Crackling from mono amplifier.

[Windy Miller]

Hello all. I wondered if I might seek the thoughts of those with more experience than I have to resolve an issue I have with amplifiers.

I recently changed the power amplifiers I’m using from a Moon 330A to 400M monos. The sound is great and the extra power really does control the speakers superbly.

However, one of the amplifiers creates a crackling noise which is clearly audible through the tweeter and mid-range driver. This crackling is present through a single channel even if all the other components are turned off and the XLR cables removed from the back of the power amplifiers. I’ve turned off absolutely everything else in the house off and the noise persists. Swapping the amplifiers over results in the same crackling noise switching channels with no difference to volume or sound.

I’ve had the amplifiers returned to the dealer and to the distributor who say there is no fault and the solution offered was to try different cables.

To my ears the sound is affecting playback with music as though it is breaking up, particularly with guitar and piano.

I’m going back to the dealer next week but thus far no solution has been offered which has made any difference. I’ve tried various power blocks and DC blocking with no change. Does anyone have any experience of this or any possible solution?

Cheers Ian.

 

[Juancho]

Hello all. I wondered if I might seek the thoughts of those with more experience than I have to resolve an issue I have with amplifiers.

I recently changed the power amplifiers I’m using from a Moon 330A to 400M monos. The sound is great and the extra power really does control the speakers superbly.

However, one of the amplifiers creates a crackling noise which is clearly audible through the tweeter and mid-range driver. This crackling is present through a single channel even if all the other components are turned off and the XLR cables removed from the back of the power amplifiers. I’ve turned off absolutely everything else in the house off and the noise persists. Swapping the amplifiers over results in the same crackling noise switching channels with no difference to volume or sound.

I’ve had the amplifiers returned to the dealer and to the distributor who say there is no fault and the solution offered was to try different cables.

To my ears the sound is affecting playback with music as though it is breaking up, particularly with guitar and piano.

I’m going back to the dealer next week but thus far no solution has been offered which has made any difference. I’ve tried various power blocks and DC blocking with no change. Does anyone have any experience of this or any possible solution?

Cheers Ian.

Hi, I don't know these amps at all but recently had a similar issue with a Tresham amp. This amp uses two relays in the output circuit for slow start and safety cut out. The relays are mounted in octal sockets. I traced the fault to an intermittent contact in one of the relay sockets despite both looking in good condition. Of course none of this was visible on the 'Scope, and only occurred at decent volumes with heavy bass or piano for example. There's a lot of things your fault could be but something similar could explain the dealer staying there's nothing amiss to you experiencing a cracking sound.

 

[audio_PHIL_e]

Swapping the amplifiers over results in the same crackling noise switching channels with no difference to volume or sound.

Do you mean that if the L&R amplifiers are swopped the noise moves with the amplifier, or that the noise comes out of the same speaker regardless of which amplifier is driving it?

Your other test results would suggest the noise comes from the amplifier, but IMO if the former is true then the problem is actually in the amplifier, whereas if the latter is true the problem may be in the power source for the amplifier in that position (assuming that the amplifiers are in different physical locations and powered from different sockets).

 

[Windy Miller]

Do you mean that if the L&R amplifiers are swopped the noise moves with the amplifier, or that the noise comes out of the same speaker regardless of which amplifier is driving it?

Your other test results would suggest the noise comes from the amplifier, but IMO if the former is true then the problem is actually in the amplifier, whereas if the latter is true the problem may be in the power source for the amplifier in that position (assuming that the amplifiers are in different physical locations and powered from different sockets).

It’s definitely the amplifier as the noise follows it when I switch it to the other channel. I did wonder about the location and if it was the power chord or it’s proximity to the wall supply but it’s neither of those it would appear.

 

[Windy Miller]

Hi, I don't know these amps at all but recently had a similar issue with a Tresham amp. This amp uses two relays in the output circuit for slow start and safety cut out. The relays are mounted in octal sockets. I traced the fault to an intermittent contact in one of the relay sockets despite both looking in good condition. Of course none of this was visible on the 'Scope, and only occurred at decent volumes with heavy bass or piano for example. There's a lot of things your fault could be but something similar could explain the dealer staying there's nothing amiss to you experiencing a cracking sound.

Thanks ever so much. I have zero knowledge of electronics but I’ll discuss things with the dealer when I pop back next week. Cheers Ian.

 

[bigrod]

Has the dealer heard the problem in your system
If he’s just checking them out in his shop he wouldn’t really know what he was listening for

 

[audio_PHIL_e]

It’s definitely the amplifier as the noise follows it when I switch it to the other channel. I did wonder about the location and if it was the power chord or it’s proximity to the wall supply but it’s neither of those it would appear.

I reckon that if you put a scope on the HT rail you might see spikes (up or down) that correspond to the crackles you hear. Otherwise you might like to trace back from the o/p stage via various coupling capacitors to find out which one is introducing the noise.

 

[Juancho]

I reckon that if you put a scope on the HT rail you might see spikes (up or down) that correspond to the crackles you hear. Otherwise you might like to trace back from the o/p stage via various coupling capacitors to find out which one is introducing the noise.

You might indeed if you scoped it with a speaker connected. If you use a dummy load as I did there's no bass to rattle the relay connectionbut again in my case the noise was quite a lot lower than the music signal so I don't think anything would have shown up

 

[toprepairman]

Good luck with that.
It's a transistor amp directly coupled with lots of NFB.
Doubt if there's a single coupling cap at all except for perhaps one at the input.

 

[audio_PHIL_e]

Doubt if there's a single coupling cap at all except for perhaps one at the input.

That clearly reduces the number of places to look. tbh dying coupling caps usually make a background grumble so it's not the first thing I'd look at.