A simple bridged TDA2003 Amplifier

Discussion in 'The Projects Forum' started by Fenris, Nov 24, 2008.

  1. Fenris

    Thread Starter Active Member

    Oct 21, 2007
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    Hi all

    I could do with a little bit of advice please. Now I know the TDA2003 chip is not the best thing in the world to be using but it is what I have and up to a point its working fine in a bridged format. @12V I believe I am getting around 11W into a 4ohm speaker. to test the unit out I am using a 12V battery an mp3 player and a 4ohm speaker. The problem is, without input there is a lot of 'white noise', or hiss, present so the input of audio has to be cranked a bit to be heard 'just' above the noise but is present and can still be heard whatever increase I apply to the input. Ideally I will be putting line level input if I can clean up the noise a bit. Is there a way of depreciating the hiss? is it sound to noise ratio related even though it is present without input. Here is the schematic I used and the PCB I drew up from the awful online PDF image of the PCB. All capacitors are polyester except C5 which is a large green mylar I think. R1 is made up of 2 values as I didn't have the exact value and the electrolytic is the correct value. I know with the simplicity of the circuit there are bound to be sacrifices but if it's possible to tweak it to 'good enough' I will be happy.

    regards

    Fenris
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    Your circuit has no negative feedback. So its voltage gain will be many thousands, is noise output will be high, its high frequency response will be nothing and its distortion will be horrible.
    C5 and C6 need a 1 ohm resistor in series as shown on the datasheet.

    The elec-free site has another circuit with bridged TDA2003 ICs and more parts but I don't know if it works.
    Cana-kit has a kit with more parts than you have but I couldn't find a schematic.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    I am sorry to double-post but I found your circuit in a datasheet from ST-Micro and a slightly different circuit on a datasheet from Contek. They call it a low cost circuit but they both show a better circuit.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Here you go:
    http://datasheet.digchip.com/670/670-00274-0-UTC_TDA2003.pdf
    Look at the top of page 6. You should be able to mod your board to incorporate the extra components.
    [eta]
    Never mind - the datasheet I posted is a Unisonic equivalent TDA2003, but has the exact same schematic that AudioGuru posted just before I did.
     
  5. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
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    So the circuit basically is beyond reasonable hope? I thought it might be to good to be true :( This resistor in series with C5 and C6, is it strung between the GND of both or are they both attached to one end of the extra resistor which then goes to GND? I have an EPE mag Vol 31/No5 that has a special on audio amplifiers one of which is a bridged TDA2003. 18 components all up a clear PCB pattern which I have duplicated ready to make my own PCB of it. I will fall back on this if the current circuit is untenable. Its a shame because what I was looking for was a compact circuit. The possible replacement is a lot bigger than I wold like but beggar's can't be choosers :D

    Just spotted your posts thank you both I will look into this. Perhaps the compact amp is still in the running :D

    regards

    Fenris
     
    Last edited: Nov 24, 2008
  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yes....in fact it could be in an actual state of oscillation, which could cause ALL the symptoms you're seeing. An oscilloscope is your best friend.

    eric
     
  7. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    One day I will own an oscilloscope............until then it's fingers crossed :D

    regards

    Fenris
     
  8. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi All

    Having looked at my first PCB and the slight differences with the new schematic circuit I took the plunge and with a little bit of shoe horning and tweaking I have been able to relatively easily make the required changes. The new PCB is slightly larger but still small enough. I must look into better heat sinking though.
    Heres a pic of old and new. Thanks for the heads up again guys.

    regards

    Fenris
     
    Last edited: Nov 25, 2008
  9. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi all I'm just getting together an order for some components including those I need to make the bridged amp. The only small problem is I can't seem to find a 15uF electrolytic cap from my supplier. Is there a nearest value I can get away with? or would a tantalum bead be OK as I have found these @ 15uF although I think I may be mistaken in these having a polarity despite them having a + mark on one side? R1 is also unmarked in the schematic as far as value goes but I am taking a 'semi educated' guess that R1 and C5 are a Zobel network? Looking at the datasheet the similar pairing of these 2 on a single chip amp suggests a 1 ohm resistor. Thanks in advance.

    On a separate point I noticed the 'simple schematic' on the data sheet which I am using as suggested to build the circuit that is above it has the 1nF cap in between the 15uF cap and the 620 ohm resistor whereas in the failed version I tried based on a similar diagram had the 1nF cap between pin2 of the TDA2003 and the 15uF cap. Is this why it may have failed?

    Found some 15uF caps :D so it's just the resistor to clarify please.

    regards

    Fenris
     
    Last edited: Nov 25, 2008
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Fenris,
    The big reason your original amp had noise is because the amplifiers were running open-loop gain.

    One thing left in question is the value for the resistor in the Bucherot cell connected on pin 4; it's not indicated in any of the schematics I've found for similar designs. You could try 1 Ohm and see how it works.
     
