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captain 10th October 2004 03:40 PM

Newbie wants to build a "GainClone-Like" 5.1 Channel Battery Powered Amplifier
 
My first post...
This is a fantastic site...

Anyway...I've been lurking for too long...trying to digest what this whole "GainClone Thingy" is. And, now it's time for some questions...but first some background.

I am striving for something "minimal" in a total system and have seen some specs on the latest Toshiba DVD players SD-6915 and SD-4960. Not only do they have all the latest bells and whistles...but they also have a "full complement" of 5.1 analog audio outputs (as well as an normal set of 2-channel analog audio). It appears all the MP3, WMA, Dolby Digital, DTS, DVD Audio, SACD is handled internally by the DVD player itself...(yes it says it has all these features). As part of the "DVD Player audio set up" it even has settings for speaker size...etc...and will generate test tones to adjust the volumes...just like my Denon Receiver. That also seems to point to a "master volume control" on the remote labeled "TV volume". I'm assuming that this will control the volume on all the analog outputs at the same time (the 5.1 as well as the separate 2-channel) but you never know. I'm sure there are some gotcha's. The owners manual is fairly pathetic.

The bottom line is, I've never seen this much capability at a consumer price poing. The next thing you know they'll put in an FM/AM radio. No fancy front panel display required...everything comes up on a large TV screen. Now, just what will that do to the full blown AV Receiver business???

That only leaves a Power Amplifier requirement. So, since I want to follow the "minimalist approach" (I don't listen to the radio and already have adequate speakers)...this seems to be all I need...

So, I want to build a battery driven 5.1 channel amp (+-12 volt rails) using two 12 volt SLA (Sealed Lead Acid) batteries. I want to use batteries because I'm not enthusiastic about screwing around with mains and bulky transformers. It also seems to me that it will "by default" provide smooth power source leading to better sound. Although batteries themselves are bulky, they along with the chargers can sit down on the floor and only +12, -12, and GND need to come up to the amp enclosure.

The NS LM4782 3-channel chip seems to be a good option. They're rated at 25 watt...which is a little less oomph than the LM4781 chips (also 3-channel) that are rated at 35 watt. But I guess the 25 watt chip is is probably a better choice with the lower voltage rails.

I plan on following the application design schematic given on page 23 of the LM4782 PDF data sheet.

Questions:

1. Will the voltage +-12 (really +-13.7 fully charged) be enough to drive this chip? I think chip recommends a minimum of +-10 volts.

2. Since the juice is coming from a battery (with presumably no ripple)...does this change the capacitor size on the lines that feed the the power. The datasheet shows 3 capacitors (2200uf, 10uf, and .1uf) on each rail.

3. Heatsinks...the chip is fairly wide (dimensionally) and it seems that the majority of T0-220 stock heat sinks (such as Avvid brand) won't work...the chip is too wide. Does this chip fit onto any stock heat sinks?

4. I was going to ask about different capacitor varieties but I see a post a little before mine addresses this. I want to stick with Panasonic Capacitors. But Digikey has Pansonic SU-Series, M-Series, NHG-Series, Z-Series, FC-Series, EB-Series, KS-Series, KA-Series...etc. It all leaves me very confused. Is the FC-Series the good old Panasonic stand-by that everyone seems to use?

I just wanted to run this by anybody who has had experience with this LM4782 chip and those who have dabbled in using batteries as power supplies.

Also, I wanted to share with everyong a fairly complete explanation of lead acid batteries with respect to selection and charging (there are nine .htm pages).

"www.ibexmfg.com/appnotes/app01.htm" thru "/app09.htm".

It is a very thorough reference manual and seems to point to the simpler (and cheaper) 2-mode float charger as the way to go in using Batteries as Power Supplies. The 2-mode chargers can stay powered on and attached to the batteries while the amplifier is running. This in itself will add some ripple. The other option that I've seen is to put the cargers on timers set to come on overnight. That means during music play the power is totally smooth battery generated.

So, that's my goal.
I guess you could say the concept falls into the GainClone category. Something very minimal...and yet with some quality output.

Any feedback would be appreciated...
Sorry for the length of this post...

psychosteve 12th October 2004 11:31 PM

hey bud, as it seems no one else is going to answer, ill have a go. but i havnt seen the chip or data sheet.

1, dont see why not, could run a bit short if the batterys are low, you get oscilation with low voltage.

2, yes, the large one is probly ripple suppresion and a charge hold, to supply a bit of umph when driven hard so keep but you could probly get away with smaller, the other smaller ones id keep as they are, they probly filter stray freq. picked up from other stuff.

3, yes, its called aluminium bar. you can buy plain sink, by the length, plain flat one side finned the other, just cut to lenth and drill holes where needed.

4, dont ask me on that one, i usualy just buy kits or salvage stuff from old amps.

5, i know there wasnt a Q 5, but on batterys and charging, id look at a 4pole switch, one pair turns on the amp, the other wired the other way round, turn off the charger at the same time!! charge when not playing, no charge no ripple when amp is on. then the batterys are always charged ready to play.
unless you use the amp all day every day with no down time!!

hope that helps, see you later bud, steve.. ..

captain 13th October 2004 01:48 AM

Thank's much Steve.

I was beginningj to get a complex.
My original post was just too long.

By the way...good idea on the on-off switch.

Maybe if someone else reads this they can let me know of a source of stock aluminum heatsink here in the States.

psychosteve 13th October 2004 11:24 AM

on batterys look at lm1875, and some answers to cap. sizes look here, http://www.diyaudio.com/forums/showt...threadid=42472
and id forgoten about BYOB, bring your own battery. try his site for more info on battery powered gain clones. hope this helped, steve.. ..

psychosteve 13th October 2004 12:12 PM

as for heat sinks, i know maplins in england has them, try a computer sink, computer fairs have surplus or over stock / old models for sale dirt cheap!! see you later, steve.. ..

Sherman 13th October 2004 01:52 PM

Quote:

Originally posted by captain
...Maybe if someone else reads this they can let me know of a source of stock aluminum heatsink here in the States.

American Science and Surplus has some very nice heat sinks sufficient for your purposes at under $2 US. I've used them in Gainclones and have been very happy with them. I picked them up at a retail outlet but you can order them from their website also.

They have had a smaller one (that I've used) that measures about 4 inches by 3 inches. The base plate is between 1/4 inch and 1/2 inch thick and the fins are 1/2 inch apart and about 1 inch high. The ones I got were a dull gold in color.

They have also had a larger one that was about 8 inches by 3 inches with 1/2 inch fins spaced at about 1/4 inch. I don't know if that type is still available. That one is bright aluminum.

HTH,

jkesa 14th October 2004 03:06 PM

A good source of sinks besides old amplifiers, are old big monitors. I got a 8inch by 12inch by 1in sink out of one of them.

psychosteve 15th October 2004 12:35 PM

saftey!!!
 
there was another post on the forum about the saftey aspect of stripping CRT equipment, tv's and the such like, i think it was in the thread, salvaging transformers, or some thing like that.
im sure the moderator would say dont try it on saftey grounds unless you are very confident you know what your doing. the voltages used to power CRT run upwards of 10,000volts!!! so be careful, but yes there are some nice heat sinks in there, whether its worth it, i picked up a 3x2x4 inch sink for 3, about 1.75 dollars
see you soon, steve.. ..


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