Hello to everyone,
I'm Fabio, and I'm working on a personal layout of the TDA7498E circuit as described in the Evaluation Board Application Note by ST.
I will try to be brief but all-encompassing to explain you at better all the elements of my situation.
I was a record producer until 2020 with big live experience and a lot of passion in electronics and, latter discovered, in precision mechanics, especially in the audio field.
With my small and new enterprise (since october of the past year) in the south of Italy, I'm preparing a prototype of a special portable amplifier for travelling musicians, and this small class-D amp appeared to be the best choice for the purpose. Please consider that in the small enterprise I'm the only worker and the inventor of the product, and at the moment I'm facing substantially everything (general&administration, project R&D, patenting, CNC lathe and mill machining for any part, circuit designing and building), so I'm facing the last phases of a huge work started four years ago, when I made the first, very simple and basic version of this portable amplifier.
Also, I would ask sorry in advance for my poor english and for my limited competence in electronics because especially in this field I'm totally a self-taught.
The PCB I developed for this project is a single-supply unit powered via Li-ion battery pack with 36V and 10Ah (with BMS inside) and shares rails for auxiliaries voltage regulators, a class-AB power amplifier for the tweeter and finally the TDA7498ETR dedicated section.
The two channels of the TDA7498ETR are connected to a small dual-coil woofer (sell as subwoofer), STEREO mode and gain set to 35.6dB (directly connected to VDDS).
The signal comes from a BOSS preamplifier/compressor unit at the moment. The signal level, checked on the scope, doesn't reach more than 4Vp/p as requested from the TDA7498 data sheet.
Despite my layout is very compliant with the Application Note, starting from:
-decoupling and snubber filter in DUAL solution toward ground as SMT components positioned extremely close to the amp IC;
-same way for any other requested component near the TDA7498E in the input section;
-solid and simmetrical design on the board;
-signal ground isolated by ground and connected without vias directly to negative terminal of the 4700uF bulk capacitor dedicated to the amp (supporting another 2200uF for anything else); 15uH chokes with Isat 6.25A;
-in short: fully compliant to the Application Note;
and the whole board works like a charm (after three different revisions), I'm experiencing a strange clipping issue not discussed elsewhere, the reason why I ask the community help.
Next to the battery pack input connector on the board I provided a multimeter, set as Ammeter, to check the whole quiescent current of the entire circuit and everything's fine for my expectations: less than 200mA.
But what I noticed is a very very bad clipping from the speaker with high transients in the LF part of the signal, when the current measured in the circuit goes over 1A RMS.
Initially I tried different solutions, swapping the 4700uF bulk capacitor with a 10000uF, tried with different chokes and also chokes in parallel (reducing the inductance in the output filter to 7.5uH), changing capacitors in the output filter and also improving main switch cables and removing bleed resistors from the two bulk capacitors on the board, but with no luck.
Most importantly, this kind of clipping seems not due to some sort of built-in protection circuitry because its destructive behaviour (after different trials, the TDA7498ETR explodes).
Before it fatally reached this point, I was looking to the output pins of the IC on the scope, noticing a "strong compression (40-60%) with slight distortion" in the PWM train when my volume reaches the clipping margin.
The strange clip occurs when the total current of the circuit goes beyond 1A RMS... but it happens with transients only.
In example, turning fully counter-clockwise the volume and plucking the bass string, then rising the volume for the sustained note, the Ammeter can give up to 5A and more.
In the reference schematics, you can see the decoupling capacitors of 1uF on the positive input pins. With the floating input the circuit switches on/off very fine, but with the preamplifier connected directly, the sistem starts with a big oscillation under 2Hz, that stabilizes and disappears gradually, so I provided another 1uF in series between the preamplifier signal and the input capacitors, solving the oscillation trouble.
Then, while troubleshooting, I noticed an improvement (more potential headroom on the volume knob before clipping) changing this further decoupling capacitor from 1uF to 100nF before the two positive input pins (so in series with the 1uF decoupling caps described on the reference design).
Clearly lacking a bit of bass frequencies.
