Post on 08-Jan-2018
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Preamps and Analog MixersTufts University – ME 93October 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 Level5-50 mV
Line Level
50 mV – 2V
Speaker Level50-100V
Preamp Poweramp
Impedance
50-200ΩOutput
1500ΩInput
4-16ΩOutput
100ΩOutput
10,000ΩInput
Microphone
Preamp/Mixer/InterfaceMic Level Input
Line Level Output
Power AmpLine Level InputSpeaker Level
Output
Bridging Setup = 10:1Load Impedance ≥ 10(Source Impedance)
Preamp SpecificationsImpedance > 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 (Vrms)• 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
INPUTs
1
2
3
4
BUSSES
MASTERS
L
R
Channel Assignment
s
Pan Pots(L/Odd)(R/Even)
Faders
OutputAssignment
s
Pan Pots(L/Odd)(R/Even)
Faders
CR1604 Channel Strip
Digital EQ, inserts, routing, mixing and logic
01V96 Channel Strip
01V96 Channel Strip
Pro Tools Channel Strip
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