| What's an Attenuator & Why on Earth Do I Need One?? |
Chances are that if you're here reading this, you already know what an amp attenuator is. But, in the off chance that you don't, let's cover that quickly. The Merriam-Webster Online Dictionary defines an attenuator as "a device....for reducing the amplitude of an electrical signal without appreciable distortion." That captures the concept very concisely, because the point of an amp attenuator is to allow you to crank down the signal to your speaker(s), while still maintaining a high output from the amp itself. Why do this, instead of just turning the amp's gain/volume settings down? Because guitar amps--specifically tube amps--sound best when they're cranked up. This pushes the amp's power tubes into a condition called "saturation", and when that happens, the amp begins to distort. While that may seem like a bad thing, it's not, because that type of distortion--controlled and gradual--is what many people consider the essence of rock guitar tone. You'll hear a variety of terms used to describe it, like "warm" or "creamy" or "brown" or "crunchy" or many others. It is a sound--a broad range of sounds, actually--that is revered, coveted and ardently sought after by guitarists the world over.
But because of how it is generated--by pushing the power tubes hard--with it comes VOLUME....often deafening, ear-splitting volume. And if you're playing a gig in a large room or similar venue, that may be exactly what you want and need. But what if you're practicing in the family room late at night? Or if you live in a small apartment and want to lay down a few ZZ Top or EVH licks without the neighbors calling the cops? Do you have to forego that cherished "overdriven" tone to keep the peace? Au contraire, mon ami!
That's exactly where an amp attenuator comes in. This devices allows you to reduce (i.e. "attenuate") the amp's output signal to the speaker system. By installing the attenuator between the amp's output and the speaker(s), a portion of the amp's output signal is converted to something other than sound--typically heat or noiseless mechanical work, depending upon the attenuator's operating principle. And the point is to accomplish that reduction with as little change as possible to the original output tone--to get that same overdriven sound, but at a much reduced volume level. I won't go into further technical details here, as there are many good reference sources on attenuators available on the internet (HERE is a good place to start). But suffice it to say that these devices are a godsend to the guitarist who won't settle for sacrificing tone just because he or she needs to keep the volume down.
| Hey, Look What I Found! |
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I had been considering an attenuator for some time, but many of them are high wattage units designed for the gigging musician, and priced accordingly. But all I needed was something big enough to handle my 30W Peavey Delta Blues. While certainly modest by tube amp output standards, anybody who thinks 30 watts isn't loud should try cranking up the Delta Blues in a small room. Yikes!! The volume knobs on the DB go from 1 to 12, and I had never had the clean channel past 3!! Anything higher than that in the small (roughly 12' x 12') room I practice in was physically painful. Needless to say, that wasn't nearly enough gain to push the DB's power tubes into saturation.
So anyway, while poking around on eBay a few days ago, I did a buyer's search on "attenuator" to see if there were any good prospects for a modestly priced unit that would meet my needs. One of the items returned by the search was an attenuator called the "TubeJuice", which I hadn't seen before (see photo at right). The description sounded pretty interesting--a nice, simple one-knob box rated for 30W and selling for a Buy-It-Now price of $65 plus $6 shipping within the US. Since high-end attenuators like the THD HotPlate go for well over $200, that seemed like a relative pittance to pay....IF it worked well. I checked the guy's eBay feedback, which was excellent, with several positive comments by previous TubeJuice buyers. There were also two very positive reviews posted on Harmony Central. For $65, it sure seemed worth the risk, so I went ahead and bought one.
The seller, Mark Wood, builds these units himself and sells primarily through eBay, though he does have a website. He's obviously trying to get a small business going, and appears to take a strong interest in each sale. His communication was prompt--within minutes of buying the unit, I received an e-mail asking whether I wanted an 8 or 16 ohm version--and shipment was immediate. I had the unit in three business days. So far, so good!
The TubeJuice is a simple affair, to be sure--a small plastic box with standard 1/4 inch "In" and "Out" jacks and one knob (see photo below), which increases or decreases a resistive load housed inside the box. You have to provide the connections between your amp, the TubeJuice, and your speakers. If you use a head/cabinet set-up, you're halfway there already, and just need another section of speaker wire with 1/4" jack plugs. But at 30W or less, most of us will be using this unit with a combo amp, which may require adapter pieces with 1/4" plugs on one end and male or female spade-lug connectors at the other. I had previously bought a set of THESE, which came from Weber, in anticipation of an attenuator purchase, and they work great for my Delta Blues.
