When I first took to modifying my own guitars – if tasks got anywhere near the electronics, I usually handed the job straight over to a tech. It’s not that I wasn’t interested in the possibilities, or the concepts. I really enjoyed electronics lessons and Physics at school, and I became fascinated with wave, sound and colour theory. It’s just that somewhere down the line – I developed a kind of blind spot whenever it came to the practical side of electronics. (I’m the same with plumbing).
When I first began to care about my own particular “sound” – I realised it wasn’t all necessarily down to just FX pedals and string selections, so when I eventually got round to becoming more involved with circuits within my own builds – I tended to experiment with complete pre-wired harnesses, or by trying pickups with a particular “character”. It was much easier that way – but much less satisfying, and it’s quite limiting too – buying something you hope, at best, does exactly “what it says on the tin”. In that scenario – the best you can ever hope to achieve is to sound just like someone else. What you’re really searching for, is the understanding of how to shape your own sound.
A step up from buying-in pre-wired harnesses, is soldering the whole shebang up from scratch – but even then, the uninitiated must rely on standard diagrams and schematics. At one level, it’s just a questionj of “joining up the dots” as-indicated on a diagram. More involved is the question of how, and why a circuit works the way it does. It then takes another level of understanding entirely, to design and specify a custom schematic based on the predicted performance of a particular combination of pre-selected electrical components – and, of course, all this must take into account a host of other physical factors which might also go to influence the final sound of any particular instrument. To have the knowledge and skill to pre-design a specific circuit, and pre-gauge it’s suitability by being able to “read” the way it’ll perform against a particular tonewood or construction method – well, you’re talking guru-level genius there.
As with most things – you just can’t beat experience. But where does that leave the humble hobbyist or budding builder, who is learning the craft? Can it ever be more than just a question of trial and error? Even a partscaster builder has already pre-selected a particular form for a project, (and with that usually comes an idea of a corresponding, finished “sound”). As long as I stay true to the usual components and materials – with the help of my limited experience, and some excellent resources out there on the Internet – I’m confident I’ll be able to come up with something which sounds reasonably “Strat-like”.
But to take everything a logical step further – If I look at some working examples of typical circuits and modifications, study the principles at work, and learn a little about how, and why they work the way they do – then hopefully, I can learn to modify a predictable, reliable, standard schematic – and then refine it to better fit my purpose. Ultimately, there’s no reason why I shouldn’t be able to piece together my own “bespoke” Stratocaster circuit, and personalise my build, and my tone. Isn’t that what customisation is all about?
If I take my gold, hardtail Stratocaster build, and fit a set of Fender Vintage Noiseless pickups – then as long as I follow the recommended Fender schematic, I’d expect the end result to sound, something not unlike, a vintage Strat. I want to achive a classic clean, open, vintage-y, chime-like, bell-like tone – with a nice tight bass response, and clear, but not-too-shrill trebles. A detailed sort of sound, with rich harmonic depth. All that should be achieveable from a well setup Stratocaster. Surely, if I put Fender “Stratocaster” badged pickups in place, then I shouldn’t be far off?
However – online reviews seem to indicate that the Noiseless pickups are significantly stronger than traditional single coils. So much so, in fact – that there’s an apparent danger that the pickups can sound shrill, and might have a tendency towards the dreaded, single-coil “icepick”. On studying the enclosed installation diagram – well, that just doesn’t look like a typical vintage Stratocaster circuit either. I’m not exaxtly a Stratocaster expert – but things don’t look quite like I’d normally expect…
Firstly – the potentiometers, (pots), which came supplied, appear to have a much higher rating. There’s also an unfamiliar looking capacitor in there, and what looks a bit like a “treble bleed”, capacitor and resistor pairing. I’m also pretty sure the wiring diagram makes it look like the tone controls aren’t quite in the usual configuration. You don’t normally have a tone control dedicated for the bridge pickup, and the neck pickup doesn’t normally route out to the second knob. Hmm… I might need to break this down a bit. Hopefully, I can find a way to re-jig the circuit in a more familiar way, integrate a few modifications, and present the pickups in a manner which better suits my purpose, and my ear. In researching the tone I’d like to get out of the Noiseless pickups – I was particularly impressed by Tone Man’s “Blues 64” wiring harness, as demonstrated by Jack Fossett. I’d like to take a few pointers from Tone Man’s, (apparently somewhat different), approach – but if I’m going to learn anything about why their circuit differs so much from Fender’s own – then I’ll have to start by looking at some of the individual components, and work out what individual parts they have to play in the scheme of things.
