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Testing amplifiers
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Author:  ZBill [ 10 Jun 2018, 14:46 ]
Post subject:  Testing amplifiers

I'm asking for opinions.

What would the impact on using a dummy load across a speaker, so that I can test amplifiers at their load limits for extended periods of time, and determine if the amp can withstand this type of abuse, and avoiding the need to replace blown speakers.

Using a speaker to simulate a real world condition is one of the main criteria for this form of testing.So, just replacing speakers dummy loads is not an option.

Adding a dummy load across the speaker or some sort of series/parallel combination will have some effect on dampening,Q and bandwidth, but will it be enough to invalidate this type of testing?

So, is there a design for a Reactive/Resistive hybrid that will accurately simulate a real world condition and add more durability to the speaker.

The amps being tested are semiconductor class A/B or class D

Author:  gofar99 [ 11 Jun 2018, 15:38 ]
Post subject:  Re: Testing amplifiers

Hi, Since it seems what you are most concerned about is not how the amplifier responds, but whether or not it will operate at high power for extended periods of time. I would not concern myself about simulating a real speaker. A resistive load would IMO be a better choice for a number of reasons, first because it is not reactive and would not confuse the measurements. Second it will be consistent. Now to add to that I don't know of any audio application that requires an amp to operate at full power for any extended time. The power rating of an amp is a bit misleading in many cases. In theory at least it is the maximum output it can deliver for musical peaks, not usually average. You often see the words "continuous power etc" Yeah sure, you can possibly use it to light light bulbs, but it doesn't tell you much about how the audio performance is. Average audio is not usually over about 10% of the max . The reason is that you want to avoid clipping. This can be very harmful to tweeters and possibly even the amp. Solid state ones are the most prone to the problem. When over driven they tend to put out something that looks a lot like a square wave. Tube amps tend to compress the output and overload more gracefully. I would in you case just use non-inductive power resistors to make what tests you need, but would not run the amps at full output long, 1/3 to 1/2 power used to be the standard for testing solid state amplifiers as it is the level that caused the most thermal loading on the output devices. For class D amps this might not be the same though.

Good listening
Bruce

Author:  ZBill [ 11 Jun 2018, 16:10 ]
Post subject:  Re: Testing amplifiers

I appreciate your response, and I realize this is not a typical test. To clarify, I am testing for worst case scenarios. The amp/s, which are used in mobile systems will be used in some very adverse conditions, whereby the user will test the limits of the amp in contesting or just showing off, or just mishandling. This is not the intended use, and we don't guaranty that this type of abuse is serviceable,however knowing the limits will give us an idea of the amps life expectancy, and based on as close to real world conditions as possible. Hence the need to use reactive or speaker loads,which can be driven into as low as 2 ohm loads.

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