As the whole apparatus is intended to be a sealed box, and I was experimenting the functionality of the electronic boards with the speaker mounted into the opened box, I noticed a further improvement (quasi-full potential headroom on the volume knob) simply closing the box.
At this point, my suspects were pointing on the small woofer because its strange Thiele&Small characteristics, having measured a very small linear Xmax... something like 2mm.
My choice went on this specific speaker because I was looking for the best tradeoff between costs and performance for my project. And it was performing quite good, so I decided to work on it as project reference.
Could the solution be in the damping network, that must be redefined due to the electrical characteristic of this particular (abnormal kind of) woofer, commercially known as subwoofer? Clearly I'm expecting the best of its 100+100W output from this small ST monster... after so much work and expense on it.
Still sorry if I dwelt. Hoping and waiting for any hint or suggestion from You and thanking in advance, I wish you a good evening and a nice weekend
Fabio
I'm Fabio, and I'm working on a personal layout of the TDA7498E circuit as described in the Evaluation Board Application Note by ST.
I will try to be brief but all-encompassing to explain you at better all the elements of my situation.
I was a record producer until 2020 with big live experience and a lot of passion in electronics and, latter discovered, in precision mechanics, especially in the audio field.
With my small and new enterprise (since october of the past year) in the south of Italy, I'm preparing a prototype of a special portable amplifier for travelling musicians, and this small class-D amp appeared to be the best choice for the purpose. Please consider that in the small enterprise I'm the only worker and the inventor of the product, and at the moment I'm facing substantially everything (general&administration, project R&D, patenting, CNC lathe and mill machining for any part, circuit designing and building), so I'm facing the last phases of a huge work started four years ago, when I made the first, very simple and basic version of this portable amplifier.
Also, I would ask sorry in advance for my poor english and for my limited competence in electronics because especially in this field I'm totally a self-taught.
The PCB I developed for this project is a single-supply unit powered via Li-ion battery pack with 36V and 10Ah (with BMS inside) and shares rails for auxiliaries voltage regulators, a class-AB power amplifier for the tweeter and finally the TDA7498ETR dedicated section.
The two channels of the TDA7498ETR are connected to a small dual-coil woofer (sell as subwoofer), STEREO mode and gain set to 35.6dB (directly connected to VDDS).
The signal comes from a BOSS preamplifier/compressor unit at the moment. The signal level, checked on the scope, doesn't reach more than 4Vp/p as requested from the TDA7498 data sheet.
Despite my layout is very compliant with the Application Note, starting from:
-decoupling and snubber filter in DUAL solution toward ground as SMT components positioned extremely close to the amp IC;
-same way for any other requested component near the TDA7498E in the input section;
-solid and simmetrical design on the board;
-signal ground isolated by ground and connected without vias directly to negative terminal of the 4700uF bulk capacitor dedicated to the amp (supporting another 2200uF for anything else); 15uH chokes with Isat 6.25A;
-in short: fully compliant to the Application Note;
and the whole board works like a charm (after three different revisions), I'm experiencing a strange clipping issue not discussed elsewhere, the reason why I ask the community help.
Next to the battery pack input connector on the board I provided a multimeter, set as Ammeter, to check the whole quiescent current of the entire circuit and everything's fine for my expectations: less than 200mA.
But what I noticed is a very very bad clipping from the speaker with high transients in the LF part of the signal, when the current measured in the circuit goes over 1A RMS.
Initially I tried different solutions, swapping the 4700uF bulk capacitor with a 10000uF, tried with different chokes and also chokes in parallel (reducing the inductance in the output filter to 7.5uH), changing capacitors in the output filter and also improving main switch cables and removing bleed resistors from the two bulk capacitors on the board, but with no luck.
Most importantly, this kind of clipping seems not due to some sort of built-in protection circuitry because its destructive behaviour (after different trials, the TDA7498ETR explodes).
Before it fatally reached this point, I was looking to the output pins of the IC on the scope, noticing a "strong compression (40-60%) with slight distortion" in the PWM train when my volume reaches the clipping margin.
The strange clip occurs when the total current of the circuit goes beyond 1A RMS... but it happens with transients only.