Fender Noiseless Pickups
Until the 1980’s, a typical Fender Stratocaster would have used only single-coil pickups. (In fact – some purists will always say that, “if it’s not got single coils – it’s not a Strat”). But as technology changed over the years – and amplifiers became more powerful – there was a natural desire to lessen the troublesome noise of EM interference. Single-coils are notoriously prone to noisy interference – (especially in a domestic setting). Humbucker pickups were originally developed, and they use opposing magnetic fields to cancel out the extraneous “hum”, but the extra winds of copper wire involved, means that the output of these “hum-bucking” transducers is significantly increased. This increase in output comes with an effect on the signal produced, and hence the sound, and tone. Whilst Fender single coils were renowned for their clean, bell-like chime – often described as having a “scooped”, pronounced bass and treble signature, with a slight mid-range cut – the louder Humbuckers came louder, fuller, and with a much fatter mid-range. Sure – Fender engineers would like to make their single coils noiseless – but how to do that without sacrificing the signature Stratocaster tone?
The answer was the Fender Vintage Noiseless line of pickups. Still in production, although not everyone’s cup of tea – they became common throughout the 90’s, and were even standard for a time, on Fender’s Eric Clapton Signature production model. They certainly look a little like single coils – but there’s a significant difference.
In fact – under those “vintage” cream covers – they’re actually much closer to humbuckers in construction. There are two stacked coils wrapped around the magnetic poles, and these produce the desired opposing field / hum-cancellation effect. But because of all that extra copper in those packed coils – the output is significantly raised. These pickups are hotter – and looking at that circuit diagram, it looks like other modifications must have been made to try and “tame” the signal produced, and to try and keep things in traditional, Stratocaster territory. When Clapton used the Noiseless pickups – they were incorporated with an active, (MDX), circuit, which took additional power from a small battery pack. This circuit was designed to electronically boost the output, and to allow the sound to be shaped in particular ways. The circuit board might well have been able to provide Clapton with a signature, Stratocaster sounding tone somewhere within the range of adjustment – and even an expanded pallette beyond that – but can I still use the same pickups successfully in a more traditional, passive setup? – or do I need all the extra electrical gubbins installed as well? – just to correct the natural sound and keep it within Stratocaster territory?
An indication might be found by testing the stock resistance of the pickups, and comparing that with more typical values. A set of Fender, Vintage type pickups (Custom Shop 54’s) might normally have resistance readings of: Neck/Middle: 5.9K, Bridge: 6.5K. Straight out of the box, these Noiseless pickups read out at: Neck/Middle/Bridge: 9.8K. That’s a considerable gain, and this – together with the higher relative neck/bridge values – probably indicates one reason, at least, why the noiseless circuit is so different from standard.
So how do the other circuit components play their part in shaping the overall signal, produced by the pickups?
Known to many simply as “volume knobs” or “tone knobs”, the potentiometers or “pots” beneath the pickguard, to which the knobs are actually connected – are variable resistors, which allow the player to manually adjust and set signal levels, “onboard”, before they’re sent down the cable for outside processing and amplification. Crucially – on a passive circuit, (which has no additional energy input), it’s important to see the pots as devices which can only limit the full potential signal – albeit in a tapered, gradual manner. On a passive circuit, pots cannot “boost” a signal – merely attenuate it. (The alternative scenario – an “active” circuit – requires a source of external power. This is usually from a small battery secreted somewhere within the guitar body).
