BPA200 usage / bass responce

[drummer_Dave]

MY plan is to build a stereo version of the BPA200 with dc servo's
and a 24V 600VA toroid(an-6224) or maybe the 22v 500VA (an-5222). These voltages would be approx 36VDC and 30.8VDC respectavely which according to nationals AN-1192 (which uses 42VDC unregulated) should be ok, please correct me if i am wrong. I would like to use this unit for a PA amp and run my electronic drum kit that i made through it (through my mixer actually, a mixer that I also made ). my question is

"would this be a suitable use for the lm4780 chips?"

I know that the bass response of the lm3886 and lm4780 has been discussed here

Paralleling LM4780/3886: any impact on sound quality?

but i was hoping someone might be able to speak from there experiences as using the chips as guitar/bass/keyboard/PA amps.

I plan on picking up some 8 ohm PA speakers ( i dont know alot about speakers unfortunately) any recommendations for a pair for under $400? i am not against just buying the speaker and building the cabinets, i just need to be pointed in the right direction (what speaker to buy and dimensions for the box lowering and raising the "Q" or whatever you guys do ).

If you cant tell I would like to eventually have almost all my PA/recording gear home made, mostly because its fun.

Any help would be much appreciated. Thank you for all your input

Dave

[AndrewT]

Hi,
the BPA200 relies on four contact surfaces for all it's cooling needs.
PA is a very heavy user of power. The chips will need all the coolling they can get for this duty. It is asking a lot and fanned sinks may not keep the chips cool enough due to the heat flow bottleneck caused by those four thermal interfaces.

For PA work, I recommend discrete where one can design in the number of cooling surfaces by changing the output device count.

As an example for a hypothetical 200W amplifier:-
Domestic duty on high efficiency 8ohm speakers, 200W from one or two pair of output devices on a small to medium sink.
Domestic on low efficiency 8ohm speakers using two pair on a medium to large sink.
PA on high efficiency 8ohm speakers, three pair on a big or fanned sink.
PA on medium efficiency 8ohm speakers, four pair on a very big sink that is also fanned and with thermal cut-off.
Note in the last case one has 8 output device contact surfaces and the preceeding stages are separately cooled.
It might be useful to remember that these chips were designed for TVs and similar, that needed cheap power to convince the impressionable. Don't try to stretch them too far. The silicon might break.

[drummer_Dave]

thank you very much, that is exactly the response i needed to hear (but maybe didnt want to hear). I was kind of guessing that It may be unreasonable to just start bridge/paralleling a bunch of these amps together for such a demanding applicaation. I guess i will just go ahead and build a standard 2 x50 watt home theater amp. Looks like i will be heading over to the solid state forum for some advice on building a PA.

Thank you

Dave

[Arx]

Originally posted by drummer_Dave
thank you very much, that is exactly the response i needed to hear (but maybe didnt want to hear). I was kind of guessing that It may be unreasonable to just start bridge/paralleling a bunch of these amps together for such a demanding applicaation. I guess i will just go ahead and build a standard 2 x50 watt home theater amp. Looks like i will be heading over to the solid state forum for some advice on building a PA.

Thank you

Dave

On the other hand, I really can't see any reason it wouldn't work quite well.

I'm working on a PCB layout for a bass guitar amp right now. I'm guessing that's probably just as demanding as a PA. I'll be using 6 LM3886 chips. I figure with some well designed cooling I should be good for a few hundred watts.

I'm just going with blocking caps instead of servos to keep things simple. I bought some 30uF polypropylene caps on sale for about $5 ea. Not much more expensive than an opamp, and makes the PCB layout a lot easier.

-Nick

[drummer_Dave]

i guess really the best way to find out is to try to blow the darn things up normally i would probably leave the servos out, but my work wants me to start working on schematics and layouts so they want the boards a little more complicated so i have more chances to screw up (and learn) then they are making the boards for me Ceramic, not FR4 less skin effect bla bla bla much smoother great for analog boards. Well if i do go ahead with it I will put 2 fans in and make sure the sink is over calculated.

by the way ARX do you have schematic / link somewhere for your project. What I really want this amp for is my Electronic drums, and it would be great to see your preamp section. I know i will need more EQ but its still good to see what everyone is doing out there.

Thanks

Dave

[Arx]

No schematic yet. I'm still working on that right now. I'm going to build the amp first, and then the preamp. I'll be putting them in the same chassis, but on different boards.

The amp will be pretty much identical to the appnote "basic" version at the end. My output resistors are very slightly smaller at 0r07 instead of 0r1 (I think that's what they are.. don't have the sheet handy), and my dc blocking caps are 30uF, because they were on sale for a couple bucks cheaper than the 22uF

I've got some interesting effects in mind for the preamp section. I don't know how much I'll be concentrating on the standard tone controls though, since my bass has a fancy 3 band eq with a variable midrange frequency. I'll probably put in something basic though. I've got another idea which I've never seen done (though I haven't looked hard) which is to have adjustable linearity. One end of the scale is square wave, the other end is a pulse, with a smooth variation in between.

I'm more than willing to share my schematics and board layouts though. I could certainly use any input I can get. I'll post them once I get something done (hopefully this weekend)

I should probably do a page for the project as well. Keep your eyes open for it.

-Nick

Originally posted by drummer_Dave
i guess really the best way to find out is to try to blow the darn things up normally i would probably leave the servos out, but my work wants me to start working on schematics and layouts so they want the boards a little more complicated so i have more chances to screw up (and learn) then they are making the boards for me Ceramic, not FR4 less skin effect bla bla bla much smoother great for analog boards. Well if i do go ahead with it I will put 2 fans in and make sure the sink is over calculated.

by the way ARX do you have schematic / link somewhere for your project. What I really want this amp for is my Electronic drums, and it would be great to see your preamp section. I know i will need more EQ but its still good to see what everyone is doing out there.

Thanks

Dave