Now, two more questions.
A) It has been mentioned that the source impedance changes with volume. I wonder-how much? I plan to test around 5 V. At least one of his amps is a Dynaco ST-70. How much different is the source impedance likely to be near full output than from 5 V?
B) A 20 ohm resistor parallelled with a 10 ohm is recommended for testing the 8 ohm tap. How about the 4 ohm tap? Should he parallel a 5 ohm resistor, (easily made with two 10 ohm resistors in parallel), with a single 10 ohm resistor for the 4 ohm tap? Or just go with the original 10 ohm/20 ohm resistor test?
A) It has been mentioned that the source impedance changes with volume. I wonder-how much? I plan to test around 5 V. At least one of his amps is a Dynaco ST-70. How much different is the source impedance likely to be near full output than from 5 V?
B) A 20 ohm resistor parallelled with a 10 ohm is recommended for testing the 8 ohm tap. How about the 4 ohm tap? Should he parallel a 5 ohm resistor, (easily made with two 10 ohm resistors in parallel), with a single 10 ohm resistor for the 4 ohm tap? Or just go with the original 10 ohm/20 ohm resistor test?
Hey Keltic,
The most dramatic changes in output impedance occur over changes in frequency. As far as volume is concerned, a few watts of output is enough to get a decent read on things as it is a realistic level. Remeber, twice as loud takes 10 times the power... so a 75 Watt amp putting out 7.5 watts is at "half" volume.
Part B... Correct. The idea is get values for Rload that are just above AND below the anticipated load... but far enough apart to get a good reading. You need two points of measurement; so it just makes sense to "straddle" them around target.
The most dramatic changes in output impedance occur over changes in frequency. As far as volume is concerned, a few watts of output is enough to get a decent read on things as it is a realistic level. Remeber, twice as loud takes 10 times the power... so a 75 Watt amp putting out 7.5 watts is at "half" volume.
Part B... Correct. The idea is get values for Rload that are just above AND below the anticipated load... but far enough apart to get a good reading. You need two points of measurement; so it just makes sense to "straddle" them around target.
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