Tuning / tweaking TDA2003 BTL Hifi bass power amp

[Freedom666]

Tuning / tweaking of a Chinese BTL mode TDA2003 Mono amplifier.

It has some mediocre working Bluetooth 2.0 which I do not use.

If Bluetooth is needed I recommend a more modern 5.0 Bluetooth preamp.

I put on the electrolytics 0.1 microfarad foils in parallel. Also same size power decoupling foils between legs 3 and 5 of the TDA chips.

100picofarad on the inputs between plus and minus against oscillation.

There is an smps power supply I left untouched.

I put 1.3 microfarad and 4.5 ohms paralleled in line with the 4 ohm loudspeaker in order to attenuate a fullrange driver and to lower distortion by using Esa Merilainens simple resistor method for a bit current drive. More on this on his website current drive info.

 

[Freedom666]

Added 2x100 microfarad on pins 3 and 5 of TDA2003 chips for better decoupling.

 

[Freedom666]

Added to another board some foils for the smps electrolytic, too. For the 400 volt 10microfarad type an x2 type mkp 275 volt 0.22 microfarad.

 

[Freedom666]

External wall wart 2.5ampere 12 volt had less hum than the internal on board smps.

And sounds better

 

[Freedom666]

On the output the ohms are reduced from 4.5 to 0.8 ohm as this reaches the aim of lowering distortion of the loudspeakers sufficiently.

 

[abraxalito]

470uF decoupling on a chipamp is a bit small if your aim is to clean up the sound, try 100X that if you have enough room.

 

[Freedom666]

This small amp has 1000 microfarad in the power supply. But no decoupling caps on the chips like described in the data sheet.

There is a smps power supply on board.

A test on another chip amp with smps wall wart showed more distortion with higher capacitance. So I just added 2x 100 microfarad for the chips directly at their legs.

 

[abraxalito]

There is a smps power supply on board.

A passive filter (LC) between that and the amp chip provides a nice improvement in my experience. SMPSUs tend to have several tens of mV of ultrasonic noise at their output, as a minimum.

 

[Freedom666]

Would have to check the schematic for that, cut traces to add components. If it's too noisy I use external wall wart.

However I like this amp as it has USB input for a music stick. Smartfone can be connected via cable.

 

[Freedom666]

Second Hifi Bass Power amplifier in use now.

Depends on the smartfone if you manage to connect to the 2.0 Bluetooth of this mono mini amp.

https://www.diyaudio.com/community/...loudspeaker-sandwich-cone.402917/post-7536566

 

[Freedom666]

That's the chip inside, manufacturer is Huajing Microelectronics

 

[Freedom666]

Listening test with and without 0.8ohm with 1.5 uF wima mks shows that it has sonic benefits putting a resistance in series to the driver.

Directly coupled amp plays a bit louder.

With the series network distortion goes audibly down.

 

[Freedom666]

I have the same marble box with the same loudspeaker drivers with identical amplifier.

But with 2.5 ohms in series to the loudspeakers instead of 0.8 ohms.

The 2.5 ohm version sounds more tube like (in a positive way). There is less distortion and a "bigger" sound. But at the expense of some lost watts in the output.

 

[Freedom666]

After some time my smartfone now connects very well to the Bluetooth 2.0 Hifi Bass Power Amp. It starts even automatically the music player in my Huawei smartfone. Nice.

The ohms in line with the speaker could be provided with a parallel switch taking it out if all the power from the small amp is needed to get it as loud as possible.