I don't understand the physics of bad leads

[alyctes]

Recently I noticed (far too late) that with a good-quality lead, my basses are silent (no hum, buzz or crackle) regardless of what I do with the controls. (The strings are different )

I also noticed that with duff leads, the hum, buzz and crackle varies depending on the bass control settings. I don't get it. Okay, the lead is part of a circuit which also includes the bass electrics. But, the things I'd expect to make a difference (lead length is the obvious one) don't seem to matter.

Can anyone explain what's going on, please? I am reasonably happy with science (at least to A level standard).

Edited August 24, 2013 by alyctes

[MB1]

MB1,
Physics of bad leads?
Earthed?
...Is anything?

[Grangur]

Are you saying you have 2 leads and with one all is well, not crackles etc,. Yet when you change the lead for another you get crackles and interference?

You need to make sure it IS the lead that's the problem. There's not a lot to go wrong in a lead.

[TimR]

First thing to check is that you are using an instrument lead and not a speaker lead. They're different but can look the same on the outside. Instrument leads have a sheath and core. Speaker leads have the two cores running parallel with no sheath. It should be written on the cable or you may be able to unscrew the barrel of the jack.

A few things can go wrong with leads.

Dirty plugs. If the plugs aren't making good connection with the sockets then every time you move you'll break the circuit. That'll give you crackles.

If the sleeve is not giving a good connection then your bass won't be properly earthed and you'll get hum.

If the resistance and capacitance created by the dirt is high enough then the lead will act like a filter. As you alter the restance of the volume knobs this changes the filter characteristics.

Google RC filter for an idea of how your tone control works.

Also leads have electrolytic properties and can act like capacitors because the sheath runs round the outside of the core. If the insulation round the sheath is not good when the cable is wiggled you can cause static build up.

This shouldn't happen with modern cables.

Also the terminations in the jacks can break. If it isn't a moulded one unscrew the barrel of the jack and inspect the connections. Otherwise wiggle the lead at the jack with the bass plugged in. If it crackles then you probably have a broken connection. Cut off the plug and solder a new one in.

Edited August 24, 2013 by TimR

[BILL POSTERS]

Sometimes with cheap, loose cable or even old cable, as you shake it the outer braid moves, this varies the capacitance, and the cable acts a bit like a condensor mic. If you have ever tried using ordinary co ax for audio, you'll know what I mean.

There are, or were a few years ago, alarm detectors which worked on the same principle, with a loosely screened cable either clipped to a metal fence, or sometimes buried in gravel or under turf. With an analyser, which in some brands included a speaker. Quite effective, you could hear quite well with them.

[url="http://www.statewide-security.com/intelflex.htm"]http://www.statewide...m/intelflex.htm[/url]

Edited August 24, 2013 by BILL POSTERS

[geoffbyrne]

It has also been noted that some Planet Waves leads seem to have either a slightly bigger radius, or some kind of flange which makes it seat more securely. Unfortunately in some instruments it also seem to stretch the internal contacts so that when you put in a standard jack it is slightly loose and this is when you get crackles & pops.

G.

[Lozz196]

The physics of leads is easily dealt with - buy all your leads from Basschats OBBM. Quality products, incredibly reasonable prices, swift turnaround.

[TimR]

[quote name='Lozz196' timestamp='1377343086' post='2186459']
The physics of leads is easily dealt with - buy all your leads from Basschats OBBM. Quality products, incredibly reasonable prices, swift turnaround.
[/quote]

I have a soldering iron and an account with studiospares.

[spinynorman]

My Planet Waves leads are marked at one end that's supposed to be plugged into the amp. That I really don't understand.

[TimR]

Is it a silent jack? The silent end goes at the instrument end to silence the sound when you change instruments.

Otherwise it'll be because the electrons flow better when the lead is always used in the same direction. They wear a path through the copper. Or something. I could have made all that up though;)

[BILL POSTERS]

[quote name='TimR' timestamp='1377366572' post='2186820']
Is it a silent jack? The silent end goes at the instrument end to silence the sound when you change instruments.

Otherwise it'll be because the electrons flow better when the lead is always used in the same direction. They wear a path through the copper. Or something. I could have made all that up though;)
[/quote]

No, Its true...

[Roger2611]

[quote name='TimR' timestamp='1377366572' post='2186820']
Otherwise it'll be because the electrons flow better when the lead is always used in the same direction. They wear a path through the copper. Or something. I could have made all that up though;)
[/quote]

Easy chap that was sounding like a Mark D Phillips type quote

[alyctes]

Thanks TimR, appreciated.

[quote name='TimR' timestamp='1377325679' post='2186179']
First thing to check is that you are using an instrument lead and not a speaker lead. They're different but can look the same on the outside. Instrument leads have a sheath and core. Speaker leads have the two cores running parallel with no sheath. It should be written on the cable or you may be able to unscrew the barrel of the jack.

A few things can go wrong with leads.

Dirty plugs. If the plugs aren't making good connection with the sockets then every time you move you'll break the circuit. That'll give you crackles.

If the sleeve is not giving a good connection then your bass won't be properly earthed and you'll get hum.

If the resistance and capacitance created by the dirt is high enough then the lead will act like a filter. As you alter the restance of the volume knobs this changes the filter characteristics.

Google RC filter for an idea of how your tone control works.

Also leads have electrolytic properties and can act like capacitors because the sheath runs round the outside of the core. If the insulation round the sheath is not good when the cable is wiggled you can cause static build up.

This shouldn't happen with modern cables.

Also the terminations in the jacks can break. If it isn't a moulded one unscrew the barrel of the jack and inspect the connections. Otherwise wiggle the lead at the jack with the bass plugged in. If it crackles then you probably have a broken connection. Cut off the plug and solder a new one in.
[/quote]