using LME49810 to drive multiple TDA7293 ?

[rcownie]

Hi,

I'm slowly designing a 2 x 200W amplifier intended for live music performance
(see my band at http://www.elh.org) to drive a subwoofer + a Bose Stick-style
mid/high main speaker. The goal is to match or exceed the Bose Stick
system for about $300 in parts ($150 for car audio speakers, $150 for amp)
instead of the $1800 of the Bose - which would be fine if I didn't need 3 or
4 of them for the whole band :-(

I've been looking at something like the quekky PI293 triple TDA7293, as
that seems relatively simple and robust while having enough power. But
I've read some comments suggesting that the TDA7293 sound quality
suffers in master/slave mode due to slow slew rate.

I've also been inrigued by the great specs of the LME49810, but don't like
the separate-driver-board confiurationgs in the techdiy kit, and am not enough
of an analog guru to build an output stage myself.

So I'm wondering if there might be a neat design using an LME49810 as the
voltage-gain stage but then driving multiple TDA7293's in slave mode.
Hmm, maybe that doesn't work with the source/sink output of the LME ?

Alternatively, is there a good way to buffer the front-end output of the TDA7293
without introducing too much distortion ? Or is there some other good
voltage-gain stage which would do the job accurately with enough drive
to maintain the slew rate for 3 (or more) TDA7293 ?

I really like the fact that you can hook up multiple TDA7293 output stages
without any ballast resistors, and thus get a high-current output with all
the beneifits of thermal and overcurrent protection, and very few external
components.

Thanks for any comments
Richard Cownie

[Dag]

Did you search???

Check this out:
More Power out an TDA7294/3

Last schematic is used by Linn in their Chakra amps with excellent results!!!!

[rcownie]

Thanks to the reference to an interesting thread, but really my idea is the other
way round: I like the output stage of the 7293 because it's fairly bulletproof
with its MOSFETs and thermal protection, and can be paralleled to provide
more current. What I'm concerned about is the low slew rate - perhaps
especially with multiple slaves. So my thought is to use the better front-end
voltage-gain stage of the LME49810, and then just use the the output stages
of multiple TDA7293's.

[BWRX]

Hi Richard. Instead of using parallel chip amps, have you thought about just using the LM4702 or LME49810 with discrete output devices to obtain the output power you're after? That or maybe even some ready made class d modules would be a better solution than paralleling chip amps.

[rcownie]

Brian - thanks for your reply

I guess it depends what you mean by "better" ... As I said, I like the idea of
all the thermal/overcurrent protection built into the chipamp output stages -
really don't want to blow up the output transistors permanently in the middle
of a gig :-( I realize LME49810 is really intended to be used with a
discrete output stage - just wondering if there's another possibility that
leverages the cheap ($6) and bulletproof TDA7293.

I'm very intrigued by the class D technology - especially for the high
efficiency and the ability to get low distortion even at high output levels.
But I also get the feeling it's a little tricky to get it right, and while there are
plenty of prepackaged solutions for lower power, 200W+ seems a bit
beyond those.

The other part of this whole project is using shielded Cat5e ethernet cable
to get power and multiple audio signals around on stage - probably power
+ 5 audio channels per cable. You wouldn't believe the amount of cables
we have to carry around for a 5-piece band, and the setup and tear-down
is a real pain. Ideally the amps would be in a powered mixer that just had
a couple of RJ45 jacks providing 10 input channels. And then you want
the whole thing to be small, light, and robust - so I'm tending towards having
a single PCB, rather than a whole bunch of modules and a rats-nest of
wiring. And maybe fitting it in a 1-gallon paint can - a neat, cheap, and
easiily luggable enclosure, which can also act as a chimney to improve
cooling.

All a little unorthodox, and I don't know when I'll find time to build it.

[BWRX]

Consider that you could get around 125W @ 1% THD+N with a single pair of output devices driven by an LM4702 and you could easily get 200W with 2 or 3 pairs of output devices driven by either the LM4702 or LME49810 for not a whole lot of money. While the LME49810 circuit would not have quite the same protection features as a TDA7293, it does have a clamp function that "keeps all transistors in linear operation when the output goes into clipping," which could be useful for pro audio use. Check the part datasheet for more info.

Originally posted by rcownie
while there are plenty of prepackaged solutions for lower power, 200W+ seems a bit beyond those.

There are three main manufacturers of class d modules discussed on these forums who have modules that can handle up to 400W - Hypex, Coldamp, and NewClassD. You might want to check them out.

Originally posted by rcownie
And then you want the whole thing to be small, light, and robust... I don't know when I'll find time to build it.

Small and light point towards class d and not having time to build it points towards ready made modules. Of course the DIYer in you will greatly influence your choice no matter what anyone on here says

[rcownie]

Thanks for your info, Brian

Those class D modules are really neat ... but not cheap :-( If I ever
get this whole project done, I'll probably want 8 amps in all - 3 sets
of subwoofer + full-range, plus one spare set. Going the (mostly-)chipamp
route I can shoot for $40 each rather than $200+ And my DIY side likes
the idea of something simple enough to build and fix myself.

But putting a discrete output stage on the LME49810 probably does end
up simpler (especially with MOSFETS) and cheaper than using parallel
7293's - and also would allow voltage beyond the +/-60V maximum of
the 7293.

[SpittinLLama]

Another advantage to using a LM4702 or LME49810 type of part is that your supply can be all over the place without worry. You want run to run about +/-70V for a nice 200W amp (8 ohms) but because the max rails are +/-100V you have plenty of headroom. With chip amps it is always a problem to get the supply you want under load and stay under the max voltages, if you want the most power out of the chip amp. Just makes some things easier.

When you pick your output stage device type then you can pick the best driver part. I hears some more drivers are coming out soon from National.

-SL