Posts tagged ‘pot’

06/10/2016

Buying an electric guitar, part 3 – Assessing a guitar’s condition

How do you assess the condition of an instrument?

In my view, the condition of any guitar can be gauged by dividing up any possible issues into three groups:

Group 1 – Things that can be changed/corrected easily:

++ truss rod settings

++ dead strings/”wrong” string gauge

++ intonation

++ string height (action)

++ pickup height

++ pickup model (if no woodwork/modification is required)

++ worn-out tuners (if no woodwork is required)

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Group 2 – Small and slightly bigger issues that a qualified repairperson can solve:

++ a cracked top nut

++ string slots in nut too deep or not deep enough

++ a faulty vibrato system

++ worn frets or high/low frets

++ crackling controls

++ faulty switches

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• Group 3 – Issues that are difficult and/or expensive to repair:

++ a badly warped neck (so-called corkscrew)

++ a set neck that is out of alignment

++ a broken truss rod

++ unrepaired (or badly fixed) cracks in the wood (for example a broken-off headstock)

++ a botched DIY ”customisation”

Would you buy a guitar from Pete?

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Here’s one way of assessing the condition of a guitar systematically:

• Tune the instrument and play it for a minute or two. You’ll get an idea of the current set-up, as well as of the general condition and sound of the instrument.

• Is the neck correctly aligned to the body (especially important in set-neck instruments)?

Look at the distance of the e-strings to the fingerboard edges at the 14th fret. If both e-strings are approximately the same distance from the edge of the fingerboard, you’re good to go.

• The truss rod setting (aka relief):

Press the bottom E-string down simultaneously at the 1st and 14th frets (you can use a capo at the first fret), and use it as a straightedge. Take a look at the string at the 8th fret; there should be a small gap between the top of this fret and the E-string – that’s what we call the relief. If the gap is around 0.5 mm, the truss rod is set as it should be. Check the treble e-string in the same way. If there’s a substantial difference between the relief at the low E and the treble e, you’re most likely looking at a warped neck.

If the truss rod setting is not ideal (too tight = no relief; too loose = relief greater than 0.5 mm) you should ask the seller to adjust the truss rod for you.

• Check the nut slots:

Each string is pressed down in turn at the 3rd fret. The string should now be resting on the second fret. Look for a small gap between the 1st fret and the string you’re pressing down. Using a regular 009- or 010-gauge set, there should be a tiny gap beneath the treble e-string and the first fret (when fretting the string at the third fret), just about large enough to fit a sheet of printer paper in there. Because the bass strings need more clearance to vibrate freely, the gap between the first fret and the bottom of each string increases slightly going from the top e-string to the bass E-string.

If the nut slots aren’t cut deep enough, the guitar will be hard to play, and sound badly out of tune in the lowest (open) positions, regardless of action settings and intonation. A luthier will be able to correct the matter for a small charge using a set of special nut files.

If the string slots are too deep (= the strings rest on the first fret, when pressed down at the third), a nut replacement will be in order (except with locking nuts that can be shimmed). Nut slots that are too deep will result in rattling open strings, even if the action and the truss rod have been adjusted correctly. Note: You should check for string rattling using clean amp settings. Playing the guitar unamplified might make you whack the strings harder than necessary.

In most cases replacing a nut is an easy procedure for a repairperson.

• The condition of the frets:

On a used guitar, slight wear marks on the frets are the result of normal use, and this light wear won’t cause any problems.

If the frets are very worn (like the ones in the picture below), you should take the cost of a fret dress (or even a complete refret) into consideration, and maybe try to get the seller to lower his/her asking price.

Refretting bound fingerboards is more complicated and time-consuming than dealing with unbound ’boards, which is usually reflected in the cost. Ask you luthier.

• Check the bridge:

Are all the screws and bridge saddles in working order? Is there ample scope for intonation adjustment?

If the guitar’s set-up is unsatisfactory – the action may be too high or too low; the intonation may be off – ask the seller to adjust the guitar for you before making a buying decision!

• Check the electronics:

Play around with all controls and switches – is everything working as it should? Do all the pickups work?

