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Author Topic: Help with TDA2003 amp, a big project.  (Read 532 times)

Victor Van Dort

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Help with TDA2003 amp, a big project.
« on: November 03, 2017, 04:18:29 AM »

Hello guys, my first post here.
I want to realize a big little amp for practice for my electric guitars.
After some mini amp I would like to build something louder. I found this mini amp:

None schematic, but I know it based on TDA2003. I already built a Triple Wreck to use as hi-gain channel, but also a Tonemender to use as clean channel. I like both when I tested them with the guitar and my main guitar amp.

Now I built the TDA2003 power amp taken from the last part of this schematic:

Of course, I have omitted the input stage.

But, testing the TDA2003 circuit I have many problems. I partially shielded with tinfoil.
I connected the circuit with a cheap homemade cab with a guitar speaker 8", 8 Ohm, 15w.
The PSU is a 12v 3A.

1. Too much hum when I increase the volume.
2. Some ground problem, I guess, I feel through my fingers a kind of... tingle? when I touch the hardware of the guitar as well as the strings.
3. I wanted a clean amp, but this start to clip too soon. At max I got about the distortiom of a LM386, and not more volume then my Noisy Cricket (LM386 based).

Need help.

Thank you!


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Re: Help with TDA2003 amp, a big project.
« Reply #1 on: November 04, 2017, 12:39:00 AM »

No amount of shielding will fix a noisy power supply. Try running the amp from a 12 Volt battery. Next, measure the Voltage to ground from each IC pin and post the results here.

Victor Van Dort

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Re: Help with TDA2003 amp, a big project.
« Reply #2 on: November 04, 2017, 04:02:14 AM »

I don't have 12v battery. Can I use a 9v as well? At least about the noise.

Update: Tried the 9v battery. No noise, just a bit of hum, but it still oscillate when the pot is over the half and when the volume guitar pot is to zero. Because the flying connections of the clips and wires I didn't shielded it with the tinfoil this time.

Tried to put in front of it a Fetzer Valve or a Woody Acoustic Simulator. No changing about oscillating. It still too much distorted at half volume.
« Last Edit: November 04, 2017, 05:25:15 AM by Victor Van Dort »


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Re: Help with TDA2003 amp, a big project.
« Reply #3 on: December 01, 2017, 09:29:42 AM »

A 9v battery doesn't have enough capacity to power that amplifier, that's why it oscillated.

What you need is to connect the "negative" wire from the power supply to ground. Your power supply either uses one of those 2-prong outlet plugs, or the negative isn't grounded, to keep the 12v "floating" (aka isolated from ground references), which isn't something you really want for audio.

Either get a proper 12v 7Ah sealed battery for your tests, or find a way to ground the negative of your power supply.


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Re: Help with TDA2003 amp, a big project.
« Reply #4 on: December 03, 2017, 01:26:45 PM »

At 9V, the chip would have less than 2W of output with an 8 ohm speaker (isn't even on the datasheet), so it really cannot be than much louder than a LM386 based design. Also, the input sensitivity is in the 100mV range and your preamp probably delivers much more, so these two things explain the output and the distortion. Oscillations might then also be coming from long flying leads and high gain.

Victor Van Dort

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Re: Help with TDA2003 amp, a big project.
« Reply #5 on: January 11, 2018, 06:54:09 AM »

Hi, I'm sorry for the long pause.
This project, the power amp section at least, it's became enough hard.

Ground noise: Attaching the ground wires with the clip alligator in the same spot I reduced the hum and cancelled the oscillating. I also tried to shield the circuit with a tin foil.
PSU: I tried an alternative 12v PSU, that of my external hard drive for test, this more than else it's been what is really reduced the hum. But I still got distortion.
Then I tried another PSU of 15v. Slightly more volume, but still distortion.
Gain resistor: I encreased the R8 (if you look the schematic above) from 2.2R until 10R. I got a sound enough clean, finally, but I reduced the volume. (I even lost some treble, but I guess I can encrease the high acting on R7).

Now the problem is the PSU.
I want to use a 18v PSU for more headroom and volume, and the speaker is 8 Ohm, the only one I can use. I didn't find out how much will be the current draw though I read the datasheet. It's really hard for me to find a right PSU, 18v, a lot of Ampere, the right jack, low noise.

The PSU of a laptop could be really really good, theorically, because usually work at 18-19v, them can have even 4-5 Ampere, but I don't have a my own to test, I should to found one with a Boos pedal style plug, and I can know just after I bought if it's silence beacuse, of course, the PSU laptop are made for laptop and not for audio.

My only hope is a 18v PSU, apparently made for pedals (and I hope low noise), right plug, 2000mA. So this is the reason I want to ask about the consuption about whole amp. I predict that the two channels, the relays, and a buffer in front and a 78L09 regulator will be no more than 300mA.

Thank you!


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Re: Help with TDA2003 amp, a big project.
« Reply #6 on: January 12, 2018, 08:04:56 AM »

Katoda has already given you the reason for distortion. That chip will never be able to do clean if the input is too large. You need to reduce the input signal otherwise it will just distort.
A simple voltage divider will do that,, an internal trim pot is a variable voltage divider so set it to a level that gives clean and close the lid,, that is the best you will get out of such a small chip.
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