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Old 12th August 2008, 10:28 AM   #1
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Default schematic for 20 watt lme49830 needed

Ihave chosen to built a small portable amplifier based on the lme49830 dip has any one built a small wattage with speaker impedance around 6 - 10 ohm range will be running pairs of 4 ohm speakers in series and 8 ohm
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Old 12th August 2008, 11:25 AM   #2
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Strange choice. A high quality IC with the need for additional MOSFET transistors that needs at least ±20V as power supply and is good for several hundred watts on the one hand. A serial connection of 4 and 8 Ohm speakers on the other hand, which is very likely to sound as bad as any speaker can get.

For a portable amp there are manifold ICs out there that were designed for use in cars, and that run perfectly from a 12V or so battery. E. g. TDA1557, TDA7374 or µPC2500. If you want something small and more efficient, go for class D, e. g. here

Serial connection of speakers already has drawbacks, when the same type of speaker is used. For different speakers, like in your case, it is a waste of time and money. Speakers form complex impedances. The voltage division formed by serially connected speakers results in an unpredictable and uncontrollable frequency response of either chassis. If you don't want or need a crossover, use the two speakers in parallel with an amp than can cope with the resulting low impedance.
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Old 12th August 2008, 11:44 AM   #3
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for portable use
I would not say you need LME49830 mosfet driver.
Maybe it is even a bad choice. LME49830 is a high voltage/ higher power masfet output stage driver.

first thing we like to know, in order to advice,
is

1. what power Watt RMS output is your need?
2. what sensitivity and impedance your speakers will have?
Impedance is OHM. Sensitivity is DB SPL.
3. what power supply will you use?
re there several power supply options .. or only one Car Battery(~12 VDC)?

If you power need is more than 12 VDC can give into your impedances
then you have to try metyhods to increase, double the voltage.
Otherwise you must parallel many 4 Ohms speakers = more power out.
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Old 12th August 2008, 08:43 PM   #4
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Default speakers

The 4 ohm speakers that are operated in series are identical speakers so shouldnt they balance out each other in the impedance and thanks for the suggestion on the tda7374 chip for i can use the lm317t in conjuction

120 ac to 24ac to rectifier bridge to lm317t to tda 7374
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Old 12th August 2008, 08:43 PM   #5
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Default speakers

I do not crank up the speaker I hardly go above 1 watts for I have a small room and I have a Denon DRA397
The speakers are all about 85 to 95db/spl at 1w
some of the speakers are Bose and I will be using crossovers the mid range is where I am using the 4 0hm speakers bass tweeter are 8 ohms and I will be using a 4 way crossover
I would not wire none identical speakers in series
I am sort of using the Bose 901 speaker idea
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Old 12th August 2008, 08:43 PM   #6
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Default i forgot something

this is for testing the speakers not for regular use for I am determining the best frequency response for the different speaker so that I can determine the best crossover points
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Old 13th August 2008, 07:55 AM   #7
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Ah, I see, I misunderstood the first thread. Still a serial connection of speakers has drawbacks. But with two 4-Ohmers you have little other choice.

Seems I also misunderstood what you think of as portable, if you have AC power supply.

The LM317 might be a bit tight for that task. But again, with a 24 V transformer you have little other choice than to use a regulator for that IC.

Or use an unregulated supply with something like the LM1875, TDA2030 or so in single supply application. Even better with a different transformer and split power supply.
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Old 13th August 2008, 07:11 PM   #8
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Default Speaker Builder amplifier

What about something incredibly simple? Actually, what about mine? Beginner's Gainclone, HiFi LM1875, The Amplifier Board

Its been durable and lovely.

Omit the 470R for your application. Its an equalization to cope with variety that's generally expected to happen whenever using a capacitor to block dc at the input. Instead, omit both the 470R and omit the variety as well. Reference: The Audiosector amplifier specifies Blackgate "N" 4.7uf for the job of DC blocking at the input. So, that ought to do it fine.
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Old 14th August 2008, 01:42 AM   #9
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Default other ic regulator chip

I think the other regulator ic I have is the ua723 I was originally planning to use with the 49830 to get a very clean test signal and using a 5k precision pots for the feed back and rl to find the right balance to find a starting point

To give a better idea of what is going on

laptop and audigy nx for spectrum analyzing and tone generation using virtins software
audigy nx to amplifier to capaitor, resistor switch board to speaker(s)
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Old 14th August 2008, 05:51 AM   #10
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This is perhaps beyond my ability to contemplate because of the speaker that's built in a different room than it will be employed, built to a machine when an ear will use it later, and built on a different amplifier than will be used during performance. To me, it seems that these variances would exceed the entire dynamic range of a recording, because the speaker isn't built to its purpose. My apologies, but I have no idea how to help you with that approach.
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