Ask Rudy
September 26, 2000
Ask Rudy is a column based on questions submitted by users like you. We are currently taking a break from the column, so please hold off on submitting new questions.
How can I get more bottom from by combo amp?
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"I like to hear a lot of low end from my guitar, but when I turn my amp up to about 3 my speakers buzz. I know they aren't busted, they just can't handle the bass. My amp is a 2x12, open back combo. Do I need new speakers?"
--Jerry Kerr
Via the Internet
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For a guitar tone with gobs of low end, take a cue from our bass-playing buddies and use a closed-back (rather than open-back) speaker cabinet. Here's why: When air pushed forward by your speaker cone wraps around the cabinet and reaches the loudspeaker from behind, lower frequencies get cancelled out. The simplest way to avoid this is to make sure that there's no free-air path from the speaker's front to its back.
I have an old 2x12 Fender Bassman cabinet loaded with Celestion Vintage 30s. It's a sealed-back cabinet, but I measured its frequency response both with and without the back installed. Only one of loudspeakers was active during the testing.
From 100 to about 200Hz (the circled area in the plot), there's 4 to 8dB more level with the back installed (the red trace). If these numbers make your head swim, consider this: These frequencies fall in the domain of the kick drum. If you're looking for a punishing thump when you palm-mute and grind away on deep chords, extra beef in this bottom octave is a good thing.
-- Rudy
What's the secret of Eric Clapton's tone?
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"I am a U.S. Soldier (Army) living in Germany, but my wife and I are originally from Hershey, Pennsylvania. During a recent leave home, I bought a 1989 EC Signature Strat. The guitar's great, but I'd like to make it sound as authentic as possible. What are Eric's pickup heights? I've done many searches on the Web and come up empty-handed."
--Howie Smith
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I'm afraid I don't know the specifics of Clapton's pickup heights. Experiment to find a tone you like. Moving a pickup closer to the strings increases its output, but also increases the affect of the magnetic field on the free motion of the strings.
So what is the secret of Clapton's tone? Here's some insight from Benny Rietveld (http://www.bennyworld.com), who plays bass for Santana. As you may know, Clapton played on a track of the new Santana record Supernatural. EC also sat in with the band at Tokoyo's Budokan Theater on April 28, 2000. Benny reports that Eric didn't bring any of his own gear. Instead, he played one of the Santana tour's spare rigs -- a Strat through a Twin Reverb. Benny has heard many well-known guitarists play this setup, but when Clapton plugged in, it immediately sounded like Eric Clapton's guitar.
The moral of Benny's story: It's the player, not the instrument.
Carlos Santana, Benny Rietveld, and Eric Clapton
(photo by Adam Fells) |
-- Rudy
What do direct boxes do?
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Two recent questions concerned "Direct Boxes."
What is the function of a DI box?
--Steve Ng
Singapore
My acoustic guitar has a built-in pickup and on-board equalizer/preamp. I have always plugged straight into the mixer. Where does a DI box fit in -- and is it necessary?
--John Bohannon
Media, PA
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You'll often see a direct box (sometimes called a DI) used on electric bass, pickup-equipped acoustic guitar, and occasionally on keyboards and drum machines. They are not commonly used on electric guitar (unless you seek an amp-free tone). But what do they do? A little explanation is necessary, so hang with me a moment.
A bass, acoustic guitar, or synth typically has an "unbalanced" output -- either a weak "instrument-level" or somewhat hotter "line-level" signal. Unbalanced signals -- especially low-level ones -- are susceptible to picking up buzz, hum, or radio frequency interference. The lower the signal level of the source (i.e., your guitar), the more you'll need to boost your instrument at the mixer. Unfortunately, the noise gets boosted along with the source; the longer the cable, the worse the problem.
"Balanced" audio connections and cabling combat this problem. The output of a professional, balanced microphone can run hundreds of feet and stay clean, while an unbalanced mic could be unusable after just a 20- or 30-foot run.
FYI, a balanced cable uses three wires (hot, cold, and ground), and the connections are usually either XLR (like the typical mic chord) or 1/4" or bantam-sized Tip/Ring/Sleeve (TRS) connectors. Unbalanced connections use two wires (hot and ground), like your guitar cord or the typical RCA connector. Balanced cables pick up the same interference, but the noises get cancelled out at the mixer's input.
Whew! With that out of the way, we can now answer your questions. A direct box takes an unbalanced signal from a guitar, bass, or other unbalanced source and converts it into a balanced audio signal. In other words, an unbalanced guitar cord comes in, but balanced XLR (mic-style) cable comes out. To get the most from a direct box, your mixing board must have balanced mic and/or line inputs! (Note that some mixers offer both XLR and 1/4" balanced inputs -- check your manual.)
Use a direct box if you are experiencing hum, buzz, or radio interference, or if your instrument's cable is longer than 20 feet. Keep the cord from your instrument to the direct box as short as you can and make up the rest of the run with a balanced XLR cable. Some DIs offer ground-lift switches, which can break ground loops, another source of hum. Finally, many pro-oriented DIs require power, supplied either by phantom power from the mixer or an internal 9V battery.
-- Rudy
How can I stop my pickups from squealing?
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My guitar (a Les Paul copy) is feeding back even at low volumes. It's not cool feedback-- just this constant, high-pitched squeal. This guitar has the best clean tone, but it doesn't cut it when I kick in the gain. Is there a solution, or will I have to go out and buy new pickups?
--Matt
Essex Junction, VT
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When you hold your guitar and hear wild squealing, it means one of two things: You've become fantastically popular with teenage girls, or your pickups are suffering from "microphonic feedback." The diagnosis (especially with a solid-body guitar) is pretty simple: if you completely mute your strings to prevent them from moving but the feedback keeps shrieking away, it's probably microphonic.
If the coils wound into your pickups are free to vibrate, a noise results. That noise runs through your amp and out its speakers. The resulting sound waves interact with your pickup. This makes the coils rattle a bit more and the result is … you guessed it, squealing feedback.
Many (but not all) magnetic pickups are dipped, or "potted," in a wax solution during manufacture. This wax coating seeps into the windings, minimizing unwanted vibration. The potting also helps keep the pickup cover snug. Over time, the wax loses its effectiveness. (Perhaps in your case, there was no wax to begin with.)
You could replace the pickups, but since you're happy with their clean tone, I suggest getting them re-potted with new wax. Don't try this at home! If the wax is too cool, it won't saturate the entire coil. If too hot, the coil windings will be damaged! Seymour Duncan is one place to turn for this service; they tell me it normally runs about $25 per pickup.
On the other hand, if your problem is screaming fans, just smile and keep playing!
For more info: http://www.seymourduncan.com/
-- Rudy
An Acoustic Fuzz Update
Thanks for your letters, folks! Several readers commented on a recent item -- using a fuzz box on an acoustic guitar. Danandkelli811@aol.com reports: "Limp Bizkit's guitarist Wes Borland uses distorted acoustic guitars, centered in the mix, to thicken his heavy tone."
Eric Grover wrote about his own experience, saying: "I use an acoustic guitar with a fuzz pedal while leading worship on a regular basis. To get a tighter sound, I use a DOD Edge pedal before going into the fuzz pedal. It creates a much thinner, more metallic tone, and it takes away a lot of that 'tubby' sound that you described in your listening examples."
Finally, David Deaton, a musician and recording engineer from Shreveport Louisiana says: "When I run my Gibson EAS Standard acoustic into a Line 6 POD, the sky's the limit! Serious tone, really magic."
Thanks for the tips, guys!
-- Rudy
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