Replacement for TDA2050v

[JonathanAnon]

Re: Replacement for TDA2050v

@redwire
I've had it up and running for about a day now..... This circuit with the 1875T will simply not work without input filter caps, unlike the very similar circuit with the TDA2050V (which I had breadboarded and working fine without any filtration on the voltage source)... I also initially left out the feedback cap on the TDA2050V circuit initially, thinking that it was not mandatory, but the circuit would not work at all without it in place...

@budm
input voltage is 12.2V and the voltage at the point between the resistor ladder (R1 and R2) is 5.98V, so it's pretty much 1/2Vcc

I had some problems with it sounded distorted / muffled after a period of time, but I added a temporary heatsink to the IC, and a pot to limit the input and it's been running fine for the last five hours. I find that if I allow too much signal on the input, the output will distort badly... But I guess this is due to a higher gain in the 1875T circuit.... Gonna keep testing it with voice and music inputs for a few days...

[JonathanAnon]

Re: Replacement for TDA2050v

I tried out the 1875 for a few weeks, and I just dont like it.... I built the two circuits and the TDA2050V is somehow more powerful, much less noisy and it just works. So I'll probably buy a few on the cheap from China.

I'll work with a view to using a DC to DC converter in future projects and a chip that works with a higher voltage.

[ben7]

Re: Replacement for TDA2050v

@redwire
I've had it up and running for about a day now..... This circuit with the 1875T will simply not work without input filter caps, unlike the very similar circuit with the TDA2050V (which I had breadboarded and working fine without any filtration on the voltage source)

I've thought that you should always have some supply decoupling capacitors...

I also initially left out the feedback cap on the TDA2050V circuit initially, thinking that it was not mandatory, but the circuit would not work at all without it in place...

Yeah, leaving out the feedback cap definitely would cause issues.

I had some problems with it sounded distorted / muffled after a period of time, but I added a temporary heatsink to the IC, and a pot to limit the input and it's been running fine for the last five hours.

You ran it without a heatsink previously?!

I find that if I allow too much signal on the input, the output will distort badly... But I guess this is due to a higher gain in the 1875T circuit.... Gonna keep testing it with voice and music inputs for a few days...

The output is probably clipping. Basically, it's getting too close to the supply rails for the amp to handle, and the signal gets distorted, or "clipped" off, making the sound less than desirable.

Also, reading the datasheet, I see that it is suggested to keep power supply traces/wires away from the input wires, to reduce coupled currents.

I tried out the 1875 for a few weeks, and I just dont like it.... I built the two circuits and the TDA2050V is somehow more powerful, much less noisy and it just works. So I'll probably buy a few on the cheap from China.

I'll work with a view to using a DC to DC converter in future projects and a chip that works with a higher voltage.

DC to DC converter might make noise in the output, especially depending on how your grounds are wired, and the filtering on the output. But it is possible (think: car audio power amps)

I suggest trying a D class chip in the future. Less power loss in the chip itself, so you don't have to worry about dissipating that as much as with a regular amplifier.

Finally, you can try using a lower impedance speaker if you can, that will give you more power output with the same input voltage.

Oh well, one last thing is, you can do a bridge mode where you have two amplifiers driving one speaker, using a single ended power supply (no negative voltage rail). That will give you more output power, as the speaker will be able to get +-12V, instead of +-6V. (I think that is right, isn't it?)

-Ben

[JonathanAnon]

Re: Replacement for TDA2050v

You ran it without a heatsink previously?!

Would you believe me if I said that I'm still running it without the heatsink and it's still working perfectly. I have an infrared temperature detector and it didnt get that hot. But the plan is to fit in a proper heatsink anyway.

Finally, you can try using a lower impedance speaker if you can, that will give you more power output with the same input voltage.

I've had trouble finding a chip to drive the 4 ohm speaker with the same power as the (now defunct) TDA2050V... The TDA2050V is perfect but no longer in production and doesnt seem to have an equivalent. Not using the 12V anyway, which is why I'm talking about DC-DC converters. I think you may be right about the 1875 I think it just needs a higher input supply to work properly.

This is the circuit that I am playing with at the moment. The left side of the circuit is for a RC circuit + momentary switch, so I can hit the button and the speaker stays on for a few minutes (while I'm in the shower) then switches itself off automatically. I'm building it on stripboard, cos I'm poor and dont have any proper PCB tools :-)



The second after posting this I spotted a few mistakes, but I'll correct them later ...

