Dimmers

The means to controling intensity of instruments.

Switches: simple, but abrupt.  Some sort of dimmer preferable.

Dimmer types: archaic

--Salt water dimmers
--Resistance dimmer:  first really practical portable dimmer
  Very heavy and large, both DC and AC
     Needed resistance 5 times load to dim out
     Turned excess current to heat
     Piano boards

Transformers:
1000 turns : 500 turns
200 volts : 100 volts
but
Power remains constant, so:
50 Amps @ 200 v. = 100 Amps @ 100 v.

Autotransformer:  used magnetic impedance rather than resistance, AC only
   Primary & secondary combined in transformer coil
   Heavy and large, but didn't waste current as heat
Magnetic amplifier:  used saturable core principle
   First commercial remotely controllable dimmer
   Very heavy & large, not very lineal dimmer curve, expensive but durable
Thyrotron tube:  first electronic dimmer:
   Large vaccum tube, remote controllable
   Cheaper than mag-amps, but required more maintainance
   Tubes burned out and had to be replaced

Solid State dimmers:

Short intro to electronics:

Semi-conductors: PN junction
   Diodes:  2 layer device
   Transistors:  3 layer devices
   Silicon control rectifiers: 4  layer devices
   Triacs:  5 layer devices

Silicon Control Rectifiers:  solid state thyrotron tubes
Used in reverse pairs.
     --Smaller than more dependable than thyrotrons
     --Remote controlable
     --Independant of load (mostly)
     --Electronically noisy: the voltage spike and need for chokes 
      (inductance coils).

Triacs:  bipolar version of SCR, only one needed for controlling AC
   Much less robust and hard to make in larger sizes.

SSR's or Power cubes:
Solid State Relays
   Depend on high speed timing circuit for control.
Like SCR, controls when in sine wave current turns ON.
Also requires use of a choke.

IGBT Dimmers (Integrated Gate Bipolar Transistors) Primarily being built and promoted by Rosco Technologies.
     --Does NOT require a choke.
     --Has no electronic noise, less electronic interferrence.
     --Rosco claims it needs no cooling fan.
     --More dependant on integrated microprocessor control.

Competitors claim it is more delicate and still unproven.

©2000, Mick Alderson