About Integer Audio
With three decades of experience as an electrical engineer, I decided to pursue my passion for music and audio design and started Integer Audio. I played guitar for years and built some of my own home recording equipment. I became very interested in ribbon microphones. I appreciated their design simplicity and "natural" sound that's true to the source. I found ribbon microphones clearly had characteristics that could benefit from using a preamp design optimized for ribbon microphones. After almost two years of design, simulation, prototyping and listening I introduced the Integer RMP2, a dedicated Ribbon Microphone Preamp.
Integer RMP2 Design Philosophy
Selecting preamp input impedance for use with ribbon microphones must consider both impedance bridging (voltage transfer) and electronic damping. The typical modern ribbon microphone output impedance is 250-300 ohms. The input impedance should be about 10 times the microphone's impedance to reduce “loading” and maximize voltage transfer. If the microphone output and the preamp input impedance were equal, the input signal would be attenuated by –6dB and the S/N ratio 6dB worse. If the preamp input impedance is too low the microphone may become unduly loaded, add distortion and sound "thin". Preamp input impedance must also account for the microphone's electronic damping requirements. If the input impedance is too high the microphone may become under-damped or cause issues related to microphone transformer resonance. This can result in some frequencies being hyped or exaggerated. The end result should minimize signal loss, lower distortion, and provide an accurate microphone frequency response.
Ribbon microphones have low sensitivity where many sources may require 60 dB or more of gain. This is near the maximum gain of many preamps, where noise can become an issue. Minimizing noise associated with the Integer RMP2 was a major design goal and not only at maximum gain (which is 80 dB) but throughout the gain range.
Most preamps have phantom power with additional circuitry and components not required for ribbon microphones. This may include transformers, electrolytic DC blocking capacitors, current limiting and "phantom" resistors, protection diodes, and 48 VDC power supply. These components (which can add phase delays, noise and distortion artifacts) have been eliminated from the RMP2 design. The circuit path is simplified.
The discrete versus Integrated Circuit (IC) based op amp debate is interesting. There is much marketing hype touting "fully discrete class A". The best choice for optimal low noise performance in a preamp front end is discrete. The RMP2 uses matched bipolar transistor arrays in its front end. However for other areas such as gain staging, buffers, servos, etc., IC based op amps are a better choice versus discrete. IC's can offer measurable superior performance specifications, less PCB real estate, less heat, lower cost, and eliminates error prone component "hand matching" requirements. It would be very difficult to consistently meet the repeatable high performance of IC based op amps with a fully discrete design. Today there are many excellent op amps available designed and optimized for use in audio.
The RMP2 is designed to be a "transparent" amplifier not a signal processor. Signal processing is best left to tools specifically designed for that purpose. Using a preamp to add "color" (distortion), via transformer, discrete circuits, etc., is less than optimal due to the inability to control that "feature".
The RMP2's minimalist two-channel design is best applied where accuracy in source reproduction is of the utmost importance.
Ribbon microphones have low sensitivity where many sources may require 60 dB or more of gain. This is near the maximum gain of many preamps, where noise can become an issue. Minimizing noise associated with the Integer RMP2 was a major design goal and not only at maximum gain (which is 80 dB) but throughout the gain range.
Most preamps have phantom power with additional circuitry and components not required for ribbon microphones. This may include transformers, electrolytic DC blocking capacitors, current limiting and "phantom" resistors, protection diodes, and 48 VDC power supply. These components (which can add phase delays, noise and distortion artifacts) have been eliminated from the RMP2 design. The circuit path is simplified.
The discrete versus Integrated Circuit (IC) based op amp debate is interesting. There is much marketing hype touting "fully discrete class A". The best choice for optimal low noise performance in a preamp front end is discrete. The RMP2 uses matched bipolar transistor arrays in its front end. However for other areas such as gain staging, buffers, servos, etc., IC based op amps are a better choice versus discrete. IC's can offer measurable superior performance specifications, less PCB real estate, less heat, lower cost, and eliminates error prone component "hand matching" requirements. It would be very difficult to consistently meet the repeatable high performance of IC based op amps with a fully discrete design. Today there are many excellent op amps available designed and optimized for use in audio.
The RMP2 is designed to be a "transparent" amplifier not a signal processor. Signal processing is best left to tools specifically designed for that purpose. Using a preamp to add "color" (distortion), via transformer, discrete circuits, etc., is less than optimal due to the inability to control that "feature".
The RMP2's minimalist two-channel design is best applied where accuracy in source reproduction is of the utmost importance.
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