In specifying pots – many of the options are of a direct, practical bearing – in that they just address particular fitting options. Details like how the actual knobs attach, (push on or screw fasten), and how far they sit into the guitar cavities, metric or US sizes etc., etc.. For my scratchplate and setup, I’ll need US 3/8″, short, split shaft pots, and I’d like to use a quality manufacturer where the construction and tolerances of the pots might suggest a longer, more dependable life. The Tone Man build I’m looking at for inspiration, uses Bourns pots – but these can sometimes be hard to find, here in the UK. For me – practically and financially speaking – the required specification likely means CTS Premium, brass shaft pots – but even then, that leaves two additional specification issues which will have a direct effect on use with my chosen pickups. I need to decide on the pots’ impedance and taper. The Fender Noiseless pickups are supplied with two 1 Meg tone controls, and a 500k volume control – wheras the Bourns pots on the Tone Man harness are all rated 500k.
Potentiometer impedance, or resistance, is measured and expressed in thousands of Ohms. On guitars – values like 250k, 500k and 1000k, (or 1.0Meg), are typical. This value, indicates what effect the variable resistor is capable of, when fully applied – ie when the knob is fully turned down to 1, (or 0). It’s a value which reflects the type, and amount, of resistive material in the pot. And that’s important – because even when the pots are fully turned up, there’s an inherent, internal resistance brought about by that same resistive material. On higher rated, 1000k pots, that extra bit might only amount to a couple of Ohms. However, for 500k pots and lower – the internal resistance can quickly rise from 10 to 100 Ohms. And even that small, internal resistance is enough to noticeably affect the sound produced.
If we take the example of a 1000k pot – it’s low internal resistance means that, when turned up to 10, the pot will typically allow more of the fragile high frequencies within the signal through – resulting in a much brighter signal. That signal can be “turned down” or attenuated all the way to 0, and a full 1000k of resistance can be brought to bear, incrementally. At this point, the resistance is so great that all of the signal is affected.
In comparison – a 250k pot, with it’s higher internal resistance, when turned up to 10, typically cuts some of the harsh, high frequencies, and so has a slightly darker character – but it’s one which Fender have traditionally chosen for use for guitars with single coil pickups. Single coil pickups can, notoriously, produce quite a shrill, treble, “icepick” harshness, and the darkening effect of a 250k pot has become synonymous with the characteristic Fender Stratocaster sound, and is part of the usual Stratocaster “DNA”. Compare that with the effect of the 1000k pots Fender tend to use on their Jaguar and Jazzmaster models. Both models are famed for their clear, articulate output – both usually having a much thinner, and stronger treble character to their sound. Also – early Telecasters supposedly used 500k pots – presumably accounting for some of the characteristic “Tele” twang and bite.
The attenuation offered by the pots can be exploited in slightly different ways to control volume and tone. However – the internal resistance is inherent in both uses, and so the same basic effect on the guitar’s tonal character would appear to be the same, whether the pot is being used to control tone or volume. Additionally – at certain points during the rotational travel of higher value, 1000k pots – the resistance, and therefore the attenuation effect, should reach levels which are similar to those offered by lower rated, 500k and 250k pots. One important thing to understand and take from all this is, whilst a 1000k pot might be able to be turned down to also reflect the effects of 500k and 250k pots – the opposite isn’t necessarily the case. A 250k pot cannot be turned “up” any more than it’s inherent resistance allows for. Neither can a 500k pot – although that, in turn, will turn “down” to reflect a 250k.
So – boiling it all down – the accepted rule of thumb seems to suggest that:
250k pots are ideal for single coil pickups. That goes for Stratocasters, and they are an established way of voicing a Stratocaster, and dealing with the dreaded “icepick” tone
500k pots are better suited for Humbuckers – where the pots can better allow through the fuller signal response produced by all of those additional copper windings.
