Newsletter
Guitar / Bass Amplifier Info & Education
Switchable Wattage on Tube Amplifiers: The Nitty Gritty
Many tube guitar amplifiers on the market today come with a feature that can either switch or vary the maximum power output of the amplifier section. Simply put, this allows you to adjust the maximum output of the amplifier, making it higher or lower at the flick of the switch. If you have a tube amp with a lot of clean headroom and plenty of power for any gig, you may be wondering why you can’t just use the volume knob to get it to the level you want.
The difference lies in how a tube guitar amplifier’s power section distorts and the interaction between the preamp and power amp. There are many ways that guitarists describe the sound of a tube amp pushed into clipping- overdrive, saturation, crunch- but the causes are quite different when it comes to preamp clipping and output power tube clipping.
The sound of your overdriven guitar is shaped by a combination of your picking, finger attack, preamp volume level, and the volume of the amplifier’s power amp. Really cranking an amplifier saturates the power tubes, causing your signal to break up. Clipping a power section of EL34 power tubes (a common choice in amplifiers) results in natural compression and increased harmonics and touch responsiveness, but to get the full effect, your amplifier has to be cranked up full.
At the same time, playing guitar with a heavy pick attack, using a clean boost pedal, or turning up the input volume will get the preamp tubes working, adding gain and drive. Since the preamp essentially takes your guitar signal and amplifies it to a level that the power tube section can output, running both hot can work to give you a sweet overdrive sound.
However, the overall volume that results from your amp being cranked can be overkill for some smaller venues, and typically will blow the band off the stage. Unless, you are the rock god that owns the show that everyone came to hear, this is where the wattage switch comes in. Like with Carvin Audio’s V3 series, you can switch down from 100 watts to 50 or 25 watts. This means that you can send the power amp into clipping at a lower output level for a nice crunch without blasting your ears off. In most situations, you are on average using very little output amp wattage, so it is very difficult to get the power tubes into distortion. With the switching power level feature switched down to 25 watts, you can achieve power amp clipping distortion more often. This distortion is very different from the preamp distortion generated using the drive knob turned up and master volume turned down. The power amp distortion is not continuous and adds flavor to the peaks. In the days before master volume knobs this was a big part of the distortion heard. Because it only happens on the peaks, it is very dynamic and you can call on it with more intense playing or back off to clean it up a little.
V3 100W 3 Channel Tube Amplifier
If you’re a guitarist who plays in a wide variety of different venues and needs an amp that can provide versatility and consistent great tone, an amp with switchable wattage is a great option.
Note:
In solid state power amplifiers, clipping should be avoided. In tube amplifiers the output tubes and output transformer still produce rounded clipping for most of the peaks. In solid state amplifiers, clipping very quickly becomes square waves which can damage speakers very quickly.
Comments
On the v3, does that watt cut switch actually “remove” tubes from the cicuit or shut one or two tubes off?
good information. I have the V3 micro… Love it!
I surely didn’t appreciate the fact that I just bought a 112 speaker cabinet for my Carvin V3-M, and within weeks you came out with the birch line of cabinets. Obviously someone had to know the change in cab. Design was coming. I feel I should have had the opportunity to wait for the new style, or take the old style. Pretty weak marketing. I certainly don’t appreciate that I have the wonderful opportunity to relieve you of your now obsolete stock. I certainly would have waited. Bruce Hatch. Klusew@aol.com. President, Reflex Productions.
Thank you very much for this very insightful and educational article. I have been playing piano and keyboards for over fifty years. I am a huge fan of Carvin and have many speaker and amplifier components. I am well aware of guitar players cranking up to get tone and, in the process, blowing out everyone’s ears. I was aware of overdriven preamp tone but this article was the first that I had heard about overdriven power amp tone. Thank you for explaining the difference. Keep up the good work. R.
Not a bad explanation of why you may want to reduce your amps power section. I would however not use the word “clipping” when describing the squashed signal produced by overdriven tubes. “Clipping” was first used to describe the COMPLETELY FLAT wave limits (tops and bottoms of a sound’s waveform as depicted on an oscilloscope) when semi-conductors reach their output limit (are overdriven). This depiction of a transistor’s output in this overdriven state looks like someone took a pair of scissors and “clipped” off the tops and bottoms of the waveform. Transistors “clip”, tubes do not. A tube’s wave does deform into a squat version of itself when overdriven, but they don’t flatten to the point where the sound’s waveform starts to resemble a “square wave” as semi-conductors do. I hope we can preserve the use of the word “clipping” to describe the nasty signal produced by an overdriven transistor and not use it to describe the beautiful squish of an overdriven tube. Please, please, please don’t contribute to the dumbing down of the English language. Anyway, not a bad article.
The first articles I received from Carvin were EXCELLENT discussions concerning sub-woofer use. They were very informative and technical while remaining accessible to non-engineers. Since then I’ve received a lot of advertisements disguised as info written for an audience of 14 year olds. Although this article isn’t as informative as those first two about subs, at least it attempts to convey some information that may not be universally understood. “Blues” guys, of course, know that a little amp on 10 sounds much better than a big amp with the gain turned up, at least to their ears. Metal guys may disagree, but there’s certainly room for everyone’s sound. Power limiting switches and knobs are a huge advancement in guitar amp technology, greatly increasing an amp’s versatility by allowing a player to have both of these great sounds on hand from a single amp. I am so happy that Carvin incorporates them in their tube amplifiers.