8 X LM3886 design sought

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gary h

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Joined 2006
#1
Hi all,

my next speaker project is an actively eqed design and will require 8 modest (~50W) amps to drive all the speakers. This LM3886 design has been recommended:

http://www.national.com/mpf/LM/LM3886.html

I am a newbie at amp building. I'm wondering if I can incorporate 8 amps with 8 power supplies in one chassis and use one transformer. Basically I'm trying to consolidate the package. If there are any designs available or anyone with experience with this kind of project I would appreciate some advice.

thanks,

gary
 
#3
gary h said:
Hi all,

my next speaker project is an actively eqed design and will require 8 modest (~50W) amps to drive all the speakers. This LM3886 design has been recommended:

http://www.national.com/mpf/LM/LM3886.html

I am a newbie at amp building. I'm wondering if I can incorporate 8 amps with 8 power supplies in one chassis and use one transformer. Basically I'm trying to consolidate the package. If there are any designs available or anyone with experience with this kind of project I would appreciate some advice.

thanks,

gary
Click to expand...

Hi gary,
i also making similar kind of project but only problem i am facing it of PSU , can u give me some detail on it

Regards
Elnec
 
#5
Re: Power supply

tiltedhalo said:
A Chip, 3886 is an AB amp and achieves about a 60% efficiency so at 50W output you need between 70 and 80W's of supply. then multiply by the number of amps, 8*80W=640W+ 10% for overhead. Just find a trans in that range and away you go.
Click to expand...


hey tiltedhalo,
thanks for your suggestion good 700w PSU for this as i'm not able to find it .please tell me or give a link on schematic for this PSU

thanks in adv

regards,
Elnec
 
#6
You can cut down the number of chips by using the LM4780 which is a pair of LM3886's in one package -- I think Peter Daniel or someone sells a PCB for this.

You won't actually need the theoretical max power unless you are using the chip to run servo motors in a laboratory -- saying this, however, a number of people are using the transformers from John Ango at www.antekinc.com -- they are now advertising in AX which means they support the DIY community. These trafos are really beefy -- for CNC machine use and a bit of overkill -- but the price is right.

Jack
 
#7
jackinnj said:
You can cut down the number of chips by using the LM4780 which is a pair of LM3886's in one package -- I think Peter Daniel or someone sells a PCB for this.

Jack
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Hi Jack,
first of all, i live in india & LM4780 is not available in india & so can u suggest any other alternative for this, your suggestion are welcome

regards,
Elnec
 
#11
gtforme00 said:
I second the Antek recommendation. I purchased two of the 20V + 20V 600VA for my 12 channel LM3886 project. I used boards from www.chipamp.com for the LM3886.

PM me for more info, I might even have some extra parts laying around.

Regards,
David
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hey david,
can u give me list of part that r lying around at your place so that if i need any, i can ask u

thanks

regards,Elnec
 
#12
Thanks for all the replies,

The project involves a pair of speakers, TMWW configuration, each getting one amp. The 50W spec is for Max output and should provide plenty of power. I believe the most difficult impedence won't be less than 4 ohms but I'm not sure of the driver's yet.

Indeed I am planning on building a pair of Orion speakers shown on the Linkwitz site. He suggests the 3886 chip project on the NS site for those without the funds for the 12 channel amp he uses. I will check out the 4780 too but my first concern is learning how to plan this all out. I can solder and understand what caps, resistors, diodes, etc. do but not how they work together.

For instance, how do I divide up the 700W transformer supply to the individual PSUs?

Thanks for all the replies, I have already landed on the chipamp site, plan to use their boards and will go to antekinc now. Also, how about some ideas on heat sinks. Am I correct that each one must be mounted directly to the amp?

gary
 
#14
Sure gary! I built an Orion clone using LM3886 as the amplifiers. Tweeters are 27TDFC with waveguides, woofers are RS225-4, subwoofers are RSS315HF. I used a DCX2496 as the crossover. Each driver has a separate amplifier.

Details on power amplifier: My amps were built into the speakers, 6 channels on each speaker (I have the 2 spare channels in case I needed to bridge for more woofer output).

