Sphinx Project eighteen User manual

SERVICE MANUAL

PROJECT EIGHTEEN

TRUE DUAL MONO

POWER AMPLIFIER

SPHINX Project Eighteen Service Manual

1. UNPACKING.......................................................................................................................................3

2. SPHINX WARRANTY CARD ..............................................................................................................3

3. CONTACTING THE MANUFACTURER.............................................................................................3

4. THE POWER AMP AT A GLANCE.....................................................................................................4

Front panel...................................................................................................................................................4

Rear panel ...................................................................................................................................................5

5. TECHNICAL SPECIFICATIONS.........................................................................................................6

6. GENERAL CHECKLIST......................................................................................................................7

Optical connections .....................................................................................................................................7

Switching the amp on...................................................................................................................................7

Protection mode...........................................................................................................................................7

Shorted output .............................................................................................................................................7

Cables..........................................................................................................................................................7

7. ADJUSTMENT PROCEDURES..........................................................................................................8

High Bias .....................................................................................................................................................8

Low Bias ......................................................................................................................................................9

Offset ...........................................................................................................................................................9

Common Mode ..........................................................................................................................................10

8. PROBLEMS AND SOLUTIONS........................................................................................................11

9. DIAGRAMS AND PARTS LISTS ......................................................................................................12

Connecting diagram for testing the project 18...........................................................................................13

Connection diagram for common mode adjustment..................................................................................14

Schematic layout of all relevant parts........................................................................................................15

Schematic overview of the Project 18 mainboard......................................................................................16

Project 18 logic..........................................................................................................................................17

Project 18 supply & relay control schematic..............................................................................................18

Project 18 blockdiagram left ......................................................................................................................19

Project 18 blockdiagram right....................................................................................................................20

Project 18 amplifier diagram left................................................................................................................21

Project 18 amplifier diagram right..............................................................................................................22

Project 18 power supply left.......................................................................................................................23

Project 18 power supply right.....................................................................................................................24

PCB drawings of Project 18.......................................................................................................................25

Partlist........................................................................................................................................................26

SPHINX Project Eighteen Service Manual

The Sphinx Project Eighteen design

The Sphinx Project Eighteen was designed for the

ever-increasing group of quality-conscious

audiophiles.

We are very proud of the tradition connected with

the SPHINX name, especially concerning audio

quality perfection.

This service manual will help you to optimally

service and repair the Sphinx Project Eighteen True

Dual Mono Power Amplifier.

The power amp handles the largest signal peaks

and transients with ease, and has no problem with

any size and type of loudspeaker load: even the

most demanding.

These characteristics are the result of several new

technologies and components. For instance the

unique power supply which assures a stable and

noise free operation. The special toroidal

transformer (one for each channel!) of 650 VA has

the size of a 1000 VA model: safely over-specified.

Thanks to the generous energy reserve of 66,000

µF (formed by 30 capacitors in parallel), unlimited

power is available for the largest signal peaks.

Furthermore there are three completely separate

power supplies for the input section, driver section

and the logic and indicator section.

Much attention has also been paid to the physical

layout, the positioning of components and the

internal grounding. This results in a equivalent input

noise value of <1 µV (<-120 dBV): remarkable for a

pre-amp, but really astounding for a big power amp

with two transformers.

All of this means that the Project Eighteen can work

with all kind of loads from every loudspeaker: even

the most difficult ones like electrostatic and

magnetostatic...

To obtain the maximum quality from this power amp

it is necessary to use it with top quality audio

components preferably with other Sphinx

components.

1. UNPACKING

Before leaving the factory every Project Eighteen is

subjected to stringent and extensive technical and

exterior quality inspections. This ensures the user

many years of high quality audio from a perfect-

looking product.

Attention: The power amp weighs over 24 kg!

Never lift it out of the box without someone

helping you.

We recommend owners to ship the Project

Eighteen in its original carton.

After unpacking the Project Eighteen we therefore

recommend you carefully check it for any transport

damage.

If you find any damage and the product has not

been shipped in the original carton the ensuing

repair costs will not be covered by the warranty.

2. SPHINX WARRANTY CARD

To be entitled to any warranty repairs the owner

must have send the filled out warranty card to

Sphinx or a distributor where it has been registered.

Other regulations may apply in your specific

country: when in doubt, please consult the proper

authorities.

