STAX SRA-14S Integrated Amplifier for Electrostatic Earspeakers Instruction Manual

STAX SRA-14S Integrated Amplifier for Electrostatic Earspeakers

Congratulations for selecting the Stax SRA-14$. a superb example of today’s high-end audio engineer­ing. To ensure optimum performance and many years of trouble-free service, please study this manual carefully and keep it handy for future reference.

Features

•  The SRA-14$ is an integrated amplifier which can directly drive any Stax electrostatic earspeakers (headphones) of the SR series. It also serves as a top quality preamplifier. (It cannot directly drive dynamic headphones or loudspeakers, however.)
• Two earspeaker outlets (NORMAL. PRO ONLY) are provided, which supply different bias voltages. With the help of an extension cord (SRE•l5, optional) and a connector box (SRE·B3, optional). up to 4 ea-r• speakers can be connected.
• The SRA-14S accepts three optional phono equal• izer circuit modules (EMM·l, EMC·!. ECC·l) and an additional line level input module (JB.J, optional), permitting direct connection of a variety of MC. MM and $tax electrostatic phono cartridges as well as analog and digital line level sources. Two modules can be installed at the same time for greater system flexibility.
• The power supply is housed in a separate unit to preclude any interference between power supply and signal path circuits.
• All circuit components have been selected with extreme care. Large
• crystal, oxygen.free copper is used in the wiring. The seamless core power supp”I)’ transformer has been designed with generous capacity and minimized flux leakage. Distortion is minimized by the use of purely ohmic resistors, while the chassis is made of non•magnetic aluminum. Sonic purity has been the absolute priority in every design aspect, down to the tiniest detail.

Front Panel Facilities

Rear Panel Connection

Precautions during Operation

Connections
Be sure to always tum the power of the SRA-14S and the units connected to it OFF when making or chang­ing connection. Also tum the power off when instal­ling or removing input modules.

Earspeakers
Stax Professional type earspeakers can be connected to the NORMAL outlet, but will not achieve their optimum performance.
Conversely, conventional Stax electrostatic earspea­kers must not be connected to the PRO ONLY outlet. Listening through speakers at excessively high volume levels for extended periods of time is detrimental to your hearing.

Installing and Exchanging Optional Input Modules
Wilen installing an optional input module, make sure that secure electrical contact is established and that the two fastening screws are properly tightened. Loose contact can cause noise and hum due to im­proper grounding of the module and will otherwise affect its performance. For proper installation, see p. 4.

Connection Cables
All connections in a hi,fi system must be made with shielded connection cables, preferably those with low capacitance and low hot-side (inner core) resistance. Keep cable runs as short as possible. High cable capacitance can negatively affect high-frequency response and cause noise problems. Amplifier operat­ing stability may also be affected by improper cables.

Shock & Switching Noise
Momentary surge currents (“shock & switching noise”) are caused when a phono cartridge is lowered on a record and when other system components are turned on and off, which could conceivably damage your speakers. Always turn the volume down before performing such operations. Turn the components on in the following order : (I) timetable(2) tuner and/or tape deck (3) SRA-14S (4) power amp. To tum them off. follow the reverse order.

Placement of The External Power Supply:
Under certain circumstances, the location of the external power supply may slightly affect the signal­to-noise ratio. Find the position that results in the lowest noise.

Auxiliary AC Outlets
Only units of low power consumption (tuner, turnta­ble, CD player, cassette deck) may be connected to the auxiliary AC outlets on the rear of the external power supply. Always connect your power ampli­fier (s) directly to an AC wall outlet. Power amp­lifiers. drawing considerable current. can cause line voltage drops which can negatively affect the performance of the SRA-14S.

Ventilation
The SRA-14S. containing a class A power stage for driving electrostatic earspeakers develops some heat. Proper air circulation must be assured and the ventilation holes must not be obstructed. Never expose t.he unit to moisture -internal high voltages may pose a shock hazard. Never remove the cover or insert screwdrivers, paper clips or other objec1s through the ventilation holes.

Notice Concerning the SRA·l4S Feet
To provide the best sound quality possible, the feet of the SRA-14S utilize the ”tiptoe” concept to reduce the contact area between the unit’s aluminum feet and the surface on which the unit is placed to the absolute minimum. This design is based on the belief that protecting an amplifier from vibrations results in better sonic performance. If, however, you prefe·r softer feet, these “tiptoe” feet can be replaced with the plastic feet which are also supplied with this unit.

