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Datasheet Jargon Translation Required

Started by Cursitor Doom July 11, 2021
John Larkin <jlarkin@highland_atwork_technology.com> wrote in
news:l1cueg5reelo61nsv36q1tidtcf9bdkq6d@4ax.com: 

> 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. >
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
John Larkin wrote:
> On Wed, 14 Jul 2021 20:31:31 +0100, Martin Brown > <'''newspam'''@nonad.co.uk> wrote: > >> On 14/07/2021 14:26, jlarkin@highlandsniptechnology.com wrote: >>> On Wed, 14 Jul 2021 09:09:55 +0100, Martin Brown >>> <'''newspam'''@nonad.co.uk> wrote: >>> >>>> On 13/07/2021 23:18, Cursitor Doom wrote: >> >>>>> So... what's the issue with the diagram I linked to? >>>> >>>> It just shows how to use the chip as a simple inverting amplifier >>>> without having it oscillate like crazy due to stray capacitance at the >>>> input. Which part of make R1*C1=R2*C2 do you not understand? >>>> >>>> The real practical difficulty is matching your dynamic microphone to the >>>> "ideal" amplifier for lowest possible distortion and maximum signal. >>>> >>>> John is asking to see that part - not the gain block after it. >>> >>> There are all sorts of subtelties about a dynamic mic amp. The >>> inverting opamp is a bad start. >> >> 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. >> >> http://www.cordellaudio.com/preamplifiers/dynamicmicpreamp.shtml > > 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 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 -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
whit3rd wrote:
> On Wednesday, July 14, 2021 at 12:43:07 PM UTC-7, John Larkin wrote: >> On Wed, 14 Jul 2021 20:31:31 +0100, Martin Brown >> <'''newspam'''@nonad.co.uk> wrote: >>> This example looks to me like it might possibly satisfy the OP's >>> unspecified requirements. The topology looks about right to me. >>> >>> http://www.cordellaudio.com/preamplifiers/dynamicmicpreamp.shtml >> 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. > > 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. > >> Do microphones have significant Brownian noise, from air molecules >> bashing the diaphragm? > > Yes, of course. So do your ears. Listen to a conch shell lately? >
With dynamic mics you also have to worry about what the load impedance does to the damping. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On Wed, 14 Jul 2021 13:21:33 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Wednesday, July 14, 2021 at 12:43:07 PM UTC-7, John Larkin wrote: >> On Wed, 14 Jul 2021 20:31:31 +0100, Martin Brown >> <'''newspam'''@nonad.co.uk> wrote: >> >This example looks to me like it might possibly satisfy the OP's >> >unspecified requirements. The topology looks about right to me. >> > >> >http://www.cordellaudio.com/preamplifiers/dynamicmicpreamp.shtml >> 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. > >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.
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.
> >> Do microphones have significant Brownian noise, from air molecules >> bashing the diaphragm? > >Yes, of course. So do your ears. Listen to a conch shell lately?
Conch shell sound is Brownian noise?
On Wed, 14 Jul 2021 16:53:23 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>John Larkin wrote: >> On Wed, 14 Jul 2021 20:31:31 +0100, Martin Brown >> <'''newspam'''@nonad.co.uk> wrote: >> >>> On 14/07/2021 14:26, jlarkin@highlandsniptechnology.com wrote: >>>> On Wed, 14 Jul 2021 09:09:55 +0100, Martin Brown >>>> <'''newspam'''@nonad.co.uk> wrote: >>>> >>>>> On 13/07/2021 23:18, Cursitor Doom wrote: >>> >>>>>> So... what's the issue with the diagram I linked to? >>>>> >>>>> It just shows how to use the chip as a simple inverting amplifier >>>>> without having it oscillate like crazy due to stray capacitance at the >>>>> input. Which part of make R1*C1=R2*C2 do you not understand? >>>>> >>>>> The real practical difficulty is matching your dynamic microphone to the >>>>> "ideal" amplifier for lowest possible distortion and maximum signal. >>>>> >>>>> John is asking to see that part - not the gain block after it. >>>> >>>> There are all sorts of subtelties about a dynamic mic amp. The >>>> inverting opamp is a bad start. >>> >>> 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. >>> >>> http://www.cordellaudio.com/preamplifiers/dynamicmicpreamp.shtml >> >> 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 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
But it's 15 nV/rthz!
On Wed, 14 Jul 2021 20:31:31 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