3. CONTACTING THE MANUFACTURER

In case of any problem not covered in this manual

or if you have other questions you may contact the

Sphinx International Service Department in The

Netherlands (local time: GMT +1h) during office

hours at the following numbers:

Telephone (+31) 35 602 0302

Fax (+31) 35 602 2806

E-mail [email protected]

It is always very helpful and efficient if you have all

relevant information about the specific product and

the problem ready.

Please also refer to the User Manual of the

Project Eighteen for information about

functions not described in this manual.

It is important to familiarise yourself with the

special functions, operation and possibilities

of the Sphinx Project Eighteen.

SPHINX Project Eighteen Service Manual

4. THE POWER AMP AT A GLANCE

Front panel

1. LED: Indicates the selected function:

stand-by red

on green

2. STANDBY: To switch the component on and off.

SPHINX Project Eighteen Service Manual

Rear panel

3. RIGHT OUTPUT: To connect the cable from the

right loudspeaker:

red +

white -

4. CONTROL IN: To connect the optical cable

from another Sphinx component like a pre-amp.

5. BALANCED RIGHT: To connect the XLR cable

(balanced cable) from the right output of the

signal source.

6. CINCH RIGHT: To connect the cinch cable from

the right output of the signal source.

7. CINCH/BALANCED INPUT: With this switch

you may select between the inputs:

up unbalanced (6 and 8)

down balanced (5 and 9)

8. CINCH LEFT: To connect the cinch cable from

the left output of the signal source.

9. BALANCED LEFT: To connect the XLR cable

(balanced cable) from the left output of the

signal source.

10. CONTROL OUT: To connect the optical cable

going to another Sphinx component.

11. LEFT OUTPUT: To connect the cable from the

left loudspeaker:

red +

white -

12. ON/OFF: This is the mains power switch.

13. AC POWER: Connect the power amp to a

mains outlet (230 - 240 VAC).

The mains fuse is placed behind the cover.

14. Manufacturer's label: This shows important

data for the component, such as serial number

and mains power voltage.

345

8 9 10 11 12 13

SPHINX Project Eighteen Service Manual

5. TECHNICAL SPECIFICATIONS

Bandwidth 0 – 100,000 Hz (+0/-1 dB)

Phase response error <1° (0 - 20,000 Hz)

Gain 30 dB max.

Minimum Power Output (1 - 20,000 Hz, 1 W = 0

dBW) >2x 160 W into 8 ohm (22.0 dBW), THD <0.01%

>2x 280 W into 4 ohm (24.5 dBW), THD <0.01%

>2x 420 W into 2 ohm (26.2 dBW), THD <0.01%

Output voltage / current, max. 36 V / 43 A

THD+N (IHF-A) <0.01% (@1 W into 8 ohm, 1 - 20,000 Hz)

IMD <0.01% (@ 100 W into 8 ohm)

S/N ratio (IHF-A) >120 dB

Common Mode Rejection Ratio >80 dB (@ 100 Hz)

Slew rate >50 V/µs

Damping factor >2000 (1 – 20,000 Hz)

Input XLR balanced / cinch WBT unbalanced

level, nominal 1.25 V (1.9 dBV) / 1.25 V (1.9 dBV)

impedance 600 ohm / 20 kohm

Supply capacitance 132,000 µF total

Power consumption 1500 W max. (70 W standby)

Power transformer, primary 230 VAC / 115 VAC

secondary 1 & 2 42.5 V / 7.1 A

secondary 3 & 4 15 V / 1 A

secondary 5 & 6 60 V / 0.1 A

Maximum DC-offset +0.5 V and –0.5 V

Short circuit protection Fuse per channel

Dimensions (h x w x d) 143 x 482 x 452 mm

Weight 24 kg

This unit conforms to the EMC interference regulations issued by the EU and to the CE standards.

This unit complies with safety regulation VDE 0860 and therefore with international safety regulation IEC 65.

Technical specifications may be changed by SPHINX without prior notice if technical developments make this

necessary.

SPHINX Project Eighteen Service Manual

6. GENERAL CHECKLIST

Before you test or service the Project Eighteen

please check the following items. They will give

information about the current status of the amplifier.

Note: The Project Eighteen will become warm, so

correct placement is critical. Do not position it on

top of or close to other heat-radiating equipment

(such as other power amps) or in direct sunlight.

Please ensure unrestricted ventilation around

the component.

Optical connections

The optical CONTROL IN (4.) is light-sensitive. A

strong light source might therefore activate the

CONTROL function and switch the Project Eighteen

to Standby.

