Yeh, mini humbuckers. If you are desperate to add the ability to split then you would have to look at some of the alternatives for Hofner pups (they are out there). I think you could also fit the humbucker alternatives for the Rickenbacker toaster pups. (The cavity is big enough but you may have to make new pickup rings) The mini humbuckers that come with the kit sound ok to me, but then I only play through a 25W Rumble.
The easiest way to check for single coil or humbucker construction is to go back to a school science lesson level, put a sheet of paper over the top of the pickup, sprinkle some iron or steel filings on the top and see whether you get a pattern from one or two sets of magnetic poles (don’t let the filings get onto the pickup). Rubbing bits of steel wool together or on metal is a quick way to make your own filings.
Another way is to use a magnet. Passing a north or south pole of one over the top from side to side, you should get both an attraction an then an repulsion (or vice-versa) if it’s a humbucker, and just an attraction or repulsion if a single coil. Not quite as easy as you think it should be to tell using this method, especially on mini humbuckers where the poles are close together. Alternatively the north of a small handheld compass should be attracted to one pole and the south to the other pole of a humbucker, but only the north or south to a single coil. Again, this is never as as straightforward is it should seem, and my own experience with a compass on humbuckers shows that you have to go in from the two sides and not just pass the compass over the top with humbuckers. Whichever pole the magnet latches on to first keeps the needle pointing in the same direction as you pass over it, so come in from either side and you should get a N and a S indication for a humbucker and just a N or S indication with a single coil.
You can’t tell using a multimeter as all you can easily measure is the DC resistance. And that depends on the wire gauge used and the number of turns of wire around the coil. As a rule of thumb, Strat-style single coils tend to have a lower DC resistance (6k-7k) than vintage -style humbuckers (7.5k-9k), but move away from those and anything goes. The highest DC resistance pickup I have measures a massive 28k ohms and that’s an uber-hot P90 single coil.
If using a magnet to test the pickup, don’t use very powerful ceramic or neodymium magnets. Using these can reduce the pickup magnet strength when putting the same poles together. The more powerful magnetic field can reset some or all of the domains in the weaker magnet, and you can demagnetise a magnet completely. It’s a method used to ‘age’/weaken magnets for a more vintage sound, but this needs to be done carefully and gently and using a gauss meter to check the level of field strength reduction so you don’t go too far.
Pot resistance selection is one way of tuning the frequency response of a pickup. The higher the pot resistance, the higher the resonant peak of the resonant filter circuit caused by the pickup's impedance, inductance and capacitance, the volume pot resistance, the amps input impedance and the guitar lead's capacitance.
Sometimes you may want to tame a high level of treble, which is why you normally find 250k pots with bright Fender single coils and 500k pots with naturally darker-sounding humbuckers. But on a bass, you may not want the same level of brightness as on a guitar, so you may well choose 250k pots.
The pickup construction can also affect how bright sounding it is, and so affect the choice of pot resistance. For a given coil winding, the more powerful the pickup magnet, the brighter the pickup will sound (as well as having a 'hotter' output).
You can achieve similar pickup output levels using a ceramic magnet with fewer coil turns versus an Alnico II magnet with more coil turns. But more turns = more inductance = less treble and more mids; so this particular Alnico II pickup will end up sounding duller than the ceramic one. But ceramic magnets are often used in high output pickups with lots of coil turns, where the ceramic magnet both adds brightness and power compared to the same pickup if used with a weaker Alnico magnet.
So by combining different magnet types with different numbers of windings, pickup makers can fine tune the sound of their pickups. Wire gauge selection is a function of the physical size of the pickups and the number of coil turns required, as for a certain size of bobbin, there is a maximum number of turns you can fit on. Once you reach that, you need to go to a thinner wire gauge to fit more turns on.
Pickup DC resistance is a function of the number of coil turns and the wire gauge used. Each step in wire gauge to a thinner wire gauge adds on average an extra 27% to the DC resistance per coil turn. So a 7k 42AWG pickup, if wired with the same number of turns in 43AWG wire, would now have a DCR of 8.89k, but the output should be exactly the same. So DCR itself is not a good measure of relative pickup output levels unless you know the gauge of wire used. The sound of the pickups will probably be slightly different, as the width of the thinner wire coil will be smaller, and so be slightly brighter sounding as a result, and it's capacitance value will be different as well, slightly modifying the sound.
So, aftermarket pickups that are very different to the original maker's selection may be a lot brighter or a lot duller than the originals, and may benefit from a different volume pot value.
