How To Get The Best Bargain Whenever Buying Power Amplifiers

By Mike Heller

Selecting a decent amplifier for your loudspeakers is not a trivial chore. You wish to make certain that your amplifier matches your speakers. I will clarify some important amplifier terms and give some recommendations to help you select the perfect amplifier.

Audio amplifiers appear in all different shapes and sizes. They use different technologies and have many technical specs. By following some simple rules, you will be able to pick the type that best fits your application and budget.

Amplifiers vary in their size and range from types that will take up a good part of your living room whilst some of the latest mini amplifier types are as small as a deck of cards. A large number of amps are the size of a typical rack. This enables your amp to be stacked on top of your other audio equipment. The huge majority of recent audio amplifiers are solid state amplifiers versus more conventional tube amplifiers. Tube amplifiers have been dominant a decade or so ago. Regrettably, tube amps have relatively large audio distortion which describes how much the audio signal is degraded by the amplifier.

Tube amps will have audio distortion of up to 10%. Solid state amplifiers will have less audio distortion depending on the amplifier technology that is utilized. Several of the most accepted technologies in the past have been "Class-A" and "Class-AB" technologies. These technologies use different arrangements to amplify the sound. Amps based on any of these technologies are also named "analog amplifiers". While amplifiers employing these technologies normally have low audio distortion, power efficiency is only 10% to 30%. This means that the majority of the electrical power provided to the amp is wasted as heat while a tiny fraction is used to amplify the audio signal.

In comparison, "Class-D" amps which are also known as "digital amplifiers" have a power efficiency of usually 80 to 90%. This allows the amp and power supply to be made a great deal smaller than analog amplifiers. The downside is that many digital amplifiers have larger audio distortion than analog amplifiers though several of the latest types make use of a feedback mechanism to minimize distortion to levels of 0.05% and less.

"Class-D" amplifiers, on the other hand, which are also named "digital amplifiers" have a power efficiency of no less than 80% and are smaller and have a smaller power supply than similar analog amplifiers. The disadvantage is that many digital amps have larger audio distortion than analog amplifiers although some of the latest types employ a feedback mechanism to reduce distortion to levels of 0.05% and less. The amp should be able to deliver adequate output power to sufficiently drive your speakers which will depend not only on how much power your loudspeakers can handle but also on the size of your listening environment. Speaker power handling is given as peak power which describes the maximum amount of power during short bursts while average power refers to how much power the loudspeakers can handle constantly.

If you have a fairly small listening area then 20 to 50 Watts of power should be sufficient despite the fact that your loudspeaker might be rated for 100 Watts or more. Low-impedance speakers generally offer high sensitivity and are easier to drive to high volume than high-impedance loudspeakers. Be sure that your amplifier can drive your speaker impedance. You can without problems find the rated speaker impedance range in your amplifiers user manual.

Last but not least, be certain that your amplifier introduces little noise and has a broad enough frequency response. High-quality amps will have a signal-to-noise ratio of no less than 100 dB and a frequency response of a minimum of 20 Hz to 20 kHz.

About the Author:

Check out helpful infos concerning mini amps at this webpage.

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Power of HTML CSS and jQuery collapsible CSS Table

It’s generally recommended you ensure the vast majority of your web page content is immediately visible when someone accesses it – but there are exceptions where you would want to display only the summarized view to not clutter up the page and expand to the details as and when required by clicking on a button or an icon. Here is a very simple tutorial on HTML, CSS, and jQuery that shows how to create a collapsible table. The following code snippet has embedded CSS with the style tag and jQuery with the script tag. The HTML defines the DOM (Document Object Model) structure. The CSS is used to hide and unhide the relevant rows. The jQuery is used to add and remove CSS styles.

Try using this example on Firefox with Firbug turned on or on Goggle chrome with the dEV tools turned on with the "F12" function key. This will enable you to inspect the HTML elements and the styles.

<!DOCTYPE html>
<html>
<head>
    <title></title>

    <script src="http://code.jquery.com/jquery-1.8.3.js"></script>

</head>
<body>

<h1>demo for hiding and unhiding table rows </h1>

<button id="myappSummaryCollapse">
    <span class="collapse">Collapse</span>
    <span class="expand">Expand</span>
</button>

<table class="collapsible">
    <tr class="collapsible"><td>collapsible row</td></tr>
    <tr><td>not collapsible row</td></tr>
</table>


<script>

    jQuery(#myappSummaryCollapse).click(function () {
        var button = jQuery(this);
        var tables = jQuery(table.collapsible);

        if (button.hasClass(collapsed)) {
            button.removeClass(collapsed);
            for (var i = 0; i < tables.length; i++) {
                jQuery(tables[i]).removeClass(collapsed);
            }
        } else {
            button.addClass(collapsed);
            for (var i = 0; i < tables.length; i++) {
                jQuery(tables[i]).addClass(collapsed);
            }
        }
    });

</script>



<style>

    #myappSummaryCollapse .expand,
    #myappSummaryCollapse.collapsed .collapse,
    table.collapsed tr.collapsible {
        display: none;
    }

    #myappSummaryCollapse.collapsed .expand {
        display: inline;
    }

</style>


</body>
</html>

Very often, simple examples like the one above can clarify things to go on and do more complex scenarios. In the CSS, #myappSummaryCollapse is the element id and ".expand" is the style class name. "display:none" is used to hide and "display:inline" is used to display. The jQuery is used to add and remove the CSS classes.


Similar results can be achieved using JavaScript directly as shown below.

document.getElementById("p2").style.color="blue";

or

<button onclick="document.getElementById(id1).style.color=red" type="button">
</button>

But, jQuery selectors are very powerful and let you achieve similar results with less code.

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The power of regular expression and testing tools like regexpal com

Regular expressions are also known as regex, and they are very powerful and used widely in JavaScript, Unix scripting,  development tools, monitoring tools like Tivoli, and programming languages. So, it really pays to have good knowledge of regexes. This post is about a handy tool named "regexpal.com" that helps you not only learn regex, but also to quickly verify your regexes while working on a project. If you google for "regex online validator" you will find other similar online validating tools.



Step 1: Open up a browser and type regexpal.com on the address bar. Yo will get the online validator.

Step 2: Type or copy/paste the regex at the top window and the text to apply the regex on the second window.

As indicated in the footer, use RegexBuddy for a more powerful regex testing. The regex keywords are highlighted in blue. Also the matched phrase is also highlighted. In blue for the exact match and in yellow for any other string match.

The above example matches any string followed by one of "Monitoring", "MYAPP", or "CASHFORECAST". The "|" in regex means "OR". What if you want to literally match "Monitoring|MYAPP|CASHFORECAST"? You can escape "|" with "" as shown below.

Now, the  "|" is not highlighted in blue as it is escaped.

Change the text as shown below. The "CASHFORECAST" is changed to "TRADEFORECAST" and match is no longer found as the text is not highlighted.

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