While this mode has priority the amplifier can not

be activated with the Standby switch at the front

panel.

Before you start connecting equipment it is always

wise to check whether all the mains cables of all

components are disconnected from the mains

outlets!

This will prevent any damage to the loudspeakers

and amplifiers caused by incorrect wiring or

settings.

Connect the mains cable after you have connected

all other components in the system and have

double-checked all connections.

Switching the amp on

Before you switch the power amp on you should

always first:

•connect a pre-amp

•connect the pre-amp’s Control Out to the power

amp’s Control In

•or place the dummy plug in the Control IN

connector

After switching the amplifier ON it will select

Standby mode and the following will happen:.

1. The output relays are disconnected.

2. The input relays are disconnected.

3. The Control Out will show a red light.

4. The biasing relays reset the bias current to

standby level.

5. The red LED (1.) will light.

Pressing the Standby-button (2.) will activate the

amplifier and the LED turns to green.

Protection mode

If at any time the output DC-offset exceeds 500 mV

the protection mode will activate.

This will reset the amp to Standby mode and the

green LED (1.) will change to red.

Note: Externally there is no way of telling whether

the amp is in protection or standby mode!

This can only be checked inside the housing: LED

LD 102 will be illuminated in protection mode.

The protection mode can only be deactivated by

readjustment of the DC offset voltage (according to

the procedure “Offset” at page 9).

Shorted output

If one of the outputs is shorted the fuse F203,

F204, F403 or F404 will blow.

Cables

Always use loudspeaker and audio cables and

connectors of the highest quality.

Siltech cable is used throughout internally and we

recommend using this same cable for all external

connections.

If you have the choice between longer loudspeaker

cables or longer audio cables, choose the latter

(cables between pre-amp and power amp will

cause the least signal quality loss).

SPHINX Project Eighteen Service Manual

7. ADJUSTMENT PROCEDURES

The Project Eighteen has eight adjustable settings,

meaning four adjustment procedures per channel:

1. High Bias: to set the bias current of the power-

transistors for normal use

2. Low Bias: to set the bias current of the power-

transistors for standby mode

3. Offset: to set the minimal DC voltage for the

output

4. Common Mode: to maximise the common

mode rejection of the balanced input

Re-adjustment of one or more might be necessary

due to ageing or when parts have been replaced or

repaired.

After removing the top cover plate you will clearly

see the two separate channel sections.

High Bias

With this procedure you set the proper bias level for

the power transistors. This ensures their Class A

operation at low power levels.

Connect the amplifier according to the drawing

“Connecting diagram for testing the project 18”

(page 13).

The input of the amplifier must be shorted (by way

of the MUTE function of the oscillator).

•Switch the amplifier ON (not in Standby

Mode!) and wait until it has reached the proper

operating temperature (this takes an hour).

•Set the millivolt-meter to the DC-range.

•Place the two measuring clips of the meter

across one of the emitter resistors

Left Channel: R468, R469, R472, R473, R476,

R477, R480 and R481.

Right Channel: R268, R269, R272, R273, R276,

R277, R280 and R281 (see schematic at page

15).

•The level should be 60 mV DC (±3 mV).

If not: adjust potmeter P402 (Left) or P202

(Right) until the level is 60 mV.

•Switch the oscillator on and set it to 1 kHz and a

level of 0 dBu.

•Check the distortion with a THD analyser: it

should be at the specified value (0.01% IHF-A

@ 1 kHz).

•If this is correct the procedure is finished.

•You may now switch off the amplifier or

continue with another adjustment procedure.

Attention:

When re-adjusting any setting please ensure that

there is no loudspeaker connected to the output!

Otherwise the loudspeaker may be seriously

damaged.

Attention:

The amplifier is able to generate high output

voltages of over + or -60 V.

Please be very careful during the adjustments!

Attention:

All emitter resistors should show the same 60 mV

value. If not, the corresponding power transistor may

be defective.

SPHINX Project Eighteen Service Manual

Low Bias

With this procedure you set the proper bias level so

the power transistors will remain at operating

temperature during standby mode.

If this setting is too low, the operating temperature

will drop too much causing an unnecessary

increased warm-up period after switching the amp

on.

If this setting is too high the amplifier will consume

more electrical power than necessary.

Connect the amplifier according to the drawing

“Connecting diagram for testing the project 18”

(page 13).

The input of the amplifier must be shorted (by way

of the MUTE function of the oscillator).

