I have the following 15 watt amp kit and have a question about it.
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Datasheet for the TDA-2005
https://www.st.com/resource/en/datasheet/tda2005.pdfWith a speaker connected upon turn on it puts out -4.5Vdc for about 1-2 seconds then settles to under 100mV and draws about 2A briefly.
No load it is about -11Vdc.
If the cap connected between pin 5 and ground is lower than the recommended value of 2.2uF it makes the amp have a high turn on pop. The stock value of the amp kit is .1uF.
I tried 2.2uF and it didn't reduce the turn on voltage all that much if any.
Looking at the datasheet example circuit I saw that those two caps were the same value.
So I tried a 10uF cap and now the issue is greatly reduced with maybe a 1/2 second dc voltage that is maybe -2Vdc. I can take a voltage measurement tomorrow.
One thing I did to eliminate a phase shift at 20Hz was to increase the cap in series with the 470 ohm resistor to 1,000uF from its stock value of 100uF, but this issue was happening before I made that change.
Also I eliminated the 680pF cap as it caused a phase shift at 20KHz and a slight reduction in output starting maybe about 13KHz. I saw no instability at all measuring the amp with my scope (had to do just one speaker wire and ground), but I know that isn't a true indicator of 100% stability
What I don't get is the datasheet has a ready made example circuit so why did the kit designer use a different circuit unless the different circuit was better in some way shape or form?
Any idea how to fix that issue?
I may try another 10uF cap in parallel with the existing one to see if that further reduces the issue. If not I'll need some sort of fix if one is available.
Also are there any improvements that can be made?
If all else fails I can use a relay, cap and resistor to make a time delay circuit to where the speaker isn't connected until after 2 seconds.
The same company who makes this kit also makes a speaker protection circuit, but one side of the circuit is referenced to ground and unless I use two supplies that are not connected to each other I could not make that protection circuit work.
The amp is flat from at least 20Hz to 20kHz with minimal phase shift at 20Hz and 20kHz. The amp can go out to maybe 50kHz (can take a measurement tomorrow) without the 680pF capacitor. I don't need that high of a response, although the amp seems fully stable.
EDIT:
The heatsink does seem seem get warm in normal operation, but not too warm. I've thought of adding a small fan but that requires a hole in the case and a 12 volt regulator or resistor to power the fan.
Also I didn't post a picture of the bottom of the case, but I put a hole in it so that I could adjust the pot on the board without having to remove the case.
The pot was the original way to control the volume, but I added a separate volume control and that trimpot now sets the maximum level so that the main volume control isn't overly sensitive.
Also I'll do a load test with a 4 ohm load to see how much wattage it actually produces.
I do have another question though.
How can I measure the output of the amp across both speaker terminals when the scope is grounded and the audio generator is also grounded without using an isolation transformer or transformer between the speaker terminals and scope?
EDIT:
I tried a 10uF cap in parallel with the 10uF cap connected to pin 5 and the issue got worse so apparently the cap on pin 1 and the cap on pin 5 must be the same exact value to minimize the turn on DC voltage across the speaker terminals.
I am thinking of adding a relay cap and resistor to form a delayed connection of the speaker. That way no DC will pass to the speaker.