently put a DSpeaker unit between the subs and the preamp and this essentially blocks the noise however I would prefer not to have this additional A-D-A stage in my system.  I have tried cheater plugs on both units to try to isolate a ground loop to no avail. The SB-4000 subs have DSP and im wondering if this is some unchecked digital noise leaking into the system.

I know this might not be the website forum for this but I am thinking more and more that this is a digital related noise so I thought I might look here for advice. Any thought wisdom or advice from the community would be appreciated. Has anyone come across this phenomenon? I would really like to keep these subs in my system but before I move on I would like to have an idea of what is happening so I can avoid this moving forward. I am happy to provide input and output impedance numbers for the units if somebody feels this might help. Thanks for any help or advice in advanced.
Regards,
Steve C

 

 


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The other thought is that is some type of impedance mismatch happening between the tube amps and the solid state amps being on essentially a Y-Splitter at the preamp.

 

No. Because:

 

Quote

However if I plug the mains amps directly into the subs high pass output which removes the preamp from the system I still get the squealing sound.

 

Btw, if your preamp is now disconnected from the poweramp, my "No" counts.

 

Also, I think you'll have low level INput and high level INput there. If all is right, when you connect the poweramps directly you will be connecting to the high-level input. Correct ?

I suppose it is possible to have this twisted around (put poweramp output to low-level input or preamp output to high-level input) and incur for a possible situation like this at both situations (either the sensitivity of the input of the subs is too high, or you need to put up the volume on the sub too much, respectively. Btw, this will be a way too long shot, but you'd still need to have this right anyway.

 

Peter


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Peter 

 

Thanks for jumping in so quickly and taking the time to help out. To answer your first question. The subs power cords do have a three prong cord with ground.

 

The subs do not have a high level input. The have a left and right low level input and a left and right high pass output that allows one to run their amp off the sub to take advantage of the dsp crossover. I do not intend to use this in my setup as I do not want an A/D/A conversion above 80 hertz. However I do get the squealing noise from my mains if my amps are looped through the subs or if they share a line level signal. I have two of these subs and monoblock amps and in both instances they create the same squealing noise. The level or pitch of the squealing noise is unaffected by any changes I make on the sub control panel (Volume, polarity, phase etc.) 

 

The only thing that has mitigated the squeal is putting the DSpeaker unit between the sub and the preamp and when I do have both the subs and the monoblocks connected to the preamp and I turn the output levels all the way down the noise disappears. This happens whether or not the preamp is powered on or not. My preamp (Decware CSP2+) has input and output trim pots as well as a volume control. The volume knob and the inputs trim pots have no effect on the squealing noise. 

 

Do you know if a potentionmeters ground is lifted when turned all the way down? This does seem to point to some type of grounding issue.

 

 

 

 

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4 hours ago, sandston said:

Do you know if a potentionmeters ground is lifted when turned all the way down?

 

What I understand of it, is that the pot meters you talk about are for gain control.

 

4 hours ago, sandston said:

I turn the output levels all the way down the noise disappears. This happens whether or not the preamp is powered on or not.

 

This looks to be crucial and seems to point at some feedback (OpAmp like) situation which turns into oscillation. This would be the sound you're hearing IMO and which in the end could be some high frequency I-don't-know-what from the sub, that spitting back into the input or actually anything up to the mains.

Having said this, if the preamp is completely out of the way (like put it upstairs in a box), you should not be able to copy this behavior. I had the idea you still could. That not assumed:

Best would be to put this kind of idiot idea to the preamp manufacturer and propose some kind of ferrite (filter) around the interlink towards the sub(s).

image.png.30bda0e0e4874e299c238e7c9352aae8.png

 

If the manufacturer could agree with this, make the suggestion "what about the mains then ?". And it may give him other definite ideas like sending back the subs.

 

The subs will use some means of Class D amplification which is known not to be the most easy on the environment, so to speak. I would, for example, experiment with a parallel grounding wire next to the interlink going from the preamp to the sub(s). Thus, clamp a crocodile (etc.) to the metal part of the interlink's outside part of the RCA connector, do that at both ends (preamp and sub) and of course a wire to connect the both. See if it makes a difference (less of the squealing sound).

 

Try to put the subs in a wall socket without protective earth (invest in a long extension block/cord to reach an other room, if necessary).

 

Try testing with one sub at the time; they may influence each other or even "loop" via the preamp to each other and oscillate (back).

 

5 hours ago, sandston said:

Do you know if a potentionmeters ground is lifted when turned all the way down?

 

I don't think so; If I am correct on the idea of feedback and how it happens, it should be a kind of passive signal to ground resistor change circuitry which remains in the signal path just *because* it is passive (no power required). If the resistance becomes very high, no feedback as such will occur hence no oscillation either. The oscillation should be about a too high frequency of what this means of gain (looping) can handle (it starts to bounce - think of feedback as a correction). But this is all enormously wild guessing (full with mistakes) because of not knowing the circuitry which should be passive.

