Microphone, Line & Instrument Inputs

Microphone preamplifiers

ASP800 has eight Class-A microphone preamplifiers based on the preamp used in the ASP8024 console. The circuit uses a discrete eight-transistor front end and a second gain stage, providing 0–70 dB of gain and an equivalent input noise of less than −127.0 dBu.

The microphone inputs are on rear-panel Combi XLR connectors. The front end has high input headroom and accepts a wide range of microphone output levels.

Line inputs

The 1/4-inch TRS socket in each rear-panel Combi connector is a balanced line input with an input impedance greater than 8 kΩ. It is attenuated by 10 dB before the microphone preamp and then follows the microphone-preamp signal path.

Because the line inputs pass through the microphone preamp, they retain access to the −15 dB pad on every channel. Channels 1 and 2 also provide polarity reverse, HMX and IRON. This makes the line inputs suitable for keyboards, drum machines and other line-level sources, including sources that you want to colour with the RETRO stages.

Discrete JFET instrument inputs

Channels 1 and 2 provide front-panel Class-A JFET D.I. inputs. Inserting a 1/4-inch TS plug automatically selects the instrument signal in place of the corresponding rear-panel input.

The 1 MΩ input impedance is intended to reproduce the loading of a classic guitar amplifier input. Passive guitar and bass pickups may have source impedances from approximately 6 kΩ to 40 kΩ, depending on the instrument’s volume and tone control positions. A high input impedance avoids loading the pickup excessively and helps retain its signal and tone.

JFETs are valued for tube-like behaviour when overdriven. The ASP800 D.I. circuit can add second- and third-harmonic distortion, and the channel can also feed the HMX and IRON stages.