Basically i have built this amp 4 times now and used 2 different ICs using the schematic in the datasheet. I am doing a bridge design and using a +/-12V supply. All times all I get is a hum which is expected because of the unshielded cable I'm using to test it and no audio out into the speaker although one time I did get audio out although very quiet and noisy and if I turned it up too much I would get really heavy cracking noise too. So this time I now just have the hum and no audio out. I have checked over my work so many times now it's really annoying.
Can anyone help me?
Thanks
Boscoe.
Can anyone help me?
Thanks
Boscoe.
Basically at some point you have to admit that your circuit is not what is printed in the datasheet.Sometimes doing that as a first step helps a lot, makes it easier to find the difference. How about a close-up pic?
Here, this is really getting my nerves now!
The resistors around pin 5 are linking pin 10 and 2 and then 4 and 6.
I do yes. Nothing else electrical is attached to it.
I meant what is the circuit connected to pin 5. What is the voltage on pin 5 to ground. Are your supplies actually +/- 12V?
All the grounds should be separate runs to nearly a single point.
The supply bypass caps could be closer, and the datasheet recommends having no less than 1000u/.1u right next to the chip.
All the grounds should be separate runs to nearly a single point.
The supply bypass caps could be closer, and the datasheet recommends having no less than 1000u/.1u right next to the chip.
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My supply is exactly +/-11.5V.
All grounds run to pin 9 and then all other grounds like signal grd run to that.
I assumed that the 1000uF was for smoothing and as I was already using 4700uF I didn't think it would be necessary! I'll give that ago tomorrow.
Thanks
Exactly. The transistor and Zener-diode that are recommended in the datasheet for that taks are not visible in the photos.
Floating means not connected. I don't think that will work for this particular amp however.
The schematic shows a transistor to switch the mute pin. There are several versions in the datasheet, some with Zener diodes others without. You need to find the right version for your requirements.
The important thing is that that pin 5 needs a voltage that is more than 6 V lower than the positive rail voltage. If your rails are e. g. ±12 V power supply, then the amp will work when the voltage at pin 5 is lower than +6 V. If the transistor and Zener networks are too complex for your taste, use a simple voltage divider that maintains pin 5 between 6 and 10 V below the rails during all load situations. You could try e. g. a 100k trimmer with the wiper at pin 5 and the outer pins at V+ and GND. Then adjust it so that the amplifier works at all volume settings. Take the trimmer out and measure the resistance from pin to pin. Use resistors of similar value, the next higher value from V+ to pin 5 and the next lower value from pin 5 to GND.
I though that is what it meant and that is how it is portrayed in the schematic also.
Okay didn't work anyway. I attached the caps on on the vs+/- inputs and put 5V on pin 5 and nothing has changed.
The chip gets warm and the rectifier gets too hot to touch but this also happened before.
Any ideas?
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If the rectifier gets too hot, you need to check the current consumption. There don't seem to be fuses after the transformer secondaries that would blow in case of a short-circuit. You don't use a light-bulb tester to limit the current in case of failures either, do you?
Does your supply voltage remain at 11,5 V when the amp is connected to the power supply?
Your transformer seems to have several secondary windings. One that only leads to 11,5 V DC is probably intended for auxiliary circuits and may not be able to deliver the amount of power that your amp needs. In that case the voltage would drop and if it drops too much, the amp will not work.
A short on the amp board would also lead to a voltage drop.
Does your supply voltage remain at 11,5 V when the amp is connected to the power supply?
Your transformer seems to have several secondary windings. One that only leads to 11,5 V DC is probably intended for auxiliary circuits and may not be able to deliver the amount of power that your amp needs. In that case the voltage would drop and if it drops too much, the amp will not work.
A short on the amp board would also lead to a voltage drop.
The windings I'm using were used to drive a little 2x25W amp for the rear speakers in a 5.1 amp so should cope and the voltages stay pretty much the same prob down to about 11.4V.
I have thought about a short but can't find anywhere on the board for one to occur either. I will test for a short next.
Thanks.
EDIT - Just measured it pulling 4.65A and voltage dropping to 2V so it is pulling far too much which I kind of thought. But I have not shorted anything (checking over) and the components are in the right places, both rails are exactly the same so it's not like I have just got a little short on one of the tracks or something.
I have thought about a short but can't find anywhere on the board for one to occur either. I will test for a short next.
Thanks.
EDIT - Just measured it pulling 4.65A and voltage dropping to 2V so it is pulling far too much which I kind of thought. But I have not shorted anything (checking over) and the components are in the right places, both rails are exactly the same so it's not like I have just got a little short on one of the tracks or something.
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Boscoe,
before you do anything else, build up a light bulb tester.
It saves almost every circuit/transformer from damage if there is a wiring error between the mains and the amp.
the materials list:
incandescent light bulb
light bulb holder
mains output socket
mains plug top
some 3core mains cable
a box to contain the mains voltages from contact with humans/animals etc.
before you do anything else, build up a light bulb tester.
It saves almost every circuit/transformer from damage if there is a wiring error between the mains and the amp.
the materials list:
incandescent light bulb
light bulb holder
mains output socket
mains plug top
some 3core mains cable
a box to contain the mains voltages from contact with humans/animals etc.
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Well, step 1 is to follow AndrewT's recommendation and use a light bulb aka dim bulb tester. Step 2 is to add fuses to the circuit. It is also wise not to connect the speaker until you know for sure that the amp works as intended.
Can you post pictures of the solder side? From the photos in post #3 it is a bit hard to guess what goes where. It appears that C3, C5, C8, R2 and R4 of the datasheet schematic on page 9 are very far from the TDA. C3 and C5 should be right next to the TDA's pins to avoid oscillations. R2, R4 and C8 should not be too far away from the TDA to keep the feedback loop short and avoid picking up any disturbances into the feedback loop. They should be kept separate from the power supply lines as far as possible just like the input.
If you disconnected the red, black and blue wires from the PSU board, you could measure resistance from wire to wire and see, if there is an obvious short. If there is none, you will have to recheck the amp board against the schematic again until you find what is wrong. Should everything be wired correctly, the fault can still be in the layout (see above) or components (value, defective).
Is the tab electrically isolated from the heatsink? The tab is connected to pin 6 i.e. V-. Your vice seems to be isolated from ground, but it is hard to be sure from those photos.
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