Groove Tubes: Tubes vs. Solid State Microphone Electronics

Tube Electronics

The music industry is one of the few places where tubes have value in the face of more modern electronics. Even here, harnessing this somewhat arcane technology is somewhat of a black art. Groove Tubes has dedicated itself to optimizing tube technology for musical applications over the course of many decades. In fact, Groove Tubes built its reputation supplying top-quality tubes for guitar amps to the most discriminating guitarists and manufacturers. Groove Tubes doesn’t scavenge old tubes from yesteryear. Instead, the Company manufactures its own designs and marries them with specially designed modern circuitry to maximize their performance. The quality control is so high that we reject more tubes than we accept in order to give them the Groove Tubes name.

The Myth of Tube Warmth There is a common myth that tubes are “warmer” sounding. It certainly can be said that cranking up a tube amp will make an electric guitar sound “warm,” “fat” or “distorted.” That scenario, however, is one in which distortion is desirable. On the other hand, distortion is the enemy of the engineer who is attempting to record a sound source faithfully and realistically. Here, you want accuracy and transparency rather than any coloration that might be described subjectively with a word like “warmth.” Fortunately, there are many types of tubes and related circuitry that result in comparatively transparent sound. It has also been said that tubes warm up digital recordings. This implies that there is something inherently deficient in digital recording. While some purists will always make a case for analog over digital, the fact is that a vast number of today’s pro recordings are made with digital technology such as M-Audio’s 24-bit/96kHz Delta cards and USB solutions. Rather than saying that tubes “warm up” digital recordings, it would be more accurate to say that tube mics deliver a truer, more pleasing sound when auditioned against the comparative dynamic improprieties of a solid state mic. That’s because digital recording significantly increases the dynamic range, allowing us to better hear the dynamics of what is coming into the system. When the technology was first introduced, people were quick to blame digital recording as “cold” when using solid state mics. After swapping out for a tube mic, everything suddenly sounded “warmer” by comparison. Digital recording gives us the means of hearing differences we couldn’t before—such as the fact that tubes are dynamically more true than solid state.

TIP: One of the first things to be aware of is that not all products advertised as tube mics employ tubes in the main signal path. Some popular low-cost mics utilize less expensive solid-state circuitry, putting a tube in the side-chain. (You can literally cut the tube out of the circuit on some models and the mic will still work.) The theory is that the tube is used as a sort of processor to “warm” up the sound. The reality is that these are still solid state mics masquerading as tube mics as cheaply as possible. Needless to say, Groove Tubes tube mics employ the highest-quality tubes in the primary (and only) signal path.

It’s a fact of life that average tubes exhibit more inherent noise than solid state electronics. While this has been an acceptable tradeoff in light of other considerations like dynamic distortion, Groove Tubes has constantly worked on ways to minimize tube noise for the cleanest sound possible. In general, it holds that smaller tubes are better in this regard. Larger tubes have a greater propensity for being microphonic, i.e. generating noise from mechanical movement of the internal parts. They also use higher voltages that result in more heat—and subsequently more noise. Most manufacturers’ tube mics employ larger 12-volt tubes like the 12AX7—an older tube design that is noisier when used in microphone design. All Groove Tubes tube mics employ a smaller, quieter and more modern 6-volt tube (half the voltage, half the noise).

Due to the physics behind tube operation, tube mics have classically been subject to certain physical restriction on the length of the cable between the microphone and power supply. As a result, tube mics are normally restricted to cable lengths of about 15 feet. This has sometimes required the use of solid state mics in scenarios such as drum overheads, remote recording or orchestral recording. All Groove Tubes tube mics come with a specially designed external tube power supply with load-sensing circuitry that finally allows cable runs approximating 200 feet without altering the sound. Groove Tubes tube microphones include the GT44 medium-capsule, as well as the Model 1B, GT66 and GT67 large-capsule models.

Solid State Electronics

Solid state microphones cost significantly less to manufacture than tube mics. As a result, they are found in the less expensive condenser mics on the market. (As stated earlier, some manufacturers put low-quality tubes in their solid state mics like an effects circuit in order to advertise products as tube mics.)

In most solid state condensers, the key components are a series of op amps. All Groove Tubes solid state mics employ FETs (field effect transistors) instead. Logic says that op amps should be preferable because they have lower measured amounts of THD. As discussed previously, while that difference in THD specs is measurable, it is not audible in well-executed microphone applications. Op amps, however, can have much more dynamic distortion than FETs—something you can hear. Moreover, many designs use multiple op amps to do the job of one FET. The difference is so profound that many people think that Groove Tubes’ solid state mics sound like most manufacturers’ tube mics.

Groove Tubes solid state microphones include the GT33 medium-capsule, as well as the Model 1B-FET, GT55 and GT57 large-capsule models.

This story is excerpted from our free Record Now: Choosing and Using Microphones guide (2.49MB PDF), which covers microphone technology and techniques. It’s available either via download or at your local M-Audio dealer.

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