Repurposing wooden amplifier box

Joined 2021
Paid Member
Hi there.

I got a used wooden amp box cheap, 7USD. It has a TDA2030a for the bass and it worked in a test when I moved cables, the main output is burnt, shorted speakers were connected.

I found it interesting because it has a 4th order band-pass in the box. I hadn't seen it before, but I hadn't seen too much so maybe this is common. The back of the speaker in the photo is isolated with the sealed part. I couldn't find similar devices it with image searches nor with the model in the label.

The transformer gets hot, wondering if it's because something's shorted in the board. I'll test in a few days.

I think I'll try using a TDA7850 for 2 full range drivers and 2 tweeters and a Tpa3118 for the speaker that came in the box. I watched this review for the TDA7850 and by reading the datasheet I think that by pulling less watts and using 8ohm it could sound good.

I could build another front panel and reuse the glass if I put a Raspberry PI I have around, with display.


Thoughts welcome.


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Last edited:
Joined 2021
Paid Member

One restriction is that if I change the volume of the transformer too much I will ruin the computation of the bandpass.

I noticed that I could get used toroidal transformers here with a 30 day warranty. Price was good. So I grabbed two and a smaller one.

I have a switched power supply that is dead silent with a FOSI TPA3116d2 but full of noise/hum with the simple board I have for the TDA7850. That one could be external.

I've been studying theory and doing simulations of different alternatives of ripple removal. Also used linear regulation with capacitor bank and only a little Hun left but not enough.

More work to do. I also got a lot of noise when the laptop that has the DAC was on power with the TDA7850. None with the TPA3116d2.

I know I hace a very cheap board and I cannot expect much. Using the class D would imply less work but I want to make the AB work.

Also learning new stuff such as how to simulate a capacitor multiplier has been fun.


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Joined 2021
Paid Member
Hi again. I had luck with a capacitance multiplier + linear regulator, TDA7850 has no noise. Quite silent, at least playing from the phone.

I measured the 4th order band-pass with no eq. Graphs follow. I could use the enclosure space for electronics and use an external sub.

It would be nice to keep the 4th order band-pass working though... Would you?

Port 1/48:


50cm 1/48: