Pickup Leads To Short

Danny Letz · From: Old Glory,Texas, USA 79540

I am reassembling a Zum that had been taken apart. When they removed the pickups, they cut he leads from the switch. Now they are too short and won't reach to be soldered back. What is the correct way to lengthen them. I have several inches of the same lead that I cut from another pickup that I installed on another guitar. Can I just splice this on with solder and heat shrink? What about the woven shield wire?

Mike Wheeler · From: Delaware, Ohio, USA

In this case, Danny, splicing the two cables and shrink wrapping them, should be OK. I seriously doubt that any hum or noise will result from it. Shielding the connection can be done, but it's a pain, looks crappy, and not worth it IMO.
_________________
Best regards,
Mike

Jim Bob Sedgwick · From: Clinton, Missouri USA

Mike is correct. As long as the ground is not compromised, there will be NO PROBLEM.

Jim Sliff · From: Lawndale California, USA

And to repeat, use shrink-wrap, not tape. Tape eventiually leaves gummy residue where you don't want it.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Robert Leaman · From: Murphy, North Carolina, USA

Make the leads long with soldered splices and shrink wrap. Then, twist the leads together so that there are about 6 or 7 twists per inch. Twisted leads have great noise (hum) rejection that usually exceeds that of shielded coax. I took part in an experiment years ago to determine which type two-wire cable to use for industrial closed loop systems. Twisted two-wire cable won hands down. Incidently, the US Navy used twisted two-wire cable since about 1930 for communication circuits.

Here is theory. If it were to be possible to have two conductors occupy the exact same physical space in time, then signals from outside sources will be equal in both conductors (common mode rejection). Guitar pickup signals are differential and good amplifier input circuits reject common mode signals. Of course, such physical existence is not possible in the real world. However, when two conductors are twisted together, the average plane of existence is equal for both conductors. The tighter is twist, the greater is signal rejection. Also, twisted two-wire cable has lower capacitance that coaxial cable.

The pickup cables on my Sierra D10 gearless are twisted. Much of Sierra guitar's design was done by an aeronautical engineer. Aircraft cables use twisted pairs for noise rejection which some think is important for aircraft quality.

Brint Hannay · From: Maryland, USA

Robert, thanks for that very clear and informative post. I've been pursuing an understanding of electronics as applied in musical instrument and amplifier circuits for years, and I don't recall any of the many books I've perused addressing the theory behind twisting wire pairs or twisted vs. coax, at least with anything approaching the concise clarity of your explanation.

Robert Harper · From: Alabama, USA

Hen the difference in CAT 3 and Cat 4 cable. And in the telephone CO we use twisted pairs. However it is mostly going away to be replaced by fiber optics

Mike Wheeler · From: Delaware, Ohio, USA

Though Robert is spot on, as always, guitar amps don't have common mode inputs. They're single ended, so twisted pair doesn't help there. Thus the need for single conductor, shielded cables.

Mic preamps do have common mode inputs, though, and that's where Roberts info really comes into play.
_________________
Best regards,
Mike

Robert Leaman · From: Murphy, North Carolina, USA

I didn't stste that guitar amps have common mode inputs. I said that such rejects common mode signals. Guitar amps have differential inputs since guitar pickup output is differential. If microphones had common mode outputs, there will be no signal since common mode has no potential difference. Microphones have differential outputs placed in common mode with respect to earth ground.

Since guitar pickups are not made with optic outputs, we are constrained to use metallic conductors instead of glass fibers. Therefore, fiber cable is only of academic interest.

Mike Wheeler · From: Delaware, Ohio, USA

Pardon my mistaken terminology, Robert. (it's been a while) You are, of course, correct that guitar pickups, in fact, have differential outputs. But they are not utilized to take advantage of that capability in todays guitars.

I was only trying to point out that guitar amps don't have true differential inputs, as most mic preamps do. Although many guitar amps nowadays use ICs which are capable of being configured for differential input, they aren't used in that fashion. The IC's associated circuitry is configured for single ended input...a signal input and associated ground/shield. In that case, the shielded, single conductor cable is most commonly prefered.
_________________
Best regards,
Mike

Paddy Long · From: Christchurch, New Zealand

Actually the best way to wire up your pickups to the switch is the way Carters do it:

http://www.steelguitar.com/support/puwiring.html

I wired one of my Zums this way because the pickup wires were too short..... you attach a "solder block" to the underside of the guitar at the pickup end, and run a wiring snake to the switch. You then wire your two pickups to the solder block as described in the schematic above. Just double up the extra wire from the pickups and tie it down. The other advantage is that if you want to change pickups it is a lot easier because you don't have to run wires to the switch, just to the solder block.

Check it out !

Jim Sliff · From: Lawndale California, USA

Danny Letz · From: Old Glory,Texas, USA 79540

You guys got over my head real quick. I like Paddy's idea on the Carter hookup. If I had a solder block, I might do it this way. I am really trying to keep this 85 Zum as original as possible, but some alterations have to be taken. Where would I get the solder block, Radio Shack? I live 60 miles for a town of any size, with the price of gas we don't get there as often as we used to.

Mike Wheeler · From: Delaware, Ohio, USA

Give them a call first. Not all Radio Shacks are stocked the same...they cater to the local market...but the company carries them. You can also order their stuff on-line.
_________________
Best regards,
Mike

Paddy Long · From: Christchurch, New Zealand

Danny any electronics supplies place should carry them and there only a couple of bucks at most ! You want a 4 post one.

Brint Hannay · From: Maryland, USA

Jim Sliff · From: Lawndale California, USA

Brint, I worded the first part of my post a bit badly. I was agreeing with you - and adding one common example of twisted pair wiring often "adjusted" by techs...probably partly because there's not much theory behind it presented in typ[ical amp books.

Anyway, sorry if it sounded like I was disagreeing with you - exactly the opposite.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

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