Adding some bass boost to a TDA2003 - diyAudio
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Old 12th September 2012, 07:26 AM   #1
HiZ is offline HiZ
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Default Adding some bass boost to a TDA2003

Hi!

Advice from another part of this forum suggests by best option for improving the bass on my retro radio (now fitted with TDA2003 circuit and airport express) is to add some eq rather than physical changes.

I've used a bass boost and small speakers default eq setting in itunes and its much better. How do I go about adding this modification to the TDA circuitry so its permanent?

Im using the standard design circuit and opted to lower the gain by replacing R2 with a 56R. So the gain is now 220/56 which is great for my small driver and line level audio from the airport express.

Can I simply add a cap across R1 to reduce -ve feedback at higher frequencies or am I better to add some mid-trebble reduction on the front end?

Sample circuit ued here http://www.datasheetcatalog.org/data...cs/mXutuqt.pdf and in my case, Cx & Rx are not fitted.

A sample circuit or advice much appreciated!

Thank you.
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Old 26th February 2013, 04:44 PM   #2
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HiZ,

I think that it it is possible to boost low end in standard TDA2003 application circuit by using more than 1000uF at output, say, 4700uF, or even more, and to put 10uF, or more, at input.

This power IC is of the current feedback topology and in my opinion, the bright sound, which I like, is the consequence of that topology. It is made for car audio and is not intended to give full bottom end.
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Old 26th February 2013, 05:44 PM   #3
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In the ST datasheet, there is a note to add some bass boost consisting of a resistor in series with a capacitor, both placed across the feedback resistor. You can try different cap values, but in some combinations with feedbak resistances can broke into oscillations at high frequencies.

See this at
TDA2003 datasheet - 10W Car Radio Audio Amplifier
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Old 27th February 2013, 12:10 PM   #4
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"Sample circuit ued here http://www.datasheetcatalog.org/data...cs/mXutuqt.pdf and in my case, Cx & Rx are not fitted"

If I read the data sheet correctly,
removing RX (essentially making it bigger) = danger of oscillation;
removing Cx (essentially making it smaller) = wider bandwidth.

So my three penny worth = you have a LW transmitter going there, and this WILL make it sound bright. I'd try putting those components back even if just to try temporarily....

Do you have oscilloscope etc to test for oscillations, if you have, use probe on x10 NOT x1 to check. x1 has sufficient capacitance to "hide" oscillations.....
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Old 27th February 2013, 12:17 PM   #5
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Quote:
Originally Posted by blu_glo View Post
"Sample circuit ued here http://www.datasheetcatalog.org/data...cs/mXutuqt.pdf and in my case, Cx & Rx are not fitted"

If I read the data sheet correctly,
removing RX (essentially making it bigger) = danger of oscillation;
removing Cx (essentially making it smaller) = wider bandwidth.

So my three penny worth = you have a LW transmitter going there, and this WILL make it sound bright. I'd try putting those components back even if just to try temporarily....

Do you have oscilloscope etc to test for oscillations, if you have, use probe on x10 NOT x1 to check. x1 has sufficient capacitance to "hide" oscillations.....
Yes, buy it not only depends on the RX CX network, in fact the ap works pretty well without them, but the important fact is to pay attention to the minimum gain the IC needs to be stable, if i'm not wrong, I believe 30dB minimum. Try a bigger gain, and then, the compensation network to give bass boost you want.
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Old 27th February 2013, 01:22 PM   #6
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Quote:
Originally Posted by Osvaldo de Banfield View Post
Yes, buy it not only depends on the RX CX network, in fact the ap works pretty well without them


- Have you measured to confirm this?

but the important fact is to pay attention to the minimum gain the IC needs to be stable, if i'm not wrong, I believe 30dB minimum. Try a bigger gain, and then, the compensation network to give bass boost you want.
- Quite right in fact the bass boost resistor should be calculated to give the >> 20dB then the overall feedback resistor could be calculated from that value!
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Old 27th February 2013, 01:46 PM   #7
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Quote:
Originally Posted by blu_glo View Post
- Quite right in fact the bass boost resistor should be calculated to give the >> 20dB then the overall feedback resistor could be calculated from that value!
Measured what? If the amplifier works without this network? I can affirm yes, I have 3 of them working almost every day from since 12 years to today.
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Old 27th February 2013, 06:13 PM   #8
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Well, measure distortion and noise for starters! Any how if it sounds right to you and lasted 12 years there can't be much wrong .

Just a question - you write "there is a note to add some bass boost consisting of a resistor in series with a capacitor, both placed across the feedback resistor" but I see no mention of this in the datasheet suggested apart from Rx/Cx and the break frequency of these is approx. 105kHz - hardly what I call BASS boost.....
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Old 27th February 2013, 06:16 PM   #9
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BTW, I think the OP has long moved on - we've both been answering an old post that only popped up because ivanlukic answered it!!!!
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Old 27th February 2013, 06:28 PM   #10
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Quote:
Originally Posted by blu_glo View Post
Well, measure distortion and noise for starters! Any how if it sounds right to you and lasted 12 years there can't be much wrong .

Just a question - you write "there is a note to add some bass boost consisting of a resistor in series with a capacitor, both placed across the feedback resistor" but I see no mention of this in the datasheet suggested apart from Rx/Cx and the break frequency of these is approx. 105kHz - hardly what I call BASS boost.....
Because you may play with the values of such materials to lower the 105KHz pole until the newer you want. Each time you multiply the cap by a some constant, call us it "a", the frequency limit will decrease a times. Then, the gain at the corner will be defined by parallel Rx and Rf, and with Ri at higher frequencies in which the Cx value can be neglected, and Rf and Ri when it isn't.
I refer Ri the resistor from inverting input to ground, and Rf the R from output to inverting input of opamp.
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