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Klipsch KSP-300 Hum question


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Built a new house on a shoestring budget. Own it. Wife said NO WAY are the Cornwalls going in the new (smaller) living area, sold them. Researched (apparently not thoroughly) KSP-300's after finding a minty pair by original owner. They BLEW me away. Bought them. FF 2 weeks to last night. Have the power supplied via Monster 1500, switched it on. HUMMMMMMM. Hooray. Pissed. Searched the forums last night, service manual pdf's no longer valid. Called Wayne M 15 minutes ago and left a message. Anybody have the service manual for these? Please. Thanks, JJ.

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Klipsch Amplifier Service Manual KSAMM-008

TABLE OF CONTENTS

SPECIFICATIONS....................................................................................................................................... 2

Model: KSP-300 ........................................................................................................................................ 2

THEORY OF OPERATION........................................................................................................................ 3

INPUTS....................................................................................................................................................... 3

SIGNAL CONDITIONING.......................................................................................................................... 3

OUTPUT..................................................................................................................................................... 3

POWER SUPPLY........................................................................................................................................ 3

OTHER FEATURES ................................................................................................................................... 3

TROUBLE SHOOTING GUIDE ................................................................................................................ 4

PARTS LISTS............................................................................................................................................... 5

SCHEMATIC DIAGRAMS......................................................................................................................... 8

Page 1

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Klipsch Amplifier Service Manual KSAMM-008

SPECIFICATIONS

Model: KSP-300

Rated Power Output 150 Watts Continuous into 4 Ω

Maximum Power Output 200 Watts into 4 Ω

Frequency Band-width 10 - 75Hz

THD < 1.0% @ 1 Watt

< 0.5% @ Rated Power

<10.0% @ Maximum Power

Signal to Noise 90dB or better

60 Hz Hum <800μV

Input Sensitivity for Rated Output Line Input = 200mVrms @ 28Hz

Sub(LFE) Input = 400mVrms @ 28Hz

Speaker(HI) Input = 1.5Vrms @ 28Hz

Input Impedance Line & Sub Input = 33KΩ

Speaker Input = 680Ω

Auto-on Sensitivity Line Input = 10mVrms (20Hz - 2kHz)

Sub(LFE) Input = 20mVrms (20Hz - 2kHz)

Speaker input = 65mVrms (20Hz - 2kHz)

Auto-On Delay 1-2 Seconds

Auto-Off Delay > 15 minutes

Low Pass Fixed @ 55Hz with 12dB/Octave Slope

Page 2

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Klipsch Amplifier Service Manual KSAMM-008

THEORY OF OPERATION

KSP-300 Amplifier

INPUTS

This amplifier utilizes two types of signal connectors. RCA connectors for LINE LEVEL and LFE Inputs,

and 5-way binding posts for the SPEAKER LEVEL Inputs.

SIGNAL CONDITIONING

All pre-amplification, filtering, and signal conditioning is accomplished using dual op-amp devices U1,U2,

U4, U5, and U8. U2A and U2B are buffer stages linking the Line In & LFE In signals to the associated output

jacks. Op-amps U1A and U1B are gain stages that perform the necessary buffering and isolation of the input

signals. After the buffer stages, the signals pass through the appropriate level controls to the input of stage U5B.

U5B is a low Q HIGH PASS filter with a slope of approximately 6dB/octave below 20Hz. Stages U5A and U8A

are fixed low pass filters tuned to 55Hz with a combined slope of 12dB/Octave above cutoff frequency. U8B is an

additional gain stage which drives the input of the Power Amp section.

OUTPUT

The Power Amplifier(PA) section of this amplifier consists of a balanced pre-amp U1 and output

transistors Q1and Q3. The maximum output capability of the amplifier is determined primarily by the transistor

type, and the DC rail voltage/current supplied by the power supply. The value of feedback resistor R10 determines

the sensitivity of the PA section. Transistors Q2 and associated components establish the DC offset.

POWER SUPPLY

The power transformer has single primary windings and dual center-tapped secondaries. The unregulated

DC rail voltage for the power output section of the amplifier is produced by the bridge rectifier D2 and filter

capacitors C6, & C8. The low voltage power supply section furnishes +12Vdc and -12Vdc for the Filter and Signal

Processing circuitry. These voltages are generated by bridge rectifier D1, voltage regulators U6 & U7, and filter

capacitors C8, C9, C10, & C11.

OTHER FEATURES

AUTO ON/OFF

This amplifier features an automatic on/off circuit that allows the user to set up once and forget it. The low voltage

power supply in the amplifier is active once the unit is plugged in to an AC outlet. With the power switch in the

“AUTO” position, a switching circuit consisting of U4, D2, and Q1, senses an input signal. From this switching

circuit, the power relay (RL1) is activated connecting the output of the power transformer to the high voltage power

supply. This supplies the rail voltage to the PA section. For the protection of the speaker, there is a short delay

before relay (RL1) is activated. The sensing circuit will turn off after the input signal is absent for approximately

15 minutes or more. With the power switch in the “ON” position the signal sensing circuit is bypassed and the

power relay (RL1) is always activated. A bi-color LED indicates the status of the amplifier at any given time. The

LED will be RED when the relay control circuit is activated and GREEN when not activated.

Page 3

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CAUTION!

Lethal voltages are present and exposed when cover is off of amplifier.

􀀱

Only qualified service technicians should attempt to repair subwoofer amplifiers.

PROBLEM POSSIBLE CAUSE

1 Blows fuse with nothing connected 1 Check output transistors.

to the output.

2 Check filter capacitors C6, C8, PA Board and

C8, C9, EQ Board for shorts.

