Hi all,
Long time since I've posted here, I went off and wrote TcMenu Arduino framework that I suspect a few here may have used to build their menu systems. However, instead of helping others build their firmware, I now find myself needing a bit of help with PCB design.
Background:
I have this long-term project that I've been trying to start on for a while now, to build a high-quality but small system for my office. My plan is to do this in phases, this amplifier was the first phase, and also my first attempt at building my own PCB. For context this amp was designed for desk based sattelite speakers with a separate sub.
Before building I checked the schematic carefully against the reference design (several times), I believe it to be correct. Then, after building the circuit board, ensuring all devices were in the right way around, all wiring was correct, etc.
Situation:
I failed at the first hurdle but as the saying goes, but the only real failure is one that you don't learn from. So, I'll explain what happened here and what I've drawn from that in the hope anyone has any other ideas that could have caused this issue. This is all a case of closing the door after the horse has bolted but I wanted to discuss this before another cycle.
Known Mistake 1: So firstly, and rather embarrassingly, I embarked on this with the soldering iron tips in bad condition, they had all slightly tarnished at the end, and instead of replacing them, I tried to push through, I believe was mistake #1.
Known Mistake 2: Layer 2 (back) was a ground layer, I did not leave any thermal relief around the pads, which resulted in great difficulty soldering, combined with mistake 1, I believe this really compromised the build, and I think this renders the PCB useless. No matter how much I tried to resolder the joint at higher temperatures, I could not get a good result.
On powering up the board, with the chip in standby all seemed to work and voltage read off as expected, but on activating standby and mute pins, the device it basically kept tripping my bench top PSU into over current mode (24V, 3A) . Further, whenever I pressed on the board with a plastic stick near any of the ground connections, a distorted signal was output through the speakers and then it would trip again. I was using a pico scope to output a 1khz signal, and looking at the output on another channel, when I pressed on the ground, a somewhat distored output appeared for a short time.
Here are two screenshots, one of the schematic, one of the errors I immediately noticed on the PCB, unless someone can see an obvious error that I have missed, I think the amp is very close the reference design.
Many pin holes had no relief.
I've since made sure that all fill areas have proper relief, and I've also taken the opportunity to do a bit of other re-routing to reduce feedback/bootstrap loop length (as I am pretty confident the first PCBs are not usable). But please be honest, is this design even worth continuing with?
BTW if anyone else was interested in this project, I'd be happy to put it onto GitHub and collaborate on it, eventually I'd like to get it to a point where it had small sattelite speakers, a sub, both analog and digital in with USB Audio, and a TcMenu/EmbedControl based control system.
Thanks,
Dave
Long time since I've posted here, I went off and wrote TcMenu Arduino framework that I suspect a few here may have used to build their menu systems. However, instead of helping others build their firmware, I now find myself needing a bit of help with PCB design.
Background:
I have this long-term project that I've been trying to start on for a while now, to build a high-quality but small system for my office. My plan is to do this in phases, this amplifier was the first phase, and also my first attempt at building my own PCB. For context this amp was designed for desk based sattelite speakers with a separate sub.
Before building I checked the schematic carefully against the reference design (several times), I believe it to be correct. Then, after building the circuit board, ensuring all devices were in the right way around, all wiring was correct, etc.
Situation:
I failed at the first hurdle but as the saying goes, but the only real failure is one that you don't learn from. So, I'll explain what happened here and what I've drawn from that in the hope anyone has any other ideas that could have caused this issue. This is all a case of closing the door after the horse has bolted but I wanted to discuss this before another cycle.
Known Mistake 1: So firstly, and rather embarrassingly, I embarked on this with the soldering iron tips in bad condition, they had all slightly tarnished at the end, and instead of replacing them, I tried to push through, I believe was mistake #1.
Known Mistake 2: Layer 2 (back) was a ground layer, I did not leave any thermal relief around the pads, which resulted in great difficulty soldering, combined with mistake 1, I believe this really compromised the build, and I think this renders the PCB useless. No matter how much I tried to resolder the joint at higher temperatures, I could not get a good result.
