Red is top side and is ground, and bottom is blue and is power plane and stops at the regulator. I don't know how to show the bottom side as all the information is already in that pictureLater on, after I replace the oil in my bike and give it a nice wash I will add some more capacitance on the output of the board and make the tests. I have a couple of 8ohm 100W resistors.
take a snap shots of the actual board and I can compare to the earlier image to see if the ground plane overlaps. I used to use MOSFETs and a function generator to make dynamic PS tests with dummy loads too.
I have done some more tests with various output capacitor configurations.
Basically there is no change. I used 50hz as test frequency for the input signal into the amp. I should have chosen something else but anyway I made a test with 16ohm resistance load and I saw no ripple whatsoever.
So this is with 2x10uF tantalum output capacitance (the way I'm using it right now):
This is with one 330uF/25V Panasonic FC:
This is with 1500uF/25V Samwha RD (standard capacitor, not low-esr):
This is with the same 1500uF Samwha capacitor but I added another Samwha SD series (same, standard capacitor, normal ESR) 4700uF/50V half way between the PS board and TDA amp:
This is with 16ohm resistor (two 8ohm in seris) added directly on the output of the PS board. I want to mention that with 8ohm the board did not output the full voltage/current. With 16ohm I got 16.5V at 1A.
Also I'd like to mention that this is what the oscilloscope shows when I have the PS turned off, so it's some noise picked by the whole circuit from the surroundings. So between on/off there's no change.
My oscilloscope was set on AC coupling, 10x probe and I had my DMM measuring the current.
This is what the PCB looks like:
Top side:
Bottom side:
Basically there is no change. I used 50hz as test frequency for the input signal into the amp. I should have chosen something else but anyway I made a test with 16ohm resistance load and I saw no ripple whatsoever.
So this is with 2x10uF tantalum output capacitance (the way I'm using it right now):
An externally hosted image should be here but it was not working when we last tested it.
This is with one 330uF/25V Panasonic FC:
An externally hosted image should be here but it was not working when we last tested it.
This is with 1500uF/25V Samwha RD (standard capacitor, not low-esr):
An externally hosted image should be here but it was not working when we last tested it.
This is with the same 1500uF Samwha capacitor but I added another Samwha SD series (same, standard capacitor, normal ESR) 4700uF/50V half way between the PS board and TDA amp:
An externally hosted image should be here but it was not working when we last tested it.
This is with 16ohm resistor (two 8ohm in seris) added directly on the output of the PS board. I want to mention that with 8ohm the board did not output the full voltage/current. With 16ohm I got 16.5V at 1A.
An externally hosted image should be here but it was not working when we last tested it.
Also I'd like to mention that this is what the oscilloscope shows when I have the PS turned off, so it's some noise picked by the whole circuit from the surroundings. So between on/off there's no change.
My oscilloscope was set on AC coupling, 10x probe and I had my DMM measuring the current.
This is what the PCB looks like:
Top side:
An externally hosted image should be here but it was not working when we last tested it.
Bottom side:
An externally hosted image should be here but it was not working when we last tested it.
At the moment I would prefer to "fix" this board if that's possible. Adding other components outside the board + heatsink etc would be too much effort. I'd prefer to make the board all over again.
Also, since I'm using this amp at about 0.05 - 0.1W usually, I don't see why I'd change anything. I'm just curious about this effect that I'm seeing, I would like to learn about it and know what I did wrong. And maybe fix it. But I wouldn't make the whole pcb again, not worth it.
At the PSU output. As I've said before, ground is on C5 negative leg and signal from C6 positive leg.
Hi
so your static load test shows you are losing regulation somewhere between 1 and 2 amps. > seems low for an audio power amp driving two 8 ohm speakers?
IMO you should be able to support at least 6-4 ohm (short term) static load and still have good regulation if you want full volume from the power amp for stereo 8 ohm speakers. otherwise you will be seeing ripple and noise at peaks. IDK lower the output voltage some?
PS I can recommend some AC enhancements to the power supply later , but you'll probably have solve the ambient noise pickup 1st.
so your static load test shows you are losing regulation somewhere between 1 and 2 amps. > seems low for an audio power amp driving two 8 ohm speakers?
IMO you should be able to support at least 6-4 ohm (short term) static load and still have good regulation if you want full volume from the power amp for stereo 8 ohm speakers. otherwise you will be seeing ripple and noise at peaks. IDK lower the output voltage some?
PS I can recommend some AC enhancements to the power supply later , but you'll probably have solve the ambient noise pickup 1st.