•Switch the amplifier ON (but in Standby

Mode!) and wait until it has reached the proper

operating temperature (this takes an hour).

•Set the millivolt-meter to the DC-range.

•Place the two measuring clips of the meter

across one of the emitter resistors

Left Channel: R468, R469, R472, R473, R476,

R477, R480 and R481.

Right Channel: R268, R269, R272, R273, R276,

R277, R280 and R281 (see schematic at page

15).

•The level across each resistor should be 5 mV

DC (±0.25 mV).

If not: adjust potmeter P403 (Left) or P203

(Right) until the level is 5 mV.

•Then switch the amplifier ON (LED is green).

•Switch the oscillator on and set it to 1 kHz and a

level of 0 dBu.

•Check the distortion with a THD analyser: it

should be at the specified value (0.01% IHF-A

@ 1 kHz).

•If this is correct the procedure is finished.

•You may now switch off the amplifier or

continue with another adjustment procedure.

Offset

The Offset adjustment procedure minimises the DC

offset value of the amplifier output. This DC offset is

important when capacitive loads are used, such as

electrostatic loudspeakers. These loudspeakers

often use a very low-impedance step-up

transformer. The amplifier ‘sees’ this load as a

short to the DC voltage.

Connect the amplifier according to the drawing

“Connecting diagram for testing the project 18”

(page 13).

The input of the amplifier must be shorted (by way

of the MUTE function of the oscillator).

•Switch the amplifier ON not in Standby Mode!)

and wait until it has reached the proper

operating temperature (this takes an hour).

•Set the millivolt-meter to the DC-range.

•Place the measurement clips of the meter over

the output terminal.

•The level should not exceed +5 or -5 mV DC.

If not: adjust potmeter P404 (Left) or P204

(Right) until the level is within this range.

•Switch the oscillator on and set it to 1 kHz and a

level of 0 dBu.

•Check the distortion with a THD analyser: it

should be at the specified value (0.01% IHF-A

@ 1 kHz).

•If this is correct the procedure is finished.

•You may now switch off the amplifier or

continue with another adjustment procedure.

Attention:

Be careful not to trip the offset protection mode. It

will activate when the output DC offset exceeds

+/-500 mV.

This is indicated by Internal LED LD 102.

This mode will be reset if the DC offset is adjusted to

within the proper limits.

Please be careful during the adjustments!

SPHINX Project Eighteen Service Manual

Common Mode

The Common Mode adjustment procedure

minimises the amplification error of the (internal)

differential amplifier.

If the balanced input amplifier receives an identical

signal at the normal (+) and inverted (-) inputs the

output signal will be zero. This helps to reduce the

effect of external noise signals while these will be

induced at the same level in both signal

conductors.

The Common Mode adjustment is optimally set

during manufacturing (the error is as low as

possible).

Connect the amplifier according to the drawing

“Connection diagram for common mode

adjustment” (page 14) and use the special input

connector. This connector supplies both the plus

(+) and minus (-) input pins of the XLR with the

same signal.

If there is no signal analyser available you may use

an oscilloscope at the output to view the waveform.

•Switch the amplifier ON (not in Standby

Mode!) and wait until it has reached the proper

operating temperature (this takes an hour).

•Switch the oscillator on and set it to 1 kHz and a

level of 0 dBu.

•Adjust potmeter P401 (Left) or P201 (Right)

until the minimum level is set.

When using a phase meter the minimum point

is reached when the output phase is at 180° re.

the input.

•Also check the setting at 10 Hz, 100 Hz and

10 kHz. Readjust when necessary.

•If the common mode is at minimum level at all

frequencies the adjustment is completed.

•You may now switch off the amplifier or

continue with another adjustment procedure.

SPHINX Project Eighteen Service Manual

8. PROBLEMS AND SOLUTIONS

At the moment of writing the Project Eighteen has

one known specific problem.

If in the future you encounter any problem(s) you

may enter the info in this table. This table can then

be used for future reference.

Please also send (by fax or e-mail) the specific

information to the Sphinx International Service

Department (see page 3): this info can then be

added to the general database to aid others.

Problem Cause Solution Refer to

page/file

Level problems and/or offset

problems. CN222 (Right) or CN422 (Left)

not inserted correctly. Insert XLR-plugs correctly

into CN222 & CN422 Pj18Main.PDF

SPHINX Project Eighteen Service Manual

9. DIAGRAMS AND PARTS LISTS

The next pages contain a complete set of schematic drawings including the associated parts lists (if applicable).