Preamps and Analog Mixers Tufts University – ME 93 October 1, 2015

Outline Review signal level and impedance Preamp construction and variables Mixer construction and variables Classifications and specifications of preamps & mixers Next steps

Signal Level Mic Level 5-50 mV Line Level 50 mV – 2V Speaker Level V Preamp Power amp

Impedance Ω Output 1500Ω Input 4-16Ω Output 100Ω Output 10,000Ω Input Microphone Preamp/Mixer/Interface Mic Level Input Line Level Output Power Amp Line Level Input Speaker Level Output Bridging Setup = 10:1 Load Impedance ≥ 10(Source Impedance)

Preamp Specifications Impedance > 1000 Ohms What load is presented to the microphone? Noise (EIN) < -110 dB (relative to +4 dBu) How much noise does the preamp introduce? Maximum Gain > 60 dB How much amplification can the preamp provide? Maximum Input Level > +4 dBu (V rms ) How much input level can the preamp receive from the microphone before distorting? Distortion (THD+N) Below 0.05% How much distortion does the preamp introduce at MIL?

Preamp Specifications

Preamp input section

Low-noise preamp circuit

Preamp Biasing Preamps are often the noisiest part of a signal chain Thermal noise Be aware of component tolerances and durability DC Bias helps achieve low noise Adjust resistors while listening to the output Tweak values of R1 & R2 until the noise is low

8x4x2 Mixer signal flow INPUTsINPUTs BUSSESBUSSES MASTERSMASTERS L R Channel Assignments Pan Pots (L/Odd) (R/Even) Faders Output Assignments Pan Pots (L/Odd) (R/Even) Faders

Digital EQ, inserts, routing, mixing and logic

Work with what you have We have more than the Beatles had Performance, placement, and gain staging are more important than the gear Use your ears, but be cautious of hype

Next Steps The hardest part is the power supply… ICs Preamp Kits Jobs in transducer and analog systems design Fishman Earthworks THAT, Analog Devices Crowely & Tripp