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Old 14th January 2009, 03:34 PM   #1
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Default Chip Amp General Question

Hi, I'm new to electronic design and I'm working on a USB DAC project.

I'm thinking of adding a power stage to this project but I don't have any experience in Audio Power Amps and not much time to spend.

If I take a Chip Amp (LM4780 for example) and connect it as per data sheet, is it gonna be ok? I'm not interested in extremely high quality.

Is the LM4780 an easy IC for a newbie? If not, which one do you suggest?

Thank you very much
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Old 14th January 2009, 04:01 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
the 4780 is a two channel chipamp.
I think the single channel version 3886 is likely to perform better. It can certainly be kept cooler due to using two surfaces to dissipate the internally generated heat.
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Old 14th January 2009, 04:16 PM   #3
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I need a stereo one.

Are you suggesting to use two monos instead of a stereo?
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Old 14th January 2009, 04:21 PM   #4
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Quote:
Originally posted by bluetech
I need a stereo one.

Are you suggesting to use two monos instead of a stereo?

Hi,
Unless you are cramped for space in the chassis, it would be better to use 2 LM3886 instead of a single (stereo) LM4780 as the two chips will dissipate heat more effectively than the single unit.
What voltage will you run this at?
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Old 14th January 2009, 04:33 PM   #5
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I don't know yet. I guess something like -/+ 24 or 27 or something similar

I found on the data sheet a single-supply circuit. Is that recomended?
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Old 14th January 2009, 04:58 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
your low supply voltage of <=+-27Vdc is normally used for 4ohm speakers.
If you require best quality, use high efficiency 8ohm speakers preferably >=95dB/W/m (real watts in to an 8ohm load).
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Old 14th January 2009, 07:12 PM   #7
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Bluetech,

It depends on how you are going to implement it and your soldering skills.

Are you going to buy a pcb kit? are you going to etch your own pcb? are you going wire it point-to-point?

unless you are using a kit, LM4780 is not so easy to work with because of the fine pin spacing

as this is your first amp project, go for 2x LM3886 for simplicity

much easier to work with and better heat dissipation

LM4780 is essentially two LM3886's in one

Good luck!
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Old 14th January 2009, 10:11 PM   #8
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I'm going to make my own PCB

Thank you very much for your comments
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Old 14th January 2009, 10:14 PM   #9
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Quote:
Originally posted by AndrewT
Hi,
your low supply voltage of <=+-27Vdc is normally used for 4ohm speakers.
If you require best quality, use high efficiency 8ohm speakers preferably >=95dB/W/m (real watts in to an 8ohm load).

What voltage will be able to drive better 4 ohm speakers?

Thank you for your comments
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Old 15th January 2009, 07:02 PM   #10
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Quote:
Originally posted by bluetech
I don't know yet. I guess something like -/+ 24 or 27 or something similar

I found on the data sheet a single-supply circuit. Is that recomended?
Single V+ supply not recommended.

I used an adjustable power supply in my first LM3886 project, with 2 off LT1084 regulators and 2 off 10,000uf filter caps

http://www.shine7.com/audio/gainclone.htm

LT1083 is 7.5A in the weblink but I myself went for the LT1084 with 5A

The speakers are 4ohm and I am currently using +/-28V with good results, but I have experimented with +/-24V and had no problems

Again, as this is your first project, go for the flexibility of an adjustable regulated PS my opinion. You can set it up to whatever voltage you like.

Personally I love the sound of a reg. PSU despite what people say about stiff behaviour etc. Benefits are low noise and good bass for relatively little money. If you think LT1083 is too expensive you can use LM317 (with transistor for increased current capability)

So if you go for a regulated PS, don't forget the heatsinks for the regs - the more voltage drop across them, the more heat they will dissipate. But they don't need to be too large though.

Let me know if you need a schematic.

Finally I personally like soft-recovery bridge rectifiers, instead of the commonly used MUR860 diodes which are fast-recovery and induce ringing plus are not cheap (you'll need 16 of them). Either would be okay if used with reg. PS

Good luck
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