In example, turning fully counter-clockwise the volume and plucking the bass string, then rising the volume for the sustained note, the Ammeter can give up to 5A and more.
In the reference schematics, you can see the decoupling capacitors of 1uF on the positive input pins. With the floating input the circuit switches on/off very fine, but with the preamplifier connected directly, the sistem starts with a big oscillation under 2Hz, that stabilizes and disappears gradually, so I provided another 1uF in series between the preamplifier signal and the input capacitors, solving the oscillation trouble.
Then, while troubleshooting, I noticed an improvement (more potential headroom on the volume knob before clipping) changing this further decoupling capacitor from 1uF to 100nF before the two positive input pins (so in series with the 1uF decoupling caps described on the reference design).
Clearly lacking a bit of bass frequencies.
As the whole apparatus is intended to be a sealed box, and I was experimenting the functionality of the electronic boards with the speaker mounted into the opened box, I noticed a further improvement (quasi-full potential headroom on the volume knob) simply closing the box.
At this point, my suspects were pointing on the small woofer because its strange Thiele&Small characteristics, having measured a very small linear Xmax... something like 2mm.
My choice went on this specific speaker because I was looking for the best tradeoff between costs and performance for my project. And it was performing quite good, so I decided to work on it as project reference.
Could the solution be in the damping network, that must be redefined due to the electrical characteristic of this particular (abnormal kind of) woofer, commercially known as subwoofer? Clearly I'm expecting the best of its 100+100W output from this small ST monster... after so much work and expense on it.
Still sorry if I dwelt. Hoping and waiting for any hint or suggestion from You and thanking in advance, I wish you a good evening and a nice weekend
Fabio
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Some news and correction to the past post:
-the small woofer (subwoofer) is, not obvious, a 4+4 double coil. Total length of the coil 10mm.
-bypass capacitors, not decoupling, discussed here
This morning I tried to bring total reservoir capacitor to 15000uF (plus 2200uF to support other sections) to exclude limitation on the BMS of the battery pack. Doesn't seem to be here the problem.
I removed small locking header connectors for the output (to the speaker) because they seemed to be faulty, soldering the output cables directly on the choke but no improvement here.
So I reduced the pre-input decoupling capacitor from 100nF to 47nF, this further improved transients handling.
I've noticed incredibly different behaviour changing how much the "ideally sealed box" is effectively sealed (not only the rear panel: consider any component going from inside to outside, switches, connectors, controls and the holes in the walls).
It's pretty clear that: better the box is closed and sealed, in the same way the clipping threshold of the amplifier increases.
The current drawn in the whole circuit, measured with the Ammeter, showns that current increases drastically if I touch the cone (going from 0.6A beyond 1.2A), manually damping its excursion. This happens without changing the volume level, so I'm pretty sure the crisis is in the woofer and how its short excursion interferes with the amp stage.
Still waiting for your thoughts, thank you
-the small woofer (subwoofer) is, not obvious, a 4+4 double coil. Total length of the coil 10mm.
-bypass capacitors, not decoupling, discussed here
and signal ground isolated FROM ground, my english is poor, sorry.
This morning I tried to bring total reservoir capacitor to 15000uF (plus 2200uF to support other sections) to exclude limitation on the BMS of the battery pack. Doesn't seem to be here the problem.
I removed small locking header connectors for the output (to the speaker) because they seemed to be faulty, soldering the output cables directly on the choke but no improvement here.
So I reduced the pre-input decoupling capacitor from 100nF to 47nF, this further improved transients handling.
I've noticed incredibly different behaviour changing how much the "ideally sealed box" is effectively sealed (not only the rear panel: consider any component going from inside to outside, switches, connectors, controls and the holes in the walls).
It's pretty clear that: better the box is closed and sealed, in the same way the clipping threshold of the amplifier increases.
The current drawn in the whole circuit, measured with the Ammeter, showns that current increases drastically if I touch the cone (going from 0.6A beyond 1.2A), manually damping its excursion. This happens without changing the volume level, so I'm pretty sure the crisis is in the woofer and how its short excursion interferes with the amp stage.
