Stewart Audio DA-70-2 Manuale utente

DA-70 Series

Professional Power

Amplifiers

Owners Manual

Safety

Before using your Stewart Audio Power Amplifier,

please read this owner’s manual carefully to

ensure optimum trouble-free performance.

Warning: To REDUCE THE RISK OF ELECTRICAL SHOCK,

DO NOT EXPOSE THIS AMPLIFIER TO RAIN OR MOISTURE.

DANGEROUS HIGH VOLTAGES ARE PRESENT INSIDE THE

CHASSIS. DO NOT OPEN THE COVER. REFER SERVICING

TO QUALIFIED PERSONNEL ONLY.

CAUTION: TO REDUCE THE RISK OF ELECTRICAL SHOCK, DO NOT

REMOVE 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 shock to persons.

The exclamation point, within an equilateral triangle, is intended to

alert the user to the presence of important maintenance (servicing)

instructions in the literature accompanying the appliance.

-Important Safety Instructions -

Please Read Prior to Product Installation.

All of the safety and operating instructions should be read be-

fore the amplifier is operated. Retain these instructions for fu-

ture reference. All instructions should be followed; all warnings

on the amplifier and in the operating instructions should be ad-

hered to.

This amplifier should not be used near water, for example,

near a bath tub, washbowl, kitchen sink, laundry tub, in a wet

basement, near a swimming pool, etc

The amplifier should be situated so that its location and posi-

tion do not interfere with its proper ventilation. For example,

the amplifier should not be placed 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 Connections 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

likely to be walked on, tripped over, or stressed. Pay particular

attention to condition of cords and cables at plugs, and the

point where they exit from the amplifier. To prevent risk of fire

or injury, damaged cords and cables should be replaced imme-

diately.

Clean the amplifier with a damp cloth. Do not use solvents or

abrasive cleaners. Never pour any liquid on or in the amplifier.

The amplifier should only be serviced by qualified service per-

sonnel.

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

Contents

Special Features……………………………………………….……...…6

Front Panel Features……………………………..…………….…...10

Rear panel Features …………………………………………….…… 11

Installation……………………………………………………………...….12

Troubleshooting………………………………………………………....15

Technical Information………………………………………………...17

For The Record

In the spaces below, record the Model, Serial number

and Purchase information of your Power Amplifier.

Model Number: ____________

Serial Number: ____________

Purchase Date: ____________

Purchased From:___________

Retain this information for future reference.

Special Features

Stewart Audio’s new “Compact Series” Power Amplifiers utilizes the latest in Digital Au-

dio Technology. The new, all Digital DA Series Power Amplifiers were developed by Stew-

art Audio’s Digital Audio Team and represent the pinnacle of Stewart Audio technology

anddesign.

Please take a few moments to read through this section of the manual, which provides

anoverviewofthefeaturesthatmakesthisamplifierunique.

How is the DA-70 Amplifier different from other Amplifiers?

The primary difference between the DA-70 Series and other

amplifiers is that it is all digital and it has much higher effi-

ciency. Current digital audio systems use Class A/B amplifiers

to amplify analog signals produced by a DAC. Analog designs

have low efficiencies because of the power consumed in the

active components as a result of the voltage difference be-

tween the amplifier's output and it's power supply. This con-

tinuous control of the supply voltage results in peak efficien-

cies of about 50%. As a result a large power supply and heat

sink are required.

Class D switching amplifiers were developed to overcome this

problem by discretely connecting the load to the power supply.

Higher efficiency is achieved, but Class D is still essentially an

analog solution because it utilizes an analog interface and con-

trol. Stewart’s approach was to develop a new Class D ampli-

fier that utilized digital control. This approach enables lower

cost through digital integration, as well as, eliminating per-

formance degradation due to analog component variations.

What is Damped Ternary Modulation?

