Hi everyone,

I'm Antonio from Italy and I'm quite new to this foru and electronics in general, so please forgive me if I'm making some basic mistakes.

I'm converting an old, non-working Commodore 1541 5.25" floppy drive into a self-contained audio player.

Inside it I have installed:
-a Pioneer IDE CD/DVD-ROM drive, used to play audio CDs;
-a small IDE CD-ROM audio controller with display and remote control;
-a TPA3118 mono Class-D amplifier;
-a small Bluetooth audio receiver;
-a 3.5 mm AUX input;
-a 3-position source selector to choose between CD / Bluetooth / AUX;
-an internal loudspeaker.

Everything is powered from a single switching PSU originally intended for an external hard disk. It provides:
+12 V / 2 A
+5 V / 2 A
common GND

The CD-ROM uses both 12 V and 5 V. The amplifier is powered from 12 V, while the controller and Bluetooth board use 5 V.

I have attached some pictures of the components and a hand-drawn diagram of my current power wiring.

The problem
Everything works, but I have significant noise problems.
There are three situations that may help identify the problem:

1. AUX input selected with nothing connected
If I select AUX while there is no cable/source connected to the 3.5 mm jack, I get a very loud hum/noise from the speaker.
When a cable/source is connected, the noise disappears or is greatly reduced.

2. Noise when the CD-ROM is running
When the CD-ROM motor starts spinning or is reading a disc, I can clearly hear interference/noise through the speaker.
This happens even when another audio source is selected, for example Bluetooth or AUX.

3. Noise even when no input is running to the amplifier, I can still hear some noise from the speaker.

I'm very new to electronics and I don't own or know how to use an oscilloscope, so I'm having difficulty understanding where the noise is coming from.

I fear I may simply have made some basic mistake in the way I connected the power supplies, grounds or audio signals.

Could someone have a look at my wiring diagram and suggest how I should troubleshoot this?

If necessary, I can also draw a more detailed schematic showing exactly how the audio connections and the 3-position source selector are wired.

Thanks in advance for your help!
Antonio
Attachments

 

"NOISE" is quite a vague description ofan unwanted signal. HUM, BUZZ, and HISS are descriptive terms thatpoint towards sources. xz

 

After reading post #1 again, It seems like the problem would be load currents for the different devices flowing thru the same conductor. That would probably be the "common" supply connection, very often the black wire on a computer hardware power supply. Also it is called a "ground loop", which can be a confusing term.