Full Digital Amplifiers with PSVC (Power Supply Volume Control)

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Hi,
According to TAS5558 datasheet:
The TAS5558 supports volume control both by conventional digital gain/attenuation and by a combination of digital and analog gain/attenuation. Varying the H-bridge power-supply voltage performs the analog volume control function.The benefits of using power-supply volume control (PSVC) are reduced idle channel noise, improved signal resolution at low volumes, increased dynamic range,and reduced radio frequency emissions at reduced power levels.

The TAS5558 also features power-supply-volume-control (PSVC), which improves dynamic range at lower power level and can be used as part of a Class G Power Supply when used with closed-loop PWM input power stages.

I wonder is there any examples of Full Class D amps which implemented this (or similar) concept on volume control stage? I think this concept overcomes one of the big concerns in audio when used with full digital amps.
 

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One of the earliest Full Digital Amps did this over 20 years ago - the TacT Millennium : SoundStage! Equipment Review - TacT Millennium Digital Amplifier (6/1999)

But if you output a steady voltage, how do you handle the volume? Not without reason have digital volume controls been looked upon with suspicion. You actually need an awful lot of bits to implement them without a very real loss of resolution. Well again, TacT has come up with a very clever solution. Since the output voltage is fixed from the power supply during replay, they simply vary the power-supply voltage to the output stage. Thus, the volume control is not in the signal path at all. Neat.
 
I'm pretty sure I had the SA-XR25, which did this also.

Remember, volume is logarithmic - so the power supply voltage is going to go down quickly - perhaps down to the minimum the amp chip runs at - then digital to get to zero volume.

If you can live with whatever the lowest volume level is - any lower than that is off - then perhaps you can do just the power supply voltage technique. Unsure if the voltage feeding the class D bridge tied load is separable from the rest of the amp's circuitry.

Of course most consumers would expect the control to work just like the analog counterpart.
 
One of the earliest Full Digital Amps did this over 20 years ago - the TacT Millennium : SoundStage! Equipment Review - TacT Millennium Digital Amplifier (6/1999)

But if you output a steady voltage, how do you handle the volume? Not without reason have digital volume controls been looked upon with suspicion. You actually need an awful lot of bits to implement them without a very real loss of resolution. Well again, TacT has come up with a very clever solution. Since the output voltage is fixed from the power supply during replay, they simply vary the power-supply voltage to the output stage. Thus, the volume control is not in the signal path at all. Neat.

It seems TacT did that due to absence of high quality digital attenuators during that time of period.

If you can live with whatever the lowest volume level is - any lower than that is off - then perhaps you can do just the power supply voltage technique. Unsure if the voltage feeding the class D bridge tied load is separable from the rest of the amp's circuitry. .

You mean, pot controlled any adjustable reg (LM317, LT3045 etc) can do without involving any digital stuff, control registers etc? I think covering reasonable listening levels are just enough.
 
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I was actually thinking about this fairly recently. I'm really new to audio but currently building a TAS5805 based fully digital DAC/amplifier with a STM32 handling the USB Audio device 1.0 to I2S conversion at 96kHz/24-bit.

The STM32 has a 12-bit DAC output, and I was thinking of adding a buck converter to the input and biasing the voltage control feedback with the MCU DAC. Would be a pretty nice and efficient way of doing this. The TAS 5805 should work down to 4.5 V. From there the STM32 could switch over to updating the gain setting of the TAS3805.

The first board spins already in the mail to me right now, but i the next version I'll definitely look into this.
 
Hi,
I think this concept overcomes one of the big concerns in audio when used with full digital amps.


The dynamic range of the music signal is limited by the noise in the music room.
Therefore, there is no urgent need to reduce the supply voltage while reducing the listening power. Especially if you have a real dynamic range of 106dB in the amplifier.
I am listening to a class D amplifier with a digital input with a real measured dynamic range of 107.5dB in a residential area and I do not hear any noise from speakers more than 20cm away from the speaker.


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I was actually thinking about this fairly recently. I'm really new to audio but currently building a TAS5805 based fully digital DAC/amplifier with a STM32 handling the USB Audio device 1.0 to I2S conversion at 96kHz/24-bit.

The STM32 has a 12-bit DAC output, and I was thinking of adding a buck converter to the input and biasing the voltage control feedback with the MCU DAC. Would be a pretty nice and efficient way of doing this. The TAS 5805 should work down to 4.5 V. From there the STM32 could switch over to updating the gain setting of the TAS3805.

The first board spins already in the mail to me right now, but i the next version I'll definitely look into this.

Please keep update the thread with the progress.

I am listening to a class D amplifier with a digital input with a real measured dynamic range of 107.5dB in a residential area and I do not hear any noise from speakers more than 20cm away from the speaker.

I think the concept not about hearing the noise floor or not. With this concept, you attain an analog like volume control without touching the input signal. This is what I find interesting.
 
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