Isolation/coupling: basics?

El: Not only can individual components and circuits be microphonic, you can literally hear the sounds eminating out of transistors that they are amplifying during certain conditions. In some RF amplifiers, this can be heard quite plainly and is referred to in the industry as "transistor talk". The only way that one could hear this is if the conductors inside the transistor casing were vibrating enough to resonate the outer case in time with the signal that was being amplified. If those vibrations can be transferred from inside the transistor case to the outside case, and be done in a fashion loud enough to be easily heard and understood, what is stopping external vibrations from taking a reverse path from the outside of the transistor case and modulating the conductors inside the case ??? My guess is that the same thing occurs in audio gear, but with audio gear, you typically have the system running in the same room. The sound from the speakers will smother the sound of the transistors "talking".

I've seen / heard / could not believe this, but one can talk into an inductor that is coupled to a high gain audio circuit and hear your voice come out of the speaker. It is not clear, but it is plainly audible. The inductor that i heard this demonstrated on was wound on a plastic former and dipped in wax to try and minimize microphony. Even with all of this, it was still quite sensitive to outside stimuli. Inductors are commonly found in the majority of amplifiers that are currently on the market.

As far as other "passive" devices being microphonic, much of this comes from the wire leads or legs attached to the component vibrating. As such, it is best to keep the leads on each component as short as possible in order to avoid this. Many higher quality capacitors actually come with a sleeve over the legs so as to damp any external vibrations from being transferred into the body of the cap. Sean
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If error correction and speedy digital data processing are good things, why is it that CD "burns" made at high speed typically sound "inferior" than a burn made at 1X or 2X ? At the same time, why do burned CD's have increased readability from player to player when dubbed at lower speeds than those at higher speeds ? As far as i know, digital is NOT like analogue where spreading the signal over a wider / longer surface area increases dynamic range. I'm not trying to be a smart-ass here, just trying to better understand what's taking place and interject "real world" situations into this theoretical debate. Sean
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Thank you El. I'm not saying that you are wrong, but that my experiences and those of many others seem to contradict some of what you are saying. I also know that theory is called "theory" because it is not always "reality". Granted, "theory" is reality in many cases, but the manufacturers "short cut" approach won't let the design perform as it should. Sean
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