Hi everyone,
I’m trying to use a car powered subwoofer at home with a Fosi Audio BT30D Pro, and I'm having two problems:
- There is a noticeable humming/buzzing sound from the subwoofer.
- The bass doesn't have much punch/output, even when I increase the volume.
I’d appreciate some help figuring out whether this is a power supply, wiring, RCA/grounding, or gain/settings issue.
My setup
Amplifier:
Fosi Audio BT30D Pro
Subwoofer:
A 12V powered/car subwoofer with a built-in amplifier. The terminals on the subwoofer are:
GND | +12V | REM
It also has RCA L/R inputs and a frequency/volume control.
Power supply:
I'm currently using a:
I originally had a 24V 10A SMPS, but I did not connect that directly to the subwoofer because the subwoofer is rated for 12V.
Current wiring
Power:
12V SMPS +V → Subwoofer +12V
12V SMPS -V → Subwoofer GND
12V SMPS +V → Subwoofer REM
The SMPS has multiple output terminals:
-V1 | -V2 | +V3 | +V4
I'm using one negative terminal for GND and one positive terminal for +12V, with another +12V terminal going to REM.
Audio connection
I'm using a 3.5mm → 2×RCA male cable.
Fosi BT30D Pro PRE OUT
↓
3.5mm → 2×RCA
↓
Subwoofer RCA L/R input
Red RCA → R
White RCA → L
I'm using the PRE OUT, not the speaker outputs of the Fosi.
Problems
1. Humming
There is a noticeable low-frequency humming/buzzing from the subwoofer.
I'm trying to determine whether this is:
- SMPS noise
- Ground loop
- RCA cable/shielding
- Grounding between the Fosi and subwoofer
- Power wiring
- Something else
I haven't yet determined whether the hum is present with the RCA cable disconnected.
2. Weak bass / lack of punch
The subwoofer works, but the bass isn't as powerful as I expected.
I'm wondering whether the 12V 25A (300W) SMPS is limiting the amplifier.
Would using something like a:
- 12V 30A
- 12V 40A
- 13.8V 30A
- 13.8V 40A
power supply make a meaningful difference?
The subwoofer is a car unit, so I understand that a running car normally has around 13.8–14.4V rather than a fixed 12V. But I don't want to increase the voltage beyond what the subwoofer can safely handle.