Releationship between tension and current in audio signals
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 24th October 2017, 05:00 PM #1 Joanito   diyAudio Member   Join Date: Mar 2017 Location: Maia, Porto Releationship between tension and current in audio signals Hi all, I was wondering... if an amplifier psu tensions for a 100w rms 8 ohm is about, let's say, 30v and -30v then for a 200w it would be 60v and for an amplifier that can put 1500w into 8 ohm , it would be much more then, let's say, 100v and -100v. Yet i've been searching for amplifiers on the web and i found one board mono that can put 1500w into 8 ohm and yet it only requires a +-100vdc (around that) to work... So if we graph the output of an audio amplifier ( the relationship between tension and current ) should be exponential like this, right ? reelationship between tension and current.jpg ... and not a straight line like this, right ? relationship between tension and current straight.jpg Thank you all, Cheers.
 24th October 2017, 06:31 PM #2 Speedskater   diyAudio Member     Join Date: Sep 2002 Location: Lakewood, Ohio Lets see: 100W & 8ohm = 28Vrms or 40V peak (remember to add headroom to the power supply) 200W & 8ohm = 40Vrms or 56V peak 1500W & 8ohm = 110Vrms or 154V peak 630W & 8ohm = 71Vrms or 100V peak Many in the US think of voltage, reserving tension for the power company high tension wires. __________________ Kevin
 24th October 2017, 06:38 PM #3 wwenze   diyAudio Member   Join Date: Mar 2008 Hmm... how should I start... - The red graph is logarithmic; the blue graph is exponential - Volt vs amp should be a straight line - Power is V^2 / R - BTL config can produce 4 times output power of single-ended config for the same supply voltage and assuming unlimited current capability - "Peak power" is twice of RMS power - Sellers pulling power figures out from their blackholes
 24th October 2017, 06:42 PM #4 Mooly   diyAudio Moderator     Join Date: Sep 2007 1500 watts rms into 8 ohms is possible from -/+100 volts rails if the amplifier is of a bridge configuration.
 24th October 2017, 07:00 PM #5 Joanito   diyAudio Member   Join Date: Mar 2017 Location: Maia, Porto Hello, thanks, ... Because it comes to a point that is impossible to hear, there is also no equipment that supports so many db's and it would be a problem ( or impossible ) to build the power supply. Right ? So as voltage increses, current will increase more in logaritmic form, right ? Volume tends to a value ? I've noticed that the scale around the volume pot of an amplifier is not allways equal. Per example, the first 25% of rotation of the pot will amplify more than the last 25%. I don't know if this has anything to do with the relationship between tension and current but i think it has, right ? Thanks Last edited by Joanito; 24th October 2017 at 07:05 PM.
scottjoplin
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Join Date: Dec 2015
Location: Penrhyndeudraeth
Quote:
 Originally Posted by Joanito Hello, thanks, ... Because it comes to a point that is impossible to hear, there is also no equipment that supports so many db's and it would be a problem ( or impossible ) to build the power supply. Right ?
Roughly speaking 1000W is twice as loud as 100W which is twice as loud as 10W and so on
Quote:
 So as voltage increses, current will increase more in logaritmic form, right ?
no it's a linear relationship
Quote:
 Volume tends to a value ? I've noticed that the scale around the volume pot of an amplifier is not allways equal. Per example, the first 25% of rotation of the pot will amplify more than the last 25%. I don't know if this has anything to do with the relationship between tension and current but i think it has, right ? Thanks
It's because most volume pots have an inaccurate logarithmic track resistance
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 24th October 2017, 07:20 PM #7 Joanito   diyAudio Member   Join Date: Mar 2017 Location: Maia, Porto I get it. Thanks to all. Last edited by Joanito; 24th October 2017 at 07:24 PM.
jan.didden
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Join Date: May 2002
Location: Westende Resort, BE coast
Quote:
 Originally Posted by Joanito Hi all, I was wondering... if an amplifier psu tensions for a 100w rms 8 ohm is about, let's say, 30v and -30v then for a 200w it would be 60v and for an amplifier that can put 1500w into 8 ohm , it would be much more then, let's say, 100v and -100v. Yet i've been searching for amplifiers on the web and i found one board mono that can put 1500w into 8 ohm and yet it only requires a +-100vdc (around that) to work... So if we graph the output of an audio amplifier ( the relationship between tension and current ) should be exponential like this, right ? Attachment 641962 ... and not a straight line like this, right ? Attachment 641963 Thank you all, Cheers.
The volts versus amps is linear, it is related by the constant load of (in this case) 8 ohms. V = I*R, ohms' law. So your 1st graph is not correct, the 2nd is.

If you want to double the output power you do NOT have to double the voltage - because power is V-squared / R. So to double power you only need SqRt(2) * V, about 1.4 times larger (because 1.4 squared is about 2).

Jan
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 24th October 2017, 09:04 PM #9 bwaslo   Old guy with soldering iron diyAudio Member     Join Date: May 2006 Location: Portland, Oregon! As Scott said, volume control "% rotation" isn't really a measure of anything at all. Different tapers and different amounts of gain quickly make it meaningless other than "more clockwise is louder". One thing I hear that I always have to restrain myself from jumping in about is when someone says "It's really loud and the volume control is only X% of the way!". It's pretty dang trivial to arrange gains and signal level so you run out off power in the first 1% of rotation if you wanted to! __________________ [W9MJE] Horn spreadsheet SynergyCalc/; SmallSyns SmallSyns; Crossover design Xsim; Depot diffusor super-easy diffusors
 24th October 2017, 09:31 PM #10 silverprout   diyAudio Member     Join Date: Apr 2008 __________________ Things I Should Have Learned In School (But Probably Didn't)

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