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Old 28th October 2008, 03:16 PM   #1
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Default Good chip for 5 Watts or so into 8 Ohm?

I crave the benefit of your advice:

I'd like to build me an amp giving about 5 Watts at least, to 10 Watts maximum, into an 8 ohm speaker.

I want if possible to run it off +/- 15 to 18 Volts for convenience, as the circuit will include some line-level OpAmp circuit also.

TDA2030 looks about the right spec, but I really prefer the National Semi kind of sound to the Thompson chips in general. Strong and warm rather than precise and analytical is the kind of thing I'm hoping for.

Thanks.
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Old 28th October 2008, 03:48 PM   #2
acid_k2 is offline acid_k2  Italy
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LM1875 from National

http://www.national.com/mpf/LM/LM1875.html
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Old 28th October 2008, 04:34 PM   #3
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Thanks for the link, I looked at that one but it seemed higher power than I wanted.

Will LM1875 be okay with +/- 15 Volts? I sort of gather these chips sound quite differently with different supply voltages.

If I give it +/- 25 Volts it'll put out 20W max, which is more than twice my speaker is rated for. That would make me nervous. As well as making the PSU more complex and expensive.

I'll call this chip "Plan B" I think, if nobody proposes anything more exactly fitting...

Thanks.
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Old 28th October 2008, 05:06 PM   #4
acid_k2 is offline acid_k2  Italy
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At +/-15V, LM1875 delivers about 10W (from datasheet....), and it is a way better then TDA2030.

The same PSU design will probably work.

A low-wattage speaker should not be a problem, optionally you could place a fuse in series to the speaker.
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Old 29th October 2008, 09:17 AM   #5
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If you had a single +12-15V rail you could use one of the 12V chips. TDA7350,LM4950,etc. come to mind.
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Old 29th October 2008, 10:27 AM   #6
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Quote:
Originally posted by Omega_Void
Will LM1875 be okay with +/- 15 Volts? I sort of gather these chips sound quite differently with different supply voltages.
Yes, it will be fine with ±15 V. You could expect around 9 W into 8 Ohm. Although it would be a pity to waste all that power in a regulated power supply.

Quote:
Originally posted by Omega_Void
If I give it +/- 25 Volts it'll put out 20W max, which is more than twice my speaker is rated for. That would make me nervous. As well as making the PSU more complex and expensive.
No need to be nervous. The 2x15 V transformer you need for the regulated power supply would, depending on your power supplies layout, give you somewhere between 12 and 13 W into 8 Ohm with an unregulated setup for the amp. Even 20 W will not harm 10 W speakers.

Take into account that 20 W would be the peak output, while your speaker rating is for an average power during a specified amount of time. Even loud listening hardly surpasses an average of 1 W at home. Look at your speaker's efficiency at 1W/1m. Compare that to the fact that an average SPL of 80 dB(A) in industrial environments means in many countries that you are obliged to wear hearing protection. Peaks that may reach the amplifiers nominal output are only present for so short amounts of time, they won't do harm.
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Old 29th October 2008, 04:36 PM   #7
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Looks like LM1875 will be just the ticket then. Excellent!
Thanks folks!
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Old 29th October 2008, 07:51 PM   #8
Igla is offline Igla  Slovenia
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I have LM1875 amp on +- 16V (2x12V sec; 1.5amp - small tranny; one bridge made of SB560 diods). Sounds just incredible good. LM3785 doesn't sound that good on the same PS.
I also like my TDA2050 amp on the same power supply. Hard to tell which is better (I mean by sound, not by datasheet specs).
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