Still waiting for your thoughts, thank you
Hi. For me it looks like problem related to double coil speaker . Did you tried to play the same bass with dummy load resistor of same resistance ,placed on heatsink? I think when speaker is double coil , when one channel is moving coil, in another coil some current is induced , and that makes non-ok load for another channel. Maybe try first with only one coil connected , maybe both in series and connect to one of channels of tda . You said you had kinda of oscillation,related to input capacitors capacity - that i think is ground / layout problem, maybe common supply/ground used for preamplifier, try to use cd player or phone as source to check. Also some ic's have balanced inputs , and it may help with ground problem, but you need opamp if your preamp has no balanced output. Maybe you expecting too much from this tda ? What is speaker impedance and what datasheet says about supply voltage with that load resistance ?
Double coil loudspeakers are not meant to have different amps drive different coils. You need to combine the two coils by putting them in parallel or series. Then use one amp or two amps bridged to drive what now is in essence a single coil. Ximikas is spot on imo.
Hello Ximikas,
I didn't tried the dummy resistance test, but suspecting the parasitic effect between the two moving coils I just disconnected one amp output (from locking header connector, so board side). Same bad clipping, swapping one channel or the second, leaving unconnected the other.
About the common supply/ground of the BOSS preamp: you said right.
I'm developing also che preamp circuitry on a second board, more complex than this. It has on-board soft-clipping protection system and active x-overs to be matched to the ultimate characteristics of the power amp board.
This one doesn't suffer oscillation problems when connected to the two power amps.
"160-W + 160-W output power at THD = 10% with RL = 4 Ω and VCC = 36 V"
indicated on datasheet for the STEREO mode, exactly what I would expect... maybe not from a dual coil woofer, after your thought. So thank you.
Hello Vacuphile,
your suggestion to use BTL mode, at this point, is brilliant.
The major limitation of this solution is 220W output with 3 ohm in MONO mode with TDA7498E, so could be the moment for reconsidering a single 4 ohm coil speaker as alternative to series/parallel with 4+4 dual coils.
Thank you as well!
I didn't tried the dummy resistance test, but suspecting the parasitic effect between the two moving coils I just disconnected one amp output (from locking header connector, so board side). Same bad clipping, swapping one channel or the second, leaving unconnected the other.
About the common supply/ground of the BOSS preamp: you said right.
I'm developing also che preamp circuitry on a second board, more complex than this. It has on-board soft-clipping protection system and active x-overs to be matched to the ultimate characteristics of the power amp board.
This one doesn't suffer oscillation problems when connected to the two power amps.
"160-W + 160-W output power at THD = 10% with RL = 4 Ω and VCC = 36 V"
indicated on datasheet for the STEREO mode, exactly what I would expect... maybe not from a dual coil woofer, after your thought. So thank you.
Hello Vacuphile,
your suggestion to use BTL mode, at this point, is brilliant.
The major limitation of this solution is 220W output with 3 ohm in MONO mode with TDA7498E, so could be the moment for reconsidering a single 4 ohm coil speaker as alternative to series/parallel with 4+4 dual coils.
Thank you as well!
Also speaker resistance is not constant , at some point it does increase ,at some may look like even less than dc resistance ,if speaker is moving and inducing some current . THD 10% is unlistenable level of distortion ,this is not proper power output ,its level at which you normally dislike listening because of easy detectable by ear distortions ,clear clipping... For subwoofer thats maybe sound as different bass tone . So about common ground/power to preamp - try to use voltage matched isolated dc/dc converter ,like 36/36V rated, there are lots of variants of them with different voltages and many distributors . Then no current will flow through your signal ground to preamp . You can isolate preamp inputs or tda inputs ,but preamp outputs are grounded through low output impedance ,and this is problem with using common power .If you use common power and ground ,also can try to use audio transformer for tda inputs , to completely isolate signal ground and signal ,but it will lower audio quality and mostly low frequency response ... That's not good for subwoofer especially .
Ximikas, the BOSS preamp is for testing purposes only. While for my circuitry I provided 1uF as safety for bias decoupling. At the moment the best solution for this pre-input decoupling cap is between 100nF and 47nF.
