Hello,
I am trying to use 2 TDA 7293 in bridge. Ala, each outpur feeds one part of the speaker. Then the 2nd amp board should have its + input connected to gnd and the 1st TDA feeds into the inverting input. Each TDA has its own PCB, and they are connected via a short cable. Now, when I run both amps, the 2nd one (slave) has several V DC negative, so much so it nearly blows up the speaker, or with bulbs tester the lamp turns on and there is a serious hum. After several seconds the DC is gone. I reckon there should be a capacitor. K2-2 is where the master output is connected to. Each amp on its own has maybe 5mV DC on its output.
What to do, could not find much in the web.
I am trying to use 2 TDA 7293 in bridge. Ala, each outpur feeds one part of the speaker. Then the 2nd amp board should have its + input connected to gnd and the 1st TDA feeds into the inverting input. Each TDA has its own PCB, and they are connected via a short cable. Now, when I run both amps, the 2nd one (slave) has several V DC negative, so much so it nearly blows up the speaker, or with bulbs tester the lamp turns on and there is a serious hum. After several seconds the DC is gone. I reckon there should be a capacitor. K2-2 is where the master output is connected to. Each amp on its own has maybe 5mV DC on its output.
What to do, could not find much in the web.
Try a capacitor in series with R4, but first of all mind, that the standby/mute circuit shown in the datasheet has a certain delay, within which amplifier outputs should go to zero. Say, signal time constants must be shorter than standby/mute time constants.
mute runs via switch. I.e. there is mains power, then wait a few seconds until I switch the mute off. Or do you mean something wrrong with C14, as this should put in some delay?
Realy cheap and works great.I built 4 subwoofers with this little board no complaints from customers. TDA7293 255W Amplifier Board Amplifier Parallel BTL Mono Power | eBay
I read, that the standby/mute quarter of TDA729* is picky: If you do something unorthodox there, the chip blows up. You did not stick to the datasheet, did you? Also, you do not need those subsonics, please use much smaller values for C3 and C4, say 100uF.
maybe the time constant is too long, recommended is 10k/10uF. So the 2nd one waits for the 1st one and there is an undefinded area inbetween.
Mute is switched off at the same time, as they are interconnected. There is still a minor blop when switching the TDAs on (mute off), that may get to the 2nd one which then amplifies it. It seems to draw lot of current, if the mains bulb tester comes on again. Maybe should put a small capacitor in, so it does not send DC to the inverting input of the slave.
Mute is switched off at the same time, as they are interconnected. There is still a minor blop when switching the TDAs on (mute off), that may get to the 2nd one which then amplifies it. It seems to draw lot of current, if the mains bulb tester comes on again. Maybe should put a small capacitor in, so it does not send DC to the inverting input of the slave.
in the data sheet there are 5V going to the mute switch, so I have to create them somehow.? But the specs say, max mute voltage 120V.
An externally hosted image should be here but it was not working when we last tested it.
there is a neat schematic, use a zener to get a 5Vvoltage. I reckon the schematic I used the resistor with 220k should be 22k, thats what ST is using
Last edited:
You want both IC to un-mute (and mute) at exactly the same time. What ST does is connect the pin 10 of both TDAs together and controlled from a single mute circuit.
yes, there might be some differences. Each one is switchend on via a relais, they have tolerances. Seen that, when I used the lab supply, each one comes on at a different voltage, and hence a different point in time
Here what its meant to be, just an example with TDA7294
Here what its meant to be, just an example with TDA7294
Last edited:
For a new design, you could add a connector for Pins 9 and 10. The two mute circuits will just work as one with these connections. No need to change values.
initial schematic had pin 2 capacitors the other way, so pin 2 of slave gats pin 14 of master through a capacitor. Will post image later
just found this, pin 9 and 10 connected, rest is way different
An externally hosted image should be here but it was not working when we last tested it.
https://bgaudioclub.org/gallery/albums/userpics/13622/E022035.pdf
just found this, @Mark, also note the PSU, there are 3.3uF caps parallel to the 10000uF ones.
I guess I wll just solder a small cap into the jumper lead from master to slave and see what happens
just found this, @Mark, also note the PSU, there are 3.3uF caps parallel to the 10000uF ones.
I guess I wll just solder a small cap into the jumper lead from master to slave and see what happens
I bet that the 3.3uF capacitors increase the ringing in the transformer/PSU. They are low z at high frequency, which gives you more high-frequency current through the diodes to the capacitors. Also look how capacitors interact during a charge cycle. The initial current flow is through the small cap. Then it reverses from that small cap into the larger one, repeated 100 times per second. The same happens when the PSU supplies current to a class AB amp.
The bgaudioclub amp uses K1 to connect the amp modules when they are used parallel, connecting pin 10 to pin 10 and pin 9 to pin 9 of the TDA's.
The bgaudioclub amp uses K1 to connect the amp modules when they are used parallel, connecting pin 10 to pin 10 and pin 9 to pin 9 of the TDA's.
Last edited:
this schematic is from 2002. Interconnecting mute of several TDAs this way can at times cause them to blow up all at once. I had these kit amps, happened to me as well. Went up in smoke one afther the other. Then I did that layout, with them separated via a relais.
Interesing in this schematic, how it goes in the inverting input, there is a 100nF. In that design, there were no troubles in bridge mode. The follow up design did not have a cap in the feed back loop. I guess there is small DC, gets amplified until the PSU caps dischage completely, then it stops and its quiet. By then there are chances your speaker has left the building.
Interesing in this schematic, how it goes in the inverting input, there is a 100nF. In that design, there were no troubles in bridge mode. The follow up design did not have a cap in the feed back loop. I guess there is small DC, gets amplified until the PSU caps dischage completely, then it stops and its quiet. By then there are chances your speaker has left the building.
The TDA is just fragile. I have even seen reports of the power pins bending at high power and causing a short. Connecting two pins 10 together should not change the switching time. I can only see a possible problem if one board losses power.
Good to compare the schematic from post #11 with the one from figure 2. It is really important that the master has a very low offset. Any DC voltage at the output of the master will be inverted by the slave.
Good to compare the schematic from post #11 with the one from figure 2. It is really important that the master has a very low offset. Any DC voltage at the output of the master will be inverted by the slave.
ok, thats the initial design. GND does not loop through.
I just soledered ap a cable with a capacitor inbetween, makes no difference.
What happens: When I switch off power, the PSU caps slowly discharge, after some time the TDA outputs are at several V -.
No speakers connected: When I switch power back on, amps in mute, the output voltage jumps to -1.4 or so V then slowly (several seconds) crawls up to 0, then stops at +20mV. If I then switch off mute, its a very short change in votltage, then its 0mV.
Speakers connected: it jumps to +200mV and stays there (in mute). So then switching mute off would be trouble, as that will be fed back to the master amp, which amplifies it.
Last edited:
- Status
- Not open for further replies.