TPA3116 strange output wave form - Page 1
Forum section: electronics / projects

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 13, 2020, 05:50:02 pm
content: I designed a tpa3116 board exactly as the typical application says. There 3 tpa's on the board (high, mid, bass) high and mid works just fine but I have a strange behavior on the output for the bass. At 20 HZ it starts to get a strange form at around +/- 10V ptp. At 60hz it gets better but still looks weird when its close to clipping. Strange thing is that the input signal looks the same as the output signal, but ONLY under load. Without load it looks just fine, its like the chicken or egg problem and i dont know what to do (already replaced the tpa) In the pics u can see the output at 20 and 60hz, and the input at 20hz (1V ptp)

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 15, 2020, 04:24:03 pm
content: Okay I found out that when I connect my Phone directly to the input cap of the ic its a clear sinus on the output. So it must be a Relation between the amp and preamp but only under load.Has no one an idea?

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 16, 2020, 05:59:58 pm
content: Update: I dont think its something to do with the tpa. Had a TPA board layin around and connected the output of my filter to it, so it must be my filter but only when the tpa is load es enough.. wtf?The signal comes clean out of IC1 but is distorted at the output of IC5. Its not the ic itself, already replaced it. I dont know what to do

author: SMdude
author_rank: Frequent Contributor
timestamp: September 19, 2020, 12:04:18 am
content: Is it something with the ground or power rails?Can you separate the ground and feed it from an external wire. Also are you able to power the preamp and TPA separately?It looks like clipping, but if it doesn't happen with the input from the Iphone, then it must come back to power/ground disturbances.Also I note that the setup for input/output is different for base vs Mid/high.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 19, 2020, 10:21:45 am
content: Ive tested it with another amp board justconnect Ing the output of the filter in the other board, but it was with the same power supply. Ill do that again but with a separate psu for the amp board.What do u mean by that the Setup is different?

author: SMdude
author_rank: Frequent Contributor
timestamp: September 19, 2020, 10:41:07 am
content: As in the outPr and outNr are shorted and the L outputs are shorted too.The inputs for L are shorted to gnd.That may be intentional and normal. I just noted that it was setup different to the mid and high.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 19, 2020, 11:32:17 am
content: Ahh yea, thats the Setup for bringe Mode.So I tried it out, separate psu for the other amp board in bridge Mode. Competely clean output wave till its clipping at +/-24v!I kinda knew it was something with ground, this shit can get u so much in teouble. But how do I solve the problem now?? I have absolutley no clue. I mesaured every ground connectIon around the IC 5 and 6, everything good.

author: Renate
author_rank: Super Contributor
timestamp: September 19, 2020, 11:58:12 am
content: Quote from: SMdude on September 19, 2020, 10:41:07 amYes, as counter intuitive as that is, that's how the "Parallel Bridge Tied Load" (PBTL) works.The TPA3116 specially detects hard grounded left inputs and alters its mode.Those scope photos are certainly hard to decipher.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 19, 2020, 01:08:54 pm
content: Sadly I cant get better pics. But I guess u can tell what happens (with my description too) when the input Voltage is about .5V ptp. But only under load, looks wonderfull without any load.

author: Renate
author_rank: Super Contributor
timestamp: September 19, 2020, 03:33:55 pm
content: Have you tried bypassing (shorting) your power MOSFET?

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 19, 2020, 04:08:00 pm
content: Didnt change anything. Oh and if I turn the volume up too much, the amp goes crazy and the speakers go up and down really heavy. Its like the amp is "pumping" and the current goes verry high and the voltage down, its like up and down up and dow with a awfull noisy crackling sound, till I turn the volume down or disconnect the speakers.

author: Renate
author_rank: Super Contributor
timestamp: September 19, 2020, 07:35:59 pm
content: It sounds like your power supply is not sufficient.The other question is whether the bootstrap voltage is sufficient at low frequencies.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 19, 2020, 09:34:10 pm
content: Thought that too but thats not the problem.It has to be, when I connect my Phone directly it works just fine

author: SMdude
author_rank: Frequent Contributor
timestamp: September 20, 2020, 09:34:45 am
content: Is the ground for the preamp section(audio ground) in the current path of the tpa?You need a clean ground for the preamp section that doesn't see the current consumed by the TPA.You might be able to separate the ground and run a wire from a common point for the preamp/audio ground.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 20, 2020, 10:41:58 am
content: Thats the pcb. U6 is tpa for the Bass, I guess the ground shouldnt be a problem?Edit: soldered a wire on C172 and connected it to the psu clamp (ground) didnt change anything, but I guess the ground on the pcb should be fine anyway

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 20, 2020, 11:20:44 am
content: Weird thing: when I switch the bass boost on (which is at 40hz)The input (and o the output) is going crazy at ~0.6V ptp. Without bass boost it looks just a lil out output shape.Settings for the pics:Input 0.5V/div 20hz signalOutput 10V/divTested w a 8ohm driverWhen I plug my 2 4ohm driver (parallel) in, then things r going crazy earlier, so yea its obv that its something with current and ground maybe.I can take better pics, but I guess u can tell whats going on

author: SMdude
author_rank: Frequent Contributor
timestamp: September 20, 2020, 11:59:04 am
content: I would be trying to isolate all of the grounds on the signal path, ie C54, C53, the 10k resistor(d19?), C51, C49, D10, C47, C46, RV5.I'm actually not an audio nut at all, but do design and layout some low noise circuits from time to time and one needs to be very considerate of current flows through the ground plane.I see you have a separated area in your ground plane under the bass section.Is that a 4 layer board or only 2?

