Crackling Sound In Guitar Amp

[Matthew Seed]

Hi Guys I am a bit stumped.

I have a Shur Electric guitar into a VICTORY Deputy head and cab.

When i use or even touch my guitar volume knob i get horrid crackle sounds in the amp.

Things I have tried.

1. tried another guitar and it still does it.
2. took all the cables out and used no pedals...just one guitar, one cable straight into the amp and it still does it.
3. Same as point 2 but with new guitar and speaker cable.

I can not think what it might be. It also used to do this with my last amp and guitar...but I always thought It was the guitar pot with an earthing issue, just never got round to swapping it out. So I know its not the amp either.

All this leads me to think it might be the electricity in my home...I live in a 250 year old thatched cottage so it wouldn't surprise me if the electrics were out. I ddi gte one of those little testers from amazon and it showed no fault.

Im lost for what to do !!!

Any help would be massivley apprecited.
Matthew

[Dave.P]

More learned heads will reply I am sure, but on my Strat it turned out to be the volume pot itself on the guitar.
Ok, my Strat was nearly 30 years old but the only thing I can think of is find a way to plug the guitar into a different amp or maybe directly into your interface assuming you have one just to elimate that.

[Kwackman]

Things I have tried.

1. tried another guitar and it still does it.
2. took all the cables out and used no pedals...just one guitar, one cable straight into the amp and it still does it.
3. Same as point 2 but with new guitar and speaker cable.

New guitar and guitar cable?

[Matthew Seed]

Yeah all my gear is brand new and never leaves my recording studio its all in top condition. All my cables are Klotz cables....but either way I have tried swapping out all cables and a differnet guitar and I get the same result.

By the way...If i sit and hold my guitar and touch either the metal volume knob, tone knob or metal trem I get the crackle. But If I reach out and touch the housing of a metal pedal case it stops it.

Im aware this makes it all point to a bad pot or earth issue with the guitar. But thats the mystery...when I swap all cables and the guitar for my Fender bass it does the same thing.

Im confused to say the least.

Matthew

[Wonks]

My guess is that it's probably the amp. It sounds just like what happens when you get DC voltage on the signal path that should only be AC audio signals.

Probably a DC blocking capacitor has failed.

I'm not 100% convinced this is the answer because I think any pedal between the amp and the guitar that's active (and not in a true bypass condition) should have DC blocking capacitors that should protect the guitar electrics from DC.

But the amp controls should also be crackly.

But it could also be an earthing issue within the amp.

Can you borrow a head or a combo from a friend to see if you get similar crackling from that whilst in your guitar room?

[Sam Spoons]

I think you have swapped everything except the amp head and cab that points to an earthing issue with the amp. Do you have a multimeter? If so check the continuity between the earth pin on the mains cable and the nut on the input socket of the amp.

[Wonks]

I think you have swapped everything except the amp head and cab that points to an earthing issue with the amp. Do you have a multimeter? If so check the continuity between the earth pin on the mains cable and the nut on the input socket of the amp.

As the amp's got a chromed plastic nut in a plastic jack surround, that's not a good place to check to. If you've got a guitar lead with metal jack plugs (not just plastic ones that look a bit metallic), then stick the lead in and check to the metal casing. If not, then still plug a jack in but check to the sleeve of the exposed jack plug on the other end of the cable.

It's unlikely to be an earthing issue with a modern amp and safety regs, but it's worth checking.

[Philbo King]

First try using some contact cleaner on the guitar volume pot.

[Sam Spoons]

Yes, you are right, the Victory Deputy does seem to have a plastic sleeved input jack so check using a metal jack plug*. Also worth checking the safety earth is connected to the chassis as you say.

* Checking the signal earth and safety/chassis earth are connected.

[Hugh Robjohns]

The fact that it makes these unwanted noises with different guitars means it's not related to a single dirty pot.

It's either DC on the input cable from the amp, as Wonks suggests, or screening problems within all the tried guitars — which the finger-touching malarkey hints at.

Does this unwanted noise vary if you move further away from the computer or other electrical gear in the room?

Does it change if you switch the room lights off?

