Talk:Impedance bridging

message: For the general case of complex impedance, the load voltage is maximal at Z_L = \frac{2 Z_S \bar{Z_S}}{Z_S - \bar{Z_S}}. I believe this must be mentioned. Leokor (talk) 02:57, 12 February 2013 (UTC)
thread_title:  Complex Impedance 

message: "It is a bridging connection if the second device does not appreciably load the previous device."  Which is the "second" device?  The load or the source?  How is "previous" defined here?  I'm pretty sure that this means that the source does not appreciably load the load device, but this language could be clearer.
Steve carlson 23:27, 9 March 2007 (UTC)
thread_title: "Second Device" vs. "Previous Device"

message: I'm just pointing out that the Rod Elliot reference now 404's. I found this article. http://sound.whsites.net/impedanc.htm but am not sure if it's equivalent.  — Preceding unsigned comment added by Petergcook (talk • contribs) 00:52, 28 November 2016 (UTC)
replies: text: seems to work  --AK45500 (talk) 13:08, 5 September 2018 (UTC)
thread_title:  Reference 404's 

message: There is a lot of material copied from copyrighted sources in the notes.  Does this exceed fair use? Constant314 (talk) 04:00, 17 June 2022 (UTC)
replies: text: Sorry, I probably did put too much quoted excerpt. I've removed the quote now. Em3rgent0rdr (talk) 04:46, 17 June 2022 (UTC)
thread_title:  Copyrighted material 

message: There is a question that this page doesn't address, which is if large ratios are good, then why do mic preamps input impedance only go to about 10x of typical low impedance mics  Why not use the same very high input impedance of line or pickup inputs.  I found this explanation in https://www.soundonsound.com/techniques/understanding-impedance that there would be too much noise from resistors, which maybe could be paraphrased into this page:
"Typically, most microphones therefore have an output impedance of 150-200Ω, and most preamplifier inputs offer an input impedance of between 1.5kΩ and 3kΩ — on the limit of the 'ten times higher' rule of thumb I mentioned earlier. It is a good idea to keep the input impedance of mic amps relatively low (at least compared to typical line inputs) since resistors generate noise when current flows through them; the higher the resistance the greater the noise. Since the signal level from microphones is relatively weak, a lot of gain is generally required, amplifying the resistor noise along the way. This is the reason why mic preamp specs should quote the source impedance when providing the Equivalent Input Noise (EIN) measurement; the lower the source impedance, the lower the noise will be. A good EIN figure can be achieved for the spec sheet by measuring the input stage with a 50Ω source impedance. However, this noise figure will be totally unrealisable with a real-world 200Ω microphone!"
And regarding why it is crucial for guitar inputs to be very high:
"If the input has too low an impedance, the most noticeable effect will be a loss of high end — in fact, even using guitar cables with too high a capacitance can audibly reduce high frequencies"
And in a follow up article https://www.soundonsound.com/sound-advice/q-do-i-need-think-about-matching-mic-and-preamp-impedances says both "In fact, there can be benefits in using a higher input impedance to reduce the source loading even more" than 10x, though also talks about sometimes people like the coloration from using lower input impedances. Em3rgent0rdr (talk) 06:45, 17 June 2022 (UTC)
replies: text: I think you are getting into out-of-scope system issues.  The guitar pickup is, I believe, inductive.  Any significant loading whether resistive or cable capacitance would interact with that to produce a high frequency roll off.  This isn't a bridging vs reflectionless issue. It is about making it work with a specific source, load, and cable. Constant314 (talk) 21:46, 17 June 2022 (UTC)
thread_title:  Why mic preamp input impedance isn't nearly as large as input impedance of line or pickup.