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 20, 2020, 01:57:39 pm
content: What do u mean by Isolate? I mean ground is ground?2 layer boardFor example this is a board from ebay and it works fine. Only bottom layer is filled w ground!

author: tooki
author_rank: Super Contributor
timestamp: September 20, 2020, 04:15:40 pm
content: Quote from: Michaelaudio on September 20, 2020, 01:57:39 pmNo, ground isn't ground. (There's a reason there are different symbols for earth ground, chassis ground, signal ground, analog ground, digital ground, etc.: so that they can be used separately within a circuit.) Current flows through ground, like any other wire or trace, and sometimes you want different parts of the circuit on "separate" grounds -- yes, they'll all connect somewhere, but the idea is that almost no current ever flows through that one spot.Take a look athttps://www.onelectrontech.com/pcb-layout-design-tips-grounding-considerations/-- it explains it quite well.Your PCB layout really isn't very good. I fear your power traces (VCC) may be much too thin, contributing to the problem. But also, all the caps on VCC are too far away from the ICs -- they should be located literally as close as possible, with as fat traces as possible. On your board, they meander around, creating loops that can induce currents in other traces, potentially resulting in noise and instability.I also see that many signal traces take very... creative paths. Like the output of RV5 (subwoofer out), which starts on the top layer, goes down to the bottom layer (through a via right next to the through-hole pin it came from!), then goes back to the top, then back to the bottom, back to the top, back to the bottom again, and finally back to the top to connect to C153. That literally could have been accomplished with a single via, by having it come out of RV5 on the bottom, where it has a clear shot all the way over to near C153, where it would pop back up to connect. (And with careful layout, it likely could have been routed entirely on the top, with other signals traveling beneath C153, for example.Was this autorouted? Audio is something where autorouting really isn't wise, in that you often have both sensitive signal paths as well as heavy power paths right near each other.I'm expecting my hand-routed TPA3126 PCBs from China this week. I'm of course rather curious as to how well they'll perform. I'm sure I've made some layout mistake somewhere, but I think all the important bits got covered.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 20, 2020, 04:41:36 pm
content: I dont think its a problem with the caps, many Chinese Boards are like that and they work. Um yea no.. Not autoruted but my first bcb with so many parts, as u can see.If its a ground problem, why was the problem still there as I connected another amp board to the same psu, and just feed the signal of this board into it?On the other Hand as I fed the other board with a different psu und put the signal of this board into it, it just worked fine

author: tooki
author_rank: Super Contributor
timestamp: September 20, 2020, 05:14:09 pm
content: We are doing our best to guess what you mean from your unclear descriptions.Quote from: Michaelaudio on September 20, 2020, 04:41:36 pmWell if a Chinese board happens to work OK (not that it's been tested under any kind of controlled conditions) then I guess TI must be wrong in their recommendations for their own chips. And if you're such an expert already, then why are you hereaskingquestions?Realistically, doing one thing wrong will likely not cause any trouble. But your board and circuit clearly have multiple things wrong, and that can be enough to cause real problems.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 20, 2020, 06:35:16 pm
content: Who says im an expert🤔 I just try to understand things. When the TPA ground needs to be "far away" from the signal ground, then why was the problem the same with the other board, that was directly connected to psu ground? And why did I worked with a separate psu for the other amp board? -> that would speak for the ground problem ur refering to.I just wanted to try to get this working, but it seems that I cant.

author: Renate
author_rank: Super Contributor
timestamp: September 21, 2020, 01:59:26 pm
content: Quote from: Michaelaudio on September 20, 2020, 06:35:16 pmYes, you can!How about those split rail bias supplies on the bass filter channel?Those things have a time constant of 5 milliseconds.Maybe you've got motorboating from the power supply loading being fed back.Throw a bigger cap on it and see if something changes.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 22, 2020, 02:45:56 pm
content: U mean instead of the 1uf maybe a 10uf parallel to the Resistor?

author: Renate
author_rank: Super Contributor
timestamp: September 22, 2020, 04:25:24 pm
content: Yeah, just tack solder on a bigger electrolytic as a test.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 22, 2020, 06:17:09 pm
content: Wow it worked! Thanks! Put 2 47uF on the dividers, didnt worked with 10uf. The waveform is still a little bit out of shape under 30HZ on high load but its acceptable.Now someone please explain why this worked?