1000k pots would therefore seem to be best suited in situations which demand the maximum signal to be passed unimpeded. This might be to exaggerate clarity and “presence”, or perhaps to allow through more delicate harmonic responses. This might also, however, lead to unwelcome treble peaks – but the 1000k of resistance would, at least, offer quite a wide band of attenuation, to dial in the exact tone required. It seems to me, that this is probably the reason for the specification of 1000k pots in the Noiseless pickup wiring diagram. The pots should still allow the reproduction of more characteristic 250k and 500k resistances, by dialling back a little. I think most players routinely “turn down” the signal to “clean up” the sound. This offers an additional “headroom” which can also be used as the signal hots up and begins to drive the amplifier. With single coil pickups – rather than offering a powered expansion of the usual Fender pallette – the 1000k pots seem included to allow the pickups to be fully opened up, and then “dialled back” from there.
And that brings up the question of how potentiometers actually bring their effects to bear. It’s taken that when a pot is fully open (10), it’s letting through 100% of the signal, (bar that which is stopped by the small internal resistance). Likewise – when a pot is fully closed (1, or 0), 0% of the signal is passed. It might seem logical, therefore, that when a pot is turned to 50% (5) – then the amount of signal allowed to pass should be 50%. That is true when the pot has, what is known as, a linear taper – but not all pots work that way, and it’s not how our ears work.
If you’ve ever faded out a piece of music by using a volume knob, or slider – you might be familiar with how “unmusical” a straight, linear fade out actually is. Really effective fade outs tend to sweep fairly quickly at first, but then hang on, and tail off more gradually. Musical fades are logarithmic, and since they tend to have more practical, musical applications – they’re also referred to as audio tapers, although the principle applies to potentiometers when used for both tone and volume attenuation.
A typical linear sweep upwards, might be represented like:
10, 20, 30, 40, 50 etc.
With a similar logarithmic sweep – the progression, governed by y = C log (x), might run:
1%, 10%, 100%, 1000%, 10000%, 100000% etc. (although any log base could be used).
In practice, the actual logarithmic function of the sweep is designed to build in a compensation for the uneven, progressive effect of the attenuating resistance on the signal. This makes it practically more useable. There are usually a couple of points along the full sweep, where the taper seems to change dramatically. 1 to 3 might be almost inaudible, with little obvious change – then from 3 to 5 there might be a sudden swell. This might slow from 5 to 8, and then from 8 to 10 you might not see any difference at all again. The taper points are carefully placed to make it all appear gradual, and to reflect the way our hearing works. CTS pots are manufactured with, what they refer to as a characteristic, Fender-typical “true vintage taper”, (TVT), and they’re a good starting point for use on Fender-type projects. Some players prefer linear controls for tonal adjustments, but it’s usually the norm to find audio or log tapers for volume controls.
I suppose, if you were interested in doing some old-style volume swells, then you might have much more reason to prefer a linear taper over a log taper, but technically – it doesn’t really make much difference. It’s a personal thing. For me, there’s something about an audio taper on the volume control which seems better linked to my perception of it’s actual function. Linear controls are for steam engines and things where you need an indicator to exactly match the predicted outcome. Where the controls are a little more intuitive – I think it becomes much more a matter of touch. For me – modern electronics seem just that little bit more human, when given a logarithmic response.
So – tone potentiometers and volume potentiometers are essentially the same piece of kit – just used in a slightly different way. Both attenuate signals, but whereas volume pots deal directly with the signal level – tone pots work in conjunction with capacitors, (caps), to modulate and shape specific frequencies.
