Mueta® FAQ
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Why is MUETA® better than other Class D amplifiers?
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MUETA® uses both voltage and current measurements of the output capacitor. Combined with the special modulator, this eliminates any output deviations. Good quality ‘non-MUETA®’ class D amplifiers do not use capacitor current feedback hence errors on their output, originating in the output filter, cannot be fully compensated thus causing distortion.
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Why is MUETA® so insensitive to output load?
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Unlike non-MUETA® class D amplifiers, MUETA® measures both voltage and current through the output capacitor. By controlling the capacitor current, MUETA® controls the slope of the output rather than the output voltage. This is a form of predictive control. MUETA® amplifiers are therefore very fast in detecting and eliminating output disturbances.
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Will an output short-circuit damage a MUETA® amplifier?
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No, a MUETA® amplifier will pass the ‘screwdriver test’. If full continuous over-current protection is required, a very simple addition to the power supply is recommended.
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Can MUETA® amplifiers drive electrostatic speakers?
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Yes, the MUETA® amplifier can drive any load, no matter how inductive or capacitive. Electrostatic speakers are therefore no problem at all for MUETA® amplifiers.
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MUETA® amplifiers use output/global feedback. Is that bad?
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The global feedback loop is not an error-correction loop as such, but is an integral part of the PWM modulator. All switching amplifiers apply feedback loops of some sort somewhere, even the ones that say they don’t! In a MUETA® amplifier, the output filter is an integral part of the PWM modulator. Our global feedback loop thus includes the output filter but is only as short as other amplifiers’ local (noise shaping) feedback loops. Our complete amplifier compares to others’ local feedback, thus there is no problem.
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What is so special about MUETA®’s modulator?
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The hysteresis modulator in the MUETA® amplifiers works on zero-input. Together with the controller, which regulates the error to zero, this is an ideal combination because in case of a non-zero error on its input, the modulator reacts immediately to correct this.
On the other hand, because conventional modulators make a direct translation from signal to duty-cycle, they require a non-zero input. To generate a correct filter output, an additional non-zero correction signal is required at the modulator input. This is fundamentally imperfect since the generation of this correction signal requires the error to be non-zero! To make things worse, the amount of correction required increases for higher frequencies when there is less time to generate it. This is why filter output feedback will not work on switching amplifiers with a conventional modulator.
MUETA® controls the slope of the output rather than the output voltage. This is a form of predictive control. MUETA® amplifiers are therefore very fast. Under this condition, application of feedback is no problem, and in fact enables the correction of all filter effects and bridge switching errors within the audio frequency band.
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What is a hysteresis modulator anyway?
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A hysteresis modulator is an analog relative of SD modulation. Digital SD modulation is used in 1-bit DA converters and SACD audio. The analog equivalent has no clock and therefore doesn’t quantize the signal; the modulator switches whenever necessary, without having to wait for the next clock pulse. MUETA® therefore gives high performance while switching at a rather low frequency, without the need for noise shaping.
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Why is the DC voltage supply so cost-effective?
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The MUETA® amplifier shows superb supply rejection, hence DC supply quality is much less important. Consequently, less critical (cheaper) components and simpler power supply design can be used.
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Why is the power stage so cost-effective?
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Thanks to the excellent control characteristics of MUETA®, it is no big problem to make small timing errors in the power stage. Thus slower switching is preferred for the benefit of reduced electromagnetic radiation. This alleviates shielding requirements and thus lowers end product cost.
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What are the potential financial advantages for MUETA® amplifiers?
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The excellent specifications of a MUETA® amplifier put it in the high-end of audio technology in terms of performance but not in terms of bill of materials cost. Without the need for a heavy (and expensive) heat sink, and the use of a much more economic power supply (using less critical components), it is considerably more cost effective to build than an equivalent specification conventional amplifier. In addition, as all the critical components are included in the MUETA® IC, the solution requires no adjustment or setting up which leads to a faster assembly time.
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What does a MUETA® amplifier IC or evaluation board cost?
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IC prices can only be discussed on an individual basis, and depend on the order quantities, etc. E-mail: info@mueta.com or fax (+31(0)416 699004) for more information. Evaluation boards are available on special request.
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What about the Power Supply design?
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Traditionally, all ‘digital’ amplifiers have tended to have very poor power supply rejection making power supply design very critical. In contrast, our MUETA® solution has an excellent PSRR , leading to simpler (less costly and critical power supply design. Our solution will maintain it’s excellent performance using a switched mode / PWM or a standard transformer supply. With our amplifier, it doesn't even matter if you have a few hundred millivolts of ripple because of the almost infinite supply rejection.
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Do these MUETA® amplifiers take a digital input?
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Our amplifiers are fully analog, which is one of the reasons why we are able to deliver such high specifications. If you require a digital input, you simply insert a Digital-to-Analog Converter in front of our analog input.
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Why not develop MUETA® for a digital input?
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Some people believe that keeping the signal digital all the way from the source (a CD for example) to the amplifier is the way to go. But we have experimentally demonstrated that we can get much better performance by placing the Digital-to-Analog converter in front of our amplifier stage rather than actually in the amplifier stage itself. In the analog domain, you can work much faster then in the digital domain therefore producing more realistic sound quality. It really does not matter where you place the Digital-to-Analog converter. If you have to place it somewhere, we recommend that the best place is in front of the amplifier stage. This way, all feedback loops can be analog and hence real time.
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