Crackling noise: cable problem?

allanb · 17-11-2009, 8:52 AM

I have a Marantz amplifier (PM7200) and CD player (CD5003), with Kef Concerto speakers. There is a persistent crackling noise, not all the time but usually several times in any CD, sounding very much like the static noises that you sometimes get with a vinyl record. I think - though I can't be sure - that while it's happening the actual audio sound is also degraded.

As far as I can tell it's random, i.e. it doesn't always happen at the same point on a CD.

It never appears when I'm listening through headphones. But when the headphones are in use, it can still be heard by anyone listening to the speakers.

There is quite a long cable run to the speakers, and the cable is not "special" - it is however quite heavy copper cable. I have made and re-made the connections at both ends.

I don't want to restart the debate about whether cable can make subtle differences to the audio sound. I'm talking about a gross and very obvious noise. Does anyone know whether the cable itself could induce this kind of thing?

Gaspode_TWD · 17-11-2009, 11:23 AM

RFI (Radio Frequency Interference), which is what this sounds like it could be, can be caused by a number of sources and can be picked up at various points. Do the speaker cables run close to mains cables? Perhaps they are picking up noise from a switch?

allanb · 17-11-2009, 4:08 PM

I'm not sure what you mean by "close". Behind the amplifier the speaker cables are within about six inches of the power cable for the amp itself. There's not much I can do about that, unless there's something I could wrap round them as a shield - is that possible?

They also run very close to a telephone cable which carries my internet connection. For about 8 feet they are within two to three inches, and at one point, where they have to pass through a beam, they are actually in contact (although of course insulated). Could that have anything to do with it?

I can't find any switches near them.

Obviously I've thought about relocating them, but because of the layout of the house it would be very difficult.

Roger Thornhill · 17-11-2009, 5:11 PM

What unit has the headphone socket you are using? The CD or the Amp?

Does the noise disappear when volume is zero?

If you think the wires (doubtfull) try unplugging the telephone wire (can you survive an eveing without internet?

) and see if the noise disappears.

Gaspode_TWD · 17-11-2009, 5:31 PM

If it is RFI then my only suggestion is trial & error. Move the cables (even if only temporarily) to see if it makes a difference. The reason I mentioned mains cable is that sometimes a switch 'spike' can travel along it. Another method is to try to identify the item(s) that cause the spike. It could be a 'fridge motor, central heating, something next door, etc.

If it happens a lot then I assume its something that it switching on & off regularly.

I'd also support the suggestions from Roger Thornhill.

BlueWizard · 17-11-2009, 7:56 PM

Not that there is anything wrong with the advice you've already been given, but 'hum', 'hiss' and 'buzz' are more likely to be electrical interference. 'Crackle' is far more likely to be 'dirt' in some form; dirty volume or tone controls, dirty switches, dirty cable contacts, etc....

However, it is also possible that it is a stray wire that is close to shorting an input or output. The position of this stray strand of wire changes with temperature, and it could be on the verge of making contact, and causing the crackling sound.

With no input or music playing, rotate the Volume and Tone controls up and down. Do you hear a static like crackle, if so, you controls are dirty. If it is only moderately dirty, then just quickly rotate the control up and down past the area where the crackle is. Keep doing this until the crackle goes away.

If you have a rotary switch to select the input source, try putting some left/right pressure on the control and see if you hear any static. If the control is constantly in one position, then some corrosion many have built up on that contact. Again, rotate the control up and down several times to wipe the contacts clean.

Also, check the condition of your cable connectors. They should be clean and shiny. If either the cable or the amp contact looks dull and/or hazy, then you need to polish it clean. This can be as simple as wiping the contacts with some Isoproply alcohol, use a cotton bud, or a paper towel, just slightly damp with alcohol.

It that doesn't clean them, then burnish then with a pencil eraser. Naturally, all this contact cleaning should be done with the Amplifier and inputs sources OFF, and all residue must be clean away.

Next turn the amp back on, the gently wiggle the input cables on both ends, and see if you hear a crackling sound. This could indicate a failure in the cables internal wiring.

Also, make sure you speakers wires are clean and tight, and that no stray wires are sticking out here or there. Again, with the amp on, gently wiggle the speaker wires on both ends, listening for the crackle. That could indicate a problem internal to the speaker wire, or internal to the speaker cabinet contacts.