Capacitors store electrical energy and then release it. As they do so, depending on their value, they have the effect of selectively focusing on high frequencies above a certain level, (dictated by the value of the capacitor). In a tone control, the practical effect is that the higher frequencies are filtered out and passed to ground. When a capacitor is hooked up to a potentiometer – it effectively combines to form a simple low-pass tone filter. Adjustment can be variably attenuated over the 1 to 10 range, so that the capacitors effect can be refined. Towards 1 – the filter becomes more and more effective, and a wider range of the higher frequencies affected are passed to ground. The resulting sound is richer in lower tones, and therefore darker. At 10 – the full spectrum signal is allowed to pass, unfiltered – with all of the high frequencies intact. It’s important to note again, that the system doesn’t boost bass at all. A passive system can’t boost. All the pot/cap system can do – is cut treble.
The effect of the capacitor, or capacitance, is rated in Farads, (actually millifarads, microfarads or even picofarads). The smaller the value – the higher the frequency of signal affected. If a capacitor’s value was close to 0 – the cutoff shelf would be so high, that the frequencies affected would be well above the range of hearing, and therefore inaudible anyway. The usual range of measurement found in electric guitars corresponds therefore, to practical usage within an audible range. Guitar capacitors tend to be of certain values – measured in microfarads – abbreviated as “µF” – or sometimes “uF”. (It’s also sometimes seen, expressed incorrectly as “mf”).
Typical values found, and common usages are:
- 0.1 µF (quite dark tonally. Lots of high frequencies are stripped out. Commonly seen as part of Fender’s “Dark Circuits” of the late 1950’s/early 1960’s)
- 0.047 µF (practical – but probably as big as anyone would want to go without making a circuit tend towards sounding muddy and dark. Loses treble quickly, and with less rolloff, but does have an overall effect of slightly pushing the mid-range. This was the value found on some original Stratocasters)
- 0.033 µF (uncommon, but sometimes used as a compromise – Loses treble a little less quickly)
- 0.022 µF (quite bright tonally. Very common. Used on most modern Stratocasters)
- 0.010 µF (probably the lowest value for practical tone caps – Leaves lots of treble. Typically used on Fender Jaguars and Jazzmasters)
- 0.003 µF (extremely bright -preserves most of the high frequencies. Used as part of a pre-set filter on the Jaguar “rhythm circuit” )
- 0.001µF (close to 0 value, so affecting only the highest frequencies. Typically used in conjunction with a resistor, to form a “treble bleed” modification)
The effect of different types of capacitor aside – it’s important to appreciate how the effects of different value capacitors need to be considered alongside the tonal characteristics of different value pots. Higher rated pots will inherently allow more treble frequencies through, due to their lower internal resistance. Higher rated capacitors may therefore be required, in these circumstances, to keep things in check. The balance of potentiometer and capacitor is an especially important in the design of an electric guitar circuit. Finding the “sweet spot” is key. Additionally – the previous notes on taper, apply to tone pots – just as much as they do with volume pots. Once the effect of a capacitor is applied to the varying resistive effect of a pot, with a log or audio taper – the overall effect can lead to a very poorly balanced response where, for example, high frequencies might roll off incredibly quickly – leaving the rest of the adjustment range to, almost inaudibly attenuate the remaing “muddy” signal. It seems certain value pots tend to get associated with certain value caps. Commonly paired values seem to suggest that:
250k pots pair with 0.47µF caps
500k pots pair with 0.22µF caps
1Meg pots pair with 0.1µF caps
(although there’s obviously plenty of room for experimental license and individual taste. Certain combinations of pots and capacitors may have to deviate from the “general rules” – especially when working with the output of certain pickups. Clearly – the Fender Vintage Noiseless schematic, is a case in point).
Types of capacitor
For practical purposes in electric guitars – capacitors generally tend to be of either ceramic disc, polyester film, or PIO (paper in oil) construction – although there are other types, which are more suited to different electrical applications. Each design exploits different construction methods, material properties and their physical interactions – to produce a capacitance effect. Largely because of the differences in their manufacture – each, therefore, is reputed to have a slightly different effect on the tone produced.
