Stax da 80 pwr sm
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Page 1
(9 (2 5107 0201 0202 Q203 0204 110 010 Attenuafor (l - (- Differential - (3 , Amp 08102 Bias (4) Constant Current Circuit Input Jack 0 Short Circuit P t t Overheat Protector DC Pr rector (8) NFB Circuit Output Tarminal 0205 0206 0207 0208 0109 PNP Darlington Power Amp SUMMARY OF CIRCUITRY The input is fed, via an attenuator, to the gate of the first stage dual FET differential amplifier (3). The diode connected between the two gates is the protective circuit for input overloads (1). The NFB signal (8) is applied to the gate shown. The dual FET differential amplifier functions under ideal condi- tions due to the connection of the constant current supply (4) to the common source. The current is reversed in the current mirror circuit (2), driving Q110 in the cascade amplifier (5) and 0108, which DA-80 form the push-pull configuration, at constant current. A pair of transistors with common bases and symmetrical emitters are enclosed to the same can in the current mirror circuit. This en- sures that the current flowing in each transistor is the same, independent of the ambient temperature. Q110 and Q108 are cascade connected, consisting of transistors with extremely good high frequency characteristics and equiva- lent characteristics. The bias circuit (6) gives the optimum bias as set by VR102, passes through the short-circuit protector (7), then through Q107, 0109, the drive-stage transistors for the Darlington power amplifier (9) (10), then to the power transistors Q201 - Q204, and Q205 0208, of the Darlington-connected power output stage. The configuration adopted for the Darlington power am- plifier has NPN (9) and PNP (10) tran- sistors in a fully complementary single- ended push-pull class A output stage. The circuitry has ample stability for class A DC amplifier operation, with all possible circuit elements that could cause degradation of sound quality eliminated. AID Current Mirror (2) Attenuator Overload Protector Input Jack - Differential Amp 0 NPN Darlington Power Amp (51 (9 0107 0110 0201 0202 .0 fibs V 0108 Short Circuit Ef Protector Output Tarminal (7) 0 VRI02 0) Bias 0203 0209 Cir 0109 0 0 PNP Darlington Pow r Amp v„_ Constant Current Circuit (8I Overheatt Protector Transformer DC Protector ,--0 0- G DC Power Supply +V n ,308) Vcf1( 30V) DC Power Supply C +V " +40V) ( Vr ( 40V) -L/R INDEPENDENT POWER SUPPLY INDICATION -SIGNAL CIRCUIT SINGLE CHANNEL DC Power Supply DC Power Supple +Vcc1(+30V) -..- n ( 30V) 4V,,f(*4001 V ( 40V) DA-80M Current Mirro Cascade Amp NPN Darlington Power Power Amp Voltage Selector Po e r Transfor me o- C ► +V (+37V) VI, 37V) +VGAL-37V) V«f( 37V) DC Power Supply --.. 0-ec DC Power Supply 2
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240Vr- r 117V IDLING INSTRUCTION (1) Location in use This amplifier features class-A opera- tion, and special care should be taken with respect to heat radiation. Avoid locations exposed to direct sunlight, and place the unit, as far as possible, where there is a good circulation of air. Leave a clearance of at least 5 cm (2") above the amplifier. Also you should avoid places where dust is liable to be attracted. (2) Protective circuits Four different kinds of protective cir- cuit are used to protect either the am- plifier or the speakers from damage or loss. 1. Overload (input) protection: The input needed for maximum output is 0.89 V. Should this reach 50 V, a 'clip' circuit operates to prevent the amp. from being driven to full output. 2. PC limiter: This circuit limits the current which flows through the output transistors to prevent them from being destroyed by the ex- tremely large current which would otherwise flow if the speaker terminals were short-circuited. 3. Temperature protection: This cir- cult was designed to cut off the electrical power supply to the amplifier as soon as exceptionally high temperatures are reached. It prevents the amp. from being damaged by rises in the ambient temperature. 4. Speaker protection: The speakers will be protected from direct current signals greater than ±5 V appearing at the amplifier output terminals in the face of direct current signals from the pream- plifier or from switching tran- sient noise. Protection is by cutting off the amp. electrical power sup- ply, and is effective even if the amp. itself is damaged. The above protective circuits built into the amplifier provide protec- tion against the most unlikely eventualities, but you should take care to use the amp. so that the protective circuits are not caused to operate. If, for the causes detailed in 3 and 4, the protective circuits cut off the electrical power supply, switch the amplifier off, determine the cause, and remove it before switch- ing the electrical power on again. If the protective circuit functions in the same way again, cutting off the power a second time, please read the TROUBLESHOOTING GUIDE on the 7 page. (3) When using condenser-type speak- ers Since condenser-type (or electrostatic) speakers only have a DC impedance of the order of one ohm, near-DC signals arising from eccentric or warped re- cords, or from external vibration, will cause the short-circuit protection to operate, which will be heard as a 'click- ing' or 'popping' noise. If this situation should arise, you should insert a one or two-ohm resistor (rated 30 Watts) between the speaker and the amplifier output terminal as shown, and set the AC/DC switch to AC. (4) When using the DA-80/80M as the mid- or high-frequency amplifier in a multi-amplifier configuration When the DA-80/80M is used for the mid/high frequency amplifier, the channel divider cuts out the low fre- quency component of the signal, so that there is no possibility of DC or other very low frequency signal of very high amplitude being applied to the speakers. The possibility does remain, however, of the speakers being dam- aged by the switching noise from the channel divider or by mistakenly pull- ing out an input jack plug. The AC/DC switch should therefore be set to AC, and a non-polar capacitor of 10µF in- serted in the case of driving a tweeter, and of 100 tF for a squawker. (5) Measurements This amplifier boasts extremely high quality circuitry, and if meaningful measurements are to be taken of its exceptionally good performance, only correspondingly high quality measur- ing instruments and sophisticated measuring techniques should be used. (6) Others DA-80 * The AC Outlets are not linked to the amplifier power switch. * There are two models of the DA-80, one intended for 100~117V operation and the other for 200~230 V opera- tion. In both models the switch for selection of the actual operating volt- age to be used is to be found on the underside of the amplifier. 100V-108V aria 109V-117V aria To comply with the voltage where this equipment is used, this plate has to be removed and re-set after switched to the required voltage. > A 2 i oV -2 0 V aria DA-80M A choice of mains supply voltages for the DA-80M is given by the voltage selector under the chassis. This offers a choice of 100V, 117V, 220V, and 240V. If you need to change the oper- ating voltage, first remove the protec- tive metal device, and then set the arrow so that it points to the voltage closest to that which you will use. O 200V-2 I uV aria 3