[Matthew Seed]

Thank you all for this help...Im getting really frustrated with this now.

Wonks...I do have a Multimeter...but Im not that knowledgeable on how to use one.

Could you please, if you can spare the time give me a dummies guide with what to do.

It has a load of settings on a dial on the front panel ohm etc.

I do have a guitar cabel with a metal sleeve to....so if you could just let me know what to do step by step i would really appreciate it.

Thank you
Matthew

[Wonks]

There are two basic types of multimeter - auto ranging and manual ranging. I don't know which type you've got,but for both types you'll need to select ohms.

With the auto ranging, you just need to connect one probe to the earth pin of the mains plug (obviously with it plugged into the amp but not the wall) and the other end to the metal jack plug casing. After a second or so you'll get a reading that should really be less than 1 ohm (and ideally lower and the same value as when you hold the two probes together). If it's significantly higher, or indicates an open circuit (the same value as when you hold the two probes up and not touching), then there's an almost definite earthing problem with either the amp or the lead (if you've got another IEC mains lead then try the measurements again with that).

If manual range selection, then pick the lowest ohms value available (typically up to 200 ohms). This often has a continuity beep function as well (will beep if the circuit tested has just a few ohms resistance). Test between the earth pin and jack plug sleeve as above. If you don't get a beep and and ohms reading that's only just above that of holding the two probes together, then there's a problem. You can try sequentially increasing the ohms range up to its maximum, but if there's definitely an open circuit reading on all ranges, then again, it's either an amp or a mains lead issue (so try another mains lead).

I'm pretty sure this should test out OK, but it's definitely part of any fault testing procedure.

Ef37a will say that sometimes the signal ground isn't directly connected to the protective chassis ground, but is connected through a capacitor, which may be the case here (so you would get an open circuit reading with a DC test signal from a multimeter), but there isn't a schematic readily available on the web for the amp, so best to assume that like most amps, there should be a direct connection. None of the amp schematics I've looked at have had this, though it's very very far from a comprehensive list.

I know early Fender amps had a 'death cap' which only gave any protection at all from AC voltages and after time, they would fail and you wouldn't have any protection at all, and a few guitarists did die as a result (others were just badly shocked). Replacing the 'death cap' in these old amps with a solid ground link is pretty much mandatory these days.

[Matthew Seed]

Hi Wonks. thanks so much for that.

I have just done the multimeter test. I seem to have manual version. I set it to 200ohm

touching the 2 pins together I go 00.8 and when i did the guitar lead and amp plug test it came out around the same, 00.7 or 00.8 once it settled.

[Hugh Robjohns]

0.8 Ohms is a little high for probes touching together. There may be a 'set zero' trimmer somewhere on the meter to calibrate it correctly (to compensate for a decaying battery).

If so, select the lowest Ohms setting, touch the probes together, and adjust the trimmer to move the needle to zero.

Regardless of whether or not you can calibrate the meter, a reading of 0.8 both with the probes together and when on the plug earth and guitar plug sleeve, indicates that the amp is properly grounded and, so is the guitar via a good cable.

So... that's good.

Next, I'd check out Wonks' DC theory.

Set the meter to a low DC range — 10 or 25VDC — and plug a guitar lead into the amp. Place the probes on the guitar end of the cable, one on the tip and the other on the sleeve.

Turn the amp master volume to minimum and power it on.

Observe the meter needle. It might flick as the power comes on/off, but should quickly settle at zero. If it goes negative swap the tip and sleeve probes over. If there is any DC voltage note what it is.... and power off the amp.

[Wonks]

OK, there’s no earthing issue in the amp/lead.

Do Hugh’s DC check. Up to a couple of millivolts is probably OK. Much more than that and it needs looking at.

If it’s still under warranty then I’d return the amp to be looked at. If not, you need to find an amp tech to have it checked out.

[Matthew Seed]

Thanks guys

I did the MV test at 2MV and it settles rigth bakc to zero when I fire up the amp.

Matthew

[Wonks]

As it’s not autoranging, there’s probably an AC/DC switch on the meter. Just check it’s on DC. If so fine, if not, switch to that and recheck.

