Simulating a very low music level 300Ω microphone output for low noise preamplifier tests

At your risk. Protect your ears.


This was done by connecting a series 10MΩ resistor to line out of a Sony Walkman CD player and then a 330Ω shunt resistor.


It may be better to use a 200Ω wire wound resistor as many mics have such output impedance.


Then another such attenuator was connected in cascade.


(A very important source of noise is thermal noise. Ie agitating electrons in a conductor due to thermal energy which we all receive from the sun). Hiss. See also Johnson thermal noise.


Signal path:


ABBA Voulez Vous CD - Sony CD Walkman line out - 10MΩ, 330Ω potential devider - 10MΩ, 330Ω potential devider - (in fact another one may be needed) - Sony TC-D5 Pro, limiter on - Sennheiser HD580


After the second attenuator or potential devider music is buried in noise as if listening to a very distant radio station. The noise heard should be the 330Ω thermal noise only on a good preamplifier.


When music is so low that it is almost inaudible adding a Western Electric 1:2 step up transformer stepping up the impedance to 4x ie 1200Ω makes music clearly audible.


This may show that the signal to noise ratio of Sony TC-D5 can be improved by a good quality passive or active mic booster amplifier. Examples are a good low turn ratio transformer or for example a Pleiades V6 electron tube battery powered preamplifier respectively.


And it may also show that when we accuse tape of low noise we may be in fact be acussing
preamplifier noise or thermal noise which has nothing tho do with analog tape itself.