"BPA 400"? Other high power chip amps?

[AAXenoStrange]

Is it feasable to make a "BPA 400" using 4x lm4780 -- 4 elements in parallel bridged with another 4 elements using between a +-30 and 38V swing... not sure If I'd want stability into 2 ohms or not yet... Regardless is there a better chip alternative to the lm4780 for higher power apps?

Thanks,
Dylan

[AAXenoStrange]

2 possible issues (asides from the complexity wiring this thing p2p) I am not too sure about while going ahead with this -- Very low input impedance due to 8 ICs as well as possible increase in distortion due to 4 slaves in parallel? How significant would the increased distortion be? Any way to go about calculating this?

Thanks
Dylan

[mwmkravchenko]

THe idea is feasable.
To calculate the power disapations you can download some of the excel spread sheets posted on this board. In a nut shell there will be heated areas under the LM4780 chips that you will be hard pressed to get rid of. It will make for an amp itching to die. A better solution will be to use multiple LM3886 chips and spread them evenly over a large enough heat sink. As for the low input impedance you may construct a buffer as per the BPA200 design. There are some thoughts.

Mark

[R.G.]

At some point, doesn't it make sense to go to stay at some reasonable power level with one or a few chips, and then do one amp per driver and multiple drivers?

[jackinnj]

Originally posted by mwmkravchenko
THe idea is feasable.
To calculate the power disapations you can download some of the excel spread sheets posted on this board. In a nut shell there will be heated areas under the LM4780 chips that you will be hard pressed to get rid of. It will make for an amp itching to die. A better solution will be to use multiple LM3886 chips and spread them evenly over a large enough heat sink. As for the low input impedance you may construct a buffer as per the BPA200 design. There are some thoughts.

Mark

An LM4780 is a pair of LM3886's.

I found when I built a bridged LM4780 amp that it was necessary to make a little clamp/bracket to fasten the chip onto the heatsink. But you can drive it to a full 120 watts with some forced cooling and a clamp. Using machine screws to keep the chip in place isn't satisfactory.

[mwmkravchenko]

I have to agree that a LM4780 is a dual LM 3886.
That's not news to me.

The point I was trying to make that a heat sink works more effectively thus cooling better if it is warmed in more than two hot spots. The use of eight LM3886's will spread the heat over a much larger area and therefore give you a better chance of creating an amp that won't be shut down by the SOA protection inherent in the design of the chips. Granted point to point wiring will be a real headache

I still have to make one of these beasts. I have paper designs and have crunched the numbers for almost three years. Not enough time

MArk