On powering up the board, with the chip in standby all seemed to work and voltage read off as expected, but on activating standby and mute pins, the device it basically kept tripping my bench top PSU into over current mode (24V, 3A) . Further, whenever I pressed on the board with a plastic stick near any of the ground connections, a distorted signal was output through the speakers and then it would trip again. I was using a pico scope to output a 1khz signal, and looking at the output on another channel, when I pressed on the ground, a somewhat distored output appeared for a short time.
Here are two screenshots, one of the schematic, one of the errors I immediately noticed on the PCB, unless someone can see an obvious error that I have missed, I think the amp is very close the reference design.
Many pin holes had no relief.
I've since made sure that all fill areas have proper relief, and I've also taken the opportunity to do a bit of other re-routing to reduce feedback/bootstrap loop length (as I am pretty confident the first PCBs are not usable). But please be honest, is this design even worth continuing with?
BTW if anyone else was interested in this project, I'd be happy to put it onto GitHub and collaborate on it, eventually I'd like to get it to a point where it had small sattelite speakers, a sub, both analog and digital in with USB Audio, and a TcMenu/EmbedControl based control system.
Thanks,
Dave
While not exactly the same you could have a look for inspiration:
https://www.diyaudio.com/community/threads/xmas-amp-dibyas-tda7293-by-jhofland.365002/
https://www.diyaudio.com/community/threads/xmas-amp-dibyas-tda7293-by-jhofland.365002/
Chip amps can be a little touchy.
The feedback resistor path must be as short as possible or oscillation can occur.
Try to use star grounding where possible.
If no other earth in your system connect zero volts to earth to decrease hum.
The feedback resistor path must be as short as possible or oscillation can occur.
Try to use star grounding where possible.
If no other earth in your system connect zero volts to earth to decrease hum.
H
HAYK
have a look at the datasheet: when using a power supply lower than +/-25V you should add an RC from the output to Ground. Otherwise some oscillation can show up. This could be the cause for your reading of 3A on the supply.
Do you have a connection between 'GNDD' and 'GND' anywhere? Normally pin1 and pin4 are connected together, I doubt the chip will like pin1 being left to float.
Thanks all, this has given me a lot more things to think about. The thing is, even though I could buy the PCB for twice less than I can make it (and the purchased one may even be twice as good), I want to actually make it and go through a few learning errors on what's quite a simple board. Hopefully, I'll get it at least nearly right the 2nd or 3rd time!
A few suggestions:
None of these will be the reason your amp isn't working, though.
The R+C from output to ground (Zobel network) could be helpful. You'll want a power resistor (2-3 W) and a reasonably linear capacitor there. I've used X7R ceramics in that spot with good results. C0G/NP0 or a film cap would be preferred.
Tom
- The connection from the IC to C1 could be on the green layer and thinner.
- Or you could run the connection to C1 on the red layer if you drop the connection to R3 down between the two rows of IC pins.
- I generally prefer to have all electrolytic capacitors aligned so the positive terminal (anode) faces the same way on all of them. It makes hand-assembly easier.
None of these will be the reason your amp isn't working, though.
The R+C from output to ground (Zobel network) could be helpful. You'll want a power resistor (2-3 W) and a reasonably linear capacitor there. I've used X7R ceramics in that spot with good results. C0G/NP0 or a film cap would be preferred.
Tom
Many thanks to all here, I've learned a lot from the comments about high-power analog, and nearly finished a major set of changes to the board (I'll post it here again soon).
I think the actual problem was caused by both the lack of thermal relief making soldering near impossible due to very large ground plane, and trying to operate it at too low a voltage.
I've been doing a lot of rerouting to shorten paths, and I also realized a ground plane over high and low power items is not recommended.
I think the actual problem was caused by both the lack of thermal relief making soldering near impossible due to very large ground plane, and trying to operate it at too low a voltage.
I've been doing a lot of rerouting to shorten paths, and I also realized a ground plane over high and low power items is not recommended.