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Dr. DIMENTO’S BASIC BASS ELECTRONICS MODIFICATION GUIDE

Discussion in 'Pickups & Electronics [BG]' started by luknfur, Oct 19, 2006.


  1. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    This is a simple bare bones guide to provide direction not address specific issues. It’s the approach I used and requires no particular skill or technical knowledge per se‘, just common sense and a general knowledge of how things come apart and go together.

    This Mod Guide is a compliment to the Trouble-Shooting Guide in FAQ (and to a lesser degree the Bass Tone Glossary). Hopefully repetition has been kept minimal but reading both will be complimentary and should help fill some gaps. There are also numerous links in a FAQ to threads on caps, switching, shielding, reviews, and more.

    No doubt some changes/corrections in days to come but basically this is it.

    CONTENTS

    Post 1

    What bass is worth modifying?
    Cost
    Pre-planning:
    How I Choose Pickups/Preamps

    Post 2

    Routing
    Parts

    Pickups
    passive
    active
    piezo
    location
    string relation to poles
    Capacitors (caps)
    Jacks
    Harness (pots/switches/jack and wires associated)

    passive (cut only)
    active preamps (boost or boost/cut) & battery supply
    active/Passive
    Compatibility Issues


    What Bass Is Worth Modifying?

    To me any bass that is comfortable, plays well, has desirable acoustic properties, and has no higher value of consequence as original is a candidate. Original value is not of consequence if mods are not permanent and kept reversible. Cheap basses in particular make for good lab rats cause of the low investment. Thanks to computer technology and the global market, quality control on the cheapest stuff is no doubt better than on the 60’s Fenders. The down side of cheap basses is the truss-rods are often junk.

    Another factor of consequence is the size of the control bay - since you are constrained (less routing) by it‘s volume limitations as to what you can put in it. A control bay can’t be too big but it can be too small.

    Another consideration is the neck. You want a bass with a truss-rod that is not buttered up and will at least set the neck flat with strings up to tension. I prefer bolt-on necks for lots of reasons but it boils down to I prefer their tone, their replaceable, and exchangeable to the same model bass. In my experience the acoustic tone of a bass is in the neck - swap necks and the tone will follow: http://www.talkbass.com/forum/showthread.php?t=152427&highlight=tone+neck. That reason alone is enough. If you think a neck will transfer to the same make different model bass, remote at best.

    Cost

    In general, modifying a bass will cost you nothing but your time and energy - if you buy used at fair market value (less shipping), market demand for the items remains constant, and you make modifications reversible. You need nothing more than ebay to do so. A good used preamp and set of pups will cost about $150. If you buy new it will be about double that and anything you pay beyond fair used market value is guaranteed loss, as is any shipping cost. Another way to look at it is you could mod two basses for the cost of one buying used instead of new. I’ve picked up plenty of used gear I couldn’t tell from new appearance wise and it sounds the same regardless.

    If you don't know the way to ebay read ALL of this first: http://www.talkbass.com/forum/showthread.php?t=200008 cause them waters is shark infested - Power sellers and online music dealers in particular cause they know the ropes.

    *Note: Upgraded basses rarely sell for more than the same stock bass in excellent condition. Most guys want a bass they have some idea of what it sounds like not some bass someone’s jacked with and probably screwed up. You’ll come out better returning the bass to stock and selling it and the upgrades separate. So keep the stock components cause they‘re basically worth as much as your upgrades - if you make mods reversible.

    Pre-Planning

    Assume there are holes in your plans and include alternative plans for what if's
    Keep It Simple - choose your projects in accord with your experience/skills
    Make all projects non-permanent/reversible if possible (To many reasons to list)
    Think beyond your current goals for the bass

    FWIW (For What It’s Worth), the more useful and practical bass is typically one that generates one or two quality tones that work well to a broad variety of music styles. In as much, fairly simple electronically. Such a bass is easier to plan, construct, alter, usually cheaper; and once completed easier to find and return to tone (important live and recording), more reliable, less difficult to trouble-shoot, easier to recuperate costs, and provides a solid base for getting more variety in tone elsewhere in the signal chain where it‘s plug/unplug and play - not have a seat and unsolder/solder. A bass with lots of control and tone options is just the opposite. Almost invariably in a short time one or two of the tones are used and the rest go untouched - that is if you manage to get it together and functioning as planned. That said, doing so can be useful to determine the tones you use (since you couldn't know otherwise) then stripping electronics down to that at some point. Of course you'll probably have some useless holes to deal with.

    Another thing about a bass with lots of controls is they tend to cancel each other, like too many colors mixed, too many spices in a dish, etc. This thread is a perfect example: http://www.talkbass.com/forum/showthread.php?t=283760. That harness was obviously put together by someone who knew their stuff, yet the owner can't get a tone. That's not an uncommon result of a bass that looks like that even though the guy who did the work probably is in the top 5% of his class.

