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Another BPA200 post: Need some advice on finalizing design
Another BPA200 post: Need some advice on finalizing design
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Old 10th February 2018, 07:45 PM   #41
00940 is online now 00940  Belgium
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Quote:
Originally Posted by Mark Whitney View Post
Trying to understand what is in the datasheet about the PSU.

I think they intend you to use one transformer plus bridge and two 1200uF capacitors per channel.
Two 10000uF, 470uF, 0.1uF capacitors per lm3886 and three 0.1uF capacitors per op-amp.
Since the datasheet states: "40,000 μF of supply reservoir capacitance for each supply voltage rail", I think your interpretation is right. That's... 80 000uF total for a stereo amp. Even then the supply will sag with a 4r load.

Btw, be careful of your voltages and load. Max supply for 4r is +/-28Vdc, max supply for 8r is +/-37Vdc.

Another thing to watch for are all the circulating currents between the reservoir caps, the decoupling caps and the amps. You have potentially high currents (more than 10A) going through your wires and pcb. Depending on how you organize your amp, you could have heavy current flow in between pcb. That's why I finally kept all the lm3886 on one pcb (see my thread on the same subforum). Even though, it's a very good idea to go for 2oz pcb, especially since the pins of the lm3886 don't make it easy to route wide tracks.
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Old 10th February 2018, 07:49 PM   #42
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Any thoughts on the Schematic and PCB? Also, the ground plain clearances, is 0.2mm good enough?
I'd go at least for 12mil, which is about 0.3mm. No reason to push it, we're not dealing with small package smd chips.
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Old 10th February 2018, 07:55 PM   #43
tomchr is offline tomchr  Canada
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Originally Posted by sr2002 View Post
Any thoughts on the Schematic and PCB? Also, the ground plain clearances, is 0.2mm good enough?
With ±35 V supply voltage, you'll have up to 70 V between nodes. You'll need the spacing to support at least that much. If you google "PCB trace spacing calculator", you can find quite a few good references to help you.

Tom
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Old 10th February 2018, 08:05 PM   #44
sr2002 is offline sr2002  United States
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@Mark, yes I read that. But I’m wondering what would be the consequence of putting 10000uf per rail, will mean worse bass responses im assuming? Trying see if I can keep the cost low
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Old 10th February 2018, 08:11 PM   #45
sr2002 is offline sr2002  United States
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Good suggestions, so would it be a safer bet to get a +/-18 or 22v transformer (with similar VA) instead of 25v, in case I put a lower ohm speaker at some point ?
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Old 10th February 2018, 08:15 PM   #46
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in response to post44: It will mostly compromise your ability to sustain high power as the rails will sag heavily. It means that you will have an amp able to deliver high power on transients but quite a bit less continuously. For home hifi use and considering the thermal limitations of the lm3886 that might not be too much of a deal.

in response to post45: well, it all depends on your needs. What do you plan on driving ? For a 8r load, going from +/-28 to +/-36 rails means going from about 150W to about 225W. That's not such a big deal.

edit again: btw, if you haven't ordered your transformer yet, have a look at the meanwell LRS-350-24. A pair of these would power a stereo amp on +/-28V rails with 8R load. If you need more current capacity for a lower load, another pair would be needed.
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Old 10th February 2018, 08:51 PM   #47
sr2002 is offline sr2002  United States
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the LRS-350-24 looks like a single supply, I'm not sure if that would work. Plus its a switching PSU, the "audiophile" in me will not feel satisfied with that. Which is another reason I'm not building a Class D + SMPS type of an amp haha
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Old 10th February 2018, 09:27 PM   #48
Mark Whitney is offline Mark Whitney  Netherlands
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Quote:
Originally Posted by 00940 View Post
Since the datasheet states: "40,000 μF of supply reservoir capacitance for each supply voltage rail", I think your interpretation is right. That's... 80 000uF total for a stereo amp. Even then the supply will sag with a 4r load.

Btw, be careful of your voltages and load. Max supply for 4r is +/-28Vdc, max supply for 8r is +/-37Vdc.

Another thing to watch for are all the circulating currents between the reservoir caps, the decoupling caps and the amps. You have potentially high currents (more than 10A) going through your wires and pcb. Depending on how you organize your amp, you could have heavy current flow in between pcb. That's why I finally kept all the lm3886 on one pcb (see my thread on the same subforum). Even though, it's a very good idea to go for 2oz pcb, especially since the pins of the lm3886 don't make it easy to route wide tracks.
Total of 80000uF for a mono BPA200 amp!!!
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Old 10th February 2018, 09:34 PM   #49
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Originally Posted by Mark Whitney View Post
Total of 80000uF for a mono BPA200 amp!!!
Uh, yeah, right ... where's the face palm smiley ?
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Old 10th February 2018, 11:11 PM   #50
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by sr2002 View Post
the LRS-350-24 looks like a single supply, I'm not sure if that would work. Plus its a switching PSU, the "audiophile" in me will not feel satisfied with that.
As stated in Post #46: "A pair of these..." Connect two in series for ±24 V.

Many use SMPSes for audio, myself included. It's perfectly possible to get good performance that way. Granted, I do go quite a bit beyond the naked LM3886 to ensure good PSRR as my circuits apply error correction to the LM3886, which would correct any SMPS hash on the output of the amp as well.

If implemented correctly, you get clean audio with an SMPS whereas achieving the same with a linear supply is much harder.

Tom
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