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Portable Amplifier Volume control with decreasing battery voltage
Portable Amplifier Volume control with decreasing battery voltage
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Old 29th November 2019, 02:15 PM   #1
JonRosko is offline JonRosko
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Default Portable Amplifier Volume control with decreasing battery voltage

I'm thinking about creating a lithium battery powered portable amplifier using one of the cheapo class-D amplifier boards from parts express. The only thing that trips me up is the decreasing battery voltage affecting the volume output of the amplifier over time.

Off the top of my head I can think of 2 strategies for dealing with the issue:

1. Use a DC-DC converter to supply a constant voltage to the amplifier regardless of battery voltage.

2. Implement some sort of micro controller active variable gain or digital volume controller to increase the gain/volume as the batteries drain.

I'm not sure how commercial portable systems overcome this, but I was wondering if anyone here has some thoughts or knows what might already be the standard solution for what seems to be a fairly ubiquitous engineering challenge.
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Old 30th November 2019, 01:09 AM   #2
Mark Tillotson is offline Mark Tillotson
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Full charge 4.2V/cell, drained 3.5V/cell, ratio is 1.2, about 1.6dB of reduction.


Strategy 3: Don't worry about it, 1.6dB isn't a big deal.


Strategy 4: Use LiFePO4 chemistry, much flatter discharge curve, many more recharge cycles.
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Old 30th November 2019, 01:16 AM   #3
rayma is offline rayma  United States
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The output voltage clipping level will decrease with decreasing battery voltage, but not the gain.
Increasing the gain with decreasing battery voltage would just make the amplifier clip more often.

Last edited by rayma; 30th November 2019 at 01:18 AM.
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Old 30th November 2019, 01:40 AM   #4
Mark Tillotson is offline Mark Tillotson
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Depends if its an open-loop or closed-loop class D.
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Old 30th November 2019, 02:00 AM   #5
JMFahey is online now JMFahey  Argentina
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You are not analyzing theproblem the proper way.
Quote:
Originally Posted by JonRosko View Post
I'm thinking about creating a lithium battery powered portable amplifier using one of the cheapo class-D amplifier boards from parts express. The only thing that trips me up is the decreasing battery voltage affecting the volume output of the amplifier over time.
No, it will affect *maximum possible* volume output, at clipping.
A terrible way to use an amplifier so donīt, whether with full or discharged batteries.ou must always use the amplifier at *less* than maximum power.

Quote:
Off the top of my head I can think of 2 strategies for dealing with the issue:

1. Use a DC-DC converter to supply a constant voltage to the amplifier regardless of battery voltage.
No need to, because amp must be sized so as not to clip under normal use.

Quote:
2. Implement some sort of micro controller active variable gain or digital volume controller to increase the gain/volume as the batteries drain.
Gain does not decrease on lower supply voltage, and increasing gain will send amp into clipping, as Rayma said.
Quote:
I'm not sure how commercial portable systems overcome this,
They donīt because itīs not a realistic situation.
Quote:
but I was wondering if anyone here has some thoughts or knows what might already be the standard solution for what seems to be a fairly ubiquitous engineering challenge.
Specify a proper power amplifier, with a proper sized battery so it stands the duration of the event.

If battery noticeably dies during it, then get a larger capacity one.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
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Old 30th November 2019, 02:37 PM   #6
JonRosko is offline JonRosko
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Thanks for the replys guys. Really informative.
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