I tried MONO mode, modifying the board, creating parallel connection AFTER the chokes, while datasheet show mono links BEFORE chokes.
The amp is now running at 2 ohm.
Resulting performance is much worse than STEREO mode.
Clipping is more soft now, something like a very hard compression, (than spike shot in STEREO mode).
But it occurs at very low volume level, I can measure 500mA of total current on the board when clipping kicks in.
I tried MONO mode, modifying the board, creating parallel connection AFTER the chokes, while datasheet show mono links BEFORE chokes.
The amp is now running at 2 ohm.
Resulting performance is much worse than STEREO mode.
Clipping is more soft now, something like a very hard compression, (than spike shot in STEREO mode).
But it occurs at very low volume level, I can measure 500mA of total current on the board when clipping kicks in.
Parralel mode - i doubt it should be done in connecting together after chokes ... it must be ic pins parralelled ,sync mode enabled , and only one input applied .TPA3xxx has that if i remember correctly . Summing after inductors is bad idea , because inductance and capacitors will not match ,and give different phase output . Filter should be one common for both channels in parallel . Try to read datasheet . Also you have mentioned 36v battery pack - when fully charged ,voltage not exceeds operating voltage from datasheet ? Not "Absolute maximum rating" , which is specified for idle mode ,no signal applied .I will probably look at datasheet later too . Also to note - 2 ohms is heavy load for most amplifiers ... Did you notice , tda not getting warm or hot ?
So I decided to follow the original schematics about linking before the chokes (keeping the parallel also after, as indicated in the notes) in the MONO mode.
The TDA7498E exploded after the first note.
I'm sincerely tired to waste components and time experimenting with this IC in total scarcity of literature, so I decided to go back onto the STEREO mode design that was working better.
The TDA7498E exploded after the first note.
I'm sincerely tired to waste components and time experimenting with this IC in total scarcity of literature, so I decided to go back onto the STEREO mode design that was working better.
When connecting output pins together from different channels , some pin needs to be switched, which define mode - stereo ,mono btl ,or parallel output configuration. It looks like it was not switched, tied together outputs were not in phase and you know sad result .
Ximikas,
the first task done was to modify the board to connect MODE on VDDS, getting MONO mode.
Let's consider to have a single coil for BTL MONO mode that means "output can be paralleled".
Ok to link IC pins before the output filter. At this point I can't understand how to make the parallel connection on the single coil.
This because I don't think that BTL mode was meant to be for double coils here, but mainly for single coil loads.
How to connect the parallel output to the speaker if I can't make a parallel after the chokes?
On the schematics, filters are always twins, just linked OUTPA with OUTPB and OUTNA with OUTNB. Substantially the board is the same, just change MODE pin from SGND to VDDS, link the output pins and...
About the single input on L channel, yes you got it, I was hurry and I forgot.
I could get another shot with the next IC at this point, but I'm worried about the results, and these components are expensive.
The board is mounted on an alluminum bar specifically designed to touch the TDA7498E thru a termal pad. On the bar we have also the auxiliary regulators LM317 with mica insulators and LM1875 for the tweeter.
The bar temperature is very low for this board revision (something like 30°C), although I didn't measured during the specific test in MONO mode.
the first task done was to modify the board to connect MODE on VDDS, getting MONO mode.
Let's consider to have a single coil for BTL MONO mode that means "output can be paralleled".
Ok to link IC pins before the output filter. At this point I can't understand how to make the parallel connection on the single coil.
This because I don't think that BTL mode was meant to be for double coils here, but mainly for single coil loads.
How to connect the parallel output to the speaker if I can't make a parallel after the chokes?
On the schematics, filters are always twins, just linked OUTPA with OUTPB and OUTNA with OUTNB. Substantially the board is the same, just change MODE pin from SGND to VDDS, link the output pins and...
About the single input on L channel, yes you got it, I was hurry and I forgot.
I could get another shot with the next IC at this point, but I'm worried about the results, and these components are expensive.
