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Introduction: 

 
Congratulations! You have just purchased a 
new, state of the art, Digital Power Amplifier 
which will provide you  with many years of 
reliable service. Stewart Audio’s commitment 
to innovation in design and quality 
workmanship has provided its customers with 
a unique combination of performance and 
reliability. This commitment to excellence has 
gained the respect of industry professionals 
around the world.  
 
The DA-70 Series Professional Series Power 
Amplifier utilizes a new high speed switching 
power supply and  Damped Ternary Modulation 
Digital output topology. The amplifier will 
deliver over 70 Watts of power per channel 
and may be purchased in either a 2 or 4 
channel configuration. This remarkable 
performance comes in a very compact package 
weighing a mere 3.4 pounds and occupying 
just one-half standard rack space. The DA-70 
Series Amplifiers are convection cooled and 
require no noisy fans for cooling. 
 
We at Stewart Audio strive to bring you the  
finest in professional electronics, and we thank 
you for your choice, which we see as an 
appreciation for our efforts. 

 

 

 

The Stewart Audio Design Team 

 
 

Specifications 

 

 

17 

8 Ohm Stereo Power  35 Watts/Ch 

4 Ohm Stereo Power  70 Watts/Ch 

Frequency Response 

(+0, –0.5 dB, 1W)

  20 Hz—20 kHz 

Full Power Bandwidth 

(20-Hz-20 kHz)

  

± 

.7 dB 

Signal to Noise  >93 dB 

THD+N  < .25% 

Input Sensitivity  1V (0 dBV) 

Standard Voltage Gain  17X (25 dB) 

Input impedance 

(Balanced / Unbalanced) 

20k Ohms / 5k Ohms 

Class  Damped Ternary Modulation 

Input Connectors  Phoenix Type 

Output Connectors  Phoenix Type 

Power Supply  High Speed Switching 

Cooling  Convection (No Fans)               

Controls  Power on/off, Channel Gain  

LED Indicators  Power & Clip 

Construction  Steel & Aluminum Chassis 

Dimensions (height, width, depth)  1.75”H x 8.26”W x 10.6”D  

Max Weight  3.4 lbs (1.54 kg)  

Warranty  3 years Parts & Labor 

Summary of Contents for DA-70 Series

Page 1: ...Stewart Audio 14407 Cuesta Court Sonora Ca 95370 Tel 209 588 8111 Fax 209 588 8113 www Stewartaudio com DA 70 Series Professional Power Amplifiers Owners Manual WHEN THE PERFORMANCE DEPENDS ON IT ...

Page 2: ...MOVE COVER OR BACK NO USER SERVICABLE PARTS INSIDE REFER SERVICING TO QUALIFIED SERVICE PERSONENEL CAUTION RISK OF ELECTRICAL SHOCK DO NOT OPEN The lightning flash with arrowhead symbol within an equilateral triangle is intended to alert the user to the presence of uninsulated dangerous voltage within the product s enclosure that may be of sufficient magnitude to constitute a risk of electrical sh...

Page 3: ...laced on a rug sofa or similar surface which impedes the airflow across the chassis Airflow through the ventilation openings should be unobstructed The amplifier should only be connected to a properly grounded AC outlet as indicated under AC Power Con nections in this manual Do not defeat the ground or polarization of the power plug Route all power cords and other cables so that they are not likel...

Page 4: ...cupying just one half standard rack space The DA 70 Series Amplifiers are convection cooled and require no noisy fans for cooling We at Stewart Audio strive to bring you the finest in professional electronics and we thank you for your choice which we see as an appreciation for our efforts The Stewart Audio Design Team 4 Specifications 17 8 Ohm Stereo Power 35 Watts Ch 4 Ohm Stereo Power 70 Watts C...

Page 5: ...view section on Thermal Considerations Check clip lights for indication of overdriving NOTE overdriving for a long period of time can cause thermal shutdown Distorted output Check input signal level and signal source Set gain by turning amplifier volume all the way down set preamp level to normal turn up amplifier volume to desired level Noise on output Check signal source for noise Long unbalance...

Page 6: ...interface and control Stewart s ap proach was to develop a new Class D amplifier that utilized digital control This approach enables lower cost through digital integration as well as eliminating performance degradation due to analog component variations 6 Trouble shooting If you experience difficulty in operating your new DA 70 Series amplifier Chances are good that you will be able to remedy the ...

Page 7: ... D amplifiers utilize binary or BI state op eration Binary consists of only two switching states positive power and negative power Ternary or tri state operation consists of three switching states positive negative and a zero power state The third state is unique to this design During the time when neither supply connection is required both speaker terminals are connected to each other providing d...

Page 8: ...tom and exhausted out the top The amount of airflow necessary will be deter mined by a number of factors including ambient tempera ture the amount of heat generated by other equipment in the rack the properties of the enclosure being used and how hard the amplifier is working In extreme cases it might be necessary to install a cooling fan in the rack for additional cooling In free standing install...

Page 9: ...fore while a DA 70 2 runs very cool the DA 70 4 PFC will require a little more attention to cooling Multiple amplifiers can be racked on top of one another without leaving a full rack space between them as long as sufficient airflow is maintained to allow heat to escape out the when power is not available from the wall The power supply must act as a local reservoir of power from which the ampli fi...

Page 10: ...turned on Additional LEDs one for each channel will illumi nate when the amplifier is being pushed into clipping Level Controls The DA 70 Series has been equipped with a level control for each channel conveniently located on the front panel With typical program level present adjust each channel to provide 10 the desired output level If undesirable distortion is pre sent check preceding components ...

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