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1) You have to take care doing LAB sine wave tests ( they require more from the PS and heat sinks ) maybe only test one channel at a time with lower average power
2) always keep in mind the regulator max power VS Temperature
3) you want to make sure you have regulation to support dynamic ( peak ) power ~60W. for music the average will be lower of coarse.
Find out PS Vin vs static load > up to 60W + expected regulator loss (Vin -Vo)*3.6A (make a plot at several power levels) this will determine the XFMR regulation curve
2) always keep in mind the regulator max power VS Temperature
3) you want to make sure you have regulation to support dynamic ( peak ) power ~60W. for music the average will be lower of coarse.
Find out PS Vin vs static load > up to 60W + expected regulator loss (Vin -Vo)*3.6A (make a plot at several power levels) this will determine the XFMR regulation curve
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I guess it's somewhat normal as I don't yet have a case
But noise has nothing to do with the fact that I see that frequency doubling on my power supply. It's like I messed something up somewhere. So the transformer is 80VA.
The other ta2020 amp, as I mentioned before, uses the same PS type only that it's set at 13.5VDC output. I got a 14VAC/60VA transformer for that amp. It shows similar frequency doubling at higher output. So the issue I presume is with my PS board. For the ta2020 I've used LM338 as I wanted to see if it's the LT1084 oscillating or not as it's more finicky than LM338.
So either I have to accept the fact that this kind of behavior is normal for this type of regulators, either I messed something up. And I have more chances of messing it up :
LT1084 supports 5A output under some conditions. TDA7297 has a 2A limit. And the tests are made with cold start, and last for 5 seconds tops. I also tested for 10 seconds but I don't want to stress my rectifying diodes.
PS
Forgot to mention that while testing yesterday the problem starts to appear at about 0.5A and up to 2A it gets worse. So yes, I can see it at 0.5A. I guess that moving up in frequency the issue is not apparent at 0.5A. But for lower frequencies I start to see it at 0.5A.
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I recommend testing the power supply (XFMR ) by itself forget the TDA for now I wouldn't count on 2A limit from the amp anyway ( whatever that means ). the diodes will be fine
edit> TDA spec is 2A at the outputs of which there are 4 of > so connected BTL that combines to 4A which is pretty close to my est of 3.6A.
edit> TDA spec is 2A at the outputs of which there are 4 of > so connected BTL that combines to 4A which is pretty close to my est of 3.6A.
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I can only supply 1A into 16ohm resistance. Less than that and the board will output about 0.5A at 4V or something like that, I don't know why.
It's the same when I tried to simulate the circuit in LTSpice.
I will try to look at the capacitor bank, but the output was ok into 16ohm resistor, no oscillation. This issue appears when I'm testing some output frequency with the amp connected to the power supply. I always get a doubling of the test frequency on the PS output.
It's the same when I tried to simulate the circuit in LTSpice.
I will try to look at the capacitor bank, but the output was ok into 16ohm resistor, no oscillation. This issue appears when I'm testing some output frequency with the amp connected to the power supply. I always get a doubling of the test frequency on the PS output.
Forgot to mention that I made the test with signal output from my iPhone. with everything maxed out I couldn't get more than 2A current from the power supply. So basically what you are saying is that the 2A limit is on the output of the TDA chip? I would have thought that 2A limit is the same on both sides.
I will test again the PS later on and post the results. So you say to connect the resistors between Vin and ground? Zero ohms, that's a dead short, I guess I'd fry stuff on the board. The transformer can supply 5A at 16VAC.
I will test again the PS later on and post the results. So you say to connect the resistors between Vin and ground? Zero ohms, that's a dead short, I guess I'd fry stuff on the board. The transformer can supply 5A at 16VAC.
I guess it's somewhat normal as I don't yet have a case
But noise has nothing to do with the fact that I see that frequency doubling on my power supply. It's like I messed something up somewhere. So the transformer is 80VA.
The other ta2020 amp, as I mentioned before, uses the same PS type only that it's set at 13.5VDC output. I got a 14VAC/60VA transformer for that amp. It shows similar frequency doubling at higher output. So the issue I presume is with my PS board. For the ta2020 I've used LM338 as I wanted to see if it's the LT1084 oscillating or not as it's more finicky than LM338.
So either I have to accept the fact that this kind of behavior is normal for this type of regulators, either I messed something up. And I have more chances of messing it up :
no the doubling is the small output cap charging on the rising edge and discharging on the following edge for each half of the amps output stage so double frequency is normal. 1st priority is too make sure the regulator is able to supply the peak current, then you can tune the ripple a little more by adding more RC at the amp.
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