Biamp DA28R, Operation Manual

3 

LOGIC INPUTS & TRANSFORMERS 

Logic Inputs:

  Logic Inputs 1~16 are on pins 1~16, and a common ground is on pins 17~25.  Logic Inputs 1~8 affect routing of Channel 1 

signal to Outputs 1~8, respectively.  Logic Inputs 9~16 affect routing of Channel 2 signal to Outputs 1~8, respectively.  Logic Inputs are 
triggered by being shorted to ground, usually by means of external switches, relays, logic outputs, or other such contact-closures.  However, 
they may also be triggered permanently, via a ‘hard-wired’ short to ground (see Applications on pg. 5).  Logic Inputs perform either ‘muting’ 
or ‘unmuting’ functions, depending upon the position of the ‘Invert Logic’ DIP Switches (see diagrams below).  From the factory, ‘Invert Locic’ 
is not assigned on Channel 1 or Channel 2, and both inputs are normally unmuted (turned on) at all outputs.  Contact-closures can then be 
used to ‘mute’ (turn off) either input at selected outputs.  When ‘Invert Logic’ is assigned, the associated input is normally muted (turned off) 
at all outputs, and contact-closures can be used to ‘unmute’ (turn on) that input at selected outputs.  A combination of ‘Invert Logic’ and 
normal (non-inverted) logic operation allows Channels 1 & 2 to provide an override function.  With a single switch wired to two corresponding 
Logic Inputs (i.e…Logic Inputs 1 & 9), one input may be muted, while the other input is unmuted at the same output.  This can be extremely 
effective in multi-zone, page-over-music applications (see Applications on pgs. 4). 
 
 

CH 1

phantom

invert logic

phantom

invert logic

CH 2

CH 1

phantom

invert logic

phantom

invert logic

CH 2

CH 1

phantom

invert logic

phantom

invert logic

CH 2

CH 1

phantom

invert logic

phantom

invert logic

CH 2

logic inputs

logic inputs

1

13

14

25

Logic Inputs

pins 1~8

pins 9~16

pins 17~25

assign functions

ch-1 to outputs 1~8

ch-2 to outputs 1~8

common ground

Ch-1 & Ch-2
normally 'on'

(switches mute)

Ch-1 & Ch-2
normally 'off'

(switches unmute)

Ch-1 normally 'on'

(switches mute)

Ch-2 normally 'off'

(switches unmute)

Ch-1 normally 'off'
(switches unmute)
Ch-2 normally 'on'

(switches mute)

NOTE:

 The DA28R chassis must be dis-assembled before installing input/output transformers:  

1)

  remove top panel (2 screws at bottom of 

each side panel; 1 screw at top-center of rear panel).  

2)

  remove screws from front panel (2 screws at each end).  

3)

  remove hex-nuts from 

rear panel (1 hex-nut each side of Logic Inputs connector).  

4)

  remove mounting screws from circuit board (9 screws in front of rear panel 

connectors; 2 screws behind each side of front panel).  

6)

  gently pull circuit board forward (front panel comes forward; connectors exit rear 

panel).  

7)

  rotate front panel/circuit board upward, away from chassis (leave rear portion of circuit board in chassis, being careful not to strain 

power cord connections).

Input Transformers

:  To install input transformers (see diagram at right):  

1)

 locate 

transformer positions T1 & T2 on the circuit board (circle areas located in front of input
connectors).  T1 is for Channel 1 & T2 is for Channel 2.  

2)

  un-solder & remove the 2 

capacitors located within each of the appropriate circle areas.  

3)

 install & solder an input 

transformer at each of the appropriate circle areas (transformer pin 1, designated by a red dot,
must be inserted into the proper hole, designated by a square).  Input isolation transformers
are model IT-A (P/N# 909-0010-01). 
 

INPUT TRANSFORMERS

T1

cap

cap

Output Transformers

:  To install output transformers (see diagram at right):  

1)

 locate 

transformer positions T101~T801 on the circuit board (rectangle areas located in front of output
connectors).  T101 is for Output 1, T201 is for Output 2, etc.  

2)

  un-solder & remove the 2 

jumpers located within each of the appropriate rectangle areas.  

3)

 install & solder an output 

transformer at each of the appropriate rectangle areas (transformer pin 1, designated by a red
dot, must be inserted into the proper hole, designated by a square).  Output isolation
transformers are model IT-B (P/N# 909-0019-00). 

OUTPUT TRANSFORMERS

T101

R902

R901