My wharfedale sub is making a loud intermittent crackling sound. It eventually when tested with a sub amp sound test stops putting the correct sound through altogether. I've established that it is not the amp to sub cable. Is it fixable?

Blown amp on sub woofer.

It may be the control itself too. In time, these controls can get dust build up inside it. There are volume control spray cleaners available from Radio Shack or other electronic parts stores. The cheat on cleaning the control is to just rotate it from stop to stop as many times as it takes to clear the noise.

So if you bought enclosures that are premade AND had the speakers installed, you need to see if there is a cross over network installed in them

Power sound amplifier output transistor push n pulls are dead and the q point is off the scale.
Either it is a modular amp or discreet top hat xistors

Did they charge you much for that 'fix'?

Though it may have become damaged in the original problem, the driver won't make loud sounds by itself in the absence of a signal. The internal amp is probably malfunctioning and it is very capable of destroying its own driver. Don't let it continue when it starts acting up.

Did it work correctly for more than 5 minutes after the driver replacement? Take it back and make them do it right this time.

I had a powered sub amp problem that the local guy couldn't fix so I just disconnected it and wired the driver directly out to a separate amp. Works fine as a passive sub.

Information I find online says it an Active Subwoofer, so that introduces its own amp as a possible source of the symptom. If there is another version of this model that's passive, all the more reason to believe the amp is the problem because passive speakers don't spontaneously emit sounds.

If there was a physical reason for the crackling I would think more power would make it worse or blow it up.

A poor sub signal cable connection might explain low current anomalies if random noises are entering the signal path.

Make sure the signal, speaker and power cables are not aligned parallel and close to each other.

The sound (if it makes any) will be distorted and garbled. Keep in mind that subs require amplification. If you are testing the sub without an amplifier you may or may not hear distortion because the radio by its self can't make the sub perform properly, if it has to low of voltage it may crackle because its not recieving a strong enough signal, if it is blown it may not crackle for the same reason

The S750 system is a great sounding one but unfortunatly like many similar systems all the amplifiers and power supplies are housed inside the sub box. This means they suffer badly from heat and vibration problems (they cook themselves or shake themselves apart). I have fixed a few S750 systems in the past but due to their complexity it's not for the faint hearted.

I bought my VE-28s and it did exactly that crackled, cerwin replaced part in amp but few months later problem persisted. they then replaced entire amp assembly and its been fine. i really push it to and its been fine. to test it, unplug the connection from amp/ reciever and see if it persists. if so its the sub, if not its the amp/ reciever. dont dump it, these subs really crank and can put out some deep loud bass.

could be one of the internal wires is loose, possibly where it connects to the back side of input jack.