The board is mounted on an alluminum bar specifically designed to touch the TDA7498E thru a termal pad. On the bar we have also the auxiliary regulators LM317 with mica insulators and LM1875 for the tweeter.
The bar temperature is very low for this board revision (something like 30°C), although I didn't measured during the specific test in MONO mode.
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A lot of designs based on TDA7498E run with 2ohm, it seems, there are eight Schottky diodes, two per output pin, one clamped to VCC and the other to GND to reduce spikes, but these are shown as "optional components".
During the test, probably having a parallel on the output was a bad idea as you said (without direct links on IC pins, but I can assume the worst thing was the R channel positive input not tied to ground.
So i'm looking at datasheet from ST . It states about operation at 36V and in stereo mode 3ohm load ,so you not exceed supply voltage with that .Its allready BTL - bridge mode , both speaker wires going to ic , none to ground . In MONO mode outputs needs to be connected together ( fig 3 from datasheet ) WL+ WR+ , WL- WR- , J3 , J8 , Mode pin to VDSS , you mentioned you did that . When switching mode pin to vdss , ic works in different way , uses same pwm signal to both channel drivers ,they work in parallel . Its strange that ic exploded . Also for testing after making changes i would recommend use power supply with current limiting ,instaed of battery packs .At first , set current limit , and if something goes wrong ,voltage sags and you notice that .It helped me a lot of times .Also use lower voltage for experiments ,and if all working well ,increase supply voltage and watch for possible abnormalities .Maybe fake ic ? It was purchased not from A**express ? About diodes at output - actually your load is inductive ,also output inductors are present ,so diodes are useful thing to have. Inductor can return much higher voltage pulse after few volts pulse on it ,so may stress out mosfets inside ic .But mosfets actually have similar diodes inside ,but with worse parameters ,so its "optional". But if your speaker cables are long ,better put such diodes .I don't know how important is to short second channel inputs if using mono mode ,at best is to follow datasheet .About output linking - yes ,at best is to do that as much close to ic pins and with short wire or jumper ,not introduce inductance .Also for first test try both coils connected in series , as 8 ohms , to reduce current spikes and supply sag.
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No these aren't fake, it's a lot bought from DigiKey. I bought also a lot of 20 pcs from AliExpress, only 2 came due to a mistake of the seller, so I'm waiting for the others. Expensive same as DigiKey and I think are pretty original, working the same identical way, same blister, same mechanical appearance. I'm experiencing with fake LM1875T (some working, some not) but these are extremely cheaper than the original LM1875 and, obviously, a lot more simple than TDA7498E. I can't imagine why a supplier would produce a counterfeit for such complex thing like this, with some expectation that these will works.
Cables, in my case, are very short, the portable amplifier is tailored very small.
Cables, in my case, are very short, the portable amplifier is tailored very small.
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Copying ic's is some business , when you sell them after that in big quantities and they are working somehow ,maybe worse than original ,but not everyone pushes to maximum ,to discover that . Had issues with mosfets from Eb** few years ago , looked like original ,worked ,but power supply had more losses and mosfet heated a bit more . Datasheet said 0,5 ohm RDSon, actually it had few times more (0.85 if i remember correctly),also input capacity was less than specified (too good to be true) ,so it was smaller transistor remarked or bad clone. Quality control is on the factory side , not distributor responsibility .
So you may simply have got bad batch ,if everything done properly with layout and followed all recommendations from datasheet .At high frequencies like few hundreds of khz every 10mm makes a voltage spike , very good seen with oscilloscope , yesterday i have proved that again. You have not provided your layout files for experts to check for mistakes or so , so i can only guess .
So you may simply have got bad batch ,if everything done properly with layout and followed all recommendations from datasheet .At high frequencies like few hundreds of khz every 10mm makes a voltage spike , very good seen with oscilloscope , yesterday i have proved that again. You have not provided your layout files for experts to check for mistakes or so , so i can only guess .
At the moment I think to have found a "Lazarus", one of those TDA7498E I considered dead previously, but seems fine. Right now I'm trying with it, same MONO setup with R channel tied to ground. If it's not totally dead but only sleeping, we'll see.