There are steps beyond this, but I don't recommend them for people who do not have some knowledge or aptitude for electronics.

Steve/bluewizard

cokanlan · 18-11-2009, 12:48 AM

If you have a rotary switch to select the input source, try putting some left/right pressure on the control and see if you hear any static. If the control is constantly in one position, then some corrosion many have built up on that contact. Again, rotate the control up and down several times to wipe the contacts clean.

Mark.Yudkin · 18-11-2009, 4:05 AM

The most likely cause is RF interference on the power supply caused by a motor (e.g. fridge) turning on or off. It's very common and the resolution is an RF filter plug on the affected equipment (CDP, amp). These are available at any electrical supplier. They can also be obtained at ludicrous prices and with fancier names from hi-fi dealers.

The second most lilely cause is wireless internet, although the symptoms are a little different. Try turning it off to see if that eliminates the problem.

The possibility of basic wiring issues are extremely unlikely and the symptoms rather different. I think that's the wrong direction to look into.

BlueWizard · 18-11-2009, 7:34 AM

Itty bitty teeny tiny point, I suspect Mark is using RF in a very general sense, and I realize I'm being painfully picky here, but RF is 'Radio Frequency'. Likely what Mark meant to say was EMI or EMF, meaning 'Electro-Magnetic Interference' or 'Electro-Motive Force'. Or more simply, one electrical device interfering with another.

Either way, he as a good point, and one that can be tested. Any of the large appliances in your home (Refrigerator, heater, furnace, air conditioning, etc...) can cause a transient spike when they turn on or off. This transient can radiate through the power lines as well as through the air, and be picked up by sensitive audio equipment.

By turning the thermostat in your house up and down, you can get the furnace or heater to kick on and off. Have the amp on, with the volume at normal listening levels, and have someone listen for the 'crackle' when the furnace kicks on and off.

You can do the same with your air conditioning, or your refrigerator, you can force them to turn on or off at will, and listen for interference.

Try any high current device you might have in your house that can turn on and off automatically. Consider high current devices that might not be so obvious; space heater, hair dryers, microwaves, blenders, washer, dryer, or anything with a motor in it.

If it is this type of interference, you might be able to fix it with a power strip that has a surge suppressor in it. This can be on the audio equipment or the source of the problem, or both. These are not exceptionally expensive, and should be readily available from many sources. You should really have these anyway; always good practice.

If that doesn't work, then you might have to go to something more drastic, such as the filters that Mark recommends.

There is a slim chance, that the problem might be related to the wiring in your house. If it has poor contacts with a lot of stray resistance or possibly inductance, this could be the source of the noise. For this to be true, your wiring would have to be very old, or very poorly installed.

The first thing to do is figure out the source of the problem; dirty controls, noise from high current or motorized electrical appliances, etc.... Then, once you know the source, it becomes easier to find the solution.

Though not absolutely true, generally the type of interference I'm talking about here, is more likely to be a 'crack' or pop or snap, than a crackle or crackling. Crackle more implies dirt, whereas 'snap, crack, or pop' implies EMI from high current sources or electric motors.

At least, that's my best guess.

Steve/bluewizard

allanb · 18-11-2009, 7:57 AM

Many thanks for all the suggestions. Some of them I've already tried, but you've given me plenty of new ones.

In answer to one or two points:

(Roger Thornhill)

What unit has the headphone socket you are using? The CD or the Amp? - both, but there's no audible problem with either of them.

Does the noise disappear when volume is zero? - I think so, but I need to do more testing. (You know what it's like when you're dealing with something unpredictable.)

(Mark Yudkin)

The second most lilely cause is wireless internet, although the symptoms are a little different. Try turning it off to see if that eliminates the problem.

The long phone line that I mentioned goes to a phone socket which feeds a modem (router) via a short cable. The router connects wirelessly to a desktop computer in an adjoining room, and to a laptop which could be anywhere in the house. Is that the kind of connection you meant?

(BlueWizard)

Just read your second post, for which more thanks.

If the problem is a switch, wouldn't that tend to produce a single "pop" or burst of noise as the switch opens or closes? The noise I'm getting may last for a second or for 5-10 seconds : it's not consistent.

