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Assembled Microphone Preamplifiers (Preamps)

You might have your microphone but you're not quite ready to go just yet. To effectively boost the signal from your microphone, you also need a microphone preamp. These are essential if you are using recording devices, mixing consoles, or digital audio workstations, as you will bring your mic level signals up to the required line level of your professional equipment. 

At Seventh Circle Audio, we sell high-quality DIY and fully assembled microphone preamplifiers for audio recording and studio uses. If you are a podcaster, recording studio, or musician looking to record, check out the great prices of our assembled microphone preamps. 

The Benefits of a Microphone Preamp

Some audio interfaces include a built-in preamp, but there are benefits to buying something external for your studio setup.

  • Increased gain. Some microphones need a lot of gain to work properly, which some audio interfaces cannot handle. A preamp will increase the signal level to line level to improve the sound levels of your recordings. 

  • Better sound quality. Improvements in sound quality might not be obvious at lower levels but you will see a noticeable difference when you increase the gain. 

  • Lower noise. Some internal preamps are low noise, but if you use low output microphones or record very quiet sources, a dedicated preamp might be more useful to you to achieve the quietest recording possible.

  • Special sound characters. If you're looking to recreate certain sounds, you can replicate these with an external preamp. You can capture the warm, vintage tones that were prevalent in the preamps that were used back in the 60s and 70s, for example, which is useful if you're trying to be more creative with your music.

N72 mic preamp module

Microphone Preamp Features Explained

When buying a microphone preamp, a number of features are often listed. 


The minimum requirement is one microphone input on a preamp. For studio recordings, you will often need at least two. Some preamps feature instrument inputs for those who want to plug in a guitar or bass. 


Impedance is the AC resistance of audio signal voltages and it controls the audio flow. For a mic signal to travel optimally and to minimize noise, its output impedance should match the load impedance of the mic preamp. For the best results, the load impedance of the preamp should be at least five times higher than the output impedance of the microphone. 

Power supply requirements

These specifications will indicate the voltage the preamp requires for proper functioning. 


You need gain to boost mic level signals so that they are compatible with the professional audio equipment you are using. Most microphone preamps come with variable or stepped gain control. 


Most microphone preamplifiers have a phase button. They might be labeled as 'phase,' 'phase invert,' 'phase reverse,' or something along those lines. The phase button is there to help you if the audio doesn't sound quite right (often referred to as being 'out of phase'). This is caused when multiple sources are adding or subtracting certain frequencies when mixed together. It is a feedback-controlling feature that makes subtle changes to sound waves to support the needs of the musician and listener. 

Phantom Power

You will notice that some microphone preamps include a phantom switch. It is designed to power microphones without the need for a bulky external power supply. When phantom power is turned on, the DC current is sent through the XLR cable and delivers the voltage necessary to power the microphone. It is more widely used as a power source for condenser microphones.

Fully Assembled Microphone Preamps

D11 with subpanel, Seventh Circle Audio dual DI for recording audio, SCA

D11 DI Module

The SCA D11 is a two-channel active DI that accepts a high-impedance, unbalanced, instrument-level input and produces a low-impedance, balanced, mic-level output. If required, an optional Jensen or Cinemag transformer can be fitted to provide a fully floating isolated output.

D11 DI Module Features

Switchable Impedance

Switch between 1M ohms, 100K ohms, or 10K ohms input impedance depending on your pickups. Other impedances are possible with simple resistor substitution.

Linkable Inputs

The input jacks can be jumpered so that either input can drive both outputs. This makes it easy to drive a pair of preamps simultaneously. The jacks can also be jumpered in parallel for direct pass-through to an amp.

Extremely Wide Bandwidth

Flat response to beyond 200 KHz is guaranteed to keep all the highs intact.

High current class A design

The simple, 3-transistor, all-discrete, class-A circuit has a low-noise JFET input and a fully balanced output.

Neutrik Connectors

High-quality PC mount connectors eliminate cabling and ease assembly.

Optional Output Transformer

Fit an optional Jensen or Cinemag transformer to one or both channels for a fully balanced isolated output.

Flexible Power Supply

On-board voltage regulators accommodate power supplies from +/-27VDC to +/-35VDC. Local regulation also keeps inter-channel crosstalk extremely low when multiple modules share the same power supply.

T15 with subpanel, Seventh Circle Audio high quality mic preamp for recording audio, SCA

T15 Microphone Preamplifier Module

The SCA T15 is a transformerless microphone preamplifier designed around the excellent THAT Corporation 1512 and 1646 high-performance current-feedback instrumentation amplifiers. 

With state-of-the-art chips, the performance of the T15 is able to approach that of sophisticated discrete and hybrid designs (such as the C84) while using far fewer components. While it does not have the same headroom and output drive capability as the C84, the T15 has similar noise and distortion specifications and excels in the same applications.

T15 Features

High Gain

The T15 can provide 70dB of gain, more than enough gain for most applications, especially with modern high-output condenser microphones.

Stepped Gain Control

A 12 position Grayhill switch provides accurate and repeatable gain settings in 5dB steps from 15dB to 70dB.

Gain Trim

The T15 has a gain trim control which provides up to 6dB of cut at any gain setting. This allows very fine adjustment of gain between steps. This control can also be configured as a full fader.

Phase Reverse

Inverts the signal phase.

Phantom Switch

Slow-rise phantom power minimizes pops and thumps.

Neutrik Connectors

High-quality PC mount connectors eliminate cabling and ease assembly.

Dual DC Servos

Similar to the C84, the T15 employs two DC servo circuits.

Flexible Power Supply

On-board voltage regulators can accommodate power supplies from +/-15VDC up to +/-35VDC, allowing the use of op-amps with +/-24VDC requirements. Local regulation also keeps inter-channel crosstalk extremely low when multiple preamps share the same power supply.

Do You Need A Microphone Preamp?

If you are just starting out in music and making your own demos, you might not need a dedicated microphone preamp. Most audio interfaces come with a preamp built-in so this might be fine for you at the beginning. If you are recording in a studio, they will often have a wide range of mic preamps available, so there would be no need to pay for something yourself. 

However, as you get further along with your music career and you have set up a recording studio at home, it is important to note that dedicated mic preamps will improve the quality of your recordings at the beginning of the signal chain. You can also achieve specific tones and sounds through the preamp to add more color and creativity to your recordings, which can help you stand out from competing artists. 

For these reasons, it is worth investing in a good microphone preamp.

Whether you're a recording artist or a podcaster, you will improve the quality of your work and appear more professional to your listeners. This will give you the boost you need as you take that important next step in your chosen career or pastime. 

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