TDA2030 bass amp - distortion and noise - diyAudio
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Old 2nd July 2014, 01:29 AM   #1
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Default TDA2030 bass amp - distortion and noise

Hey.

So I have built a TDA2030 bridge amp while completely following the schematic in the datasheet. I works pretty well when I play some music from my cellphone or when I plug in a guitar, but when I plug in my bass, the sound is pretty distorted when playing low notes. It improves a bit when I turn the treble knob all way up, but otherwise it distorts. Just for the record - when playing some music from the phone, if there is some more prominent bass in the song, there is distortion again.

This is when plugging in any device directly, with no preamp or anything between the device and the amp.

I tried using a simple booster circuit made with a TL072 (I think) IC. Now the distortion gets even worse on the bass side. Additionally, when the booster circuit is turned near to the max, there is some nasty sound on the output, even when there is nothing on the input of the booster (the guitar is unplugged or just nothing being played). In attachments there is a short track showing the actual noise generated. Also, the same thing happened when I use a distortion pedal and turn it up even a little bit.

The speaker is definitely not the culprit. I use the 12V rails from a PC PSU to power the circuit. The max current on the -12V side is 0.8A (as from what's written on the PSU at least).

The chips are properly cooled.

I am unsure if this could be some grounding problem (I am using shielded cable on the input BTW), or just a bad power supply, or maybe a faulty board (I double-checked the connections though), so any help is appreciated.

Thanks!
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Old 2nd July 2014, 02:12 AM   #2
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A schematic of your setup would help!!
Can't tell anything from the recording only that it sounds like a fuzz box.

jer
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Old 2nd July 2014, 04:49 AM   #3
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800mA on the negative side isn't enough. You don't mention the speaker impedance but since it's a bridge amp, each amp sees 4 ohms with an 8 ohm speaker, requiring approx 2A from the supply.

Last edited by jerluwoo; 2nd July 2014 at 04:59 AM.
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Old 2nd July 2014, 01:33 PM   #4
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Thanks for the answers!

The schematic I used: Screenshot by Lightshot

It's an 8 ohm speaker.I measured the current on the -12V line while the amp was at peak volume - it exceeded 1A. The exact voltage while zero load on the -12V rail is ~ -11.2V and it dropped by ~0.5V when loaded.
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Old 2nd July 2014, 02:02 PM   #5
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You used that exact circuit? You didn't change some of the capacitor values, and now you wonder why there's distortion when you use it as a bass amplifier?

Datasheet circuits are illustrative and often not suitable for practical use. This circuit is the perfect example of that. All the TDAxxxx datasheet circuits that I've seen suffer from the same deficiencies. The fix is easy.

Calculate the poles for C2, C6, and C1. Then you will know why your circuit isn't performing the way you want.
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Old 2nd July 2014, 02:28 PM   #6
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The pole for C2-R2 and C6-R7 is 10.6 Hz. This assures sonic intrusion (distortion) all the way up to 106 Hz. And if C2 and C6, and R2 and R7 aren't matched perfectly (which I can assure you they're not), even greater amounts of complex distortion will be introduced.

The pole for C1-R1 is 7.2 Hz, which assures sonic intrusion to 72 Hz. This is a very poor aspect of this design too.

To mitigate distortion from C2-R2 and C6-R7, you want the pole for C1-R1 to be significantly higher. You want that pole to be the dominant pole. So you see, this schematic wasn't very well thought out at all; the feedback poles dominate.

I didn't learn all this in engineering school. They didn't teach these concepts, at all. I had to figure all this out on my own (with a little help from Walt Jung ). Maybe that's why there's so much mediocre equipment out there. As far as the TDAxxxx devices, they're very popular in industry and I always see the datasheet circuits employed; even though it's super easy and super cheap to greatly improve them. There's a guy here named Daniel that has fiddled with these devices extensively. Hopefully he'll chime in.
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Old 2nd July 2014, 02:49 PM   #7
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Thank you very much for the analysis!

As you might suppose, I still have no idea what changes to do to the circuit to make it perform well, so if anyone could give me a hand, I would greatly appreciate it.

Thanks!
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Old 2nd July 2014, 03:25 PM   #8
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I just pointed out what's wrong with the circuit.

Didn't you understand my analysis? I made it as simple and straightforward as possible.
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Old 2nd July 2014, 03:36 PM   #9
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Well I am not particularly knowledgeable in this very area so I can't possibly figure out which of those caps/resistors need to be changed and the values of the new components...
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Old 2nd July 2014, 05:58 PM   #10
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Oh come on. I already explicitly stated which caps were causing the distortion, and why. Go back and read what I wrote, and then tell me which caps are the offenders and how they are introducing distortion into the circuit. Show me that I'm not wasting my time, and I'll come back and tell you what values to use, a few more critical components to change to reduce distortion even further, and the analysis of the newly configured circuit.

The components will only cost a few dollars, but the engineering fee is going to cost you dearly (just kidding).

I don't like spoon feeding people. I do like teaching people, though.

The fact that you actually have the circuit functioning means that you're halfway there.
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