3 Check Regulators U6, & U7 for shorts.

4 Check bridge rectifiers D1 & D2.

5 Check transformer.

2 Low output level. 1 One or more signal processing stages defective.

Refer to schematic diagram pg. 6-7 for signal tracing.

3 No signal output -- LED On 1 Ensure that power switch is in “Auto” or “On” position.

2 Ensure input signal is present.

3 One or more signal processing stages defective.

Refer to schematic diagram pg. 6-7 for signal tracing.

4 No signal output -- LED Off 1 See problem # 1.

5 Excessive hum. 1 Check all ground connections.

2 Check all filter capacitors. C6, C8, C9, C10, & C11.

Page 4

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Klipsch Amplifier Service Manual KSAMM-008

KSP-300 Parts List

(EQ Board)

PART VALUE/PART NUMBER KLIPSCH PART #

RESISTORS, FIXED

R20 56Ω 1/4 WATT Metal Film 1%

R22,28,36,38,40,43,56 1KΩ

R5,26,27 1.8KΩ

R55 2.7KΩ

R24 3.3KΩ

R39,42 15KΩ

R17,18 22KΩ

R7,9,25 33KΩ

R4,16,29 47KΩ

R57,63 51KΩ

R1 56KΩ

R21,53,54 68KΩ

R2,8 75KΩ

R14,15,59 100KΩ

R3,10 150KΩ

R19 200KΩ

R6 220KΩ

R23 2.2MΩ

R50,51 47Ω 1/2 WATT CARBON 5%

R11 680Ω

RESISTORS, VARIABLE

VR12,13 LEVEL & LFE LEVEL CONTROLS 50KB Linear Taper Potentiometer

CAPACITORS

C22,23 100pF Ceramic

C29 .015μF Metalized Film

C27 .033μF “

C30 .047μF “

C28 .068μF ”

C5,13 .1μF ”

ELECTROLYTIC CAPS

C1,2,3,6,10,11,18,19,20,21,25,26 10μF/25V

C14,15 100μF/16V

C7 220μF/16V

C16 100μF/50V

C8,9 470μF/25V

Page 5

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Klipsch Amplifier Service Manual KSAMM-008

KSP-300 Parts List

(EQ Board)

PART VALUE/PART NUMBER KLIPSCH PART #

DIODES

D1 PBDF101 Bridge Rectifier 1A/50V

D2 1N4148

LED

D3 T-1(3mm), 2 color (RED/GREEN)

ICs

U1,2,4,5,8 AN6551 Dual Op-Amp

U6 7812 +12V Regulator

U7 7912 -12V Regulator

TRANSISTORS

Q1 2SC2061 118778

SWITCHES

SW1 Power Slide Switch SK23H01G11-NS

CONNECTORS

J1 Line In/Out, LFE In/Out Quad RCA Jack

J2,4 Speaker In 5-way Binding Post(Red)

J3,5 Speaker In 5-way Binding Post(Black)

OTHER

Fuse Holder

Fuse: (120V) 2A/250V 5mmX20mm Slow Blow 118334

(230V) 2A/250V 5mmX20mm Fast Blow 118339

Knob (Level & LFE Level Controls)

AC Power Socket

C99 230V only 0.1μF Metalized Polyester Suppressor

TRANSFORMER

T1 (120V) PT08605V26

T1 (230V) PT08612V26

Page 6

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Klipsch Amplifier Service Manual KSAMM-008

KSP-300 Parts List

(Power Amp Board)

PART VALUE/PART NUMBER KLIPSCH PART #

RESISTORS, FIXED

R6,9 10Ω 1/4 WATT Metal Film 1%

R2,5 1KΩ

R11 1.8KΩ

R4 15KΩ

R3,10 56KΩ

R13,14 10Ω 1/2 WATT Metal Film 1%

R1,8 .22Ω 5 WATT Ceramic

RESISTORS, VARIABLE

VR7 3KΩ Trimmer

CAPACITORS

C7 0.033μF Metalized Film

C4 0.068 “

C1 0.33 “

C3 68pF Ceramic

C2 470pF “

C6,7 100pF “

C2 470pF “

ELECTROLYTIC CAPS

C5 22μF/16V

C6,8 4,700μF/63V

DIODES

D1 1N4002

D2 PBL403 Bridge Rectifier 4A/200V

TRANSISTORS

Q1 2SA1302 TO-3P 118729

Q3 2SC3281 “ 118731

Q2 2SC1815/2SC945 TO-92 118773

ICs

U1 UPC1298V preamp 118769

RELAYS

RL1 Relay - Power JW2HN-DC12V

Page 7

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  • 3 years later...
  • 4 weeks later...
  • 11 months later...

If anyone is looking for a fully refurbished pair of KSP 400, or it's little brother the KSP 300, or the K-6 600 watt surrounds & center channel, please let me know.  I bought a set of 300's from the original owner that still had working amps, but I happened to find 3 brand new (never used) European 220v amps and all I did was swap transformers and they're perfect!  Last year I bought the entire K-6 series with the KSP-400 towers that needed new amps, but all in all looked great!  However, I was not a fan of the woodgrained look as it made my living room feel like a 1970's porn flick.  A local cabinet maker owed me a favor and I had them completely refinished to match my KSP 300's.  The guy I bought the 3 KSP 300 amps from also had 1 new (or unused) KSP 400 amp and I had the other professionally fixed.  The reason I'm getting rid of them is due to the police showing up at my door for the 4th time and made it clear that I did not want them coming back a 5th time, and I also have a 15" R-115sw in each corner.  What can I say, I like bass.   

KSP and cell.jpg

KSP400 tower after steve painted.jpg

20220107_010956.jpg

small.20220107_013337.jpg

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