Ceramic disc capacitors are cheap, mass-produced, and relatively generic. The sound produced is supposedly “brighter than most other caps of a similar value” – but is often criticised for being “bland” or “anaemic”. Even then – older ceramic caps can be highly revered for their “special qualities”. Qualities which, apparently, modern manufacturers just can’t achieve, these days. Whether that’s reason alone to pay more for an original 50 year old example, or for a modern Luxe replica – built to original specification and screenprinted to look like an original – I’ll leave the reader to decide.
Polyester, (“poly”), film capacitors are again, relatively cheap – and different versions will be familiar to anyone who has ever opened up the tone circuit of an electric guitar. The tone produced can be described as “bright”, and they seem to be another integral part of modern Fender DNA. (Look for the Fender specific, “Green Chiclet”, or the similar dark red poly caps found in more contemporary Fender builds. Again – certain “brands” of poly caps seem to be held in higher regard than others, and are part of the usual “upgrade” aftermarket. You’ll find exotic names like “Tropical Fish”, “Orange Drops” and “Chocolate Drops”. “Orange Drops” are commonly found in custom and bespoke electric guitar circuits, and NOS, (new, old stock) examples can command considerably higher prices than contemporary examples. Original “Orange Drops” manufactured by Sprague in the USA, seem have the highest reputation, (and therefore price), although most of the modern ones, (nowadays produced by Cornell Dubilier), seem to do an admirable job for the money. Not all “Sprague examples” offered for sale are, in fact, provable, genuine, vintage Sprague caps. Not all “Orange Drops” are Sprague. Buyer beware.
PIO, or “paper in oil” capacitors are usually a little more expensive, in comparison. They tend to be larger, and therefore harder to squeeze into more cramped installations. They also have a shelf-life, and a changeable effect over time. Nevertheless – they’re an authentic-looking package, and their response is, supposedly, especially suited for audio use, and for guitar tone circuits. Their tone is characteristically “darker”, “smoother” or “warmer”. There are many guitarists out there who will attest to the various benefits of particular PIO capacitors. “Bumble Bees” and “VitaminQ” caps are commonly revered. I have happily used some “retro-modern” examples, badged by RS Toneworks – but am just as happy to have recently discovered a good source of Russian ex-military “K40Y-9” PIO’s, which I’ll try out on my next few projects. Once again – certain brands and original “NOS” examples can command a premium on the market. However – whether it is worth paying above the odds for examples which may, or may not, have been authentically scavenged from old Sputniks and abandoned Cold War era equipment – I’ll leave, once again, the reader to decide.
The choice of capacitor in any electric guitar circuit will primarily depend on the actual value required to provide a designed response within that circuit. Then, financial and supply factors may influence the use of particular types of capacitor over others. Beyond that – it’s usually down to a perception that particular caps sound better than others. Ultimately – whether a particular brand or construction really can offer a more suitable solution to, what basically amounts to the shuffling of electrons from one place to another – it’s open to debate and experiment. Some will say it’s all “snake oil”, “witchcraft” and “mumbo-jumbo”. Others will swear they can hear the frequencies “open up, as if they were listening through new ears”. I don’t know. I think PIO capacitors make a positive difference to my particular tone and style – but I’m not selling snake oil, and I also don’t believe in Father Christmas. If I’m wrong – I’m only fooling myself. The only advice I’ll offer, is buy some different capacitors yourself, and try things out. Theoretically speaking – there are undeniable physical differences between different types, and the way they actually move electrons around does rely on slightly different, material properties. There’s also a theoretical reason why older, original examples might gradually age, “leak” and “mellow” over time – especially with PIO’s. So there might be something in it, after all. Just don’t necessarily take anyone’s word that any one particular capacitor will make you sound more like Clapton. Use your ears, and try things out for yourself. You may accidentally discover” your own tone”.
