I’m fixing a bass where the hum gets in [and stops my mind from wondering]

Apologies for a bit of a hiatus from blogging I have been extremely busy. Among other things I Zen Duder am now trademarked so no one can impersonate me haha, and I have launched a photography studio in the past year. Just google zen duder to see some of the photos. My favorite subject is Lake James. I am primarily selling through adobe stock and have several nice studio shots available, more coming all the time.

Today I wanted to tackle the topic of instrument noises, the kind you don’t want. This is something every musician has to deal with and being a musician, you may be able to tell a c from a c sharp in a heartbeat but troubleshooting conducted and radiated EMI may just not be your forte. So let me try to help and also to do it in a way that is understandable.

I just finished refurbishing one of our studio basses, a vintage 1998 precision bass type. It was already a quiet bass, but I did a few things to make it even quieter. In the process I found quite a bit of mis information on this topic which inspired me to write.

So lets talk about instrument shielding. First of all, should you do it or not?

If you are happy with your instrument and it isn’t causing any issues, Zen Duder recommends to observe the time tested rule of “if it ain’t broke don’t fix it”.

Simple idea, really, especially if you are not totally confident in what you are doing.

You could very easily make matters worse. I say this because there are various electrical subtleties [which you understandably may not understand] that if not strictly observed will cause problems and you could unintentionally undo something important that the manufacturer did for a good reason which was lost on you.

If your instrument is causing you grief however, there are many simple things just about anyone can do for remediation.

First of all a little primer from someone who did some time at the IBM EMC lab where we tested IBM products to make sure they did not emit or recieve various types of electrical interference so that we could get agency approvals, and then sell our products.

The lession here is that theoretically you can’t buy a product that hasn’t been approved, but practically speaking, you can. So what the UL or CSA or FCC logo should mean is that the device has been tested to be safe, and not to emit excessive conducted or radiated emmissions or in the case of the FCC on the proper frequencies.

The el cheapo thing from fly by night shanghai that you or your neighbor bought on ebay, is probably not approved or possibly the approval stickers are fake. Some of these type of items are so noisy they could double as an rf jammer.

What are the main types of interference we are talking about here? What do I mean when I say conducted and radiated emissions? Let me take my engineering hat off and explain it in an easily understandable way.

The first type of interference that can present a problem to all of your gear is called conducted EMI. This is basically electrical noise [usually transistor switching noise] that gets on to the powerlines then wreaks havoc with your gear.

One poorly designed power supply can send conducted [and radiated] EMI everywhere causing problems that are very difficult to eliminate [impossible if in close proximity]. This is in fact why agencies such as UL and CSA exist, so they can certify that a product is free from irritating and trouble causing electrical noise.

In many cases, the best solution is simply to turn the offending device off or replace it. For example, in our studio, the LED lights in the restroom are a source of conducted and radiated studio noise, so we just keep the lights off when we are recording. In fact we have a checklist of everything that needs to be turned off for a session whether is is mechanical or electrical noise.

Please note that in urban settings, you often share a utility power transformer with your neighbors, sometimes quite a few of them. So this means that if they bought something with a junky power supply guess what? They are spilling conducted EMI to everything you own as well.

So if they have noisy LED bathroom lights or a 50 year old washing machine, just politely ask them not to use their bathroom or do the laundry while you are recording. Haha. Seriously, now the complexity of the issue begins to sink in right? Now you know why at 7am you hear a whine in your headphones for 3 minutes.

So step one before you even get to the instrument is make sure you have proper electrical wiring. Make sure that your primary earth ground at your electrical service entrance is good. Make sure that there are no wiring faults and that your neutral is not grounded which is a hazard and an electrical code violation even though many older homes and appliances do not observe this rule.

We run everything in our studio off of one high power tripp lite double conversion true sinewave UPS, set to output 115vac which is also suitable for our vintage vacuum tube amps.

Everything in the studio is star grounded to that single UPS and as a result we have a super low noise setup, which only makes sense for us given the investment in super low noise preamps etc. Your signal chain is only as good as the weakest link, and that includes power. It’s pretty easy to have noise wreck an otherwise good recording, so this is an extremely important topic.

