Upgrade Alexw88's BPA300 desighn?? - diyAudio
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Old 3rd January 2009, 12:30 AM   #1
madam is offline madam  Hungary
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Default Upgrade Alexw88's BPA300 desighn??

I would like to upgrade my amp in the near future, and I would like to make it as "high -end" (whatewer it is) as possible.

I've made Alexw88's (www.shine7.com/audio/bpa300.htm) Version 2.0 desighn in the summer (Thanks again Alex!!!)

I found really great, but in my version of the PCB layout I found some problems, and I would like to make another round.

I would probably use 5 LM3886 chips in paralel and bridge them with the same (or any advise to get beter result ???) way as before. /Lundahl trans./

In this case I could get even more power (I have some 8 Ohm MTM speakers...) and if I make the PCB to support 10 chips with the input transformer on board (probably in the midle) and a second PCB for the PSU (maybe a re-calculated Carlosfm style unreg. snub. PSU with a GOOOD soft-start) with the shortest possible twisted cables in the system....... maybe it would be a real upgrade 4 all of us. (GROUP BUY possibilities here..... my previous board was about 5 euro or some )

I could find some really powerfull heatshinks here.... (aprox 110 x 160 x 50 mm, but like a tank, and I run 2 BPA150 on it and have about 40 C whitout holes on the board under it) and it's cheap 4 me .... and as I can see it might be able to run 10 chips on it without a fan (or with a variable, termal dependent cooling system, with swich off as starting)

Mainly I woul like to drive my MTM fronts, with a 0.1uF high quality F-F cap between the pre and this new unit (to have a frst order Xo under 100 Hz; my MTM's are sealed box... f about 65-70 Hz) and anoher amp 4 my BIG sub with a 3rd order lowpass to 100Hz

This would be easily kill my neighbours in the capital (probably some town-rehabilitation?????)
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Old 3rd January 2009, 02:42 AM   #2
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Any more then 3 chips parallel is over kill, you are going to get the same output wattage with 3 as 5 ect......
at 35VDC+/- supply your looking at 280 to 290watts into 8 ohms, now if you drop to 4 ohms and 5 chips you will get about 380 and so on.
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Old 3rd January 2009, 08:36 AM   #3
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±35 V in a bridged configuration will give you a theoretical maximum of 229 W into 8 Ohm. Practically it will give less. BPA-200 was measured with 225 W continuous clipping power at 8 Ohm from ±42 V rails from two 385 VA transformers.

Adding more bridged pairs in parallel helps to make the amplifier stable at lower loads. While PA-100 is only stable down to 8 Ohm from ±42 V rails, BPA-200 was designed to be stable down to 4 Ohm. BPA-300 is stable down to 2 Ohm. From BPA-600 on they should be stable down to 1 Ohm.

They will all give you the same output power into 8 Ohm. P = UČ/R, where U = rail voltage - voltage drop under load - voltage drop across IC at load.

If you want the maximum achievable power, get a 2 x 30 V transformer with sufficient VA rating, but then you might have to get even bigger heatsinks as well. And don't expect too much difference. You will get 1,5..2 dB more SPL, if your speakers can handle the additional power.

Quote:
[i]Originally posted by madam[i]
This would be easily kill my neighbours
That is
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Old 3rd January 2009, 10:01 AM   #4
AndrewT is online now AndrewT  Scotland
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Location: Scottish Borders
10off 3886 amplifiers to get ~200W into 8ohms.
You'll get better performance and if you want it more power by using a single LME498x0 driver chip with a 2pair or 3pair output stage.
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