>On 14/07/2021 14:26, jlarkin@highlandsniptechnology.com wrote: >> On Wed, 14 Jul 2021 09:09:55 +0100, Martin Brown >> <'''newspam'''@nonad.co.uk> wrote: >> >>> On 13/07/2021 23:18, Cursitor Doom wrote: > >>>> So... what's the issue with the diagram I linked to? >>> >>> It just shows how to use the chip as a simple inverting amplifier >>> without having it oscillate like crazy due to stray capacitance at the >>> input. Which part of make R1*C1=R2*C2 do you not understand? >>> >>> The real practical difficulty is matching your dynamic microphone to the >>> "ideal" amplifier for lowest possible distortion and maximum signal. >>> >>> John is asking to see that part - not the gain block after it. >> >> There are all sorts of subtelties about a dynamic mic amp. The >> inverting opamp is a bad start. > >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. > >http://www.cordellaudio.com/preamplifiers/dynamicmicpreamp.shtml
Phantom power or not? That's confusing. If there's an amp inside the microphone, that changes things.
John Larkin wrote:
> On Wed, 14 Jul 2021 16:53:23 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> John Larkin wrote: >>> On Wed, 14 Jul 2021 20:31:31 +0100, Martin Brown >>> <'''newspam'''@nonad.co.uk> wrote: >>> >>>> On 14/07/2021 14:26, jlarkin@highlandsniptechnology.com wrote: >>>>> On Wed, 14 Jul 2021 09:09:55 +0100, Martin Brown >>>>> <'''newspam'''@nonad.co.uk> wrote: >>>>> >>>>>> On 13/07/2021 23:18, Cursitor Doom wrote: >>>> >>>>>>> So... what's the issue with the diagram I linked to? >>>>>> >>>>>> It just shows how to use the chip as a simple inverting amplifier >>>>>> without having it oscillate like crazy due to stray capacitance at the >>>>>> input. Which part of make R1*C1=R2*C2 do you not understand? >>>>>> >>>>>> The real practical difficulty is matching your dynamic microphone to the >>>>>> "ideal" amplifier for lowest possible distortion and maximum signal. >>>>>> >>>>>> John is asking to see that part - not the gain block after it. >>>>> >>>>> There are all sorts of subtelties about a dynamic mic amp. The >>>>> inverting opamp is a bad start. >>>> >>>> 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. >>>> >>>> http://www.cordellaudio.com/preamplifiers/dynamicmicpreamp.shtml >>> >>> 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 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.
> > But it's 15 nV/rthz! >
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 -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On Wednesday, July 14, 2021 at 11:40:00 AM UTC-4, Cursitor Doom wrote:
> On Wed, 14 Jul 2021 06:26:16 -0700, jla...@highlandsniptechnology.com > wrote: > >On Wed, 14 Jul 2021 09:09:55 +0100, Martin Brown > ><'''newspam'''@nonad.co.uk> wrote: > > > >>On 13/07/2021 23:18, Cursitor Doom wrote: > >>> > >>> So... what's the issue with the diagram I linked to? > >> > >>It just shows how to use the chip as a simple inverting amplifier > >>without having it oscillate like crazy due to stray capacitance at the > >>input. Which part of make R1*C1=R2*C2 do you not understand? > >> > >>The real practical difficulty is matching your dynamic microphone to the > >>"ideal" amplifier for lowest possible distortion and maximum signal. > >> > >>John is asking to see that part - not the gain block after it. > > > >There are all sorts of subtelties about a dynamic mic amp. The > >inverting opamp is a bad start. > 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.
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. -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
On Wed, 14 Jul 2021 14:20:16 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

>On Wednesday, July 14, 2021 at 11:40:00 AM UTC-4, Cursitor Doom wrote: >> On Wed, 14 Jul 2021 06:26:16 -0700, jla...@highlandsniptechnology.com >> wrote: >> >On Wed, 14 Jul 2021 09:09:55 +0100, Martin Brown >> ><'''newspam'''@nonad.co.uk> wrote: >> > >> >>On 13/07/2021 23:18, Cursitor Doom wrote: >> >>> >> >>> So... what's the issue with the diagram I linked to? >> >> >> >>It just shows how to use the chip as a simple inverting amplifier >> >>without having it oscillate like crazy due to stray capacitance at the >> >>input. Which part of make R1*C1=R2*C2 do you not understand? >> >> >> >>The real practical difficulty is matching your dynamic microphone to the >> >>"ideal" amplifier for lowest possible distortion and maximum signal. >> >> >> >>John is asking to see that part - not the gain block after it. >> > >> >There are all sorts of subtelties about a dynamic mic amp. The >> >inverting opamp is a bad start. >> 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. > >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.
On 2021-07-14 23:07, John Larkin wrote:
> On Wed, 14 Jul 2021 13:21:33 -0700 (PDT), whit3rd <whit3rd@gmail.com> > wrote: > >> On Wednesday, July 14, 2021 at 12:43:07 PM UTC-7, John Larkin wrote: >>> On Wed, 14 Jul 2021 20:31:31 +0100, Martin Brown >>> <'''newspam'''@nonad.co.uk> wrote: >>>> This example looks to me like it might possibly satisfy the OP's >>>> unspecified requirements. The topology looks about right to me. >>>> >>>> http://www.cordellaudio.com/preamplifiers/dynamicmicpreamp.shtml >>> 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. >> >> 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. > > Impedance matching throws half the signal away up front. [...]
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