Scratchy, crackling pots and faulty switches are quite easy for a luthier to exchange. If we’re talking about a new guitar, the shop should take care of this before you buy. With a pre-owned instrument, you will have to take care of the repairs. Note: Replacing electrical components and pickups in semi-acoustic and archtop guitars is generally much more complicated, which will be reflected in the luthier’s quote.

• Check the vibrato:

Does the vibrato (aka the tremolo or the whammy bar) work as it should? Are all the parts in working condition, or are you faced with rusty screws or even broken parts? Is there ample scope for action and intonation adjustment?

If the vibrato bridge looks very worn, or if there are structural problems, like a broken off (or loose) bridge post, you might be facing a complete replacement or a costly repair.

• And finally: Plug the guitar into an amp, and play it some more. Listen to the sound of the instrument. Check its playing feel, its ergonomics, and make a final assessment of its overall condition.

• Based on this checklist (and any possible issues you might have found) you should ask yourself two questions:

  1. Do I like this instrument?
  2. Do I think this guitar is worth its asking price?

Gretsch Streamliner G2420T – full front

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11/08/2011

Basic Knowledge: Guitar Controls

Traditionally electric guitars are equipped with two types of controls: A volume control adjusts the signal level, while a tone control usually controls the signal’s brightness.

Both controls use the same, basic electronic component – the potentiometer (or pot), an adjustable resistor with three contacts.

A horseshoe-shaped track of electrically resistant material (often graphite) runs between the pot’s two outer contacts. The middle contact is wired to a wiper which runs on top of this resistant track, and which is mechanically connected to the pot’s shaft.

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In a volume control the incoming signal is usually connected to one of the outer contacts, while the other end of the resistant track is connected to earth (=ground).

Because a current will always choose the path of least resistance, the closer the wiper is to the track’s input side the louder the signal will be. The closer the wiper gets to the other end of the track the more signal will go to ground, as the resistance between the wiper and the earthed contact is becoming more and more negligible. Sending audio to ground basically means junking it.

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In a tone control a capacitor is used as an audio filter (generally) in front of the pot to skim off the treble (=top end) of the signal. Only the treble content is then fed through the pot, with the wiper’s position determining the amount of top end that is ”flushed down the drain” by being sent to earth.

In many Gibsons (like the Les Paul or the SG) the signal is first fed through the filtering capacitor before it arrives at the control pot’s contact.

Most other guitars (for example Fender models) have the capacitor connected between the pot’s output and earth (ground).

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10/08/2011

Perustietoa: Sähkökitaran säätimet

Sähkökitaroissa on yleensä kaksi eri säädintyyppiä – volume-säädin, jolla säädetään kuinka kovaa kitaran signaali on, ja tone-säädin, jolla säädetään kitaran kirkkautta.

Molemmissa säätimissä käytetään potentiometria, eli kolminapaista säätövastusta.

Ulompien kontaktien välillä kulkee hevosenkengän muotoinen grafiittiraide, joka on potikan vastuspinta, ja keskimmäinen napa on kytketty radalla liikuvaan liukukoskettimeen.

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Volume-potikassa mikrofonista tuleva signaali on kytketty vastuspinnan yhteen päähän. Vastuspinnan toinen pää on kytketty maahan.

Koska sähkö etsii aina helpoimman tien eteenpäin (jossa vastus on mahdollisimman pieni), kulkee signaalista sitä enemmän liukukoskettimen läpi mitä lähempää signaalikontaktia liuku on. Mitä lähempänä liuku on maakontaktia sitä enemmän signaalista kulkee suoraan maahan – signaali menee silloin siis roskakoriin.

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Tone-potikassa käytetään kondensaattoria suotimena volume-säätimen lähdön ja tone-säätimen tulon välillä. Kondensaattorin läpi pääsee ainoastaan signaalin diskanttia potentiometrille. Tone-säätimellä siis heitetään ainoastaan signaalin korkeat taajuudet roskiin.

Useimmissä Gibsoneissa (esim. Les Paul- tai SG-kitaroissa) signaali saapuu kondensaattorin kautta potentiometrille.

Lähes kaikissa muissa kitaroissa (esim. Fender-kitaroissa) signaali menee kuitenkin ensin säätimen läpi. Kondensaattori sijaitsee silloin potentiometrin ja maakontaktin välillä.

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