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

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

3. Signal Level Mic Level 5-50 mV Line Level 50 mV – 2V Speaker Level 50-100V Preamp Power amp

4. Impedance 50-200Ω 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)

5. 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?

6. Preamp Specifications

7. Preamp input section

8. Low-noise preamp circuit

9. 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

10. 8x4x2 Mixer signal flow INPUTsINPUTs 1 2 3 4 BUSSESBUSSES MASTERSMASTERS L R Channel Assignments Pan Pots (L/Odd) (R/Even) Faders Output Assignments Pan Pots (L/Odd) (R/Even) Faders

15. Digital EQ, inserts, routing, mixing and logic

18. 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

19. 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