Treble Bleeds, and Resistors
Essentially – a capacitors effect is a resistive one, (although it’s effect might actually seem the opposite). Too much to go into here… suffice to say – a capacitor is a kind of resistor, but one which resists only lower frequency ranges, and passes higher frequencies.
As described above – different capacitors have different effects when their own resistive effect is combined with the inherent, and variable resistances, of a potentiometer. On a tone pot – the effect is exploited to provide a functional tone control. But capacitors also have a function when used with volume pots.
A crucial difference with the application of a treble bleed capacitor on a volume pot, is that the capacitor links the input and output, (wiper), terminals of the pot – rather than running straight to ground. In such a situation – a capacitor on it’s own, actually appears to cut bass frequencies. Adding a resistor works against this, and eliminates low frequency loss, or keeps it within an acceptable chosen range.
With modern Stratocasters – the guitar signal usually hits the volume pot after it’s been EQ’d by the tone controls. Since the volume pot has it’s own inherent resistance – it can potentially strip out even more of the, already filtered, high frequencies. This might not be absolutely critical at full volume – but as the volume pot’s taper is rolled off, the effect can strip out more and more of the high frequency signal. Players will describe particular circuits as being, “tonesuckers” – literally, the treble signal will fall steeply as the volume is turned down and, in bad cases, by the time the indicator is down to just 7 or 8 – all of the high frequencies will have been lost. This results in a muddy, dark sound which nobody really wants, and the function of the potentiometer is essentially reduced to that of an on/off switch.
A “treble bleed” modification uses a very low value capacitor, and pairs it with a resistor. The resistor can be placed in parallel, or in series with the capacitor. The physics is too complicated to explain easily – but when a treble bleed is used in conjunction with a volume pot – the modification allows more of the treble frequencies through. It’s basically a little high-pass filter, and it keeps the sound of the guitar bright, as the volume is rolled down. the important thing is – it’s supposed to help preserve as much of the full signal range as possible ,through the volume pot, after it’s been carefully shaped by the tone pots.
Because the specification of tone pots and their own capacitors is so variable, it seems the actual values of the treble bleed, resistor/capacitor system can be varied slightly to “tune” the circuit. Proprietary treble bleed circuits are readily available – Fender even market their own “Tone Saver” system. Generally, the components tend to have values within a particular range. For capacitors – that’s between 220 pF and 1500 pF. For resistors – 100k ohm up to 330k ohm. It’s likely that particular values and combinations may work slightly better, for some circuits, than others – but that’s another thing that only experimentation, and your ears, can decide upon. There’s also some difference, depending on whether the capacitors are used in series or in parallel with a resistor.
Resistors do, sometimes, also have a use in electric guitar circuits, on their own. This is usually to modify the inherent resistance of a potentiometer. This can be exploited to change the value of a pot, or to fine-tune a particular frequency response by taming some of the high frequencies above a particular level, before attenuation.
My own Fender Noiseless pickup circuit, based on Tone man’s “Blues 64” harness
If I had the money, and lived in the USA, I’d probably order a Tone Man “Blues 64” Strat harness – but I don’t, and I want to try and learn a little bit myself, about how to build and tweak a circuit for a predicted response. I don’t mean to just “rip-off” someone else’s work – but I must admit to being heavily influenced by the sound of Tone Man’s “64” harness, and by Jack Fossett’s review of it. In looking at the circuit however, I’ve tried to appreciate just why particular components were chosen, and how they might actually work with each other. The information is all out there – it’s just that I probably, sort of, copied a little bit when it came to the exam.
All that said – there are certain things I can’t know anyway from just pictures and reviews of the Tone Man harness. It looks, for example, like there may be a small component laid in parallel with the volume pot – but whether it’s a cap or a resistor, and what value it is – is hidden by some shrink tubing. Fair play – I think it’s a custom tone shaper, but if I want to reproduce something like that on my own circuit – I’ll need a deeper understanding of what exactly the filter is doing and, perhaps, a little bit of maths. Failing that – a good deal of trial and error.
