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FAQ
 
1. ABOUT POWER MEASUREMENTS OF DIGITAL AUDIO AMPLIFIERS
One of the main advantages of Digital Audio Amplifiers D-Amp is the possibility to handle in a considerately more efficient way the musical power with respect to conventional linear amplifiers, taking in to account
that music average power energy is considerably lower with respect to continuous sine wave signals of the same peak level.
In few words the main advantage of Digital Audio Amplifiers is to underperform the continuous signal power output (unusefull from
the musical point of view) in order to strongly protect the loudspeakers loads and greatly enhance power output of the useful
musical signals.
To this regard, in order to have more clear picture about the scientific approach, please make also reference to the enclosed
document "Design Criteria for an innovative professional high power audio amplifier".
Therefore the Audio Power outputs stated in D-Amp Specifications sheet must be measured in the following conditions:
1. Power RMS x Channel (1kHz, 0.5%THD):
• Maximum continuous output power delivered to the load for at least 5 minutes, then internal limiting processor reduces output
voltage swing to maximum output.
2. Power RMS x Channel in stereo working:
• Maximum EIAJ standard test output power: average of RMS output voltage squared divided by load impedance.
• Test signal 1kHz tone burst 8 cycles 0dB, 24 cycles no signal, THD 1%.

If the power measurements will follow the above conditions there will be founded the power figures very close to those stated in the
data sheets.
In the case that measurement are done with the non significant method of continuous sine wave input signals (applied for more than
30 seconds), the system is self-protected from that unusefull signals, and lower output values will be found.

It is well known that the qualitative analysis of audio spectrum characteristics for different typologies of music is showing the
presence of sequence of short burst with different peak power values and duration.
Taking in account these peculiar spectrum characteristics it is possible to introduce a new approach in designing Audio Amplifiers,
especially when a very high audio output power is required.
In effect in the normal operation the amplifier's useful output music usually is limited by its short term power capabilities and not by
the heating that results from high continuous power emission.
Based o the above consideration, our assumption was that it is possible to minimize the non realistic usual requirement for
continuous power rating, typical of conventional analogue amplifiers, and to design much more efficient Audio Amplifiers
increasing their burst power capability with respect to the continuous power rating.

For the correct design it is moreover necessary to define as valid for any typologies of music two basic parameters as: the ratio for
the peak output power to continuous power rating and the max. burst duration.
About the first parameter from specific research and analysis performed by DeMarinis (1) it results that in the worst case of rock
music compressed for FM broadcast the ratio of r.m.s to peak power is around 8 dB. This means that if an amplifiers volume
control is set to place the high peaks at the on set of clipping, the most severe continuous power demand is less than 15% (usually
under 10% ) of the amplifier's max. peak power.

About the second parameter - max. burst duration - other studies and tests as been performed (2),(3), in the past and specific
confirmations as been obtained in the D-Amp, confirming that for all the music types the burst peak power Is always reducing with the increasing of the duration of the bursts.
This general rule is represented by the following expression, and takes in to account all possible music worst cases:
10 log p/pc =-0.16 Log t
were 't' is the toneburst in milliseconds and ' pc' is the power level at 0 dB (the clipping point)
This means that the distribution of peak power bursts in function of duration can be represented in the following table:
• burst duration max r.m.s level
• 3 ms 0 dB clipping
• 30 ms -2 dB
• 300 ms -3 dB
• 3 sec. -5 dB
• 30 sec. -7dB

Based on the above results D-Amp has been in the position to define the basic requirements to design of an innovative very
efficient Audio Professional high power amplifier:
• To obtain extended duration of headroom, able to delivery burst of 1 sec. or longer at substantially higher level then normal linear
amplifiers 'continuous power rating.
• To obtain an optimized thermal design suitable to manage very high r.m.s output power within 3 dB with respect to the peak power.
This requirement will allows a margin with respect of to above mentioned experimental results.
• To obtain an automated gain control suitable to maintain for any input signal level the full dynamic capability. This requirement in
order to avoid clipping distortion and ensure the nominal r.m.s power.
The right solution to the above requirements was founded utilizing digital switching technologies (based on the principle of PWM
modulation ) with some circuitry topologies solutions.
In effect this PWM technology, through a very high frequency sampling of audio input signal (over 500 kHz) allows with the
necessary accuracy to process the signal in digital form and provides the highest power outputs with extreme efficiency (near to 97.5 %).
A well designed output filtering and processing solution provides output capabilities at the highest level of quality in terms of low
distortion, noise and bandwidth .
Based on the above, D-Amp has developed a new generation of digital audio amplifiers branded HVI Series.
D-Amp series of Professional Audio Amplifiers is a complete range of products from 4000 W to 8000 W on 4 ohms load in 1 unit 19"
rack size and 8.5 Kg weight.

