Threshold sa 12 e service manual

Page 1

I. Bias Instructions

Ill.

V. Dimensional drawing

DC warnings
Cable warning

Balanced input XLFi connector wiring

Schematics:

A. Front and board

3. Output stage

C. Power supply

Parts Layouts:
A. Front and board

8. Output stage

0. Power supply

. Paris lists:
A. Front and board

B. Output stage

C. Power supply

SA/1 20 SERVICE MANUAL
CONTENTS

(R2018-B)

86542000-A)
81702-5;
81703-3

R6541000-E)
R1 702-8
R1 703-3

P1 702-D
P1 703-0

(R2006-A)

§P6542000-A)

"Moe manual.pnos1-w12.rov C 05/11/39

Page 2

BIAS INSTRUCTIONS

The bias circuitry of the E series ofThreshold amplifiers Is designed to hold the

system at a constant temperature between 45 and 50 degrees centigrade

regardless of other parameters. This a? oaoh allows maximum bias to be

obtained In any given condition and he s the thermal characteristics of the

fifemiconductors at a constant, assuring more consistent performance and longer
e.

Bias adjustment on the E series of Threshold amplifiers generally requires only an
initial settin . The thermal trackingbgircult regulates the bias current after these
settings. T a bias current should set initially to the values shown below and
readjusted as necessary after 5 minutes to the same value.

SA4E 1.6 amps per channel
SA12E 2.2 amps total, 1 amp per each side
816005 1.2 amps each side of balanced system

After as long as two hours on the tar est amplifiers the bias will continue to track
against the thermal time constant oft e heat sinks. In the circumstance of well
ventilated 23 de ree ambient, the am Iifiers should exhibit the following bias as
measured after hours of Idle operat on:

SA4E 2 amps per channel
SA12E 3.2 amps total. 1 amp per each side
$1600E 1.5 amps each side of balanced system

0 eration into loads or in other environments will yield different figures. consistent
w h the 45 to 50 degree goal of the thermal tracking circuitry. Preconditioning per
IHF will generally result In higher bias figures.

CABLE WARNING

Both the inputs and the outputs are electrical isolated from the chassis. As a
general rule there should not be any electri connection between input signal
ground and the chassis or else noise pickup may result.

No external connection between input and output grounds should be allowed to
occur with, your Threshold amplifier. A connection of this type will significantly
degrade performance and also carries the potential for amplifier damage.

APPLICATION OF OUTPUT TO INPUT GROUNDING UNDER HIGH POWER
OPERATION CAN PRODUCE A FAILURE IN THE INPUT CABLING THAT WILL
REQUIRE REPAIR AT THE FACTORY. USE OF SUCH INTERCONNECT
CABLES IS NOT RECOMMENDED, NOR SHALL THRESHOLD WARRANT THE
REPAIR RESULTING FROM THEIR USE.

DC WARNING

As your Threshold amplifier uses no fusing in series with the output fithe sonic
operatin advantages of this arran ement are discussed in the DES GN AND
CONST UCTION section of the perating Manual PN57-OOOE) it is well to
remember that the loudspeakers can be sent full amplifier power. A moments
inattention, Such as the removal of an audio interconnection while the amplifier is