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Old 11th July 2007, 03:31 AM   #1
Leolabs is offline Leolabs  Malaysia
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Lightbulb Adjustable power supply to replace volume control

Seen that the output power of a power amplifier is proportional to the supply voltages,why not design an adjustable regulated power supply to adjust the volume level instead of using the normal volume control???
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Old 11th July 2007, 03:39 AM   #2
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Default Re: Adjustable power supply to replace volume control

Quote:
Originally posted by Leolabs
...why not design an adjustable regulated power supply to adjust the volume level instead of using the normal volume control???
Keep it up and you'll have a patent pending and folks working for you.

What do you have for a schematic/block diagram? I think this type of arrangement would only work in a "certain" operating range of the devices implemented but could easily switch between several modes of operation to ensure good performance for full attenuation and smooth response over the entire audio spectrum. Just thinking out loud...

Cheers,

Shawn.
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Old 11th July 2007, 04:23 AM   #3
Amp_Nut is offline Amp_Nut  India
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By varying the Supply voltage, the CLIPPING point / level of the amplifier will vary, NOT its gain or output swing !

Varying the supply Voltage to change the Output Volume is only possible in some forms of Digital Amplifiers ....
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Old 11th July 2007, 05:22 AM   #4
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I think the subject amplifier would need to be built for the purpose. I think the idea has merit and is worth investigating. Anything that does not subscribe to conventional methods is worth working for. These are the ideas and concepts that bring us to the next level.

Much work and planning would be required. A physics degree would help but is NOT a requirement. Just look into history for examples...there are many.

Block diagram? Conceptual function?

Cheerio,

Shawn.
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Old 11th July 2007, 05:26 AM   #5
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Quote:
Originally posted by Amp_Nut
Varying the supply Voltage to change the Output Volume is only possible in some forms of Digital Amplifiers ....
Only ? ...never say never man but this is a good place to start none the less even if it has to be digital.
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Old 11th July 2007, 10:03 AM   #6
Nordic is offline Nordic  South Africa
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The chip no. slip me now, but in one of TI's recent newsletters they had an example where they quoted the chip with snr of 85db and a second rateing of 125db with Power supply volume control, next to it....
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Old 11th July 2007, 11:10 AM   #7
Nordic is offline Nordic  South Africa
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Was bored so I looked for some info....

http://focus.ti.com/lit/an/slea038/slea038.pdf

Implementation of Power Supply Volume Control

This document gives design guide lines for applications using the power supply volume
control (PSVC). The power supply volume control increases system performance by:
Volume can be decreased without loss of audio resolution, in the range where PSVC is
active.
When supply voltage for PVDD is decreased, the noise voltage at the output decreases as
well. The ratio between noise voltage and maximum RMS voltage (DNR) then increases.
The user experiences better noise performance at usual listening levels. E.g. a system
having 102 dB in DNR and a power supply range of 18 dB will have a SNR up to 120 dB.
Reduces power consumption and heat in the system at usual listening levels, thereby
increasing the lifetime of the system.
Many EMI tests are performed at a reduced volume setting. FTC requires 1/8 of maximum
output power equal to a volume setting of -9 dBFS. By use of the PSVC operating voltage
during EMI, the test will be reduced giving reduced switching noise in the system.
The PSVC is supported in Texas Instruments PWM processors like the TAS5508, which
makes implementation easy. For other modulator types like the TAS5066 and TAS5076,
the PSVC can also be implemented. However, on these devices all calculations and
control must be handled by the micro controller.
This document gives design guidelines, how to implement PSVC correctly for the
TAS5508. To implement PSVC for other PWM processors like the TAS5066 and
TAS5076, contact the Texas Instruments digital audio applications team.
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Old 11th July 2007, 11:16 AM   #8
djk is offline djk
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The amplifier in question is digital, it's just a power DA convertor.

The patent was purchased by TI from TACT.
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Old 11th July 2007, 05:43 PM   #9
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What your really thinking about is Class H where the supply tracks the rails with just enough headroom for best efficiency of a Class AB but no clipping. The gain is then fixed and the supplies adjust for the output required. You can adjust the voltage supplies for volume control but then you also need to adjust the gain of the amp to match. Seems like adjusting two things instead of one will only result in more complication and lower performance. Except for a Class D type of design I don't think there is anything to gain from such an approach.

-SL
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