Low Volume, Fat Tone
Electronic Musician, December 2003
By Orren Merton
Found this article online and thought it would be worth having on this site. Great read on tone and recording.
An apartment-based personal studio can present a number of logistical problems, none of which is more acute than the issue of loud sound levels in close proximity to your neighbors. If you're recording electric guitar, especially through a tube amp, it can be particularly dicey.
Tube amps generally get much of their tone from saturating their power section. When the volume is too low, though, you just can't get that saturation. But if cranking the amp isn't a viable option in your studio, then what do you do?
You could opt to forget the amp and record direct through a modeling processor. Because such devices create their sound digitally, they can achieve their tone at any volume and can be monitored through headphones, eliminating the volume problem entirely.
Amp modelers do a good job of getting usable amplike sounds. But as many guitarists and tone aficionados will tell you, modelers cannot yet convincingly emulate many of the more subtle interactions between tube amps and guitars. The effect of the tubes' heat on the interplay of the amp's components is one example; the change in the amount of distortion that results when you turn down your guitar's volume is another. Real tube junkies will also tell you that the "push-pull" effect - when the amp "breathes" differently depending how you play - is inspiring, and again, modelers can't simulate that yet. Tube-amp aficionados and bands that pride themselves on an interactive, organic guitar sound will likely be satisfied only with the real thing.
But can a tube amp be tamed for the home studio? Even a 50W half-stack is loud enough to get you evicted, arrested, or divorced. Luckily, there are a number of ways to keep the volume of even monster rigs under control, each with its own advantages and drawbacks. Let's take a look at the most readily available options.
When you turn on an amplifier, it expects to feel the impedance, load, and resistance of a speaker. That's why you should never switch on a tube amp without any speakers plugged in - you'll blow its output transformer in no time. However, while the amplifier needs to see a particular load from a speaker, it doesn't necessarily need to send a specific volume to that speaker. That's where an attenuator can come in handy.
Attenuators function as a master volume after the amplifier and before the speaker. They contain a "dummy load" so the amplifier still receives the resistance it needs, and they pass on only a portion of the actual sound to the speaker. That means you can crank your amp to the volume at which the preamp tubes and power-amp tubes interact optimally, and then reduce the volume to manageable levels before the speaker. Many attenuators also include a line-out jack to allow direct connection to a speaker simulator or mixer for recording.
Attenuators usually fall into one of two categories: resistor based and speaker based. The resistor-based THD Hot Plate is perhaps the most successful attenuator on the market. Andy Marshall, president of THD Electronics, explains that the Hot Plate contains "a constant-impedance network of resistors, capacitors, and inductors. This network divides the signal fed in from the speaker output of a tube guitar-amplifier and diverts a specific percentage of the signal to the speaker." The extra power from the amplifier that's not sent to the speaker is dissipated as heat. The unit also offers Bright and Deep tone switches, as well as a line-out jack.
Speaker-based attenuators use an actual speaker coil and motor (without the cone) to react with the tube amp. The MASS attenuator by WeberVST is one popular speaker-based attenuator. Ted Weber, president of WeberVST, argues that this type of attenuator offers a "more dynamic interaction between the load and the output circuit of the amp, which provides more character and texture to the overall tone."
You should keep a couple of points in mind when considering an attenuator. Speaker-based attenuators are rated for the maximum wattage they can handle, and you risk damaging such a unit by pushing more watts through its motor and coil than it can handle. That won't happen with most resistor-based attenuators. On the other hand, if you purchase a poorly constructed resistor-based model, the quality control on the resistor network might be inadequate, and your amp might not receive the load it needs, which (as I mentioned previously) can blow the output transformer. Attenuators generally cost between $100 and $300.
A few companies make converters that let you use different power tubes than the high-wattage models that came with your guitar amp, which can significantly reduce the power output of an amplifier. A popular model is the THD Yellow Jacket, which substitutes an EL84 tube (with a power output of about 8W RMS) for higher-output octal tubes such as the EL34 or 6L6 tubes found in most high-wattage amps. Putting two Yellowjackets in a 50W amp will bring it down to about 15 to 20W RMS, which is still too loud for most apartment-based studios when pushed. But in amps with a single power tube, such as THD's UniValve, you can bring your output down to around 4W RMS (with the amp in low-power mode), which is pretty reasonable. There are other products, such as the Smicz Amplification TAD, a tube adapter that uses 6AK6 tubes that bring your amp's power output down to about 1W RMS.
One thing to consider before you start swapping your power tubes for lower-wattage models, however, is that this will change not just the wattage of your amp, but the sound as well. The EL84 tubes have a very distinct sound (think Vox and other chimey British tones), as does the 6AK6 (more of an American-amp sound). If you like the sound of your amp as it is, swapping tubes might not be something you want to do. Power-tube adapters cost anywhere from $50 to $150.
A variac, or Variable AC transformer, is not actually an audio-related device at all - rather, it's a testing unit for hardware. Its intended purpose is to test how electronic equipment will fare at different wattages. Variacs were originally used in audio rigs to regulate voltage in older or poorly wired buildings, to make sure that the equipment always saw the proper amount of power. However, adventurous guitarists discovered that if they reduced the output of the variac, from the normal 120V in U.S. AC power to about 90V, the power tubes would run at a lower voltage, saturate more quickly, and run at a slightly lower volume. Thus the tradition of using hardware-store variacs to reduce power and make an amp run hotter was developed.
The jury is out on whether using a variac in this way will damage your amp. The general consensus is that it will wear out your tubes more quickly and perhaps wear internal components faster. Some amps, however, are designed with a High/Low Power switch, which is a type of variac switch built in to the amp. These do not damage the amp at all, and unlike hardware variacs, they can often cut the power rating in half. For a low-wattage amp putting out less than 10W RMS, a variac power switch could bring the amp down to less than 5W, which is almost microwattage amp territory. Variacs generally cost $200 or more.
MICROPOWER TUBE AMPS
Another option for getting a real tube-amp sound at low volume is to get a tube amp with an extremely low power output. Such low-wattage amps are fully functional and are capable of powering a 4x12 speaker cabinet, but with a power rating of below 2W RMS. The most popular microamp used to be the now-discontinued Cream Machine by Hughes & Kettner. Z.Vex Effects and Gerhart Amplification are two current manufacturers of microamps.
To make more sense of this, it's helpful to understand the relationship between watts and volume. You need to decrease the wattage of a guitar amp by a factor of ten to reduce the perceived volume by half. That means the amp that sounds half as loud as a 100W amp isn't a 50W amp; it's a 10W amp. And for an amplifier to sound half as loud as a 10W amp, it would need to be a 1W amp. In truth, the wattage ratings tell you less about volume and more about how many speakers an amp can power and how powerful those speakers can be.
What can a tube amp offer when it puts out less than 10W? Zachary Vex, whose company Z.Vex Effects makes the 0.1W RMS Nano Head, says that "there's a very distinct texture-character difference between listening to a tiny amp blowing its brains out at full volume and an attenuated big amp." With an amp pushing less than ten watts, it's very easy to get that power-tube saturation at lower volume, so you can max it out without blowing out the windows and killing small animals.