Newbie looking to clarify input voltage terminology for power amps.
I'm trying to replace the TDA8920BTH power amp module in my VX-11 subwoofer. The remaining electronics are fully operational, and it looks like the power supply is ±25.8VDC. When I search "class D amplifier board" I see the following examples:
"Operating voltage: DC± 15V- ± 27V (recommended voltage: ± 20V- ± 25V)" or "DC dual power"
- this is what I have from the subwoofer power supply
"Input voltage: AC dual 24V voltage power supply is recommended", "Input voltage: Recommended AC dual 24V (up to 30V)"
- is this power directly off the transformer? e.g. 2 24VAC voltages 180deg out of phase?
and also,
"Working voltage: DC24-42V switching power supply (DC)"
- is this just single-rail DC power?
Do I have it right?
I'm trying to replace the TDA8920BTH power amp module in my VX-11 subwoofer. The remaining electronics are fully operational, and it looks like the power supply is ±25.8VDC. When I search "class D amplifier board" I see the following examples:
"Operating voltage: DC± 15V- ± 27V (recommended voltage: ± 20V- ± 25V)" or "DC dual power"
- this is what I have from the subwoofer power supply
"Input voltage: AC dual 24V voltage power supply is recommended", "Input voltage: Recommended AC dual 24V (up to 30V)"
- is this power directly off the transformer? e.g. 2 24VAC voltages 180deg out of phase?
and also,
"Working voltage: DC24-42V switching power supply (DC)"
- is this just single-rail DC power?
Do I have it right?
Dual rail VAC vs VDC: what are the advantages of each in an class D amplifier module? Is one more common than another?
If you have dual rails you can have single ended class D output (hot and ground). If you have a single rail you MUST use BTL topology with hot/cold outputs and no ground. Dual rail AC has no meaning because you never supply AC.
Just tying to unpack this answer. Let’s start with the easy one:
I’m not sure what that means, but I imagine if I bought a board that specs “Input voltage: AC dual 24V voltage power supply is recommended” it means the board includes a rectifier to convert the AC to DC. But I just googled the question and found that VDC into a bridge rectifier is almost a pass thru, less the voltage drop over the diodes. So it seems that you should be able to safely pass dual rail DC into a board that specs dual rail AC for the same voltage range.
But then that doesn’t explain the following warnings, unless there is something else I’m missing:
https://www.aliexpress.com/item/4000913814304.html
Of course, now I checked a number of other sellers and there are no such warnings. But still, I'd like to understand the concept.
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For a mains powered amp, you need the AC (because that's what the mains gives you) and then rectify etc to make it into DC because that what the amp runs on.
So for mains power, the answer is: you need both.
Jan
Ah, the joys of Chinglish. What they are trying to say is that this amp has its own rectifier. It looks like it's even got a bridge rectifier per channel. And thus that you cannot connect DC voltage directly. And that you should use a center tapped transformer (24-0-24 VAC). The resulting DC supply voltage will be 24*sqrt(2)=+/-34 V. Minus the diode drops and copper/iron losses in the transformer.
Yes, the joys. But did you just tell me I cannot connect 25.8-0-25.8VDC voltage directly to an amplifier board that takes up to 24-0-24VAC? or is the key factor, "a bridge rectifier per channel" that makes this a problem?
Google told me I can do this, but I lose out on power by a factor of sqrt(2). see: https://forum.allaboutcircuits.com/threads/dc-into-a-bridge-rectifier.113354/#:~:text=Yes, you can put DC,1.4 volts through the bridge (In fact, I do have 18.8-0-18.8VAC so it looks like my power supply just put that through a rectifier to get 25.8-0-25.8VDC)
Is the full answer, "you shouldn't do this because you'll lose out on power" or "you can't do this because bad things will happen"?
Just trying to understand––and buy a compatible amplifier module.
Of course you can connect DC directly. Because of the rectifiers, you can even connect it in the polarity you fancy ;-) !
But the intend is main AC supply.
Jan
But the intend is main AC supply.
Jan
Thanks. I can accept that answer. It's not going to break anything if you connect dual rail VDC to a dual rail VAC board, but you're going to get sqrt(2) less power.
Yes. You'd need about 1.5 times as high voltage (the peak voltage of the AC if you would use that).
I just mentioned it for completeness.
jan
I just mentioned it for completeness.
jan
Jan is correct. You will lose about a volt from each of your DC supply voltages but you will need a positive and a negative rail otherwise the warnings in Chinglish will become true. That is if you use a single DC voltage. Hence my remarks on the different topologies you may encounter. The amp on Jack Ma's tat bazaar seems to be a single ended amp which needs dual supply rails. Which is used in BTL mode. Oh well... See the datasheet for details.
Thanks for the clarification. These warnings (below) specifically refer to using single DC voltage in a dual-rail application. This is BAD.
But dual rail DC voltage works--and you divide dual rail DC by sqrt(2) to get the equivalent from dual-rail AC voltage. I appreciate the patience, I only learned the difference between dual-rail and single-rail DC a few google's ago. But now I understand, and hopefully so will the next noob!
