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What’s the Big Deal about Analogue Gear, Anyway? Part 1—Tubes |
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I’m sorry to say that I don’t have another Kevin Doyle article to post this month, but I’m going to do my very best to inform and entertain you with this series of articles about analogue gear. The first article, as you may have already guessed from the title, is about tubes or as they say in the UK, valves and what makes the sound they produce so sought after.
Before the advent of the almighty transistor, the vacuum tube reigned supreme in every aspect of consumer and professional electronics. They were integral to the performance of everything electronic from radios to televisions to Hi-Fi’s (stereos) to professional music production and recording equipment.
Valves are basically two or more conductive elements sealed in a glass tube that has been evacuated of all air. Depending on the circuitry, they can act as a preamp, amplifier, rectifier, etc but for our purposes, we’re going to focus on the preamp circuitry and how the tube(valve) affects the tone of the signal going through it. As discussed previously, a preamp takes the low level signal from a microphone, for instance, a brings it up to a level that is useable. If we simply amplified the microphone signal, you would get a very noisy sound that would be very hard to listen to. The following image is that of the simplest form, a diode (two conductive elements).
So, starting the signal chain, we have the input from the microphone or instrument, a variable resistor that determines how much of the signal is passed to the tube for pre-amplification, possibly some frequency controls, the tube(s) and another variable resistor that determines how much of the pre-amplified signal is passed along to be recorded or for amplification. As the signal passes from the first variable resistor through the vacuum tube, it has to literally jump from one element to the other (in this case from the negatively charged filament to the positively charged plate). As it does this, the signal is amplified and passed on to the other components of the pre-amp.
Ok, that’s all nice and fine but what gives tubes their sound and thus preference over solid state components? Well, as all that in the previous paragraph is taking place, the tube has a natural tendency to compress the incoming signal in a direct correlation to how much signal it is receiving and therefore bring out more of the harmonics in the signal. This is commonly known as “warmth”. The more voltage the tube receives from the variable resistor, the brighter it will glow as shown below (pre-amp tubes from a guitar amplifier) and the more it will compress the sound. Eventually, the signal will overdrive the tube into harmonic distortion.
Here are some sound examples: Clean guitar Mildly overdriven Full blown distortion
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