Preamps
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Buying preamps for recording at home and in the studio
If you take a closer look at any professional studio setup – or even serious home recording studios and producing workstations – you're sure to see that their users are rarely satisfied with the microphone preamps that are integrated into audio interfaces or mixing desks. Instead, external mic preamps are a more or less omnipresent fixture. These devices are available in many different forms, with different features and of course different prices – because there are just as many different reasons for buying an external preamp.
With all this choice, this buyers' guide is intended to explain exactly what the advantages of preamps are, and to help you find out which preamp is the right one for your recording setup. If you'd like to learn more about how they work and how they're used, take a look at our Online Guide to Mic Preamps. For any questions you may have, the Thomann Studio department is also on hand with advice and support at studio@thomann.de, via web chat, or by phone on +49 9546 9223‑30.
Sometimes, even with the best advice in the world, you order a device that's still not quite right. This is exactly why we offer our 30‑day money‑back guarantee, to allow producers to test their new gear at home. Once you've found the right preamp, our 3‑year Thomann warranty ensures that you can enjoy your setup with complete peace of mind.
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Variations in preamp terminology
As is so often the case in the studio world, there are a number of ways of referring to the same thing: Microphone preamps are sometimes just called mic pres or mic amps, and the terms front end and *input stage** may also refer to this first link in the signal chain.
What is a mic preamp used for?
The signal produced by a microphone is very weak. To allow it to be processed further – with low noise and without unwanted distortion – it needs to be amplified. This subsequent processing may take place in devices such as compressors and equalisers, or in analogue‑to‑digital converters that make the signal usable for a computer. After amplification by the preamp, the signal reaches what is known as line level. The amount of gain involved can be substantial: 60 dB of gain corresponds to amplification by a factor of 1,000!
While microphone signals are almost always transmitted via XLR connectors, line‑level signals come in different formats. An XLR output is common here as well, though the slimmer TRS jack sockets are also sometimes used.
Is an external microphone preamp worth it?
Whether it's worthwhile to invest in an external microphone preamp is a common question. Ultimately, there are several reasons for doing so. One is simply technical quality: In more affordable audio interfaces with a number of built‑in preamps, it's only logical that each preamp accounts for just a portion of the overall development and manufacturing budget. Of course, this means that high‑end devices like premium audio interfaces and expensive analogue mixing consoles can feature technically excellent preamps. These tend to produce very little noise even at high gain levels, introduce minimal distortion (or only when deliberately driven, and then in a way now considered musically pleasing), remain transparent, and don't "smear" the signal.
Another frequent reason for using a preamp is the desire to give a microphone's signal a specific tonal character; a mic preamp can have a significant influence on the sound. Preamp sections in mixing consoles and integrated interface pres are almost always designed to be as neutral as possible, in order to cover a wide range of applications. What this means is that, conversely, there are preamps that are chosen specifically for their sonic character: Units from manufacturers such as Neve, Universal Audio, Chandler, Summit and API are often described as colouring preamps, while brands like RME, SSL and Millennia are well‑known examples of very high‑quality transparent amps.
A more prosaic reason for buying an external mic pre is the need for additional input channels. Audio interfaces with more than eight built‑in preamps are relatively rare, so anyone needing more inputs has to expand their system. There are multi‑channel expansion preamps available, with eight microphone inputs being a common configuration. Combined preamp and AD converter units also exist, converting the amplified analogue signal directly into a digital format.
What is a valve preamp?
Valve microphone preamps have a certain mystique about them. These devices, also known as tube preamps, differ from so‑called solid‑state preamps in that they use vacuum tubes for amplification. This technology is often associated with a more coloured sound, though that isn't necessarily always the case. Tube‑Tech, for example, is a brand whose amps are widely regarded as very transparent, while Universal Audio is well known for the rich, full character of its classic 610 preamp design.
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Typical features
Some intentionally coloured preamps offer not only gain, which sets the actual amount of amplification, but also an output level control. This makes it possible to drive the preamp relatively "hot" with high gain to achieve a thick, rich sound, but then reduce the output level again: Without this function, downstream devices could easily be overloaded.
Almost all modern microphone preamps are capable of supplying 48V phantom power to the microphone. Most condenser microphones, as well as some other types, require this to operate. Another found on almost all models are high‑impedance inputs for instrument signals; usually labelled DI or instrument, they accept signals from electric guitars or basses.
Many preamps include a high‑pass filter (also just HPF, or low‑cut filter) to remove very low frequencies that would only cloud the actual signal. Some also have a phase reverse control (more accurately called polarity inversion, but also labelled 180° or simply ø) to help avoid summed signals cancel one another out: If not, this isn't a deal‑breaker, as software solutions or cable adapters can be used instead. Some preamps also offer adjustable input impedance: While the technical background is complex, in practice this results in subtle but noticeable tonal differences for microphones, especially dynamic models.
Channel strips: preamps with expanded features
Where a microphone signal is amplified, additional processing is often required as well. Single‑ and dual‑channel preamps in particular are frequently equipped with more extensive features. This can go as far as full channel strips, which essentially reproduce the signal path of an analogue mixing console channel in a single unit: They frequently include comprehensive EQ sections, for instance. Many channel strips also provide a compressor, allowing this stage of processing to be handled directly during recording. De‑essers, expanders/gates, and limiters also appear on some models. With devices offering digital outputs, anyone planning to use external analogue processing should make sure an insert point is available.
Preamp form factor: 19‑inch or desktop?
19‑inch racks are the industry standard for professional audio equipment. Both high‑end single‑channel preamps and multi‑channel budget units are commonly available in this format. There are, however, alternatives such as half‑rack formats (9.5") or desktop units designed to sit on a table or the floor. There's also a very wide range of preamps available in the compact 500‑series format. Anyone considering an external microphone preamp should take this option into account as well – bearing in mind that a suitable rack or chassis with power supply is required.
Something special: in‑line amps
You can also get small, tube‑shaped devices that look a bit like an elongated XLR connector. These so‑called in‑line amps aren't full microphone preamps in the traditional sense: Instead, they use 48V phantom power to apply a small amount of initial gain. This means they’re inserted between the microphone and a conventional preamp. Because they don't pass the phantom power through to the mic itself, they're well suited to providing an initial boost for dynamic and ribbon microphones. They're most commonly used with the weaker preamps found in mixing consoles or audio interfaces.