What’s for certain – is that Tone man’s approach is, somewhat, different from Fender’s diagram, which came enclosed with the Noiseless pickups. The choice of 1Meg pots by Fender, frankly, surprises me – and I’m equally mystified by the routing of the neck pickup to the second tone pot, with the bridge and middle combined with a cap on the first tone pot. Surely a typo?? Anyway – if they got that wrong…
Perhaps I can apply some of what I’ve learned, and make some improvements. I’ll put the components that came with the pickups to one side, and see if I can redesign and upgrade at the same time.
3 x CTS Premium, 500k pots. (2 x tone, 1 x volume) – used in place of Tone man’s recommended Bourns pots. The best I can easily get here in the UK, for build and tolerance. Fender specifies 2 x 1.0Meg pots for tone, with a 500k volume pot.
1 x RS Toneworks, 500k (or 280k) “Super Pot” – a potential switch-out replacement for the 500k, CTS Volume pot, above. I’ve also got a 280k version as another potential option. If Tone man’s mystery resistor was of a value in the region of 640k – then by using the formula 1/R = 1/R1 + 1/R2 – the combined effect might approximate the inherent resistance of a 280k “Super pot” alone. Of course – that’s a wishful guess, and the resistor could be any other value – but Fender certainly supplied a 500k volume pot for use with their 1.0Meg tone pots. Perhaps a 280k volume pot might match, in a similar way, the downgraded 500k pots. (The 280k is an “improved” value over the more familiar 250k. “Super Pots” are generally supposed to have a better taper and tolerance range. They’re specifically designed for use as volume controls, and I wonder if using one might help work out what’s going on with Tone man’s mystery tone shaper? With both 500k and a 280k examples – I should be able to experiment with different combinations of resistors and pots, to find the best possible arrangement).
1 x CRL 5-way, spring lever switch – my favourite, vintage-style spring lever switch
Cloth covered, pre-tinned (non-stranded) wire – vintage-looking, and easy to work with
1 x “K40Y-9”, 0.047µF PIO capacitor – used as the main tone cap. It looks like Tone Man uses one of the green-bodied Russian caps. This is one of the silver variants – the performance should be the same. I think the green ones were supposed to work better in higher humidity. Fender supply a dark red, 220k poly cap with the pickups. Since the tone pot values are lowered, I think the slightly higher capacitor value is supposed to balance out with the combination of modified pot and capacitor values. The fact that it’s a PIO cap seems to indicate a nod towards the reputed improvement in tonal warmth.
1 x Switchcraft, mono jack socket – my regular, and reasonably dependable, jack socket
1 x Treble bleed circuit, or “Tone saver” (to be decided) – I still need to work out the ideal values of any resistor/capacitor combination, and also whether to link in series or parallel. Since I’ll have an opportunity to do a bit of trial and error – I may look at installling a couple of temporary jumper leads to the volume pot, once the basic circuit is operable, and the guitar is set up. If I solder on a couple of crocodile clips to the ends of the jumpers – I should be able to quickly swap out different value capacitors and resistors – and see what actual effect each has. It may well turn out that a particular, recommended combination might just work perfectly for me. Fender supply a particular combination to use with their recommended schematic – but I’ve read some criticism that the volume generally needs rolling off a little in that setup, to tidy up some of the high frequencies. Perhaps I can improve on that for my particular build? Since I’ll be using different value pots, with a different tone cap – it’s likely that I’ll need a slightly different treble bleed combination to achieve a similar effect. Different, specific combinations are regularly used by PRS, G&L, Suhr, DiMarzio, Seymour Duncan and Kinman – so there are a few working “recipes” to compare. Whilst many of these will be specifically for use with humbuckers – perhaps the fact that Fender’s Vintage Noiseless “single-coils” have, in fact, more than a slight similarity to humbuckers – might also suggest a slightly different value over the usual Fender-type, “Tone-Saver” combination?