The global audio result of such new generation of Audio Amplifiers is that with such innovative design criteria it was obtained a very
cost-effective product with the best adherence to the real music professional requirements.

References
• J.V. De Marinis: "How valid is the FTC Preconditioning Rule? " - Audio Sept 75.
• P.J. Mitchell: "A musically Appropriate Dynamic Headroom Test for Power Amplifiers. "A.E.S. Pre-print 2504, Oct. 87.
• A.E.S. Convention 7/10 Oct. 93 - Pre-print: "The Dynamics of Recorded Music". Presented by J.A. Mc. Manus, Chris Evans and
P. J. Mitchell.

2.Does your limiter indicator represent true output clipping ?
No, the LED is driven only when the amplifier output fails to track the input. This condition normally results only from limited clipping (2%), which occurs when the power amp reaches either its voltage or current limit. Limiter LED is red and when light on you are at limit of clipping. The amplifier have an internal compressor circuitry to prevent excessive clipping, when the amplifier clipping reaches the point that the compressor turn on the limiter (red) and alert the operator that the input signal is being compressed. 2 Level of limiter is used, 1 at -2Db before clipping to minimise stress to loudspeaker (when limiter LED ‘’flick’’ and enable blue LED stay on, and a distortion limiter when limiter goes on and enable goes off. Limiter limit to a maximum of 2% absolute amplifier distortion.

3.Is it possible to change the input sensitivity within your amplifiers ?
In theory, yes, but only by changing certain resistor values, which requires opening the covers and exposure to dangerous voltages. This should be done only by qualified service personnel, or under the guidance of D-Amp Technical Services. See our support web page for more details on how to perform this for D-Amp series amplifier.

4.Is possible to disable the limiting circuit in the D-Amp amplifiers ?
This is not possible due to the philosophy Design.

5.The clip LED’s on my amplifier flash upon power up before the muting cycle ends. Is this normal?
During the muting cycle, the "front end" of the amplifier is internally disconnected from the output transistors, ensuring that they are fully turned off in the event of overheating or during routine on/off muting. When disconnected from the feedback loop, the front end circuits may have enough stray signal to flash the Clip LED's. This is perfectly normal, and will stop as soon as the amp enters the normal "run" state.

6.Which is the warranty on my D-Amp amplifiers?
D-Amp provides a 3 year warranty from the date of purchase of our Distributor. The warranty does not cover failures due to damage and misuse of the equipment. The customer is responsible for freight charges to D-Amp will repair the product under warranty and return it to customer free of charge.

7.Why don't you use an air filter for your fans ?
Air filters quickly clog with dust, blocking air flow and causing overheating. The fan is running automatically by a sensor which put the fan on when temperature inside the amplifier reaches 50°C. The internal air flow pattern is designed to avoid dust build up in critical places. Occasional cleaning is recommended in very dusty environments.

8.When installing D-Amp amplifiers in a rack should I leave spaces between ?
The answer is no. The airflow technology that we use in our amplifiers is designed such that it is best to stack multiple amplifiers on top of each other, with no space between. The amplifiers draw air into the back of the amplifier and exhaust it out from the front panel.
If you choose to place the amplifiers with space between them, then use solid panels between them, not vented panels.

9.Which is the hot (non inverting) pin for D-Amp amplifiers ?
In put connections are: XLR type connectors
On the rear side:
Pin 1 is ground (shield)
Pin 2 is hot (non-inverting)
Pin 3 is low (inverting)

10.Which are loudspeaker protections on D-Amp amplifiers ?
D-Amp series is equipped with an evaluation / processing circuitry for output stage behaviour. All signals that are feed to the load (i.e. loudspeakers ), are subjected to a pre processing that allows the output stage of the amplifier to deliver always non distorted and “loudspeaker safe” signals. This specific feature lead to a dramatic improvement of reliability of the complete installed system, reducing loudspeaker failures even in case of incorrect design.

11.What is mains current requirement for D-Amp 8000HVI
Mains requirement is defined by the ratio between average power consumption and mains voltage. For a D-Amp 8000HVI, power consumption is 1200VA per channel on 1/8 Max power @ minimum load impedance standard duty program, and 1800VA on ¼ Max power @ minimum load impedance heavy duty program.

12.What makes speakers fails?
A speakers can fail due to excessive mechanical stress or excessive thermal stress.

13.The output voltage on my amplifier measures from 0Vdc to 0.3Vdc. Is this normal ?
Small amounts of "DC offset" do not indicate a problem, although normally it should be less than 0.05 volts (50mv). At 0.3Vdc, we are dissipating 0.011 watts (22 mw) in an 4 ohm load which is clearly negligible.

 
 
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