author: Renate
author_rank: Super Contributor
timestamp: September 22, 2020, 06:44:18 pm
content: Quote from: Michaelaudio on September 22, 2020, 06:17:09 pmHow would I know?You've got a lot of those rail splitters.They end up low passing your power supply noise back into your circuit for feedback.The first thing to check is to see exactly how low the 24 V drops when you run it loud.Is it more than you expected?If you want to fix this while keeping the PCB as much like it was:Change the top resistor on the splitters from 10 k to about 4.7 k.Change the bottom resistor on the splitter to a 10 - 12 V zener.Increase the capacitor to whatever will fit.You should probably do this everywhere, but you can start on the bass where it's most critical.Or...You could regulate 24V to 15V to feed all the op amps and keep your splitters.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 22, 2020, 09:00:49 pm
content: Well its a switching psu so the voltage doesnt drop (havent looked at Ripple yet)Oh nooo, did that at first w zeners, all chanels where NOISY as fuck! Like white noise but WAY too loud, replaced all zeners w resistors, noise gone can onlybe hard if ur ears r close to the speakers.Read that with the zeners on a AnalogDevices article. They wrote that u had to connect a 10uf cap for supressing any noise coming from the Zener... didnt work

author: Renate
author_rank: Super Contributor
timestamp: September 22, 2020, 10:04:51 pm
content: Well, your 24 V to the splitters is jumping somehow or else that cap would not make a difference.It could be wiring or that pass MOSFET or whatever.You should probably get a handle on that.Don't like zeners? You could try a TL431, but you'd need another resistor.Why not run the opamps (and splitters) on 15V out of a regulator?You've got plenty of volts.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: September 23, 2020, 06:06:32 am
content: Yea ill look at it today, but seems really well now with the caps.Ill do another amp board in my next project but this time with help of this forum and as good and reliable as possible, guess id make it with a 15V reg next time.

author: tooki
author_rank: Super Contributor
timestamp: October 27, 2020, 12:15:58 am
content: Remember that class-D amplifiers can draw tremendous amounts of instantaneous current, even if average current isn't that high. (For example, at under 1A average current, the peaks can easily reach 10A.) A lot of switching supplies simply cut out when the current draw grossly exceeds their maximum, even if it's just for a millisecond or less. Caps provide a buffer for this, since they can provide the instantaneous current.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: October 27, 2020, 07:34:40 pm
content: Well I guess I have another (last) problem. Has to be something to do with what toki wrote. When the bass amp is running at its max. (Slightly clipping), then there is like almost the same signal on the output of the mid range amp. The mid speakers are going crazy (high excursion), when I turn the volume of the bass to zero, the mids are just fine.I tried adding a 3.3uf to that cap directly near the mid amp.Tried adding a cap (220uf) ditectly to the op amps + and ground)Added a 220uf to the 12V biasing at IC4Didnt changed anything.I Added a 220uf to the biasing of ic 3 as well, but that damaged ic 4 somehowMy smps can deliver 6.66A and the voltage doesnt drop much.

author: tooki
author_rank: Super Contributor
timestamp: October 27, 2020, 09:11:25 pm
content: How much capacitance do you have on the PVCC rail? 3.3μF is negligible. When testing with such problems with our project (which is only a single TPS3126, with one channel for the woofer and one for the tweeter), a few hundred μF didn’t help at all, so I grabbed a 2200μF and that fixed it. (On the final board, I simply laid it out to have pads for 10 caps (2x5 each on each PVCC pin) of up to around 220μF each, and we will simply install as many as needed.)

author: Michaelaudio
author_rank: Regular Contributor
timestamp: October 27, 2020, 10:34:43 pm
content: I have 2x 2200uf on the connector and 2x 220uf near the ICs (6x 220uf then) Added a 2200 as descripted but didnt change anything sadly.

author: tooki
author_rank: Super Contributor
timestamp: October 28, 2020, 07:33:30 pm
content: That’s more than enough, I think it’s unlikely current spikes are the cause.

author: Renate
author_rank: Super Contributor
timestamp: October 28, 2020, 08:06:56 pm
content: Didn't we solve this already?When I overdrive my guitar amp the unregulated high voltage drops by volts.You are using rail splitters that feed off the unregulated voltage.At low audio frequencies these are going all over the place.You can run all the low level opamp stuff off regulated or you can make sure that all the innumerable rail splitters are not affected by unregulated supply voltage jumping.

author: Michaelaudio
author_rank: Regular Contributor
timestamp: October 30, 2020, 07:23:39 am
content: I tried zeners for the rail splitters, but that didnt help. It seems like the problem is not the input stage.

author: Renate
author_rank: Super Contributor
timestamp: October 30, 2020, 01:29:41 pm
content: Well, you're missing something then. You have to troubleshoot.You already said that bigger caps on the rail splittershelpsbut doesn't fix everything.So, clearly there is a problem.Have you determined at what frequency it starts acting up?Have you determined at what frequency with bigger caps?Have you verified that there is actuallyanypower supply rejection?(Did you try that diode/switch/relay test that I proposed?)