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Old 26th August 2006, 09:52 AM   #1
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Default How much current draws a 3886 at 4 Ohm & max. power?

It's because i want to try a regulated PSU and i want to know how much power the regulation has to dissipate...
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Old 26th August 2006, 10:44 AM   #2
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Default Re: How much current draws a 3886 at 4 Ohm & max. power?

Quote:
Originally posted by Bassterror
It's because i want to try a regulated PSU and i want to know how much power the regulation has to dissipate...
You need to know the supply voltage.

Example: supply voltage +/- 35V. Max output voltage something like 32V peak, which is 8 amps into 4 ohms peak.

BUT, that doesn't mean the supply/reg has to be dimensioned for 8 amps continuous. Music has something like a 1:10 ratio of peak to avarage level, so a reg that can continuously provide a few amps and up to 8 amps for a second or so would be adequate.



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Old 26th August 2006, 12:26 PM   #3
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Hi,

Quote:
Music has something like a 1:10 ratio of peak to avarage level, so a reg that can continuously provide a few amps and up to 8 amps for a second or so would be adequate.
Hmm...
I'd like to try this one:
http://www.shine7.com/audio/pa100_supply.gif

I want it to be foolproof, and i don't want the stuff to burn when the amp is fed by a sine wave...
I want to use an MDF Case

I've got a 24V Transformer, so i should have about 34V.
For 4Ohm loads, the Chip should not get more than 30V.

If i assume the max. output voltrage will be ca 27V, I've got 19V RMS.
19V * 4Ohm = 4,75A.

4V regulation drop * 4,75A = 19W pure heat...
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Old 26th August 2006, 01:10 PM   #4
AndrewT is online now AndrewT  Scotland
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Hi,
while you are still learning, I think you should keep it simple and use an unregulated supply.
Get this working properly and you may decide not to add a regulator.

Once you have learned a bit more about amplifier power input requirements then you can consider designing a regulated supply for your amplifier.

Take it in manageable steps. You will learn more that way and maybe avoid the mistakes other beginners make, by following a recipe but not understanding what they are trying to achieve.
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Old 26th August 2006, 05:26 PM   #5
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Other member, correct me if I'm wrong here but couldn't he parellel transistors in the regulator schematic to get more current output and spread the heat dissipation across them?

Bassterror, does it have to be regulated? I made an amp out of LM3875 (lower power by a little bit) with an unregulated supply and it works fine. I can see regulating the supply if your running the amps very close to there max voltage but I don't see why for the lower ones.
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Old 26th August 2006, 09:09 PM   #6
Nordic is offline Nordic  South Africa
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Hey guys remember me...

I would say if you have the overkill attitude.. you could look at the chip's rating which I think quotes an 7.5A to 11A peak output....(varying from chip to chip)

It won't be a futile learning process... just one that is more expensive than it needs to...

Allthough Janneman is far ahead of me in knowledge... I.e. me speaking under correction... but if you fed the 3886 35V into 4ohms, it would proabably be dead long before you got it to try to pull 8A.
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Old 27th August 2006, 11:46 PM   #7
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Hi,

thanks for your replies

Quote:
while you are still learning, I think you should keep it simple and use an unregulated supply.
Quote:
Bassterror, does it have to be regulated? I made an amp out of LM3875 (lower power by a little bit) with an unregulated supply and it works fine. I can see regulating the supply if your running the amps very close to there max voltage but I don't see why for the lower ones.
Well...
I've been to get a cheap 2x24V/220VA Toroid for 3 from a flea market and i also have some TIP2955. And i just got 2 317 ICs from a friend.

If i get a cheap 18-20V toroid....
But at the moment these parts are lying idle on my desk.

Quote:
but if you fed the 3886 35V into 4ohms, it would proabably be dead long before you got it to try to pull 8A.
That's what i think too...

What do you guys think, what should i do?
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Old 28th August 2006, 07:01 AM   #8
AndrewT is online now AndrewT  Scotland
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Hi,
build a simple unregulated PSU using some of the details in the chipamp threads.
Use 8ohm speakers. They better suit chipamp current abilities.
Save the extra bits for phase two.
READ about chipamps.
Snubbers on the rectifiers.
Interference supression.
Decoupling and bypassing.
Etc.
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Old 28th August 2006, 07:10 AM   #9
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Quote:
Originally posted by Bassterror
Hi,



Hmm...
I'd like to try this one:
http://www.shine7.com/audio/pa100_supply.gif

I want it to be foolproof, and i don't want the stuff to burn when the amp is fed by a sine wave...
I want to use an MDF Case

I've got a 24V Transformer, so i should have about 34V.
For 4Ohm loads, the Chip should not get more than 30V.

If i assume the max. output voltrage will be ca 27V, I've got 19V RMS.
19V * 4Ohm = 4,75A.

4V regulation drop * 4,75A = 19W pure heat...

I your calculation it's 19W in TWO regs, so less than 10W each. And that ONLY when you do bench testing with full power sine waves.

Anyway, you have RMS figures. The peak currents are higher, and your reg must be able to provide them (on an intermittent basis).

Jan Didden
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Old 28th August 2006, 11:03 AM   #10
ash_dac is offline ash_dac  United Kingdom
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Quote:
Originally posted by ifrythings
Other member, correct me if I'm wrong here but couldn't he parellel transistors in the regulator schematic to get more current output and spread the heat dissipation across them?

Bassterror, does it have to be regulated? I made an amp out of LM3875 (lower power by a little bit) with an unregulated supply and it works fine. I can see regulating the supply if your running the amps very close to there max voltage but I don't see why for the lower ones.
Hi,

I thought a regulated supply was only needed only for class A amps ?
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