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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Distortion failure on power amps
Im doing a production test on power amplifiers using a distortion meter
to measure THD at three frequencies % THD, % THD. At % distortion. Im getting a distortion failure at 10Khz which measures 1.40% THD. No wrong value components. Because I getting a batch failure unlikely to be faulty/tolerance in components. What should I be looking for? I believe this must be a subtle fault. All I found was a PNP signal transistor was specified to be BC558B, Ive got fitted BC558C. |
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Distortion failure on power amps
"steve" wrote in message m... Im doing a production test on power amplifiers using a distortion meter to measure THD at three frequencies % THD, % THD. At % distortion. Im getting a distortion failure at 10Khz which measures 1.40% THD. No wrong value components. Because I getting a batch failure unlikely to be faulty/tolerance in components. What should I be looking for? What is the distortion floor of your test setup? Have you verified your equipment? What are you using? |
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Distortion failure on power amps
"steve" wrote in message m... What is the distortion floor of your test setup? Have you verified your equipment? What are you using? When you say distortion floor, do you mean limits of distortion meter? Amplifier is loaded across a 6ohm load. Distortion levels at input to amp acceptable. Amp under no load, distortion levels within spec. Frequency response of amp good 0.5dB The verification of the test equipment is important. Distortion is usually measured by feeding a low-distortion sinewave into an instrument that notches out the fundamental frequency and uses all remaining energy to measure THD. With no intervening circuit, the distortion floor is what you get (also called the residual distortion). Once this is established, then the circuit to be tested is inserted. The point is that the test equipment has to have a lot less distortion than the circuit under test. If your floor is well below 1.7%, then you are most likely making a valid measurement. If this is so, then the amplifier might not have enough negative feedback at 10 kHz since that is where the THD is out of spec. It's prudent to make sure of your measurement instruments before blaming the amplifier. |
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