Class D amplifier - Power issue?

[gibon0695]

I just hooked it up to a Power supply. I tried it at 12V 1A, 12V 1.5A & even 24V 1A and it does the exact same thing.

Power is not the issue.

It works perfectly with a single speaker connected (max volume, very loud).
But with 2 connected it does what you saw in the video.

What could it be? It must be something silly

 

[(*steve*)]

Reading the datasheet, you can't expect much more than 3W from a 12V supply.

For 10W into 4Ω you need a 17V Vcc.

My suspicion would be that at 12V there is insufficient voltage to switch the required current through the 4Ω load. If you have the speakers in series it is possible you're driving the amplifier into clipping before attaining the power level the chip can drive into 8Ω.

 

[(*steve*)]

Watching the video its hard to determine how the speakers are connected, but it sounds more like the short circuit protection is cutting in and out.

 

[(*steve*)]

But, I don't think that is the issue, simply because the speaker is much louder when I connect just one of them at a time

Remember that into a 4Ω load, double the current is required to achieve the same output power.

It all comes down to how a single speaker vs two speakers are connected.

 

[Alec_t]

Are you using a star ground system, so that analogue ground, power ground left and power ground right are all brought together at a single point only? If not, the heavier current from using both speakers could be causing ground bounce and introducing undesirable feedback.

 

[gibon0695]

Are you using a star ground system, so that analogue ground, power ground left and power ground right are all brought together at a single point only? If not, the heavier current from using both speakers could be causing ground bounce and introducing undesirable feedback.

Yes, all grounds are connected at a single point. Could separating signal ground and power ground make a difference?

 

[gibon0695]

Remember that into a 4Ω load, double the current is required to achieve the same output power.

It all comes down to how a single speaker vs two speakers are connected.

Each speaker is 8 Ohm, I will post a schematic shortly!

 

[gibon0695]

This is the circuit I have built:

I've hooked all grounds up to the same place.
Gain pins are selective. I have set gain 1 to 0V on my circuit for 20dB gain.
Everything else is the same!

Can you see anything wrong with this circuit that would cause the problem I am getting?

 

[(*steve*)]

Aaaaah, so you're not running it in bridged mode.

OK, so it doesn't matter which speaker is connected (as long as there is only one) that it works, and with two it fails?

I would recommend you keep the analog and digital grounds separate, perhaps wiring each separately to the negative terminal of the battery. I'd do the same with the analog and digital Vcc if they're separate too (and they are).

 

[Alec_t]

I've hooked all grounds up to the same place.

How much space does this 'place' take up? If it's more than a cm or so of heavy conductor (not just a single veroboard track) it could be a problem.

 

[gibon0695]

Aaaaah, so you're not running it in bridged mode.

OK, so it doesn't matter which speaker is connected (as long as there is only one) that it works, and with two it fails?

I would recommend you keep the analog and digital grounds separate, perhaps wiring each separately to the negative terminal of the battery. I'd do the same with the analog and digital Vcc if they're separate too (and they are).

Single Ended configuration for left and right...

Yes, exactly that. Works well with one connected. It does work with 2 speakers connected, but it won't go past about 75% of the input signal as shown in the video.

I will try what you have suggested, thank you

 

[gibon0695]

How much space does this 'place' take up? If it's more than a cm or so of heavy conductor (not just a single veroboard track) it could be a problem.

I have 4 tracks total.

2 at the top, one for + one for -
2 at the bottom, one for + one for -

Positive and negative are an entire track apart on both top and bottom.

The two at the bottom run directly from the top tracks after filtering the input

 

[gibon0695]

Aaaaah, so you're not running it in bridged mode.

OK, so it doesn't matter which speaker is connected (as long as there is only one) that it works, and with two it fails?

I would recommend you keep the analog and digital grounds separate, perhaps wiring each separately to the negative terminal of the battery. I'd do the same with the analog and digital Vcc if they're separate too (and they are).

I made an entire new Vero board design with your advice in mind. It now works perfectly.

Thank you!

 

[(*steve*)]

Excellent and well done!