Heh, just be prepared for a very in-depth discussion. Strikes me that it's good this issue came up as it points out the complexities of coming into a new community.gloups....so what you're sayin' is that i'm about to take a technical beating....
Hold on...I'll get my wife on the line.
gloups....so what you're sayin' is that i'm about to take a technical beating....
Well i'm just wondering if he doesn't agree with what was written, or just how it was phrased...
What was written. It's flat out wrong. Voltage gain isn't the primary purpose of a buffer amplifier on a condenser mic capsule. If it was, you wouldn't need a FET. Or put another way, you wouldn't need an amplifier in the mic at all, just use a mic preamp.
But the capsule is extremely high source impedance, which is another way of saying it only puts out a wee tiny current, which means that if you don't get an amplifier really close to the capsule, you won't have much signal left at all. But the open-circuit voltage is actually rather healthy. So the only thing the capsule FET really needs to do is act as a current amplifier.
That's not to say that is the only configuration of a capsule FET, but it is indeed common. The well-known Schoeps circuit, for example, has the capsule FET in phase-splitter configuration, which is unity (voltage) gain, followed by a PNP pair which is also just another current amplifier (because the source impedance of the FET is still too high to drive adequately long cables).
Why not just strap a BJT on the capsule? Because the input impedance of the BJT is far too low.
Now, do some mics take voltage gain on the capsule FET? Yes indeed, not because it's necessary to get a reasonable level of sensitivity, but in order to minimize noise in the circuit (such that the only major source of noise is the capsule + FET).
Tube mics work a bit differently; often you'll find these in plate follower configuration, which adds quite a lot of current and voltage gain. The reason for this is tube plates are better at voltage gain, and they will be followed by a transformer which swaps the high voltage for more current. Another way to do that is which a cathode follower configuration, which dumps out lots more current (but no voltage gain), but still requires an output transformer (as far as I know, I don't do much with traditional tube mics).
I mean, I hate to be rude, but these articles have the tenor of those that think there are four types of condenser mics: tube, FET, electret, and "regular"
Why does this matter? Well, because if you're going to get far in audio engineering, at some point you must wrestle with impedance, and that necessarily leads to Ohm's Law, and amplifier concepts . . . screw up the terminology, and you hinder the student's eventual progress. Most people do not need to know what I just wrote, but they do need to understand line vs. mic vs. instrument levels (voltage) and impedance (current), for example they need to understand why plugging a dynamic mic directly into a line input on a converter won't work too well, and these are all related concepts.
Off on vacation now, enjoy reading Harvey's thread!
Forum Member 1 said:
Forum Member 2 said:
What was written. It's flat out wrong. Voltage gain isn't the primary purpose of a buffer amplifier on a condenser mic capsule. If it was, you wouldn't need a FET. Or put another way, you wouldn't need an amplifier in the mic at all, just use a mic preamp.
But the capsule is extremely high source impedance, which is another way of saying it only puts out a wee tiny current, which means that if you don't get an amplifier really close to the capsule, you won't have much signal left at all. But the open-circuit voltage is actually rather healthy. So the only thing the capsule FET really needs to do is act as a current amplifier.
That's not to say that is the only configuration of a capsule FET, but it is indeed common. The well-known Schoeps circuit, for example, has the capsule FET in phase-splitter configuration, which is unity (voltage) gain, followed by a PNP pair which is also just another current amplifier (because the source impedance of the FET is still too high to drive adequately long cables).
Why not just strap a BJT on the capsule? Because the input impedance of the BJT is far too low.
Now, do some mics take voltage gain on the capsule FET? Yes indeed, not because it's necessary to get a reasonable level of sensitivity, but in order to minimize noise in the circuit (such that the only major source of noise is the capsule + FET).
Tube mics work a bit differently; often you'll find these in plate follower configuration, which adds quite a lot of current and voltage gain. The reason for this is tube plates are better at voltage gain, and they will be followed by a transformer which swaps the high voltage for more current. Another way to do that is which a cathode follower configuration, which dumps out lots more current (but no voltage gain), but still requires an output transformer (as far as I know, I don't do much with traditional tube mics).
I mean, I hate to be rude, but these articles have the tenor of those that think there are four types of condenser mics: tube, FET, electret, and "regular"
Why does this matter? Well, because if you're going to get far in audio engineering, at some point you must wrestle with impedance, and that necessarily leads to Ohm's Law, and amplifier concepts . . . screw up the terminology, and you hinder the student's eventual progress. Most people do not need to know what I just wrote, but they do need to understand line vs. mic vs. instrument levels (voltage) and impedance (current), for example they need to understand why plugging a dynamic mic directly into a line input on a converter won't work too well, and these are all related concepts.
Off on vacation now, enjoy reading Harvey's thread!
.Sorry.(but i will read that thread) But you're more than welcome to write an article that we'll put up on the site, and you even can put your signature on it if you like. Same goes for all of you. We're open to contributions from people who know their stuff as long as there's no marketing involved or brand bias.
OK ok, you're definitely arguing with the wrong guy. This isn't my area of expertise, So most of what you're saying is over my head
And you saved thousands on car insurance, too! Right?
May I humbly request that you read the first two stickies in the Microphone Forum, which date back 6 and 7 years ago?