 

It could be that others get the better ideas from this shooting in the dark. Like the preamp manufacturer himself (the guys from Ohio probably won't know too much about it anyway). Please keep in mind the prerequisite of your proof that without preamp around you can't copy the behavior. If you can after all, then it could be best to send back the subs.

 

Peter


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As Peter is suggesting, you may need to experiment with additional grounding of components.


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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3 hours ago, PeterSt said:

 

What I understand of it, is that the pot meters you talk about are for gain control.

 

 

This looks to be crucial and seems to point at some feedback (OpAmp like) situation which turns into oscillation. This would be the sound you're hearing IMO and which in the end could be some high frequency I-don't-know-what from the sub, that spitting back into the input or actually anything up to the mains.

Having said this, if the preamp is completely out of the way (like put it upstairs in a box), you should not be able to copy this behavior. I had the idea you still could. That not assumed:

Best would be to put this kind of idiot idea to the preamp manufacturer and propose some kind of ferrite (filter) around the interlink towards the sub(s).

image.png.30bda0e0e4874e299c238e7c9352aae8.png

 

If the manufacturer could agree with this, make the suggestion "what about the mains then ?". And it may give him other definite ideas like sending back the subs.

 

The subs will use some means of Class D amplification which is known not to be the most easy on the environment, so to speak. I would, for example, experiment with a parallel grounding wire next to the interlink going from the preamp to the sub(s). Thus, clamp a crocodile (etc.) to the metal part of the interlink's outside part of the RCA connector, do that at both ends (preamp and sub) and of course a wire to connect the both. See if it makes a difference (less of the squealing sound).

 

Try to put the subs in a wall socket without protective earth (invest in a long extension block/cord to reach an other room, if necessary).

 

Try testing with one sub at the time; they may influence each other or even "loop" via the preamp to each other and oscillate (back).

 

 

I don't think so; If I am correct on the idea of feedback and how it happens, it should be a kind of passive signal to ground resistor change circuitry which remains in the signal path just *because* it is passive (no power required). If the resistance becomes very high, no feedback as such will occur hence no oscillation either. The oscillation should be about a too high frequency of what this means of gain (looping) can handle (it starts to bounce - think of feedback as a correction). But this is all enormously wild guessing (full with mistakes) because of not knowing the circuitry which should be passive.

 

It could be that others get the better ideas from this shooting in the dark. Like the preamp manufacturer himself (the guys from Ohio probably won't know too much about it anyway). Please keep in mind the prerequisite of your proof that without preamp around you can't copy the behavior. If you can after all, then it could be best to send back the subs.

 

Peter

Peter

I appreciate you kicking the can around with me on this. To be clear the squealing happens with the preamp out of the equation. If I detach the preamp and hook the amps to the line level output on the sub I get the same squeal as when the amps are hooked to the input of the sup via the preamp. One of two things I have found that stops the squeal is when I turn the output voltage level pot to zero on the preamp. In this preamp the output signal goes through this pot and is then split to two RCA outputs. No circuitry between the pot and the outputs. Think of a simple y-cable. The pot does not sit between the RCA outputs. When the pot is turned to zero the squealing stops which makes me think this might somehow shunt the noise to ground. However this is beyond my technical knowledge of circuits. I will test the idea of the parallel ground wire as this would be recreating the shut to ground scenario. 

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30 minutes ago, sandston said:

One of two things I have found that stops the squeal is when I turn the output voltage level pot to zero on the preamp.

 

What this appears to tell you, is that the low level squeal is coming in via the input leads to the Preamp, or via the same leads to the amplifier directly when the Preamp is out of circuit. The output voltage potentiometer  is simply attenuating the signal down to inaudibility as it is designed to do.


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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4 hours ago, sandston said:

One of two things I have found that stops the squeal is when I turn the output voltage level pot to zero on the preamp.

 

OK. I only now understand that you can coincidentally use that as a means to prove how the squeal can go away.

 

Now what.

 

3 hours ago, sandyk said:

The output voltage potentiometer  is simply attenuating the signal down to inaudibility as it is designed to do.

 

Alex, what I got from it, is that this "output voltage pot" is no attenuator but a gain control. And a passive one at it (I forgot how I came to that conclusion - maybe it is wrong).

Additionally the normal attenuation knob doesn't take out the squeal sound (as I understood it).

 

 

 


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1 hour ago, PeterSt said:

Alex, what I got from it, is that this "output voltage pot" is no attenuator but a gain control. And a passive one at it (I forgot how I came to that conclusion - maybe it is wrong).

Additionally the normal attenuation knob doesn't take out the squeal sound (as I understood it).