Troubleshooting Guide

outlet and power unit to amp connection. If this doesn’t help, turn power off and contact authorized Stax dealer or service station.
•  Pilot lamp lights, but no sound from earspeakers.| (!)Volume control turned down. (2)lnput selector in wrong position. (3)Earspeaker switch off.| (!)Turn volume higher.

(2)Set input selector correctly. (3)T u rn earspeaker switch on.

•   Hum ()ow-pitched noise)| (!)Poor ground connection.

(2)Electrical interference from a transformer. etc. (3)()ptional input module not properly installed.

| (!)Check   turntable   to  GND terminal  connection.           Check optional input module for proper installation and securely tightened fastening screws. Also check  all  interconnects for proper contact and fit.

(2)Change relative positions of turntable or ta pe deck and SRA-14S. Try different position of external power unit. (3)T ighten fastening screws of optional input module secur •

ely.

•   Buzz (high- pitched noise)| Electrical interference from a fluorescent lamp or other electrical appliance. Also check under “hum,” above.| Check under “hum,” above. Turn off fluorescent lamp or other electrical appliances nearby.
•    Distorted sound| (l)Poor program source.

(2) Cart ridge problem (worn or dirty stylus. etc) .

(3)  Worn or dirty tape head.

(4) Excessively high power driving earspeakers into distortion.

| (l)Use better program material.

(2)  Clean st ylus tip. Check arm and cartridge for proper geometry. Replace stylus if worn.

(3) Clean tape head.

(4)T um volume down  to  normal  listening  level.  If  none of this helps, the unit or earspeakers may be damaged.

•      Poor left / right channel balance

(I )Balance shifts as volume is turned down.

(2)Poor balance regardless of volume setting.

| ****

(!)Caused by different “tracking” of variable resistors (inevitable to a certain extent).

(2)Poor stereo balance in program source. Other possible causes are faults in associated equip• ment, in SRA-14S or in earspeakers.

| ****

(!)Adjust channel balance with volume controls. Alternately, turn Interstage (IS) amp switch off and listen with volume controls turned up fairly high.

(2)Switch to L+ R mode. If sound appears centered, problem is located upstream of MODE selector, probably in cartrid• ge, turntable. tape deck or other source equipment. Check again with different program source.

If balance is shifted even in L+ R mode, problem lies in SR-A 14S or earspeakers. Contact Stax dealer or service center.

•     No signal from REC OUT 1, 2

outputs.

| REC OUT Selector in OFF position.| Set  REC OUT Selector in position SOURCE ( o r DUBBING

1> 2 or 2> 1).

.• No signal from PRE OUT l outputs.| EARSPEAKER Switch in ON position.| Turn EAR SPEAKER Switch OFF.
•   Unit gets hot.| Class• A power amp stage ( for driving earspea, kers) develops heat.| Ensure good ventilation around the unit. Avoid direct sun• light and the vicinity of heat sources.

Circuit Features 

• Pho no Equalizer Modules for MC and MM Cartrid• aes. Models EMC-1, EMM-1
  Model EMC-I is a phono equalizer amp for MC cartridges. It uses parallel high- gain. low-noise FET’s in a three-stage design. Dip switches on the EMC-1 module offer a choice of 55 or 64dB gain to accommo• date MC cartridges of different output voltages.
  “Ground reference amplification'” (U.S.PAT. JAPAN. PAT.PENO.) is used in all stages of the EMC-land EMM-1 modules to prevent noise induced by the power supply and thereby improve the overall S/N ratio.

• Pho no Equalizer Module for Electrostatic Cartrid­aes, Model ECC-1
  This phono equalizer module, specially designed for the Stax electrostatic (electret condenser) cartridge model CPY, is equipped with a super shunt power supply which considerably improves resolution of sonic detail.

• Interstage (IS) Amplifier
  A single•Stage, “Ground reference” amplifier with mul­tiple negative feedback loops but minimum negative feedback amount. Designed to avoid amp colora• tions.