Oh, and the amp does need to be fully on for this bit so it may buzz a bit.

[Matthew Seed]

Hi Wonks Thanks.

I got the manual out for the Multimeter and made sure its on DC Voltage. I had a choice of 200mV - 2V - 20V - 200V or 600V

i went for 2V

Just did it again now and come right back to zero.

Matt

[Hugh Robjohns]

Good stuff. That suggests the amp is completely fine.

So my best guess at this stage — bearing in mind I'm not a guitarist — is that your unwanted noises are due to interference getting into the control cavity of your guitar... which is a very common problem because few guitars seem to have shielded cavities when they leave the factory.

Just another example of the engineering madness that is the traditional electric guitar!

I'm sure Wonks can better describe how to check and remedy that possibility.

[Wonks]

It doesn't sound like any interference I've ever come across. Hum and buzz yes, but not crackling. I'd have to go back to an amp I was confident in and compare it to a guitar I knew was fine.

It may just be down to dirty pots. Certainly most pots will improve with many full backwards and forwards motions. or at least the crackling is greatly reduced as surface dust is removed. If t gets a lot better after maybe 20 full turns back and forth, then some contact cleaner would almost certainly help.

But then I'd also consider how the pots were mounted. Which Suhr model is it? If the pots are mounted directly on a plastic scratchplate, then if the scratchplate isn't grounded (with copper foil or conductive paint on the rear and taken to ground) then static can be an issue with some plastics used for scratchplates. It's not that common, but I have come across it a few times. Sticking copper tape on the rear and grounding that stopped all static noises.

This is all very hard to diagnose remotely! There are a lot more clues to be had when the guitar (and amp) are in your own hands.

[Music Wolf]

If you can capture a recording of the sound and post it, it might help. One man's crackle is another man's buzz.

[Wonks]

Another thought. If these are Tele-style guitars with a metal control plate, sometimes the builders rely on the metal to provide the ground link between the pots. If these pot nuts become loose, then the grounding can go to a much higher resistance or be lost altogether as the pot is moved.

I'm not a fan of this and prefer a soldered link between the pots. As a minimum there should be star washers fitted to all the pots to help stop them coming loose, but often these are missing.

Standard procedure on almost all the Tele wiring diagrams you see on line is to take the grounding wire from the output jack to the tone pot(as it's nearest the output jack), and then it depends on the diagram whether they add a link between pots or rely on the control plate.

I always say that if you rely on just the control plate, then take the ground to the volume pot. If these tone pot then becomes loose, at worst the signal becomes brighter, but with no hard ground to the volume pot, you'll definitely get crackling and possibly loss of volume control.

[Wonks]

And also check that the output jack nut is tight. A loose nut on that can also cause crackling, even though it's grounded metal against another bit of metal (provided the jack plate is metal and not plastic).

[Matthew Seed]

Thanks Wonks.

So, this morning I started again.

Turned off everything else in the room. No lights on in the house anywhere...wether they had dimmer switches or not.

Unplugged all cables. Got a two, very new cables.

Guitar straight into the amp, no effects and nothing in the loop and the same result. The guitar by the way is a new Suhr Standard Plus.

then I plugged my bass into it. A very new Fender Jazz bass and the same.

Swapped that one cable just to be sure and the same on both.

This is really odd !!!

I notice that on the guitar and bass if i touch nothing else and just with one finger touch a pole piece of the currently selected pickup it gives off this buzz. But then if i with the other hand touch the metal volume knob, it cancels it out.

I know this HUGLEY sounds like a grounding issue with the guitar, but doing the same thing on the bass just throws a massive spanner in that works.

I am going to try and take some video clips of all this happening and see if I can post it. I guess that might help.

Thank you all this far.
Matthew

[Wonks]

When you touch only a pole piece, your body is acting as an aerial and noise that's picked up is being passed into the pickup.

When you then touch the metal volume knob, that is grounded through the pot, and your body is then grounded as well, so stops acting like an aerial (or at least anything it picks up is taken to ground).

Can I assume the Suhr has metal knobs as well as the Jazz bass, as the Suhr site picture shows plastic Fender Strat-style ones?