Week 32 - Power Continued, Continued Flashcards
What is the power factor?
Power factor is the ratio of the working power to apparent power
This is caused by many factors including induction, transformers, dimming, etc
We should always factor a 15-20% margin of error when doing any power calculations
What 2 cables do we need to look out for with regards to phase?
Powercons - can be 208 or 120
Socapex - can be 208
Who inspects the electrical component of live shows?
ESA - Electrical Safety Authority
What are the three types of grounds discussed in class?
Electrical ground (earth)
Chassis ground
Audio ground
What is electrical ground (Earth)?
Creates a safety path that current can travel in the event of a malfunction or short
Creates a 0v Reference point that all other voltages can be measured
What is chassis ground?
A connection of an electrical system (or systems) to the physical enclosure containing the components
Designed to be a barrier between the user and internal electronics
Often considered a continuation of the shielding within our cables
What is signal ground?
The common connector of our signal in an unbalanced system
The shield connector of a balanced audio cable (pin 1)
Used as a 0V reference in audio equipment (similar to earth ground in an electrical system)
Why is phantom power “phantom”
Equal signal (48V) is sent to both pin 2 and pin 3
Metering from pin 2 to pin 3 will not show a voltage and is completely ignored by the audio signal
What is the main benefit of the star grounding method?
The Potential for a ground loop is greatly diminished (but still possible) if all equipment shares a common electrical ground
What is “lifting the ground” often used for, and how should we do it?
Lifting the ground pin can be an extremely effective way of eliminating a ground loop
Using an XLR pin 1 lift is a recommended practice
Lifting the AC ground removes any safety protection provided by the electrical groundings system and should be avoided at all cost
We could also use an isolation transformer, but if a transformer works, a passive DI should also work
What are some typical causes of ground loops, and how would we fix them?
Unbalanced Cables
Unbalanced cables in the system will often connect the audio signal (pin 3) to the ground. This can introduce a ground loop into the system
Lighting Dimmers
Sharing power with lighting is a huge potential for ground loops when conventional dimmers are used
Separating the audio power lighting power (isolated ground) will greatly reduce this potential
Coiled Cables
Coiled cables, especially power, can create an induction field that will introduce noise onto either chassis ground or signal ground
Figure 8 it to get phase cancellation