Keep in mind, we are a studio. Not everyone needs to go to these extreme lengths, but it’s worth mentioning if you are the type where that little buzz you have to noise gate drives you nuts. Noise gating is a band aid and we try not to use it. We almost never do. We try not to have the noise in the first place and go to great lengths to get rid of it.

So ultra clean buffered power is a good place to start. Low noise is not cheap but neither is good tone.

On top of that we are way out in the country at ZDS so we do not have to deal with the urban landscape of electrical and audible noise pollution, but it wasn’t always that way so we sympathize heavily for those with a neighbor who is a HAM radio enthusiast and your lights dim every time he keys the mic.

If that is your situation it might be best to work out a schedule where he transmits on certain hours and you play during other hours because no amount of shielding will remedy a situation such as that. The lession here is that it’s possible to drive yourself nuts trying to fix a problem that is not fixable by the means you are using to fix it.

Effective solutions for conducted EMI are whole house surge suppressors good quality point surge suppressors [I like tripp lite] , clamp on toroids that prevent high frequencies from traveling on power lines, and simply getting rid of offending devices.

In our studio we also have a toroid on every single power cable as well as in our main electrical load center panels [lots and lots or toroids] [do not use toriods on signal cables unless you hate treble]. You can buy a bag of clamp on toroids on ebay and they are not expensive.

If you are troubleshooting this type of issue [such as flourescent lights causing the noise, start with everything in the house off, and turn things on one at a time until you find the offender. Working at the breaker panel may be helpful.

Please remember however that if you are in an urban setting, you are on the same circuit as your neighbors, so their conducted EMI problems are yours too. So no recording while your neighbor is shaving in the morning and maybe you can go around the neighborhood to check that all appliances are UL / CSA approved. Lol.

The second type, radiated EMI is the biggie for istruments. There you are standing in a sea of invisible electronic noise pollution with not one but maybe even two or three super high gain magnetic pickups that want to hear it all. This is where most of the issues come from. If the noise you are hearing changes with your orientation of the neck from east to west, you are dealing with radiated emi, meaning that there is some sort of electromagnetic radiation at some frequency from one or more devices that your strings and pickups are receiving sort of like an antenna. Like a really crappy radio but a good instrument.

So lets look at some remedies as we get into the dark arts of hum and noise remediation.

First of all, should you shield your control cavity? Yes, if it is not already shielded, you should. It is easy, inexpensive and effective, and it presents no tonal or other downsides, and should increase the value of your instrument. In some cases this can help dramatically.

How do I proceed? Buy some copper tape , carefully remove the back cover, then unbolt the pots. When you have enough working room, just encase the cavity in copper tape and come up all the way to the screw holes. You should solder a wire from the copper tape to the instrument ground jack. Even though they should be touching you want a good connection to ground. Then to complete the faraday cage, do the same thing to the inside of the back cover plate. When the screws go through they will electrically mate both surfaces and viola, you have greatly enhanced your protection from radiated emi. Tell them you Zen Dudered it.

Along with this, an ideal control cavity has a soldered wire running from the instrument bridge directly to the jack ground, and soldered wires to all the potentiometer cases and switch cases back to the ground jack, as well as the main ground point for your shielded pickup cable being there. Most high quality instruments already have this unless they are quite old.

Should I shield my pickup cavity? This is not always the same answer. It depends on the instrument and issues or lack thereof. For something like a fender stratocaster type design where the whole plate and pickups come off as one piece, my answer is yes. We have a 72 Stratocaster with the pickup cavity shielded and the guitar is quiet as a mouse, and it was not quiet before… it was actually our noisest guitar in the studio. In our studied assesment, the treatment did not perceivably alter the tone of the fine vintage instrument, but it is now a pleasure rather than a PITA to record with.

That said for any bass or guitar with a shielded humbucking pickup in its own cavity, the answer is sometimes no because it can conceivably affect tone, and there is a low bang for the buck because the pickup is already shielded. A proper humbucking pickup has a soldered non ferrous metal shield, and the pickup ground is soldered to that shield coming off the pickup. All that said, sometimes for various reasons this can help so you can always try it then undo it if you are not satisfied with the result. Copper foil tape is as easy to remove as any other tape. Almost. Just don’t stick it down too hard until you are sure you want it.