Once the TubeJuice is connected, it's just a matter of dialing your amp up to the volume setting of choice, and adjusting the attenuation knob to a comfortable sonic level. I'd suggest doing that by turning the TubeJuice's dial all the way to "Min" (i.e. full attenuation/zero volume) and then backing off to the desired volume level through your speaker system.
| So Does It Work?? |
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My biggest questions about the unit were (1) will it "suck tone", as some of these attenuation devices are known to do, and (2) will it generate a lot of heat? After running the unit with both my Valve Jr. and Delta Blues, those fears have been allayed. Yes, there is definitely a loss of top-end at high attenuation, but it's really not very pronounced, and I found that I could adequately compensate with the amp's tone stack and the guitar's tone pots. Overall, I thought the two amps sounded amazingly good with the TubeJuice, even at very high attenuation. And heat seems to be a non-issue--after playing through it hard for over an hour, the box gets only slightly warm to the touch.
Opening up the case and checking out the TubeJuice from the inside (see pic at left) shows how the unit works, as well as why it remains cool. The TubeJuice uses a resistive device known as an "L-pad" to provide the attenuation. Without getting into too much detail, an L-pad is basically two resistors connected in such a way as to maintain a constant impedance for the amplifier as the output signal to the speaker is varied. The back of the L-pad "floats" inside the casing, and the large plastic knob insulates the shaft. The heat generated is passively dissipated through the six air vent holes in the top & bottom of the casing. This arrangement obviously works quite well, since heat build-up is very minimal.
As far as fulfilling its main function--allowing me to dial up the volume on my two amps to achieve power tube saturation and the nice, smooth overdriven tone that goes along with it, while avoiding permanent damage to my ears or my marriage--the TubeJuice is a rousing success. I got to hear tones from my Delta Blues that I have never come close to achieving before, turning the clean channel volume up as high as 10 (out of 12), well into the realm of power tube saturation. My 5W Epiphone Valve Junior combo amp gave similarly positive results; though I had cranked this smaller amp up to tube saturation before, the TubeJuice allowed me to get there at a much more comfortable volume level.
Incidentally, Mark Wood told me that the 16 ohm version of the TubeJuice that I bought can safely be used with amps of lower impedance, like my 4 ohm Valve Junior. I've had it hooked up to the "VJr" a number of times now, and everything seems to work fine. However, from reading information on a couple of different websites and forums, it's obvious that opinions vary on this point. I'm no electronics expert, so I can't render any meaningful judgment on this point. So it's probably a good idea to keep the TubeJuice matched up with an amp of the same (or very close) impedance rating, just to be on the safe side.
To give a flavor of what I'm talking about here, I recorded THIS AUDIO CLIP using the TubeJuice with my Delta Blues and Epiphone Dot. This is recorded on the DB's clean channel using the Dot's bridge pickup (a Duncan SH-4 JB model humbucker). Same pentatonic riff, played four times; no pedals or other effects, other than a bit of reverb. The DB volume settings are, in the order played, 1.5, 3, 5 and 8, with the attenuator off for the first one and then progressively dialed up to keep overall volume level in the same basic range. By the end, the TubeJuice is cranked to well over 90% of its attenuation range. I intentionally didn't touch any tone controls throughout, so that the impact of the degree of attenuation on tone can be heard. I threw in a little bit of one of my favorite Neil Young tunes at the end, for grins!
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Also attached at right is a screenshot I took of the graphical user interface of the Audacity recording/editing software I use to record my clips. This shows those same four repetitions of the riff in the audio clip. You can very clearly see the effect of the increasing amount of applied attenuation and the resulting compression & sustain effects on the output signal. As radically different as they "look", it's hard to believe that the four segments sound as similar as they do! Pretty cool stuff, I thought!
Only time will tell, as far as the reliability of the TubeJuice goes, or how it interacts with my amps over a broader range of use conditions. I'll update this article if any new developments arise. In the meantime, the TubeJuice 30W definitely gets the DVM Good Guitar-Playing Seal of Approval!
Bob Matthews, a.k.a. "Duh Voodoo Man"
Last Updated October 24, 2006
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