Voltage, power, impedance
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 1st April 2009, 02:56 AM #1 454Casull   diyAudio Member   Join Date: Jan 2004 Location: Toronto, ON, Canada Voltage, power, impedance I wasn't sure where I should put this, so I guess it ends up here. Anyway, I'm a little confused about the relationship between peak voltage and RMS voltage as it relates to power and impedance. Let's say I have an amp with +/- 30VDC rails and it is driving a power resistor of 4 ohms. The Vp is 30V, so the Vrms = 30/1.414=21.2V. This is the value that I use for power calculations, right? So P = V^2/R P = 21.2^2/4 P=112W Is this correct? If so, then I move on to the following calculation: an amp which needs to provide 100W to a 7-ohm load must have +/- 37.4VDC rails (assuming that it can rail), correct? Vrms=sqrt(100*7) Vrms=26.46V Vp=26.46(1.414)=37.4VDC
 1st April 2009, 03:35 AM #2 Iain McNeill   diyAudio Moderator Emeritus     Join Date: Oct 2007 Location: Santa Cruz, California That's correct. In reality, your OP trannies can't actually swing rail to rail and then the PSU usually sags a bit at full load hence YMMV. edit: oh, and a 7ohm speaker isn't really 7 ohms, well maybe at a couple of frequencies
454Casull
diyAudio Member

Join Date: Jan 2004
Quote:
 Originally posted by Iain McNeill That's correct. In reality, your OP trannies can't actually swing rail to rail and then the PSU usually sags a bit at full load hence YMMV. edit: oh, and a 7ohm speaker isn't really 7 ohms, well maybe at a couple of frequencies
Thanks for the help.

I can read impedance charts, though.

 1st April 2009, 11:27 PM #4 unclejed613   diyAudio Member     Join Date: Dec 2006 that sounds about right. a while back i made up a "power guesstimation" chart based on rail voltage, peak voltage and p-p voltage so that techs wouldn't have to mess with a calculator when testing an amp. it's mostly "ballparked" values, but it works and saves a bit of time. as they used to say "it's close enough for rock and roll"...... __________________ Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net spammer trap: spammers must die

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post rdf Parts 2 15th July 2007 10:38 PM kelticwizard Everything Else 11 25th March 2007 05:17 AM Gcollier Multi-Way 7 29th June 2006 09:54 PM FlukeSkywrecker Subwoofers 2 7th June 2005 05:32 PM theChris Chip Amps 1 28th September 2003 09:34 AM

 New To Site? Need Help?

All times are GMT. The time now is 01:05 AM.