Ok. I have a circuit with two humbucking pickups, a three way switch, 4 potentiometers(2 wired for volume and two for tone) and two capacitors in it.

Q: When the tone pots are at 0, there is almost no electrical hum. When you turn them up it feeds in a buzz. Is this earthing feedback or simply signal strength?

Bonus question: When you leave this type of circuit idle(don’t play through it but leave it on), it often develops an on and off beeping tone. Is this related to the capacitors?

All options you present are possible. To know more, you would need to supply a schematic.

Carmen_Sandiego said:

All options you present are possible. To know more, you would need to supply a schematic.

just a moment

Riff-in-Thyme said:

So you wired it up exactly as per diagram? (including the shields?)

It also depends on what the shields are connected to at the other end.

Carmen_Sandiego said:

So you wired it up exactly as per diagram? (including the shields?)

It also depends on what the shields are connected to at the other end.

Are you saying that earthing the shields will cut down noise?

Riff-in-Thyme said:

Carmen_Sandiego said:

So you wired it up exactly as per diagram? (including the shields?)

It also depends on what the shields are connected to at the other end.

Are you saying that earthing the shields will cut down noise?

What do you think shields are for?

roughbarked said:

Riff-in-Thyme said:

Carmen_Sandiego said:

So you wired it up exactly as per diagram? (including the shields?)

It also depends on what the shields are connected to at the other end.

Are you saying that earthing the shields will cut down noise?

What do you think shields are for?

Well the trouble is I only have one wire in there with shielding. The control box cavity is copper lined. Would that do for earthing the shielding?

Riff-in-Thyme said:

Carmen_Sandiego said:

So you wired it up exactly as per diagram? (including the shields?)

It also depends on what the shields are connected to at the other end.

Are you saying that earthing the shields will cut down noise?

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

Carmen_Sandiego said:

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

So what is?

Riff-in-Thyme said:

Carmen_Sandiego said:

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

So what is?

connecting to earth.

Carmen_Sandiego said:

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

so just connected to the other shields?

Carmen_Sandiego said:

Riff-in-Thyme said:

Carmen_Sandiego said:

So you wired it up exactly as per diagram? (including the shields?)

It also depends on what the shields are connected to at the other end.

Are you saying that earthing the shields will cut down noise?

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

+1

Don’t earth at both ends as this gives a path for extraneous currents to flow.

roughbarked said:

Riff-in-Thyme said:

Carmen_Sandiego said:

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

So what is?

connecting to earth.

ok

sibeen said:

Carmen_Sandiego said:

Riff-in-Thyme said:

Are you saying that earthing the shields will cut down noise?

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

+1

Don’t earth at both ends as this gives a path for extraneous currents to flow.

Gotcha. Should be sweet now. Thanks all

Riff-in-Thyme said:

Carmen_Sandiego said:

The shields need to be earthed at one end. (connecting them to the pot case is not earthing)

So what is?

The green wire that goes into the power point is a good place.

Basically, any “noise” that is induced either by RF directly or secondarily through you touching the pots need to be “conducted away”.

Not sure what the spacing is between pots etc, but any lengths of unshielded wire are something of an antenna.

Generally grounding to a common point back closest to the 1/4inch plug is probaby best.

Increasing your signal level back closest to the signal source and lowering it down the chain of amplification will give you better signal to noise.

Unless the pots etc are very close to each other i’d hop around with small diameter sheilded cable.

If it’s an old plug socket i’d check it is grounding properly, and that cable shields are not dodgy.

The arrangement may also be a bit sensitive to the input impedance of that to which it is connected.

transition said:

The arrangement may also be a bit sensitive to the input impedance of that to which it is connected.

I think there is a bit of this going on

ta

Well this thing is shielded up the wazoo. maybe a tiny bit quieter but I think the buzz is the impedance from what it is plugged into. When I pull the jack out it makes the same sound?

Remember that shielding is supposed to be an antenna, not a conductor. (It should not complete a circuit)

Well this thing is shielded up the wazoo. maybe a tiny bit quieter but I think the buzz is the impedance from what it is plugged into. When I pull the jack out it makes the same sound?

When pulling out, or when pulled out?

transition said:

Well this thing is shielded up the wazoo. maybe a tiny bit quieter but I think the buzz is the impedance from what it is plugged into. When I pull the jack out it makes the same sound?

When pulling out, or when pulled out?

when pulled out

Bonus question: Seeing as the shielding has been well and truly addressed, is there any method for dealing with impedance noise in the input unit? It is a decent brand(Roland) though only a basic unit. More complex units seem to have less of this noise?

You can damp with resistors maybe, drop a cap acrross the line somewhere, depends what sort of buzz it is, I gather it’s more a buzz than hum, probably a humming buzz, or buzzing hum.

I was thinking if the input impedance down the line is a bit high it may tend to have a bit more noise. Like I said though keeping the signal up/attenuation low at the source and reducing it downstream generally gives you better signal to noise, though this is not universally true in the case of impedance being less than optimal, especially with simple volume and tone control circuit arrangements sometimes.

There is one other possibility too, being that if the filtering/decoupling of some old or inadequate part of a power supply were, well I already said it…“inadequate”, then this may add to buzz or hum.

You could maybe try, I dunno, a 600 ohm resistor across the 1/4 inch plug ground-core, and if you can handle a bit of rolloff at your top end frequencies maybe try a capacitor across there, haven’t got a chart with me to suggest anything but reckon you could organize that.

Or try same arrangement down the chain a bit.

Oh, and if the pots are higher impedance full open or across them than the original design this’ll likely make it more inclined to pick up noise. Generally you arrange pot’s to keep the impedance constant as you change the setting, but the overall resistance/impedance is often important also.

So, for example of the original were a 10K linear pot, then you’d go for something the same or near the same.

They come in log of linear, and the total resistance across them is often important. Like if you imagine end-end it’s 10K for example, then the wiper moving one side to the other, if done right, feeding to the next thing doesn’t influence where it’s coming from or going to too much. The resistance or impedance sort of keeps the same no matter where the wiper in the pot moves, more the signal level changes but impedance roughly stays the same where it matters.