Universal Audio 1176LN User's Guide download pdf (Page 12)

Figure 2 – 1176 Input Section

1176 LN Input Section

The 1176LN 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.

from Input Circuit

To Output Amp

To Gain

Control Circuit

Sig In

GR sig

10k, 2W

R23

1uF, 40V

Q14

80uF,25V

80uf

NPN

100

R86

.22

27pF

C22

.22

200pF

C28

50uF, 6.4v

1uF

R88

68k

R17

6.8k

R85

150

R30

6.8k

R14

22k

R13

R12

R11

R84

180

R18

180

560k

2.2M

R10

10k

27k

Figure 3 - 1176LN Gain Reduction stage.

Gain Reduction Stage

This stage is the heart of the 1176LN limiter, and is where the actual signal compression

takes place. Compression is achieved by a Field Effect Transistor (FET) which is used as a

variable resistor. In the 1176LN, 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.

Figure 4 shows how the FET’s resistance determines the gain of this section. Resistor R5

and the and the FET essentially comprise a voltage divider circuit. The lower the FET’s

resistance, the less gain this stage will have. As shown in Figure 4, the FET acts like a

variable resistor, whose resistance is determined by the control voltage that is applied to it.

Note that the greater the voltage applied to the gate of the FET, the less resistance, hence

large signals cause the FET to reduce the gain. As we will see soon, a large input signal

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 18

Comments to this Manuals

No comments

Universal Audio 1176LN User's Guide Page 12

Comments to this Manuals

Related products and manuals for Audio amplifiers Universal Audio 1176LN