But the guitar wiring circuit can also have an affect on the pot resistance choice. The traditional Gibson two volume, two tone and a 3-way switch keeps the volume pots unconnected in neck-only and bridge-only switch positions, so in those positions the volume pots do present a 500k resistance path to ground. In the middle position, you end up with the volume pots in parallel to ground, halving the effective resistance to 250k, giving a duller sound. But this is offset by the two pickups in parallel having a brighter sound, so the mixed position is still perceived as the brightest-sounding position.
But some circuit designs omit the selector switch and have the two volume pots wired in parallel, or (like Rickenbacker), have the two volume pots wired in parallel after a selector switch. These circuits will halve the effective pot resistance to ground, so two 500k volume pots effectively have a 250k resistance to ground, and two 250k pots have an effective 125k resistance to ground.
Presumably the manufacturers think that with these circuits, the lower resonance peak created suits their pickup selection and presents 'their' sound to the purchaser. But sometimes manufacturers change pickups without changing the components in their wiring harness due to tradition and ease of manufacture, so you may not always get the 'best' sound from the guitar/bass that could be achieved. Obviously a 'best' sound is highly individual and may heavily depend on the amp the guitar/bass is put through.
But sometimes manufacturers just get it wrong (IMO). I sorted a Rickenbacker 650D for a friend that just didn't have any Rickenbacker chime or sparkle, and it's generally known to be a dull sounding guitar and not that well liked as a result. It had two humbuckers fitted, but kept the same original wiring layout and component values as for the original 60s single coils the circuit was designed for. And sometimes component values aren't what they should be, which makes things worse.
The standard pot resistance tolerance is ±20%, even for CTS and Alpha etc. You can get ±10% tolerance guitar pots from CTS and the like, but you have to look for them and normally pay a little bit extra. Within active, low impedance circuitry, ±20% rarely matters. But in passive high-impedance circuitry, it matters a lot. 250k then ranges from 200k to 300k and 500k from 400k to 600k.
The Rickenbacker volume pots (CTS made but with Ric codes) were stamped as being 330k, but both measured at a bit less then 250k. Being wired in parallel this gave them a 125k resistance to ground, and with the mini-humbuckers fitted, robbed all the top-end. I replaced the 250k pots with 1meg ones, giving a more humbucker-friendly 500k resistance to ground and immediately it sounded bright and like a Ric should.
The general feeling (with the exception of Fender) back in the 50s seemed to be that basses should just stick to the low frequencies and make thudding sounds with no real clarity, trying to replicate the sound of a double bass (without opening up the sonic possibilities offered). Some makers carried this on into the 60s as well. The Gibson 'mudbucker' pickup personified this train of thought.
So the original 1956 Hofner 500/1 was designed as a double bass replacement, sticking very much to low frequencies. The first batch made had wide spaced (bridge and neck) pickups, but at the end of the year Hofner then switched to a narrow spacing with both pickups situated near the neck and they didn't go back to wide spacing until 1962.
Paul McCartney's original 500/1 had the narrow pickup spacing.
I'd be tempted to pick your control circuitry first, and then decide on which volume pot value best suits the circuit.
For tone controls, I tend to stick with 250k audio pots regardless of whether it's humbucker or single coil. Yes, you loose very small amount of treble using 250k instead of 500k, but it gives a much wider range of control over the pot's travel (still almost nothing until you are down to 7 or so - but better than from 3 or less). And you can normally more than offset that treble loss (a small fraction of a dB) by making sure your 500k volume pots are on the high side of 500k.
Going to go with V/V/T. Make a control plate that is identical to the stock/ kit one so it can be swapped. So, 500k on volume pots, and 250k for the tone?
I sure did. Now I'm deciding between V/V/T, or V/T/3way. 250k pots all around. I have no interest in splitting the coils. Probably a .022 cap. Still checking things out.
Remember you have humbuckers, not single coil pickups, so original circuit values don’t apply.
Pick your circuit and then decide on the pot values. V/V/T with no 3-way or individual pickup on/off switching can often result in the volume pots wired with a parallel path to ground, halving the resistance, so 250k becomes 125k and with humbuckers, no top end at all.
Yes, the wiring diagram does put them parallel to ground. That being considered, 500k or higher pots for the volume, and a 250k for the tone. Sound about right? Thanks.
About right. If it was a guitar I’d consider 1meg volume pots, but for a bass, unless you want it to be Rickenbacker bright, 500k pots in parallel should be fine. I always think 250k is a good tone pot value.
Try 0.022uF. You can always swap it for something bigger if you don’t think it cuts enough treble off when turned right down.
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