Roger Thornhill · 18-11-2009, 8:33 AM

Quote:

Originally Posted by BlueWizard

.....................With no input or music playing, rotate the Volume and Tone controls up and down.............................................. ...............rotate the control up and down several times to wipe the contacts clean.................................

This is really good advice, for all AV equipment with 'analogue' controls (ie. not just a switch controlling an IC deep in the circuit). Do it once a month with the unit turned off and all should be ok.......................for ever!!

nik41 · 18-11-2009, 7:04 PM

it is good advice I get some awful noise on my guitar amp when I havnt been out playing in a while (at home only very small adjustments are made to volume - Women) so a good twist off the knobs makes a lot of sense once in a while

allanb · 27-02-2010, 1:08 PM

I posted this problem back in November and I'm grateful for all the replies; but although I've tried all of the suggested tests and remedies to the best of my ability, I still have the problem. I know now that it's not just a noise; there is occasionally a brief loss of signal (just a fraction of a second, but definite).

The amp has connections for two pairs of speakers; the problem is the same on both pairs, and it can appear on either channel.

It has never appeared on headphones, whether driven by the amp or by the CD player.

It is not affected by changing input: CD, vinyl, tape.

After many hours of testing, swapping components, etc, I'm just about convinced that (unless there's something really weird in the household electrics) the fault is in the section of the amplifier that drives the speakers.

The nearest hi-fi shop is a long way from where I live; they have already spent some time just listening to both the amp and the speakers in their shop, but the problem hasn't yet appeared to them. They haven't charged me anything, by the way; when I offered to pay for their time, they said "no, we won't charge you - we haven't solved your problem." They may be hoping to sell me a new amp, of course, but I wouldn't blame them for that.

If I take the amp to them again and say: "let's suppose that I'm right, and I'm willing to bet that the fault is in that particular section of the amp: can you replace all the components that could be the cause? At my expense, of course. If that doesn't solve the problem, it's not your fault."

Assuming that I trust them, would that be a reasonable proposition? In other words, should a competent repairer be able to identify and replace the bits that are relevant?

Roger Thornhill · 27-02-2010, 1:57 PM

An intermittent crackle and intermittent loss of sound, from both channels, not necessarily both at once from what i understand of your post?

This could be anything within the amplifier and i would think the company would say no to your request (i would i'm afraid) as the time to change everything and still the fault could occur because you missed the vital bit would just be uneconomic.

If you really like the amp and don't want a new one (and there's absolutely nothing wrong with this, there are components in my set-up i would not swap for anything) then you are going to have to give the amp to the company you are using (and they do sound like decent people) and be prepared to be without it for quite some time untill they experience the fault. Then some more (possibly quite a lot) time untill they experience the fault with test equipment connected and they happen to be looking at the test equipment when the fault occurs.

They may be able to lend you something while they have your amp in for diagnosis?

All this time costs money of course but i suspect (from what you've said) they will charge you an appropriate amount (they'll be working on other units whilst all the time listening to yours) in the hope that you'll come back to them and recommend them.

BlueWizard · 27-02-2010, 8:07 PM

I'm afraid I'm going to have to agree with your conclusion. From what you are telling us, and assuming you performed the many tests we suggested, it seems to narrow down to the power section of your amp.

I think the clue is the Headphones. There is little to no power available at the headphone jack, so I suspect something in your final power output section.

However, it depends on the amp. I just check the schematic for an old Pioneer amp I have, and the headphone come right off the amp's speaker terminals. It just has a resistor in series to lower the voltage to something headphones can manage.

However, is other amps, I suspect there is a separate output section to drive the headphones; a very small low powered output section.

So, again, if you've gone through all the tests, it would seem to be something internal to the amp.

Hopefully, it is something small and easy that they can fix. Otherwise, time for a new amp.

Steve/bluewizard

karkus30 · 28-02-2010, 12:24 AM

Power supply capacitors I suspect from your original description. I would get the amp looked at pronto. If you do blow a supply cap they make a hell of a mess and usually take out the speakers.

Mark.Yudkin · 28-02-2010, 12:20 PM

Unlike the others here I'm not convinced by your diagnosis, since the symptoms don't quite match and I prefer to eliminate the likely before addressing the improbable. Which doesn't means that the amp may not be faulty, of course, and karkus30 may well be right.

