Someone on this group suggested that chip as being an ideal, high-impedance, low-distortion, low-noise first stage for a dynamic mic amplifier. If you know of a better one, then by all means feel free to suggest it.
Start with the specs for the mic.
Nah, algebra rocks. One good sleazy approximation is worth a stack of SPICE output. ;)
I try to make it that way, usually with some success.
Knowing Smith charts is a huge labour saver for RF things. They're especially good for synthesis of narrow-to-moderate bandwidth things.
Cheers
Phil Hobbs
I can do sleazy approximations in my head! Guess, Spice, iterate.
That works until the complexity gets lost in space, which happens once in a while. Filters are one example... but hardly anybody designs filters with math; we use Williams or Filterpro or the NuHertz software.
Yes, narrowband and small-signal. But if you have a data sheet with all that classic stuff, it's pretty much useless for fast, nonlinear, time domain problems. Or even high-level RF. On the other hand, a good Spice model would do for both.
"Load pull" testing was the classic way to work around s-params. Just try it.
I'd have expected something more like an instrumentation amplifier configuration to take out common mode noise and a few discretes on the front end to do phantom power and initial signal conditioning.
This example looks to me like it might possibly satisfy the OP's unspecified requirements. The topology looks about right to me.
We have no idea what he wants to do.
It's basic that more transistors make more noise, and an opamp or diffamp starts with at least two in the front end.
The ancient jfet thing is really bad. But a creative design will make it worse.
Do microphones have significant Brownian noise, from air molecules bashing the diaphragm?
The figure of merit is signal/noise ratio, not noise. So, you should start with impedance matching (and a grounded-base BJT might actually win). JFET designs have good character compared to old MOS (because of surface recombination), but that's process-dependent so MOS might be better nowadays.
Yes, of course. So do your ears. Listen to a conch shell lately?
John Doe snipped-for-privacy@message.header wrote in news:scm86b$7cn$ snipped-for-privacy@dont-email.me:
You got nothing, you stupid f*ck. That is why *this* stupid shit is all you can post. You couldn't muster an intelligent post if you tried.
John Larkin <jlarkin@highland_atwork_technology.com> wrote in news: snipped-for-privacy@4ax.com:
In the '70s we used to spout "Skipland, skipland, skipland!" over the CB radio looking for long distance reflections.
I guess with this stuff its, "Stripline, stripline, stripline"... :-P
The LF356's main virtue is low input capacitance. I used to be able to do things with its decompensated brother (LF357) that are impossible with modern +- 15V op amps. The new ones trip over their own big feet.
Cheers
Phil Hobbs
With dynamic mics you also have to worry about what the load impedance does to the damping.
Cheers
Phil Hobbs
Impedance matching throws half the signal away up front. But how do you define the impedance of a dynamic mic? DCR?
And dynamic mics usually have a specified load resistance to meet response specs, usually pretty high compared to DCR. Damping maybe.
They have inductance too. Loading that hard will get interesting.
Conch shell sound is Brownian noise?
But it's 15 nV/rthz!
Phantom power or not? That's confusing.
If there's an amp inside the microphone, that changes things.
No issue with > 100k transimpedance. My old trademark TIA design, the bootstrapped cascode, doesn't work well anymore because of the e_N*C noise of just the op amp's C_in. I spent a week on it last winter, using a number of apparently-suitable chips and couldn't reproduce the LF357's performance.
Cheers
Phil Hobbs
Largely you are being jerked around because they aren't explaining that you can avoid much of the issue by using a non-inverting stage with the input on the non-inverting input which is very high impedance. This lets you tailor your input to suit the microphone. The inverting input requires other considerations because it is part of the gain loop involving feedback. I don't recall if you've provided a part number for the mic, but provide that and a link to a data sheet and you will most likely receive some very useful inputs. I think this is one area where Phil A. might just give some useful insight without profanity although he will probably give me some for mentioning it. Like saying Beetlejuice three times! He does know his audio circuits if you can kiss his ass enough to get useful comments.
Not interested in *any* input from *any* Australians, thanks very much.
You aren't doing it right then. You're supposed to *transform* the impedance to obtain a match. If you just add resistors, then yes, you're throwing away useful signal.
Jeroen Belleman
A classic CD response: idiotic, racist, and irrelevant to the points being made. Not to mention wrong.
Yes, I worked that out in the late 70s, when the 356/7 were new.
I didn't need to be that sophisticated since I wasn't interested in speed (10kHz signals), only in low noise. I managed 1pW optical noise equivalent power with a BPW34 (IIRC) PIN diode.
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