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I have a analog amplifier like device that uses USB for power via a standard USB-A male cable. I also have a variable 0-16v power supply.

My goal is to adjust the volume of the output, by adjusting power to the driver by the variable power supply and wondering if there are any suggestions as to the best way to go about it.

I have looked for a female USB A to power cables but so far haven't found any by a couple search terms. e.g. "usb to pigtails bare wire" UPDATE: I made one using this approach male to female extension, with male cut off, only red and black wires are needed for power which I later tinned and hooked to the powersupply via alligator clips, the data wires I just cut off, i used a sharpie marker to indicate which side is negative on the connector male to female extension cord, with male end, cut off, only outside 2 wires, red and black wires are needed for power

My current best thought is to take a USB extension cable and cut off one of the ends, strip the wires and then either use alligator clips to the power supply OR insert a variable resistor between the power output and the amplifier/transducer.

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  • \$\begingroup\$ Note: To draw more than 100mA, you're supposed to negotiate the power draw with the USB host (by using the data lines). However, most hosts don't actually enforce current limits. \$\endgroup\$ – immibis Sep 27 '15 at 1:04
  • \$\begingroup\$ Do you have the schematic for this appliance of yours? \$\endgroup\$ – Nick Alexeev Sep 27 '15 at 1:06
  • \$\begingroup\$ You can just cut off a cheap USB cable and use the two outer wires. Make sure you get the polarity correct. There is no guarantee the device will not immediately fail (be destroyed) if you feed it more than 5.5V or so, nor is it guaranteed to operate at low voltage. \$\endgroup\$ – Spehro Pefhany Sep 27 '15 at 1:26
  • \$\begingroup\$ @immibis this isn't intended for actual USB computer control, there's no data, it just happens to use the USB for power making the laptop an overgrown wall wart :D \$\endgroup\$ – TroyWorks Sep 28 '15 at 17:07
  • \$\begingroup\$ @SpehroPefhany thanks that's approach I'm going to use, but I had to order an extension cable with female on one end in order to connect to the male USB. It's $10 so not worried about destroying it, and operating on undervoltage shouldn't really be a killer i don't think as others use/sell variable output voltage supplies with ultrasonic foggers meant for aquariums, fountains, and fogponics. \$\endgroup\$ – TroyWorks Sep 28 '15 at 17:10
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Adafruit sells an adapter, but it won't help you if the device itself can't accept or won't change its behavior with voltages above USB's standard 5 volts.

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  • \$\begingroup\$ ah good find, thanks! Pity I just placed an adafruit order but didn't occur to look there. I went with getting a couple "Usb extension cords" off amazon amazon.com/gp/product/… at about the same price and will lop off the head and expose the wires this time. \$\endgroup\$ – TroyWorks Sep 28 '15 at 17:06
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Increasing the power supply voltage probably won't change the gain of your amplifier. It very likely has some kind of regulator and all increasing the supply voltage will do is waste power.

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  • \$\begingroup\$ Even if it doesn't have a regulator, which is also likely, it still won't change the gain. Only the headroom. The gain is set by the feedback circuitry inside the amp itself (most of the time) and must be a specific value to ensure stability. Thus, even the volume control on an amp is really a separate thing ahead of the amp itself, which still has a fixed gain. \$\endgroup\$ – AaronD Oct 21 '15 at 20:16

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