What else is there to do? A long list, please stand by.

It is critical that your instrument bridge/tailpiece is properly grounded [usually the tailpiece is grounded this is the best approach unless it’s all one piece. It can even be a safety hazard if the strings are ungrounded, A properly grounded bridge has a wire going from the tailpiece to the ground on the instrument jack. So that is really step one for any instrument. If your instrument gets noisy when you touch the strings, you almost certainly have either a tailpiece grounding problem and / or else a pickup wired reverse phase. If the noise gets really bad when you touch the pickup cover, then it is probably phase reversed [hot lead is grounded and ground lead is hot].

It is also critical that your pickups use good quality shielded wire, and it is best if your control cavity also uses shielded wire, but if the cavity itself is shielded this is not as important.

Pickup covers, on or off? Well, I will not get into the sonic debate here, but I will say this. Pickup manufacturers solder covers on their pickups because noisy pickups do not sell well. That said we understand the mojo of a les paul without the pickup covers we have a few around here, and to be honest most les paul type instruments are still very quiet with the covers off.

If you have a portable transistor AM radio, you can use that to track down interference. It’s easier than carrying your instrument around on a long cord. Just tune to a null then walk around with it until you have found the offender.

Bass pickup guards. Ha ha. This can be a real gremlin I feel your pain. Did you know that sometimes your bass handrest /pickup guard can make hum worse? Yes it’s true. So without getting into an electrical engineering course, google eddy current. If the noise is worse with your handrest on, then by all means take it off if you want to and vice versa. Also, importantly, you may want to try a non ferrous [nonmagnetic] material such as nickel aluminum or nickel silver for the cover which should not increase the hum and may possiblly even reduce it if grounded. Conceivably, both ferrous and non ferrous guards can affect the tone one way or the other, so just please remember the zen duder motto.

“Everything affects everything”

Finally, a few do’s and don’ts. Star grounding is always best. This means that there is one single ground point with all grounds on the instrument leading to that point, which should be the instrument ground jack.

Try a better quality instrument cord if you are having hum and noise issues. You can even use rg85 rf coax we use that a lot around the studio for patch cables. In our studio we use almost exclusively canare quad star and rg85 coax cable, with soldered connections. There is a lot of hype in the cabling industry but the fact is that good quality cables matter.

That said, remember how Stevie Ray Vaughn [RIP] used a coiled radio shack el cheapo cord because he felt that a good quality cord “let too much electricity through”? What he probably meant to say is that he liked the treble rolloff inherent in a long length low quality high capacitance cable. He played a strat, strats can be ice picky on a dimed amp.

What you want to look for is a copper core and a high percent shielded copper braid, the higher the better. These cables are expensive but you only need one. If it’s too bright roll back the treble control on your instrument a little bit, that’s what it’s for.

You are usually the best ground. In other words, the shortest path to ground from your instrument, it through you. Therefore, in many cases, touching the strings makes the instrument quieter which should be considered normal and which works out nicely because you have to be touching the instrument to play it anyway. So it is normal for your instrument to be the quietest when you are touching it. If your instrument makes more hum or noise when you touch it, you certainly have a grounding problem. If your pickup covers make more noise when you touch them you probably have a pickup wired reverse phase.

Pedal boards….if you are having noise issues try a straight run to the amp. If your noise goes away, you have a pedal board problem which is not uncommon, so work on that rather than your instrument.

Finally, be careful. The Duder is old enough to remember when being in a band meant you touched the mic stand real fast at first to make sure it wasn’t going to smoke you while you were also holding on to your instrument and I can still remember well what a good jolt felt like. Works better than several cups of coffee but not recommended.

Things are a lot safer these days but one bad piece of gear can give you a pretty good jolt so investing in a multi meter and learning how to use it is not really a bad idea.

I Hope this helps. We do occasional hum / noise mitigation for pro players but we don’t work cheap, we usually work just for clients so it’s really best to build the skills to do it yourself or to build a good relationship with someone skilled in this area to keep your instrument performing it’s best. Your instrument, of course, is a reflection upon yourself.

Until next time…..

Peace. ZD

 

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