Jim, The LTSpice plot shows why the stock Astatic 2-stage pre-amp with its ~ 470K-ohm input Z does little to extend low-end response.
The model also likely assumes a perfect C in series with the source. After testing several D-104 cartridges of different vintage, I've come to the conclusion that distributed resistance appears across the crystal, thereby limiting any additional benefit of an extraordinarily high inout Z beyond 10 meg-ohm. Although not shown through the model diminishing returns hits pretty fast just above 5 megohm. I've not seen any element produce a reasonably flat response below ~ 50 Hz. Still, as long as the target is about 70 Hz to hit the lowest of vocal fundamentals, there's no reason to strive for anything better unless one relishes the sound of room rumble which in turn also unnecessarily raises RF duty cycle. Paul, W9AC ----- Original Message ----- From: "Jim Tonne" <[email protected]> To: "Discussion of AM Radio in the Amateur Service" <[email protected]> Sent: Tuesday, September 22, 2009 11:07 AM Subject: Re: [AMRadio] Microphone recomendation > > I have been lurking here and reading the discussion > which seems to me to have reduced itself down to a > kind of "my daddy is better than your daddy" kind of > thing. > > The person who said the D104 microphone could be > thought of as a voltage generator in series with a > 500 pF capacitor hit the nail on the head! Exactly > correct (although I thought it might be a *slightly* > higher capacitance value). > > I have spent a few minutes with LTspice and made > a plot which clearly shows what happens when you > change the value of the load on the D104 microphone. > With a 10 megohm load the -3 dB point will be right > at 30 Hz. > > Please, fellows, take a quick peek at this plot: > http://tonnesoftware.com/appnotes/D104loadTest.gif > > The bottom line of this note is that going higher than > 10 megohms for a load is nonsense. Pure nonsense. > > - Jim W4ENE > > > ______________________________________________________________ > Our Main Website: http://www.amfone.net > AMRadio mailing list > Searchable Archives: http://www.mail-archive.com/[email protected]/ > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Post: [email protected] > To unsubscribe, send an email to [email protected] with > the word unsubscribe in the message body. > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