Peter

 I think that we need either a photo or a block diagram of the actual setup.

Alex


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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I was thinking the same thing. Below is a diagram showing the layout with the preamp in the mix. To recap there are two subs and two monblocks for the mains. The squeal occurs on both channels and is isolated on each channel. When the output pots on the preamp are zeroed out the squeal disappears. The level of the squealing is always constant. The preamp does not need to be turned on for this to happen. The volume  and the input pots on the preamp do not effect the squealing sound at all. The subs have stereo in and a high pass stereo out. If I remove the preamp from the mix entirely and hook the monoblocks up to the high pass output of the sub the squeal is still there. I think its pretty evident the squeal originates in the subs. Somehow the topology of the output of the preamp is canceling the noise out. By what electrical means I cannot say. I am wondering if there is some type of filter that would mitigate this noise and not effect the quality of sound in the subs? I should probably just return the subs but I really like the quality of the sound of these and I really like the control app that SVS has developed. I have included input sensitvities and impedance numbers for the various stages on the drawing as well as a few relevant photos of the preamp and subs for those who are more circuit curious. 

 

I have been trying Peters parallel ground suggestion but have not yet found a point between the units that mimics the effect of turning the output pot to zero. The chassis of the preamp appears to be completely isolated from the circuit so I need to open my unit up to get a common ground point in the preamp. 

 

The attached photo of the preamp attached shows the outputs in the lower left corner. My unit has four outputs and no headphone jack. The resistors that make up the "Summing Circuit" to the mono sub output on this unit are not present in my unit. 

 

 

2056148807_Preampinternals.thumb.jpg.77c0e9866dd9c4179dd07e7e840c9864.jpg

 

 

 

Again thanks again for taking the time on this with me.

Preamp.jpg

preamp internals 2.jpg

SVS amp.JPG

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image.png.584c49122270920774cf7371eed2bdd3.png

 

Strip a wire 1/4" or so, hold the bare part where you see the mouse pointer, and press on the plug of the interlink such that the bare part of the wire is caught in between the chassis terminal and the plug. Check by putting a little tension on it, whether it is fixed sufficiently.

Do this at the preamp side the same with the other end of the wire.

 

You obviously can hold the wire also inside of the RCA plug (this will work more easily). But be careful not to make contact with the pin in the middle. But if you coincidentally make this connection between ground and pin, then there is no issue at all. Only no sound.

 

 

Are you only using the Right input of each ? that is what I would do (but see the manual).

 

No further news. Maybe avoid Bluetooth, if it can be disengaged in the first place. But I suppose it is necessary for all the sub's settings (PEQ and such).


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7 hours ago, sandston said:

The level of the squealing is always constant. The preamp does not need to be turned on for this to happen.

 At minimum position the output level pot. is putting a s/c on that interconnect to the monoblock  thus getting rid of the squeal.


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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Try without Protective Earth (use a two-prong cable to the subs).

 

The more I think about it, the more I see you'd talk about what I would call a whining sound. Just 60Hz (or 50Hz) but higher pitched (still on/off at 60 or 50Hz). Rectifier stuff.

 

Can you measure the frequency with an iPad or Phone ? Notice that you will see many frequencies but one (highest peak) will be the lowest. It is about that one.


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Still no luck with mitigating the squeal attached are two screen shots showing a frequency screen grab with the sub on and the sub off. No squeal seems to be noise a several regularly spaced frequencies. I also substituted an A/V unit I had and plugged the sub input into one of the inputs on the AV unit and the squeal can still be heard with the volume turned all the way up. 

SoundAnalyzer_Sub Off.png

SoundAnalyzer_Sub On.png

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Either way, that appears to be a pretty poor S/N ratio !

 Where were you measuring it ?


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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LED lights and fluorescent ballasts are not our friend with sensitive electronics.  Before you go any further make sure that the only lighting enabled in the room

is incandescent in order to rule out interference from lighting.


Regards,

Dave

 

Audio system

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In that case you already have problems due to the very poor S/N.

Perhaps you need to sort that out first before worrying about the Sub ?


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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22 minutes ago, PeterSt said:

Maybe ask SVS what could be impeding for a 2500Hz base tone. 

 

Or maybe forum members know? 

Hi Peter

I  agree, but if he sorts out the problem that is causing such a poor S/N ,the other problem may either go away or be reduced to inaudibility.

Rregards

Alex


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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9 minutes ago, PeterSt said:

Alex, i`d agree with that too. But this is captured by microphone. Not much value in that as such, IMO. 

Point taken.:)

 The measurements need to be taken using a CRO or an A.C .Millivolt Meter.


"If you can't hear the difference between an original CD and a copy of your CD,

you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist. - Cookie Marenco"

 

PROFILE UPDATED 18-06-2019

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