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I have a Hohner Professional B-Bass 4 string bass with 2 single-coils. Controls are neck volume, bridge volume, tone (which I assume is the cutoff on a lo-pass filter). I get serious hum when using either pickup alone. And noticeable hum unless the two volume controls are not too out-of-range of each other.

I've developed a technique of rocking both volume pots together to get a smooth swell from 0 to 100, so I can find a point on that continuum and then decide how much to boost or cut each pickup relative to that base point (too far in either direction on either knob produces hum). But, it's really hard to do!

Is there a better way to avoid hum?

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I'm talking in general here so apologies if some of these don't seem relevant to your Hohner.

Making your environment less 'hummy'. The kind of hum that pickups pick up is caused by electromagnetic fields in the environment; if you can identify a particular item that is causing the hum, then you may be able to turn it off or move away from it. Items that can cause hum include mains transformers, motors, and, as Tetsujin mentions, old style CRT screens.

Even if you can't identify the source, you may be able to try moving to a different place which seems better.

Try to get your instrument not to 'catch the hum' so much. You might orient a radio antenna to catch more signal; conversely, you can often reduce hum significantly by turning the instrument around and finding the least noisy position.

Don't 'hum' yourself! If you've experienced hum getting worse as you are near the instrument, this is because your body (being mostly water) can pick up and retransmit hum from the environment. You can reduce this effect by grounding your body - often people notice this when they touch the strings or bridge of the guitar, but you could also try using a grounding wrist strap (https://en.wikipedia.org/wiki/Antistatic_wrist_strap). OK, arguably not a cool look and might not work with all playing styles, but it can help when recording! Of course please follow all relevant safety instructions - don't clip it to the nearest live wire.

Shielding the instrument - you can reduce the amount of hum the instrument picks up by surrounding (as much as possible) the pickups and electronics in a conductive foil, tape, or paint, usually applied to the inside of the pickup and control cavities, and back of the pickguard. To work best, this shielding needs to be continuous and have a good connection to earth. Although it's said not to be the best thing, I've had pretty good results with kitchen foil just crimped on to the earth wire.

Checking your wiring : make sure all the solders and connections to ground are good; make sure you have shielded cable for any non-earth connections inside the guitar (the shield would itself be connected to earth). Metal hardware on the guitar should be grounded via the bridge - check the bridge is grounded.

Battery - on an active instrument, check that the battery isn't running out of juice - this can make the electronics behave worse.

Cable - check that you are using an undamaged shielded instrument cable.

Changing your electronics - ultimately if you like the playability of the instrument but it's just too noisy, you could consider changing your pickups and associated electronics.

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    +1 One improvement I've seen over the years is that if you're recording in the control room, modern LCD-type screens are far less hummy than the old CRTs. – Tetsujin Feb 19 '16 at 9:02
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    I'd like to call out environment, shielding, and wiring as being the most likely and most effective areas to address. Very complete answer, +1. – Todd Wilcox Feb 19 '16 at 12:18
  • Your body doesn't “pick up and retransmit hum from the environment”. This can happen in the HF domain (e.g. you can increase the range of a car key by holding it to your head), but audio-freq EM fields have far too long wavelengths. The effect you're talking about is the opposite: your grounded body can shield existing fields. But that really is just testimony to the bad job most guitar manufactors do at internally shielding their instruments. (Also: the body can only shield electric fields, not magnetic ones. So it's pretty useless against the specific hum single coils pick up so much.) – leftaroundabout Feb 19 '16 at 22:45
  • @leftaroundabout The experiment I've done just now: I put left hand on my laptop transformer, and had my guitar plugged in to the amp. When I hovered my right hand near (not touching) a pickup, I heard a lot more hum. When I then kept my right hand near the pickup, but moved my left hand off (and away from) the transformer, the hum subsided. Why would that be? – topo morto Feb 19 '16 at 23:24
  • @topomorto: well right – thinking about it, I suppose it is actually possible for your body to become an antenna and increase interference. What happens is, you're in the near field, but wave decay still depends on geometric factors. In particular, a device like switching power supply will have a pretty fast-decaying quadrupole field, unless you remove the symmetry by placing your hand on it. – leftaroundabout Feb 19 '16 at 23:36
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I don't want to mess with topo morto's answer, but what I'd consider a better alternative to

Don't 'hum' yourself

The old studio trick was not to wire yourself to the ground [which feels a little unsafe], but to wire the guitar to you.

Most of the time, this type of hum goes away if you're holding on tight to the metalwork of the instrument. When you're actually playing it can come & go depending on how well you're connected to it at that moment, which can be very distracting.

The solution was fuse or solder wire [something easily bent, that will stay in place], tied round a wrist, leg, waist & then to the shield on the guitar or jack - these days a common grounding band like you use for computers, with a strap & crocodile clip would be just as effective.

Same caveats apply regarding safety.
If you need to touch any other piece of equipment, test by licking the back of your fingers & touching first. Then in worst-case-scenario, your body's reaction to an electric shock is to curl your fingers away from it as your muscles contract, rather than end up stuck to a live mic you can't let go of.

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