• Power Amplifier for Ear$peakers
  A 2-stage, de coupled design operating in pure class A
  and specially designed to fully display the excellent transient response of electrostatic earspeakers. Includes high voltage bias circuit for directly driving Stax Lambda Professional type earspeakers.

• Ground Reference Ampllflcatlon In All Stages
  As shown in the circuit diagram, the cold side of the second amplifier stage is kept at ground potential, which helps prevent noise induced by the power supply -one of the most common problems afflicting sonic quality. Other benefits of this circuit design are stable operation in the high-frequency range and the possibility to reduce NFB to an absolute minimum.

• Super Shu1nt Power Supply
  In the power supply circuitry of the ECC-1 module, Stax has incorporated a new development. the “Super Shunt” design. It prevents current fluctua­tions i.n the power supply and the ground lines under conditions of fluctuating load currents. As a result, the resolution of fine sonic detail and inner musical structures is vastly improved.
  AII-Slage “Ground reference” Amplifier Circuit

Block Diagram

Specifications

Model: Integrated amplifier for Stax earspeakers (all models)
Circuit Systems:

• The pre-amp section can be used independently as a standard pre-amp
  Phono equalizer modules – EMM-1 for MM cartridges
  EMC-I for MC cartridges
  ECC-1 for Stax CP-Y and CP-Y /TYPE 2 cartridges Interstage amp

• Power amp section-For use only with Stax Earspeakers
  Power Supply :

  • 117V, 220V, 240V /50-’60Hz + -10%

• Power Consumption :

  • 75\V (Max.)

• Dimensions (WxHxO):

  • main unit 225xl47x412 mm Power supply unit 147x96X213 mm

• Weight:

  • Main unit 3.8 kg
    Power supply unit 2.5 kg (with cord)

• Amplifier Spec I PRE-AMP

  • Frequency Response :
    EMM-1/EMC-l/ECC-l · 20Hz-20kHz ±0.2dB
    TUNER/AUXl.2/DECKl.2/JB-l · 0.5Hz-500kHz +0, -3d8

  • Total Harmonic Distortion :
    EMM-1/EMC-l · 0.003% (3V output, !kHz)
    ECC-1 · 0.005% (3V output, !kHz)
    TUNER/AUXl.2/DECKl.2/JB-l · 0.003% (3V output, lkHz)

  • Input Sensitivity and Impedance : EMM-1 · 2.5mV /47k0
    EMC-1 · Lo 0.lmV. · Hi 0.25mV /10 O 30 o, l
    JOO n switchable
    ECC-1 · J8mV/10kO
    TUNER/ AUXJ.2/DECKl.2/JB-l · lS0mV /50kO

  • Maximum Input Voltage:
    EMM-1 200mV
    EMC-I · Lo 8mV Hi 20mV at
    TUNER/AUXJ.2/DECKJ.2/JB-l: 1.2V

  • Rated Output Level and Impedance :
    EMM-1 · 150mV /220 0
    EMC-I· lS0mV/200 O
    ECC-1 · JS0mV /200 0
    PRE-OUTl.2 (when IS amp is on) · 1 V rms/220 0

  • SN Ratio (!HF-A network, shorted input)
    EMM-1 · 80d8 (at 2.5mV rated input)
    EMC-1 · 78dB (at 0.25m V rated input)
    ECC-J · 90dB (at 18m V rated input)
    TUNER/AUXl.2/DECKl.2/JB-l · l00dB (for 150mVinput)

  • Gain:
    EMM-1· 35dB
    EMC-I• 64dB/55dB switchable
    ECC-1 • 18.6dB (with ±4dB balance control)
    Interstage amp • 16.SdB

  • REC OUT Rated Output Level : 150mV

  • PRE OUT Rated Output Level : 1.0V rms
    11 POWER AMP

  • Frequency Response: DC-30kHz, +0, -3dB (at l00Voutput into
    a load presented b)’ one SR-Lambda Pro)

  • Total Harmonic Distortion : 0.01% (I00Hz-l0kHz,l00V output
    into a load presented by one SR-Lambda Pro)

  • Input Sensitivit)’ : 150m V ( for 150V output )

  •   Maximum Output : 400V rms

  • Bias Voltage : Normal-230V DC. PRO•580V DC

  • Specifications are subject to change without notice.

Performance Graphs

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