An RFI filter plug (Sorry Steve, but that's what they're called) will cost you very little from your local electrical supplier, and therefore I'd still suggest trying one on the amp first.

trailer · 28-02-2010, 12:46 PM

I would suggest getting a loan of another amp from the folk who are looking at yours to see if the fault is there still.

Roger Thornhill · 28-02-2010, 12:59 PM

Quote:

Originally Posted by Mark.Yudkin

...................An RFI filter plug..............................

Would RF interference cause a loss of audio though? The OP says when the crackle appears the audio is lost albeit for only a split second.

Mark.Yudkin · 28-02-2010, 1:04 PM

Quote:

Would RF interference cause a loss of audio though? The OP says when the crackle appears the audio is lost albeit for only a split second.

Yes, this is one of the common symptoms.

Roger Thornhill · 28-02-2010, 2:18 PM

Quote:

Originally Posted by Mark.Yudkin

Yes, this is one of the common symptoms.

Really? I can't say i have ever come across this before. All modern electronics are manufactured to withstand interference from RF, i realise the amp in question is not that 'modern' but even so.

How does RF interfere with an audio amplifier to cause a loss of it capabilities to amplify?

I am not saying you are wrong but in 20 years repairing domestic electronics i have never come across an audio amplifier which has been affected to such an extent as to lose output caused by RF interference. I would like to understand how this can occur.

Alan Mac · 28-02-2010, 2:34 PM

The headphone output does not seem to be affected, only the main loudspeaker output.

Would RFI not also affect the headphone output ?

Alan

Mark.Yudkin · 01-03-2010, 8:09 AM

Quote:

The headphone output does not seem to be affected, only the main loudspeaker output.

Yes, this is one of the reasons I have my doubts about a "power supply capacitor" problem. And depending on the amp design, RFI could affect the power amp section but not the headphone. And again, RFI is not a guaranteed diagnosis, but it is both cheap and simple to eliminate or exclude.

allanb · 01-03-2010, 5:49 PM

Quote:

Originally Posted by Roger Thornhill

The OP says when the crackle appears the audio is lost albeit for only a split second.

Not exactly. I can have the crackle with or without a brief loss of sound. But the crackle can go on for some time (typically 1-10 seconds), which makes me wonder whether it could really be caused by a switch; wouldn't the operation of a a switch produce (if anything) a single very short burst of sound?

Roger Thornhill · 01-03-2010, 6:00 PM

Quote:

Originally Posted by allanb

...................wouldn't the operation of a a switch produce (if anything) a single very short burst of sound?

No, not necessarily. I often find when a swich like an input selection switch starts to fail, it is because of oxidised contacts and these can produce the effects i think you are experiencing. The sound almost of an egg frying?

Try some switch cleaner

Contact Cleaner : Electronics Cleaners : Maplin

very sparingly in the switches.

I have done one of these amps where a transistor in the HDAM circuit for one channel was intermittently failing, causing an intermittent crackle.

Your amp is very similar to the PM-8000 whose service manual can be found here

Marantz PM8000 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine

You have to Register to be able to download the manual but it is free. I have no affiliation to this site other than i have registered.

Hope this helps.

allanb · 01-03-2010, 6:34 PM

Thank you. I should have mentioned that following earlier advice, I've already tried putting a filter in the socket that feeds all my audio equipment (it's a Belkin Surgemaster).

Mark.Yudkin · 02-03-2010, 8:37 AM

Quote:

I've already tried putting a filter in the socket that feeds all my audio equipment (it's a Belkin Surgemaster).

In which case there's a unanimity here that you'll need to get the amp serviced.

evans · 03-03-2010, 9:11 AM

I had the crackle sound from my speakers and then one of my speakers cut out not so long ago. I just moved the speaker connections at the back of my amp and all is well but i was very worried at the time that either my speakers or the amp had a problem. Could be some dirt had built up?

allanb · 04-03-2010, 6:51 AM

Well, I finally bought a new amp. I spent a nervous few hours after installing it, wondering what I would do if the crackle was still there: suicide, maybe?

But the noise has gone, and I like the new amp, and now I can actually listen to the music instead of listening to the system.

Thanks to all who offered advice.

Anyone want to buy a used Marantz amp, excellent condition, only one unidentified defect?