    I myself started out with a wall of basses with pre’s and every knob and switch I could cram into a bass. Now my bass of preference has one pickup wired straight to the jack with NO onboard controls.

    *Note 1: I buy everything used (which includes new at used price - not that uncommon on ebay).

    *Note 2: I have wired everything conceivable wrong more than once in a bass and never damaged a single component. In my experience there’s just not enough current in onboard electronics to do damage.


    How I Choose Pickups/Preamps

    Choice is typically narrowed by routings and what‘s available as replacement. I’ve gone by shape and/or measure the pups then go to the various pup sites of interest and check their dimensions - and/or go to harmonycentral.com user reviews for a given bass and see what guys have replaced in them and their satisfaction with the results. Once you have some idea of options available, in addition to what’s on TB, there are plenty of pup reviews on the net from a google search - extended range pups are just longer versions of their equivalent 4 strings. Research will typically yield a couple three pups with potential and from there it’s buy one and see, you won’t know what it sounds like till it’s installed no matter what you choose.

    What I find most useful as a determination in selecting a pickup is a lot of reviews (say 10 or more) with an overwhelming degree of satisfaction. This translates into real world application where quite a few players have tried the pup through different gear, different settings, different music, different (you get the idea), yet are still satisfied with the results. Sound clips I personally find no value in for selecting pickups (too many reasons to list). Okay for a piece of the puzzle but I wouldn’t get hung up on it or use it as a determining factor.

    If you’re confined by routings, a J bass is the way to go to maximize tone options. There have been more different J pups made than other pups combined, they come in a myriad of coil configurations, and they all sound different. PJ is a good second but quality PJ sets often sell used for twice the equivalent J set, show less frequently, and often sell separately. J sets however are more frequently being sold separately as well.

    Choosing preamps is basically the same process. The current popular Bartolini, Aguilar, and EMG preamps to me do nothing of consequence beyond boost and cut of the signal so choice is more dependent on other factors: size, wiring options, availability, etc. There are some pre’s that do more and with few exceptions you will pay more in accord.
     
  2. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Routing

    Hard to get right, easy to get wrong, no margin for error, not reversible - NOT for amateurs. Plus a router is a LOT more dangerous than your average power tool. Have no idea what it cost to have done but whatever it is would be money that could be spent buying components. Not being reversible (less you plan around it) means you’re stuck moving the upgrades with the bass which typically means more tossed coin.

    That said, I routed all my basses with a ¾” x 4” x 7” swath beneath the strings so I could use any pup placed anywhere. That was two years ago and today I wouldn’t have a bass any other way, have had NO Bass GAS whatsoever since, and with rare exception the only time I go into the TB basses forum is by accident. Pickgaurd can cover the route.


    Parts Aren’t Created Equal

    No matter how simple, there’s a myriad of variation in virtually every component in a bass (pots, screws, etc.) which typically requires modification to make them work in your bass - unless you can verify otherwise before you buy, don’t expect otherwise.

    Pots in particular deserve attention as they have different stem and thread lengths, thread and stem diameters. So they don’t fit the existing hole, knobs don’t fit, not enough thread to nut to, on and on. There are things you can do to compensate like use appropriate cut tubing as filler for gaps around pot stems but you need to think about that stuff in advance. If you buy pots without the washers/nuts/knobs, don’t plan on ones you have fitting.

    Pickups

    Like a microphone to a singer, the pup is where the signal starts and anything in the chain thereafter is simply manipulating what the pickup puts out. How significant that is depends on how much coloration there is in the remainder of the chain. With some rigging the pup is little more than a trigger and practically any pup would sound the same, with other rigs no two pickups may sound the same.

    Passive Magnetic (mag) Pickups

    To me passive magnetic (mag) pickups are basically all a single coil pickup (single wire coiled with a beginning and end wrapped around a magnet) or combinations thereof - and they can all be wired to the same harness with few exceptions. A meter will identify which leads are the ends of a given coil and they are interchangeable in terms of connection in most cases (sometimes one is grounded to the magnets and you’ll get increased hum if that lead is used for a hot lead - but it will work - and if you throw coils out of phase tone will be as much - but it will work). A pup wire that does not register a connection (isolated) with any other on a meter will be ground (often not insulated in the form of a bare or braided wire) or, in the case of active pickups, a lead to the preamp (usually a smaller diameter insulated red lead, but always insulated).

    Passive pickups are typically more raw, less refined, more natural, noisier than an active pickups. There also tends to be considerable degradation of signal from long cable runs when used in conjunction with a passive harness.

