Pioneer PL-990 User manual

Add A PreAmp On/Off Swith
to Pioneer PL-990
(ca. 2014 Model)
D. MCDONALD
14-FEBRUARY-2016

BACKGROUND
•Pioneer PL-990 Turntable has a built-in PreAmplifier
•This is useful for many because the Turntable Output is already amplified, and it
can be connected to AUX or CD (Line Level) Inputs
•If a PreAmplifier is NOT present in a turntable, then the output from the
turntable must be amplified before it becomes “Line Level” and useful.
•Old-School Amplifiers have a “Phono” Input for this express purpose
•Vintage Turntables do not have built-in PreAmplifiers, and Vintage
Amplifiers always had a “Phono” input that would appropriately
amplify the raw output signal from a turntable.

BACKGROUND
•Why would one need or want a switch?
•If you want to connect this turntable to the “Phono” input of your vintage amplifier and have it
work correctly, then a switch will help…
•If you don’t like the PreAmplifier included with this Turntable and want to use one of your own
choosing, then a switch will help…
•If you just want to have a turntable, and just want to listen to sounds from vinyl LPs, and don’t have
an amplifier with a “Phono” input that you want to use, then this switch doesn’t really matter.
•If you are more than a little picky about the quality of sounds you listen to, or if you
care about the quality of the hardware you use to produce these sounds then you
probably won’t have a turntable like this, and then this switch doesn’t really matter.

BACKGROUND
•It appears that this Turntable model was designed with the capability of
having a PreAmp On/Off switch.
•This option seems to have only been enabled rarely, if ever.
•There is a hole molded in the plastic below the platter which allows access to the PreAmp PCB
where a switch would have been/could have been installed
•The PCB includes a location for a switch and nearly all of the electrical traces necessary for such a
switch
•Note that the PreAmplifier PCB in my turntable unit is significantly different
from the one described in a service manual available online.
•But the provision for a switch is available on both versions.
•My Turntable’s PreAmp is based on a TI-DRV602 chip.

A LOOK AT WHERE THE SWITCH SHOULD BE
•2. Remove Pad,
Rotate Platter
•1. Remove Top Cover •3. Look Here
(No Switch!)

A LOOK AT WHERE THE SWITCH SHOULD BE
•Look Here (No Switch!)
No Switch (As Received)
•Look Here (No Switch!)

WHAT TO DO (SUMMARY)
•Dismantle Turntable, to gain access to PreAmp PCB
•Remove some jumpers from the PCB
•Some jumpers are present which make the PCB Default to PreAmp
Always-On
•Install some additional jumpers to the PCB
•Some jumpers will be needed to complete the electrical pathways for the
unamplified signal
•Install an appropriate switch into the position provided
•Reassemble Turntable

MY MODEL IDENTIFICATION
•Pioneer PL-990
•Mfr Date: Jan-2014
•Made in China

DISMANTLE THE TURNTABLE

REMOVE THE PLATTER
•Unhook the Belt
•Then Pull the Platter straight up

TAKE CARE OF THE LOOSE BITS
•Fix the Tone Arm
•Put the Needle Guard On
•Remove the 45 Adapter

REMOVE THE BOTTOM PLASTIC CASE
•Remove the (6) screws with
arrows pointing to them
•Take off the Bottom Cover

LOCATE THE AMPLIFIER BOARD
•There are 3 screws to remove in order
to gain better access to the board.
Note: This is an “After” photo, with
my white wire jumper installed
already.

ABOUT THE SWITCH CONNECTIONS

Switch Contact Info (Top Row = Left Channel, Bottom Row = Right):
•S1 = Unamplified, From Cartridge Input
•S2 = Output to External RCA Connectors
•S3 = Amplified, from PreAmp Circuit
S1 S2 S3

REMOVE 2 JUMPERS FROM THE PCB

•Remove Jumpers JR17 and JR18
(Little Black Things with “0” are Jumpers)
•These two bypass the switch location and by Default
send the Amplified Signal to the Outputs

ADD 2 JUMPERS TO THE PCB

Add Jumpers for L/R Unamplified Inputs
•Jumper these two pairs of points, so the unamplified input signal can reach the switch
location
J1
J2

Add Jumpers for L/R Unamplified Inputs
•Jumpers Installed
J2 –No Jumper
(As Received)
J2 –Jumper Installed
J1 –Jumper Installed. Long wire used
because no shorter connection points are
available