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The goal
I am attempting to make a small diy bookshelf speaker system using 2 16ohm, 25 watt speakers and a 2x25 watt class d amplifier board. If it matters, the amplifier board is a class d amplifier.
The Problem
Using an rca to 3.5mm aux cable with the amplifier board, I receive a variance of voltage levels across the speaker terminals and volume level ranges (while playing a sine wave of 165khz) between different inputs. As a result I had to alter the gain levels for each input. If I kept a high gain level and didn't adjust it, some inputs would produce a little distortion and noise while others would produce a crazy amount of distortion and noise. Here are a couple of scenarios I've done.

  1. Plugging the aux into my phone, the voltage levels across the speaker terminals are quite low to begin with (when playing a sine wave of 165kz). The volume is also too quiet. As a result I increase the gain setting to medium which results in an adequate performance in terms of volume.
  2. Plugging the aux into my computer, the volume levels are adequate with only the low gain setting.

Why I think this is (so I can learn from this if I'm wrong)
Does this have to do with the level of voltage the input device is creating? For instance does the computer sound card produce a higher voltage output from the start, and therefore less gain (or input sensitivity) is needed to reach the level I want. By the same line of thinking, then the phone is producing a lower voltage level output, which results in me needing to increase the gain setting on the board.
What I'm hoping to be able to do
At this stage in my understanding, I don't know if there's a way to make the gain settings on the board more accessible so it can be changed on the fly later, when the board is in a case. The amplifier board is the AA-AB32165 from sure-electronics with two switches for gain settings. However, ideally I think it would be best that all inputs were leveled out to a "base" voltage level before getting to the amp so that the gain would never need to be set on the main amplifier. Adding to this ideal might be a way for the gain setting to be automatically altered according to the input level (if the input level is what is causing the difference in volume that I described earlier).


Thank you for your help and patience.

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  • \$\begingroup\$ A simple and decent unbalanced stereo line input with adjustable gain is quite easily accomplished with a dual opamp and a handful of passive components - can you read schematics, and do you have a breadboard? \$\endgroup\$ – Tyler Stone Mar 23 at 3:10
  • \$\begingroup\$ Standard Line input has always been around 1V, Match that and you won't have to make any changes \$\endgroup\$ – Sunnyskyguy EE75 Mar 23 at 3:30
  • \$\begingroup\$ Why are you testing it at 165 kHz? \$\endgroup\$ – Andy aka Mar 23 at 9:24
  • \$\begingroup\$ @SunnyskyguyEE75 I don't think you read my question. If it is the case that the laptop and the phone are both producing 1V line inputs why do they require different gain adjustments and have different loudness? That is the main concern of this question. \$\endgroup\$ – Walrath21 Mar 30 at 16:43
  • \$\begingroup\$ @Andyaka I just wanted a somewhat stable sound where I could easily perceive volume differences and distortion differences. \$\endgroup\$ – Walrath21 Mar 30 at 16:44

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