  11. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Thanks Sgt :) I have googled it as well and partially understand what it is supposed to do. Values between 1-10ohm seem to be the normal range. Also the Wattage it can handle can be an issue. I hope a 1/4W is OK :D

    regards

    Fenris
     
  12. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
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    Further study has brought all the answers :D I just wish I could work it out
    myself rather than relying on other peoples intelligence :(

    regards

    Fenris
     
  13. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi all.

    Ok I got the new circuit built as per the schematic you guys put up for me.
    Being cunning I found a PCB pattern that was the same except for 3 or 4 extra components. I edited the pattern to reflect the removal of thes parts so the PCB pattern is in principle at least set up as was. I have built it as I said now I have a minor? problem. I have replaced both TDA2003 chips as I think initially something was wrong with one or both as there was a lot of noise present without audio. Now whats happening is only one of the TDA2003 is getting bloody hot (I may need a bugger heat sink any way) now with a pre amped mic attached I get output but it keeps cutting of in a cycle Is this because the built in safety of the chip (fine if it is) but why is only one chip getting hot? is this normal? The PCB has been checked from end to end and is correct to the schematic and so has the soldering all ok there. What is going on?

    regards

    Fenris
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    It would help a lot if you would post your PCB layout (also indicating parts placement), and the schematic that you used.
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    The old TDA2003 was not designed to be bridged.
    I would use a bridged amplifier IC like a TDA7240A instead.
    The simple schematic and a pcb design is in its datasheet.
     
  16. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi there

    Yes bit daft me expecting you all to be psychic :D Here is the magazine article I have marked the Items not used on the schematic and the PCB view. This in theory left the same 'pattern' of parts as used in the schematic you guys gave me. I have followed the values for components from 'your' schematic not the magazine article. See also 'your' schematic which I have numbered the parts of and my PCB pattern. The part numbers should follow 'your' schematic. Thanks very much.

    This is so annoying! I checked and checked and checked (as I said) once I stopped looking and asked for help I spotted the problem! Whats really annoying is I thought that the way the sound was behaving was like the cycle time of a capacitor. That is what I had wrong! C7 is round the wrong way and now I have corrected it the circuit runs great :D Now shall I just nail myself to the wall for target practice or would you like the pleasure?

    Hold hard! Something is still amiss. The other IC is getting very hot now and R3 is getting hot to the touch and is discolouring with it. a quick check shows the remaining caps are correctly orientated.

    regards

    Fenris

    PS Just dismantled a knackered TV set I have lots of big heat sinks now :)
     
    Last edited: Nov 27, 2008
  17. Audioguru

    New Member

    Dec 20, 2007
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    The power amplifier IC gets very hot when it is oscillating at a very high frequency.

    No wonder an IC is oscillating.
    Your circuit does not have the very important supply bypass capacitors. It also has the input ground connected to the ground pin of one IC instead of to a point near the power supply ground.
     
  18. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi There

    This amplifier lark is fraught with pitfalls! Having looked at the current PCB I can retro fit the electrolytic cap for the supply smoothing and the 2 poly caps by soldering them to the track side for now to 'get it going' . Interesting that the TDA2003 was never designed for bridging I assume they really had to compromise on the circuit design to do it? I have about 2 dozen of them to hand so I am just happy to play and try and learn what I can from the working and failing of the circuit. The way the input Gnd is connected is as designed by the EPE guys. I thought you had to try and keep the relative Gnd supply and Gnd input 'separate' by trace design. I have to admit that a lot of the reasons, explainations and so forth baffle me. I will try the retro fitted parts tomorrow morning and see if that helps and perhaps relocate the input ground onto the heavy Gnd trace. Thanks for your help Gentlemen.

    Just checked one of my suppliers..........they stock that chip you mentioned. I will order a couple to play with As well :D

    regards

    Fenris
     
    Last edited: Nov 27, 2008
  19. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi all

    Ok I have fitted the 2 poly caps (0.1uF) and a 220uF electrolytic cap as per the EPE schematic. A larger heat sink has been fitted though I think it may still be on the small side. Heat build up is now equal from both IC's but R3 is to my mind is far too hot for it's own good. So what's occurring was the 'simple' schematic assuming you new to smooth the supply? or what? I have a second PCB I etched at the same which I think I will load up as per the EPE parts spec and see what occurs. But any explaination of of the why's and wherefore's would be read with interest.

    Hi Again. I have built the EPE version of the circuit and it works! At least it did once I changed the 2 TDA2003's and the 220uF cap after I connected the battery to it the wrong way!!!! red faced here :D So other than tha fact that it has 3 extra components and the values them are different what went wrong? 20 minutes has elapsed and Adam and the Ants, Kings pf the wold frontier is assaulting the ears :) The heatsink is warm to the touch and no more.

    regards

    Fenris
     
    Last edited: Nov 28, 2008
  20. simasoft

    New Member

    Jan 30, 2010
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