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Releationship between tension and current in audio signals
Releationship between tension and current in audio signals
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Old 24th October 2017, 04:00 PM   #1
Joanito is offline Joanito  Portugal
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Default 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.
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Old 24th October 2017, 05:31 PM   #2
Speedskater is offline Speedskater  United States
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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.
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Old 24th October 2017, 05:38 PM   #3
wwenze is offline wwenze  Singapore
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Hmm... how should I start...

- The red graph is logarithmic; the blue graph is exponential
Click the image to open in full size.

- 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
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Old 24th October 2017, 05:42 PM   #4
Mooly is offline Mooly  United Kingdom
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Releationship between tension and current in audio signals
1500 watts rms into 8 ohms is possible from -/+100 volts rails if the amplifier is of a bridge configuration.
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Old 24th October 2017, 06:00 PM   #5
Joanito is offline Joanito  Portugal
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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 06:05 PM.
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Old 24th October 2017, 06:11 PM   #6
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by Joanito View Post
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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Old 24th October 2017, 06:20 PM   #7
Joanito is offline Joanito  Portugal
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I get it.
Thanks to all.

Last edited by Joanito; 24th October 2017 at 06:24 PM.
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Old 24th October 2017, 07:46 PM   #8
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Joanito View Post
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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Old 24th October 2017, 08:04 PM   #9
bwaslo is offline bwaslo  United States
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Releationship between tension and current in audio signals
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!
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Old 24th October 2017, 08:31 PM   #10
silverprout is offline silverprout  France
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