I used an Antek 600VA 20V + 20V transformer for each 6 channel amplifier (overkill, and probably could be easily halved for my purposes.) Each is charged through a soft-start as seen on Rod Elliott's page. If I had gone with two 300VA transformers instead (and not powered them on at the same time, maybe I would not have needed the soft-start.

There is one bridge rectifier on each transformer, with pairs of 10000uF (could probably be smaller with no ill effect) capacitors for each amplifier. Each amplifier also has local 1500uF, 100uF, and 1uF bypass caps (on the www.chipamp.com boards, very close to the chip supply pins). The large capacitors are mounted close to the amplifier boards, with wire leads to the rectifier, and star grounded to chassis ground. The idea here is to have current surges come from the capacitors, which are somewhat isolated from the transformer and rectifier by the small lead wire resistance. This is all experimental on my part, but it makes sense to me, and seems to work well.

The chipamp.com boards can be had with power supply boards that use discrete diodes. I cannot comment on using multiple rectifier bridges on one transformer, though it doesn't seem like a problem to me. You can probably find discussion on this on the chipamp forum, but I invite anyone reading this thread that has personal experience with multiple rectifier boards on the same transformer to comment on the suitability of this application.

Note that with my application L and R channels are inherently separated. Alot of people advocate separating L and R power supplies, I can't personally comment that I've heard a difference, though the theory makes sense. If you draw all of the power from one transformer and one rectifier, I would recommend getting the heftiest metal case rectifier you can find. I got mine from www.apexjr.com. I didn't need them, but uou can also get binding posts from ApexJR for a good price. Come to think of it, my filter capacitors were also from ApexJR.

Some people report having issues with hum if their RCA jacks are grounded to chassis ground, mine are on a non conductive panel and as such are inherently isolated from chassis ground. I used simple twisted pair wiring from the RCA jacks to the amplifier boards.

My system is currently in pieces and in boxes. I never got around to building a proper loudspeaker enclosure for my bachelor pad and have gotten married, moved into an apartment, bought a house, remodeled it, and moved into said house in the last 8 months, so it may be awhile before I can ever get around to playing with that system again. I still have to tile one bathroom tub surround and finish remodeling the garage!

Regarding extra parts laying around, I don't even want to think about how many boxes of parts I have that aren't getting used. Perhaps once I've finished my major home projects and have a functional workshop/garage, I can inventory my spare parts and post them in the appropriate section.

Best Regards,
David
 
#16
Even an Orion clone will provide job-site tunes while you finish your bathroom.
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Good idea there! I would like to get them up and running again, just lack a proper room.

My office is too small to place them far enough out from the walls and the living room has a plasma on the wall. Having speakers standing out in the middle of the floor, while appealing to me, is not necessarily appealing to my wife. I finally understand SAF now.

The garage holds hope, I'm going to finish it out as an electronics shop since neither of our cars are worth garaging. I'll throw a sofa in there, set the dipoles up, and maybe even get a projector!

What drivers are you using for your dipoles?
 
#17
I'll be going with Seigfried's design. Although I went to visit him recently and got to audition the speakers I didn't notice the models. I think the woofers are a Peerless and the mid looks like one of the SEAS drivers I have in my Peridots . I will get that information when I purchase the plans. I assume his eq boards solve all impedence issues.

Here's a question for you: So I'm planning on getting 8 amp boards and 8 ps boards from chipamp, and a 600 VA transformer from AnTek. How do I divide current up from the transformer to each of the supply boards? Is it as simple as splitting the secondary up into 8 feeds from a post? Also, how do I connect a heat sink?

Thanks,

gary
 
#18
Re: Power supply

tiltedhalo said:
A Chip, 3886 is an AB amp and achieves about a 60% efficiency so at 50W output you need between 70 and 80W's of supply. then multiply by the number of amps, 8*80W=640W+ 10% for overhead. Just find a trans in that range and away you go.
Click to expand...


You are considering that all chips will be at the same time at full power (RMS power), and this is INSANE...

So a 350W PSU should do the work fine ! 50%, musical power program...
 
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