[ben7]

Re: Replacement for TDA2050v

Would you believe me if I said that I'm still running it without the heatsink and it's still working perfectly. I have an infrared temperature detector and it didnt get that hot. But the plan is to fit in a proper heatsink anyway.

Ahh, well, I guess if you aren't taxing it then it won't get that hot.
I was like for a second there! xD

This is the circuit that I am playing with at the moment. The left side of the circuit is for a RC circuit + momentary switch, so I can hit the button and the speaker stays on for a few minutes (while I'm in the shower) then switches itself off automatically. I'm building it on stripboard, cos I'm poor and dont have any proper PCB tools :-)

Also, cut traces so that none of the speaker or power traces are going near the input traces (as best as possible). That will help reduce any unintended noise/feedback.
Like (L,A), (L,B), (N,K), (N,M), (N,N), (N,O) ... etc...
Especially (L,B), this will decrease the coupling from the GND to the inverting input.
Point format: (Column/X, Row/Y) The strips on the board are the rows. Just saying, 'cause I don't want any confusion :P

Next, connect the input ground to the VS- of the amp chip, directly. The way you have it here, you have a ground loop! Basically, higher currents - compared to the current of the input signal - will cause voltage drops across the GND wire, which basically will feed back into the input signal.
This can cause distortion and even oscillation (worst case). That might be the source of your poor sound quality. I'd be surprised if the TDA2050 worked well with it like that!

Also, that 680uF capacitor on the feedback, shouldn't that be more like 10uF to 22uF?

You might want to add a capacitor to the 2x 22K resistor divider, to keep it more stable. The LM1875 datasheet shows a 10uF. Of course you don't have to follow the datasheet, but it isn't a bad idea to at least try.

I personally would use a comparator with some hysteresis for the timer, but that's my way of doing things :P
That may be another reason for bad sound quality, if the FET doesn't turn off cleanly, then it will have a high voltage drop across it, and the voltage at the amp will be less, which could lead to distortion at higher signal levels.
I'm surprised how it stays on for a few minutes using only the gate capacitance of the FET!

Also, the reference board diagram in the LM1875 datasheet is really messed up. The components are out of alignment with the board. They didn't do quite as good of a job of eliminating ground loops as I would like ... weird.

-Ben

[budm]

Re: Replacement for TDA2050v

"The second after posting this I spotted a few mistakes, but I'll correct them later ..." Please do because it does not look right at all.

[JonathanAnon]

Re: Replacement for TDA2050v

Next, connect the input ground to the VS- of the amp chip, directly. The way you have it here, you have a ground loop! Basically, higher currents - compared to the current of the input signal - will cause voltage drops across the GND wire, which basically will feed back into the input signal.

I see what you're saying about the ground loop. The chips only path to ground is through the FET, and there will be a slight voltage drop, so that the grounds of the chip and the grounds of the input/output will be at slightly different voltages. But because I'm switching on/off the ground side of the circuit I cant connect the battery ground to pin 3 of the amplifier chip as this will make the RC switch redundant. Maybe I should switch the positive side?

Also with regard to the interference between outputs/inputs/power, I was trying to fit the circuit on a very small space, but this is clearly to the detriment of the operation.

I personally would use a comparator with some hysteresis for the timer, but that's my way of doing things :P That may be another reason for bad sound quality, if the FET doesn't turn off cleanly, then it will have a high voltage drop across it, and the voltage at the amp will be less, which could lead to distortion at higher signal levels.

The circuit does get noisy as the RC circuit (triggering the FET) voltage goes lower. It's not something that annoys me, but was an optimization I was gonna work on.

I'm struggling a little with the software, but here's the circuit with a few corrections.

[budm]

Re: Replacement for TDA2050v

How does VS- get to the circuit GND? I see it goes to the Center pin of the 3-pin connector. What is the 3-pin connector for?

[JonathanAnon]

Re: Replacement for TDA2050v

How does VS- get to the circuit GND? I see it goes to the Center pin of the 3-pin connector. What is the 3-pin connector for?

Hi Bud, I want it so that when I push a button the amp stays on for only a short period of time, then auto shuts off. So I'm using the FET, with an RC timer at it's gate, to control the path to ground...

I got this idea from an Everyday Practical Electronics (magazine) timer which they used as an auto shut off for a cheap multimeter. But switching the ground might not work so well for an audio circuit.

[budm]

Re: Replacement for TDA2050v

I see, so you use the Power MOSFET as the low side switch to sink the load.