Universal Audio 6176 Channel Strip - Manual (Page 36)

The Technical Stuff
_____________________________________________________________
31
Input Section
Figure 2 - Input Section
As shown in Figure 2, the 1176 input section is comprised of an adjustable passive attenuator
followed by a transformer. The purpose of this section is to reduce the signal level so as not to
overdrive the FET based gain reduction stage. Additionally, the adjustable input level is used to
control the amount of compression. This input circuit was used in Revisions A-F. With Revision G, a
differential op-amp input instead of the attenuator / transformer input stage was used.
Gain Reduction Stage
Figure 3 - Gain Reduction Stage
As shown in Figure 3, gain reduction is achieved by a Field Effect Transistor (FET) which is used as a
variable resistor. In the 1176, the FET acts like a resistor whose resistance is controlled by the
voltage applied to its gate. The higher the voltage applied to the gate, the smaller the drain-source
resistance will be.