    Active Pickups

    Active Pickups have a built in preamp and are readily distinguishable by the combination of the small isolated insulated red (usually) lead and a DCR (Direct Current Resistance) meter reading of about 2k. Also I’ve never seen an active pickup that wasn’t epoxy potted (CAUTION - there are more passive epoxy potted pups than active). Alternatively you can wire an active pup like a passive with no threat of damage - output will be audible but unusable if it’s active. DO NOT wire a passive pup directly to a battery. Any pickup I know of with an output of 4K or more will not be active. Though few, there are some passive pickups with less than 4K however.

    Active pickups are typically more refined, hi-fi, synthetic in tone, and dead quiet. You can use active pickups with either a passive (no boost or band control) or active (preamp) harness. You cannot have a passive mode with active pickups. There’s no degradation of signal of consequence from long cable runs with an active bass.


    Piezos

    I have very little experience with piezo’s but there are definitely impedance issues at stake. I have done the radio shack thing though and wired piezo’s straight to the jack with success in terms of getting output that sounded like typical piezo output. For something of quality, the buffer (preamp) route is the unanimous choice.

    The typical tone associated with piezo’s is a thin, bright, percussive, and hollow sound (woody) that is primarily used to accent the tone of another pup. However a quality piezo setup I’m told will produce output 20 Hz - 20 kHz. Never been there so nothing I’ve experienced.


    Location

    Plain and simple: the same pickup moved from the bridge toward the neck will become increasingly darker, less clear, and louder when moved in that direction.

    Takes about a J width (¾”) for me to distinguish a difference in tone. Manufacturer placements are basically common sense averages. The sweet spot concept in my experience is more fallacy than reality - it’s relative and an averaged placement with few exceptions, but there are some exceptions. For an example see EFFECT OF LOCATION/ARRANGEMENT ON SPLIT P PUP TONE Pg.4 http://www.talkbass.com/forum/showthread.php?t=127322


    String Relation To Poles

    In my experience as long as the strings are within the pup’s magnetic field the pups will read them fine - whether they line up with poles or not. I’ve never had a problem even when one string was over a pole and one was in between. I have had some pups that wouldn’t read some strings well whether they line up with the poles or not, but that is not a common occurrence.

    In terms of pickup height, altering pup height alters output, response, and tone. Simply put they loose volume, become less sensitive, and more mellow the further they're moved from the strings. Doubling the distance from the strings will drop output about 60% and result in a loss of bass and response to attack. Typically the E string is a bit lower than G becuase the larger string mass in conjunction with usual fingerboard radius results in higher output. I raise them as high as they go without impeding play, drop them incrementally till there‘s a noticeable lack of appeal, then raise them back up a bit. Some pups will distort if they’re too close to the strings and some pups (Ray constructed pups in particular) will pull on the strings excessively and could cause wolf tones.

    Capacitors (caps)

    To my knowledge the quickest, easiest, cheapest, most versatile means of making a major tone alteration to a passive harness.


    Jacks

    Are basically mono (2 terminals) or stereo (3 terminals). Active pickups or onboard preamp requires a stereo jack to prevent battery drain when unplugged. Most flush mount (torpedo) jacks require a meter to be able to distinguish the appropriate terminals otherwise it’s VERY easy to cross the hot and “neutral” terminals and you're likely to get some wierd response.

    Harness (pots/switches/jack and wires associated)

    Volume (audio/logorithmic) and tone (linear) are the basic pots in any harness. Audio pots are technically volume but can be used as tone pots in passive harness by adding a capacitor. To my knowledge, there’s no reason an audio pot can’t be substituted for an equivalent linear pot. Linear pots should not be used for volume pots. Blend pots are made in both logorithmic (audio) and linear taper.

    *Note: I always wire a new harness outside the bass and test it before installing. Doing so makes it a known working in drop-in with few exceptions. See F) Isolate the components in a harness http://www.talkbass.com/forum/showthread.php?t=276127.

    Wire

    Ideally you want to stick with the color code for that bass (which varies like everything else). You will probably use more black and white than all other colors combined, red next. Ground wires are often bare but any ground that touches a Hotpoint will short it so I use insulated wire for everything.

    Passive (cut only)

    What you want in a harness is up to you. Once I establish what the harness is to consist of, I use any wiring diagram I can find with that configuration. Guitar or bass diagram doesn’t matter (aside from cap values). Wiring is wiring functionally, primarily you just want something that works. A harness doesn’t know what pickup is wired to it. Different diagrams can produce very different tones however. Like pickups, you’ll know the difference once you’ve installed it.

    Lots of diagrams online: Fender.com, guitarelectronics.com, pup manufacturer sites etc. I also cut and paste diagrams - take parts of different diagrams and put them together. Once you’ve done enough wiring and get a feel for it, you can too. Pots are typically 250K or 500K and to me no variation of consequence. In general, the more components in a passive harness the higher the degradation of signal. There can be a significant difference in the tone of a pickup wired straight to the jack. Active pups with a passive harness typically require 25K pots. 25K pots in a passive harness with passive pickups will choke tone and output.


