Help!!!! Volume Control Using TDA8424 - Page 2 - Electronic Circuits Projects Diagrams Free

alvinyow · 14th June 2008, 04:20 AM

Quote:

Originally Posted by Mikebits

Hmm, Sounds like our doing the right stuff. Are you using point to point wiring, or pwb?
If point to point, the wiring is critical. Make sure all your analog signals are routed away from the digits. You have a good solid ground plane I assume. Do you have anyway to make sure your power signals are clean? I love my scope

The problem is i dun hv any scope to check if i had a clean power supply. I check the multimeter the 7912 had produce a voltage of -12.17 Whereas the posivite i got 12V. This two voltage is fall onto the balance-unbalance and vice versa. This could be the reason of noise introduce into the circuit. But before i intro these cct, i use to connect the signal directly to the TDA, the zipper sound is definitely there.
I think i do had a good solid ground plane. I read lots of article and this finally comes to my mind that a return signal needs to be as short as possible. Hence a good ground plane was incorporated onto my design.
Wat is pwb?

alvinyow · 14th June 2008, 04:22 AM

Quote:

Originally Posted by ronsimpson

The sound you hear may be the nature of the beast. Several digital audio volume control chips claim ‘ours don’t make a zipper sound’. Your ear should be able to hear a series of 1db steps.

Yes this is exactly wat i hear.

alvinyow · 14th June 2008, 04:27 PM

Quote:

Originally Posted by ronsimpson

Adding a resistor to the clock and a resistor to the data line reduces the current flow. I know the inputs are high impedance so there should not be current flow. I am talking about current (AC) on the edges of data and clock.

Take a look at PGA2500. I know of one high end mixer that uses them on the mic/line inputs as cores adjustment. You set it to get the level close and use a different control for most level control after that. There are several parts like the PGA2500. Look at the application notes, there may be help there.

Hi Ron
Thanks for your info. Your idea help indeed. The zipper had been very much lower compare the previous level. I use 220 in the first trial. The result get better. But it is still quite noticeable. Then for the second trial I used 3.3k and this porduce a way much better result eventhough it is not totally diminished but it improved a lots.

Besides, to all of you had been follow up this topic. I would like to thank you for your idea and explaination that guide me thru. Today I had manage to solve most of the noise problem. Finally I found the culprit that produce the noise. It is all due to the notebook that I'm using. I used HP pavilion media centre dv1000 notebook. These notebook produce too many noise that had affect my testing an had created so many problem to me. I'm using a USB - Serial convertor and the connection for the RS232 injected great noise into my board. Therefore i keep on suspecting my design problem.
After a few trial, I remove the 12Vb and tied it back to 12Va. The result is still good. To all of you many thanks for your effort.
Now, I'm still aim to totally remove the unwanted noise. There are still some though hardly hear from 2 feet away. Had to put my ears quite close to the speaker to listen to the noise. This is still need improve. Will learn more abt the grounding technique. I still belive it is the grounding issue.
Maybe will try other better chips available for my next prototype.
Thanks again guys.
Best Regards
Alvin

alvinyow · 14th June 2008, 04:32 PM

Besides, I think i need to incorporate RS232 isolator into my new design. Anyone with a recomendation?

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14th June 2008, 04:32 PM	(permalink)
alvinyow	Besides, I think i need to incorporate RS232 isolator into my new design. Anyone with a recomendation?