Ximikas, for reduced load do you mean only a coil (4ohms)? I can put a 100ohm resistor in place of the Ammeter to reduce current drawn.
Another doubt is about the BTL wiring of the load. Have I to connect the L channel output only (if the load would be a single coil)? The datasheet says "MONO OUT" where WL+ AND WR+ connect together, as well as WL- and WR- but I don't want to think that this is the "new" output for the speaker.
Please understand, I have the last two IC's and ST should have wasted two more lines about MONO mode connection. I don't want to do other blind experiments at expense of these components.
It doesn't even seem normal to me that an engineer from company X has to go crazy to figure how to work out something that should work at the first time. And this is an IC that can burn out for a mere matter of track sizing on the layout.
Another doubt is about the BTL wiring of the load. Have I to connect the L channel output only (if the load would be a single coil)? The datasheet says "MONO OUT" where WL+ AND WR+ connect together, as well as WL- and WR- but I don't want to think that this is the "new" output for the speaker.
Please understand, I have the last two IC's and ST should have wasted two more lines about MONO mode connection. I don't want to do other blind experiments at expense of these components.
It doesn't even seem normal to me that an engineer from company X has to go crazy to figure how to work out something that should work at the first time. And this is an IC that can burn out for a mere matter of track sizing on the layout.
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IC output mosfets are from output to GND and to VCC , which you connect in parallel ,if you connect two IC outputs together , two wire links or solder pins together . Inductors should not change as i understand , they just have to be same inductance ,but higher current rated .Lower ohms load - more current through inductors - more ampere rated needed .Unsure if 6Ampere rated inductors is enough for your load . Also to note - ic datasheet mentions overcurrent protection 10-14 Ampere , thats for one output . So for this protection to trip and protect outputs ,power source must be able to supply that current for some time . For two outputs in parallel ,its twice i think ,so 20-24Ampere must be drawn from your battery pack without big sag , to enforce protection ,otherwise mosfets will go into resistor mode and overheat quickly, and quickly blow . Offtopic - have tested 8A rated high side power switch with similar overcurrent protection ,but when trying short circuit after switch with power supply as source ,i got ic desoldered completely after half second ,but undamaged.It was not enough current for protection to trip, maybe same problem you have with tda when overcurrent occurs . New connection of speaker itself should be after inductors ,maybe capacitors should be changed too (lower load). Reduce load i mean connect both your speaker coils in series ( 4 + 4 ohms = 8 ohm ) for testing ,+wire of one coil to -wire of other ,whats lef to amplifier .It will reduce current few times and electrical power needed .If all fine ,try one coil ,if all fine again, try both coils in parralel ,to make 2 ohms . But for very first test still best to use resistor on heatsink ,maybe you can buy from local supplier 100w 4 ohm or 8 ohm ? Then supply sine wave lets say 50Hertz from tone program on phone in example , thus not making common ground ,not using preamp ,measure with AC voltage on resistor and increase it slowly and watch how it works . Then you will know tda is working fine . Now you have too many possibilities for problems .Maybe need to debug step by step carefully and do not push hard .
Yes, I agree with going step by step with this kind of stuff, but the main fear is the same, only two IC left, SO many possibilities until a solution in reached. I do this for any other thing in this project (electronics, mechanics, digital system programming) but as I said, with an integrated amplifier of such complexity you can not go onto riddles, "if you make a mistake you have just thrown away ten euros".
I have a pair of power resistors, rated 2 ohm 100W with their heatsink, I can use these in series to limit the whole current on board.
I'm very thankful and I'm happy about your help.
I also found a thread called "7498E BTL Mode Question" where FauxFrench suggests to use only one channel as output, being the two putting together the same power signal, removing the choke from the unused second channel.
Still thank you Ximikas
I have a pair of power resistors, rated 2 ohm 100W with their heatsink, I can use these in series to limit the whole current on board.
I'm very thankful and I'm happy about your help.
I also found a thread called "7498E BTL Mode Question" where FauxFrench suggests to use only one channel as output, being the two putting together the same power signal, removing the choke from the unused second channel.
Still thank you Ximikas