    Active Preamps (boost or boost/cut) & Battery Supply

    What an active preamp does is give you more flexible onboard tone control over a passive system. Unlikely any more than what your amp already offers, probably less, and probably nothing of particular value if you stay close to your amp.

    There’s no way I know of to know what goes to what in a given active preamp without a diagram. A preamp that's prewired less the jack and battery clip (common used) will typically have 4 unconnected leads: preamp in, preamp out, battery feed to preamp (usually red), and ground (which is often black and grounded to a pot - so there would only be 3 free leads). If it’s not pre-wired or you don’t have a diagram for it, I’d pass. Not an issue buying new but for used stuff it is. There are a lot of diagrams available online for the popular preamps. Preamps are pretty tough and very reliable up to about 10 years of age so buying used is not a concern other than knowing the wiring. I would stay away from anything that’s not modular - independent pots. The pcb (printed circuit board) factory pre’s like the Rays and PV Cirrus units are large and have fixed pot locations - neither of which is user friendly. They do not make for practical transplants.

    Pot ohm ratings vary dramatically in preamps and I stick with manufacturer ratings (another value of a diagram).

    Space is a primary concern for onboard preamps. It doesn’t take long for the volumes taken up by batteries and pre units to consume space. Know before you buy. Cramming components into a control bay is a good way to create problems that otherwise wouldn’t be. Alternatively, you can wire almost any onboard preamp as an outboard unit which makes it modularized plug and play which can be swapped out in the chain, used with any bass, without any modification to the bass.

    Onboard preamps are typically 2 band (B/T), 3 band (B/M/T) or sometimes 4 band (B/T LM/HM) with pots that permit individual control over the Bass, Treble, and Mid frequency ranges respectively. In addition some offer various switching, variable mids, parametric EQ, tone filters, variable impedance, among other options.


    Here are some +/- of note to me with the “Big 3” aftermarket pre’s. Tone wise there was nothing of significance.

    Bart: + most incorporate a gain trim pot that could be of use for volume/distortion issues, they have diagrams for various mid switching; - comparatively large volume wise and the NTMB requires a additional mid module that takes up even more space.

    EMG: + incorporate knee frequency dips which could be of use for upper frequency tweaking, the BTC just drops into a pothole, their controls can be used with any pups, seems their systems (used with EMG pups only) utilize an active blend to balance output, EMG knobs are my favs; - the BQ pre’s have a long mid PCB which can create space/placement issues in the control bay and the mid is a variable mid like it or not (which I don’t), no real alternative wiring options - what you see is what you get.

    Aguilar: + smaller than pool chalk and most control bay friendly of the 3 bands by a landslide, lots of diagramed wiring options including a variable mid if that’s what you want, several 2 band options; - the variable mid requires a stacked AND single pot for mid control alone, generally the more expensive of the bunch used or new off ebay.


    Battery Supply

    Manufacturers typically recommend the battery supply for a given preamp: 9v is typically minimal, 18v common, and 27v uncommon. These are not etched in stone as often there is some flexibility depending on need. Therefore some trial and error is a consideration. No damage can come from less than the recommended supply but I would not exceed the manufacturers recommendation. The miliamp ratings of 9v batteries vary significantly so that alone can provide considerable variation.

    Output or tone will not vary from additional battery supply beyond minimum power requirements. However headroom will increase which can prevent distortion and increase transient response (especially useful for slap).

    Active/Passive

    This is a bass with passive pickups and active harness (preamp) with a by-pass that cuts out the preamp. Most active basses have passive pickups. Any bass with a battery is considered active. Not exactly the best of both worlds as usually passive control is minimal since the controls are wired in with the preamp (which has been cut out of the passive circuit). It’s primarily a backup setup in case the battery/preamp fails. In addition most by-passes are not true by-passes and can suck tone from the passive mode.

    Compatibility Issues

    I have really not ran into compatibility issues between pickups in terms of function but in terms of tone some work well together and some don’t. There are impedance issues between Mag and Piezo pups as mentioned. Passive harnesses are very forgiving when mixed other than the 25k pot mentioned. Active preamps are less tolerant to internal modifications as they’re designed with specific options in mind (usually spelled out by the manufacturer). Variations outside the preamp (like using them with different pickups) are more acceptable and after-market units are designed pretty much to work with anything in order to maximize market share. OEM pre's are less tolerant cause they are designed for more specific application for that manufacturer. Even so, if the manufacturer uses that preamp in a lot of their basses (like the Fender Deluxe), then it will likely be more generic and adaptive to mixing with pups from other makers. In general, preamps don't care what pickups are wired to it -but there are always exceptions to everything.
     
  3. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Test 2, 3, 4 take up space
     
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    May 7, 2021

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