[mlundy57]

I finally got around to troubleshooting the hissing/crackling sound in my Wedgie system that could only be heard when music wasn't playing or was playing at very low levels (-40 on the volume display).

I traced it to the in-line filters I built. Also, if I touched the filter housing and moved it just a little I could set up a much louder hum that could be heard over the music. Touch and slightly move it again and the hum would go away.

Here's a picture of the filter.




The housing is a non-conductive schedule 80 PVC electrical box. As you can see, the channels are separate and do not touch each other. When I check for continuity I get readings I would expect i.e. shorts going input to output through the caps and through the by-pass legs, opens between positive and negative parts of each leg, the outputs of the filtered and by-pass legs and opens between the two channels.

Correction: I put a new battery in my meter and am getting different readings. With the new battery the readings are as described above except that I now get opens through the caps. This is the same whether I check at the Cardas connectors or the leads coming out of the caps.

The connectors are Cardas.

Any thoughts/ideas on what is going on here?

Thanks,

Mike

[Peter J]

Mike, can you isolate the noise to a specific channel or is it in both equally?  Also, does it remain constant on both sides of filter? Meaning on the pass thru and filtered sides.

[mlundy57]

Peter,

It's both equally.  When I take the filter out of the system and run direct from the preamp to the power amp the noise goes away.

It is only on the filtered legs to the Wedgies.  It is not occurring in the subs via the by-pass leg.  Also, it is most pronounced in the tweeters.

I edited the readings in my earlier post. My meter was acting up so I put a new battery in and got different readings through the caps.

Mike

[HAL]

Mike,
The reading across the filter caps should read open, not shorted.  The ground legs should read short as you describe.

Sounds like some of the solder is possibly shorting across the input or output RCA connections and might be causing the problem. 

[Folsom]

Does it occur with only one amplifier on?

[mlundy57]

Mike,
The reading across the filter caps should read open, not shorted.  The ground legs should read short as you describe.

Sounds like some of the solder is possibly shorting across the input or output RCA connections and might be causing the problem.

HAL,

I'll borrow my wife's magnified lamp to take a closer look

Does it occur with only one amplifier on?

Folsom,

The way I trouble shot it was to start with everything on and the noise coming from the Wedgies.

First I disconnected the speaker cables from the power amp, everything still on to see if the cables were picking up noise. Nope, all sound, including the noise went away.

So I plugged the speaker cables back in, sound and noise came back.

Then I disconnected the RCA input interconnect from the power amp. Sound and noise went away so I plugged the interconnect back in to the power amp. Sound and noise came back.

Next I disconnected the other end of the power amp input interconnect from the filter. That's when I noticed the increase and decrease in the noise when I moved the filter box.

At this point I suspected the filter was the culprit so I connected the preamp directly to the power amp and the sound came back but the noise was gone.

Culprit identified, the in-line filter.

Next step is going to be to follow HAL's suggestion and carefully inspect the connections under magnification.  If this is the problem, I expect to find bad connections on the output side of the filter legs.  If the bad connections were on the input side I would expect to have heard the noise in the subs as well but I didn't.

Mike 

[Folsom]

I'd almost guarantee it's a grounding issue. There's a solution for that, but it's somewhat still in the testing phase. It works fab for me, and hard to say with another forum member whom has yet to discern what qualities are with what piece of equipment. Also, Tyson has my unit ATM so maybe he'll be able to say shortly.

If you'd like I can provide you with the simple plans.

Also you might be surprised about what can interact that's insulated/non-conductive if any capacitance forms between it. A non-grounded case is prone towards this without a doubt. Is there any affect on noise if you touch the case and an RCA barrel ( ground ) ?

[mlundy57]

I checked all the solder connections.  There is no cross contamination between the + and - positions on any of the connectors.

Not sure how grounding fits in. Since the noise doesn't exist when the preamp is connected directly to the power amp, only when the signal passes through the filter, if it is a grounding issue it would have to exist in the filter box wouldn't it?

Right now I have the filter out of the system so I can't try touching the case and barrel at the same time. However, the case itself is non-conductive (it's designed to safely house exterior electrical connections) so it should not act as a ground. 

[Folsom]

I can't help if you do things entirely different, or tell me you don't think it's going to matter. Grounding just within the box? No....... Ground paths exist between all the components and back to your breaker box. Which ones are active, and how active, is another story. If the equipment is smart it is likely to break/prevent unwanted paths but typically they exist even when "disabled", as an inactive or relatively inactive path.

Don't bother touching without it in the system.

Does it make the noise when the filter is in but only with one amp plugged into it?

[Danny Richie]

It sounds like it is somehow creating a ground loop.

[Folsom]

It sounds like it is somehow creating a ground loop.

Right, which is part of the information I'm asking for, so hopefully we'll get it solved in short order.

[G Georgopoulos]

the crackling sound is a result of bad connection
you cant inspect connections with a magnified glass
you have to resolder/reheat them (all)

good luck

[mlundy57]

I'll put it back in the system in the morning and check out the touching and one amp at a time

[Folsom]

the crackling sound is a result of bad connection
you cant inspect connections with a magnified glass
you have to resolder/reheat them (all)

good luck

In both channels? Hm, now that isn't easy to locate. I'm not convinced it's not RF or ground noise. You might be impressed what sorts of odd noises can jump on ground when the loop goes all the way back to the breaker box.

[G Georgopoulos]

yes in both channels if it is a stereo amp with common ground
i dont know what filter is this,it appears as coupling caps and distribution
network at the same time...

[Folsom]

yes in both channels if it is a stereo amp with common ground
i dont know what filter is this,it appears as coupling caps and distribution
network at the same time...

George, there's no common ground in the filter for R/L besides parasitic capacitance. This leave the aux amp that isn't used without the filter as a place to have a common broken solder connection. This is unlikely given that amps preferably don't mix the grounds right at input, in the audiophile world (commonly).

[gregfisk]

Have you tried disconnecting the woofers on the bypass side of the filter to see if that is causing the ground loop?

[Folsom]

Have you tried disconnecting the woofers on the bypass side of the filter to see if that is causing the ground loop?

The woofer's themselves won't contribute to the group loop likely unless maybe if the subwoofer amplifier was some estranged balanced output device or CSS driven without a ground/virtual ground... etc. But disconnecting the amplifier for the subwoofers as I suggested would in fact tell us just thus! Perhaps that's what you mean Greg, but I just wanted to make sure because not having speakers connected with a powered amplifier isn't advisable.

[Captainhemo]

the crackling sound is a result of bad connection
you cant inspect connections with a magnified glass
you have to resolder/reheat them (all)

good luck

this seems more likely to me as well, especailly if you are able to touch the  filter  and move it slightly  resulting in a change in the  crackle / noise.
If it were  a ground  loop, would it not  be there with just the  pre and  amp  regardless of the  filter being added , the filter isn't adding an additional ground, it's just  inline between the two components 
The last ground loop I dealt with  was  being generated by the  coax feeding my cable box that was in my system, it was introducing an additional ground  via the cable itself. But it  was more of a 60 hz hum, not a crackle that changed  when i touched the  box

I don't see how that filter could be adding an additional ground  aside from something being  shorted to the existing ground in that circuit

EDIT  DOH,  sorry, I wasn't paying  close enough attention... didn't even realize there was a bypass  passing to the sub amps.   After re-reading  I too would disconnect those amps and see where  that leads
jay

[G Georgopoulos]

I agree with you

however

this filter is strange...