Vacuum tubes in Guitar pedals
How are they different from digital effect?
Origin of the warm, crisp sound of vacuum tube guitar effects originated in vacuum tube amplifiers, used throughout 60’s until late 90’s. These got later replaced by solid state amplifiers, which were cheaper to manufacture, easier to maintain and can last longer than vacuum tube amplifiers.
Vacuum tube amplifiers and vacuum tube pedals work both on the same principle, with little difference in the input current. While amplifiers are running 110V/230V of current, guitar effects are powered by 9V/12V.
Vacuum tubes amplify the signal that is input in the circuit. Same way, the 8 pin 4558 chip of Boss OD-1 is replicating. There are few downsides to tube amps, as the lifespan of the tube is only few years of constant use at 110V/230V.
Good news for everyone who wants to try a vacuum tube pedals, is that these tubes last for much longer, as the current running through them is much lower. Characteristic for tubes is that they offer more texture and realism to instruments, richer midrange and warmer tones than digital circuits.
This is especially beneficial to players who don’t have a vacuum tube amplifier in the first place. Thanks to the properties of the tube inside pedal, input signal goes through similar process to the one in large tube amplifiers. Most audio technicians and scientists theorize that the 'even harmonic distortion' produced by valve tubes sounds more pleasing to the ear than transistors, regardless of style.
Behaviour of tubes is very complicated and therefore hard to emulate. As Patrick Quilter, 45 years in the electronic industry sums it up:” The “non distortion” part of the tube sound stems from the interaction of a low damping factor power amp with a typically reactive speaker. This is where the “warmth”, “bloom” and “breathing” emerge, that is valued even by clean players. These properties also enhance the sound of overdrive distortion.”
How much distortion tube can produce depends on many factors.
Firstly, there is the type of tube used. Standard for preamps is 12AT7, which is producing warm tone with high gain, ideal for overdriven sound. On the other hand, 12AX7 is producing less distorted sound, better for enhancing the tone and increase the low-end response. Always look for the type of tube used in the pedal, to know what to expect out of it.
Secondly, the analog/digital circuit that pedal uses. It comes down to the pedal maker to decide how to utilize the tube. If the tube is to produce distortion, circuit needs to consist of few transistors to increase the gain in high-ends to distort the signal. On the other hand, if the maker utilizes the tube just to enrich the tone, you will often find digital chip in the pedal to emulate the distorted sound.
How to maintain a vacuum tube pedal?
Maintenance is fairly easy and can be done in few minutes. Most important thing is to make sure that the tube is not touching the metal frame of the pedal/stays in its casing.
What can happen is that when the tube gets out of the casing and you drop your pedal, tube can break and once it loses the vacuum inside, tube no longer works and the whole circuit is dead.
As the vacuum tube lights up, make sure it is not overheating because this can reduce the lifespan of the tube. If this happens, bring it back to the shop and have it replaced with a new tube.
When the tube turns white, it is a good indicator that the tube needs to be replaced. Another indicator is that the pedal starts to sound weak and loose its power.
Quick tip: Vacuum tubes need time to get to the operational temperature, therefore we recommend letting the tube sit for at least 1 minute after plugging in for best results and reduced stress on the tube.
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