Conventional Class D amplifiers utilize binary, or BI-state operation. Bi-

nary 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 damping to the

loudspeaker, hence the name damped ternary. The figure below shows the

advantage of the damped ternary compared to binary modulation for a

sine wave. In binary the cancellation of two full level signals is required for

small outputs. Thus, the amplifier is continuously providing full output!

This represents wasted power. It also produces unwanted RF energy that

must be kept from radiating. In contrast, the damped ternary design only

supplies power to produce a signal.

Damped Ternary Advantage over Binary

In tests using the same hardware configured for ternary and then for bi-

nary, ternary's high frequency energy at zero output is attenuated over 20

dB below binary operating into the same filter! This means higher effi-

ciency and smaller filter components.

What is the efficiency advantage of the DA-70 Series over other

amplifierdesigns?

As shown in the figure below, the ternary design has a 20% advantage

over binary Class D at music levels (typically 15% of full scale) and about

3 times the efficiency of analog

amplifiers!

The Power Supply

The foundation of all amplifier design is the power supply. For years

Stewart Audio has pioneered leading edge, power supply technology. All

Stewart Audio amplifiers feature a High-Frequency Switch Mode Power

Supply. Because of this use of advanced technology some explanation is

in order.

Conventional Power Supplies operating at 60Hz (standard line frequency)

recharge only 120 times per second, requiring their storage capacitors

and transformers to be quite large to supply the energy needed during

the intervals between cycles

when power is not available from the wall. The power supply must act as

a local reservoir of power from which the amplifier circuits draw. This

storage function is responsible for much of the bulk, weight and cost of

traditional power

amplifiers.

High Frequency Switch Mode Power Supplies

Stewart’s famous, High Frequency Switch Mode Power Supplies fully re-

charges 1000 times faster than conventional supplies, requiring far less

capacitance for filtering and storage. This high-speed recharging reduces

power supply “sagging” common with other designs.

The New DA-70 Series Digital Amplifiers utilizes a new, regulated,

forward converter design Switch Mode Power Supply operating at a fre-

quency 2/3 faster than our old standard supply.

Power Factor Correction

Models with a PFC designation utilizes Power Factor Correction circuitry in

their power supply. This circuitry automatically adjusts the power supply

to provide stable, full output over a wide range of mains voltages, typi-

cally from 90VAC to 240VAC. This feature makes the DA-70 Series oper-

able anywhere in the world, and is a very useful feature when

operating from unstable or questionable AC mains.

This power supply’s remarkable conversion efficiency combined with

Damped Ternary Modulation translates into major savings of energy

drawn from the AC line. The benefits are reduced heat dissipation, and

downsizing of most major components. This saves space and weight

without sacrificing the Sonic excellence Stewart Audio is famous for.

Bridging

Bridging of the DA-70 Series is not possible due to the high

efficiency design of the Damped Ternary Modulation.

Balanced / Unbalanced Inputs

All DA–70 Series amplifiers feature Phoenix Type input Connectors, which

will accept either balanced or unbalanced signals.

See Input Wiring in the section on Installation (Page 13) for more details.

Output Connections

All DA–70 Series amplifiers feature Phoenix Type output Connectors, one

for each channel. NOTE: Do not attempt to Bridge this amplifier or tie the

commons together. Serious damage to your amplifier may occur if this is

attempted.

Total Protection

The DA-70 Series amplifiers employ circuitry which fully protect the ampli-

fier while avoiding sonic compromise.

Front Panel

Simplicity is a design objective in the development of all Stewart Audio

power amplifiers. These amplifiers remain simple and intuitive to operate

even while incorporating some of the most advanced technology available

today.

Power On/Off and LED Clip Indicators

The front panel provides visual feedback of the amplifiers status. The front

panel power switch is accompanied by an LED which will illuminate upon

power-up. (Note there is an initial delay of up to 30 seconds when the am-

plifier is first 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 the desired output level. If undesirable dis-

tortion is present, check preceding components and make necessary ad-

justments.

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