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#1
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Test Equipment
Can someone recommend a satisfactory test unit to measure 'peak'
frequency coming from an amplifier. Thanks |
#2
Posted to rec.audio.high-end
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Test Equipment
Michael wrote:
Can someone recommend a satisfactory test unit to measure 'peak' frequency coming from an amplifier. Thanks What exactly do you mean by "peak" frequency? An amplifier typically reproduces the input signal, with a little bit of distortion and noise added. Are you talking about the frequency response of the amplifier, or are you looking for oscillations? For the former, a scope and a function generator works fine. For the latter, you need a good scope or a spectrum analyzer. In both cases, you need to have a load that resembles speakers used (assuming you are testing power amps). |
#3
Posted to rec.audio.high-end
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Test Equipment
Chung wrote:
Michael wrote: Can someone recommend a satisfactory test unit to measure 'peak' frequency coming from an amplifier. Thanks What exactly do you mean by "peak" frequency? An amplifier typically reproduces the input signal, with a little bit of distortion and noise added. Are you talking about the frequency response of the amplifier, or are you looking for oscillations? For the former, a scope and a function generator works fine. For the latter, you need a good scope or a spectrum analyzer. In both cases, you need to have a load that resembles speakers used (assuming you are testing power amps). I am testing for ultrasonic frequencies (greater than 100khz) coming from SACD's through my amplifier. I want to know what the highest frequency that is reproduced. |
#4
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Test Equipment
Michael wrote:
Chung wrote: Michael wrote: Can someone recommend a satisfactory test unit to measure 'peak' frequency coming from an amplifier. What exactly do you mean by "peak" frequency? I am testing for ultrasonic frequencies (greater than 100khz) coming from SACD's through my amplifier. I want to know what the highest frequency that is reproduced. That's not "peak frequency" you're trying to measure, it's the bandwidth. Normally, if you were measuring the trhoughput bandwidth, you'd simply have a source, such as an oscillator, that can produce at least the frequency range you expect, along with a meter, such as a wide voltmeter, to measure it. Pick a frequencyb in the middle to set your reference point, note the amplitude on the meter at that point, and then tune the oscillator to a high enough frequency that the meter drops by some amount, say, 3 dB or 20 dB or whatever you decide defines the band limit. That's your highest frequency. However, because you're looking for the highest frequencies from an arbitrary signal, it's more complicated. You have no control over the content of the signal, so you need to use something capable of doing broadband (100 kHz or greater) spectrum analysis. These days that means, generally, FFT or similar analysis. TO get that sort of capability in a stand-alone instrument is not at all cheap, and 100 kHz is and above is well above the range of pretty much all PC-based measurement tools (even though some cards may advertise a 192 kHz sample rate, that still only gives you a maximum high frequency limit less than 96 kHz, and the real bandwidth may be substantially less. I was once asked to evaluate a 96 kHz samplking system that was to be used for gunshot transient analysis, and at 96 kHz, it still only had a 20 kHz bandwidth). Now, are you looking for spurious signals above 100 kHz, such as clock noise and such, or are you looking for real signals. If the latter, you're going to spend a huge amount of money and effort to achieve a null result. If the former, you're going tro spend a huge amount of money and effort to possibly achieve a result that neither you, the manufacturer of the equipment, or the whole SACD world in general really don't want to know. |
#5
Posted to rec.audio.high-end
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Test Equipment
Michael wrote:
Chung wrote: Michael wrote: Can someone recommend a satisfactory test unit to measure 'peak' frequency coming from an amplifier. Thanks What exactly do you mean by "peak" frequency? An amplifier typically reproduces the input signal, with a little bit of distortion and noise added. Are you talking about the frequency response of the amplifier, or are you looking for oscillations? For the former, a scope and a function generator works fine. For the latter, you need a good scope or a spectrum analyzer. In both cases, you need to have a load that resembles speakers used (assuming you are testing power amps). I am testing for ultrasonic frequencies (greater than 100khz) coming from SACD's through my amplifier. I want to know what the highest frequency that is reproduced. In that case you are looking at the frequency response of the amplifier. The "highest frequency that is produced" is not a good measure since your amplifier has a smooth roll-off. It can probably reproduce a 100KHz input, but the gain at that frequency will be lower than that at 1 KHz for instance. A common spec is the -3dB bandwidth of the amplifier. You need a function generator that goes up to the highest frequency you want to test for, and you need a scope to measure the level of that amplified signal. And you need a load for the amplifier. |
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