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Old 7th August 2011, 11:03 AM   #41
AndrewT is offline AndrewT  Scotland
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That is the advantage (and extra cost) of using monoblock amplifiers located right next to the speaker terminals.
You can use them to drive any combination of speaker/ speaker driver.
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Old 7th August 2011, 11:26 AM   #42
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I was just looking at PA100 DIY 2x LM3886 in parallel gainclone audio amplifier and noticed that he uses 3 x 0.5ohm (1W) resistors in parallel on the output of each LM3886 in his parallel configuration. This ends up 0.1666 ohms (3W). He is using 30 volts and 4 ohm load. So does this mean he is dropping (.166 / 4.166) x 30 = 1.19 volts across the resistor pack, and also power dissipated in the resistors, (1.19 x 1.19) x 0.166 = 0.2 Watt.

On his BPA300 watt design, he uses single 0.2ohm 2 watt resistors on the output. How closely matched do these resistors have to be?

Also, on the feedback loop of each amp, the resistors have to be very close also, but what happens if they are not? I assume the dc offset is affected.
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Old 7th August 2011, 11:41 AM   #43
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Since you will never be able to match the amps 100 % it is necessary to put a ressitor in series to each chip amp's output and create the summed output of the parallel amplifier after those resistors. Those are the load sharing resistors, because they ensure that the load is more equally shared among the amps.
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Old 7th August 2011, 12:11 PM   #44
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Is there a way to calculate the value of output resistors needed, or just go for a low value, like 0.2 ohms and make sure it's power rating is high enough?
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Old 7th August 2011, 01:59 PM   #45
AndrewT is offline AndrewT  Scotland
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Hi Port,
do not consider building a PA100 or similar until you have learned how to answer all those question for yourself.

The complex Multi-chip implementations of the National (and other manufacturers) are not for beginners.
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Old 7th August 2011, 02:52 PM   #46
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Hi Andrew, I'm going to have a good read through AN-1192.pdf until satisfied I understand it.
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Old 7th August 2011, 05:19 PM   #47
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OK. Re-read the pdf and got a way better idea of bridged and parallel setups. I think everyone thinking of paralleling or bridging should read it.
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