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Building a 5 channel GainClone
Building a 5 channel GainClone
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Old 22nd September 2006, 08:31 PM   #1
Kevinwil is offline Kevinwil  United States
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Join Date: Sep 2006
Default Building a 5 channel GainClone

Hey Everyone,

Well, my Sony ES-333 died, and it was time for me to buy a new amp! I had built a gainclone in the past that was Bi-amped that I use in my office, and I like it so much, I decided to build one for my surround speakers.

The amp I am thinking about building would be 5 lm3886's and I am likely going to use some chipamp boards when they become available again.

The 5 channels do not include the mains, I am going to bite the bullet and upgrade to 7.1, so this amp should never have much current draw, except maybe for the center channel.

I have a few questions about the power supply, and what I should do. I have two exact 200va 48vct transformers that I was thinking about running in parallel to up the amperage. The main reason I wanted to take this approach is so I have full current available to all chips at all times, also, it seems like it would be a little cheaper for the rectifiers/caps. (I'm doing this as cheaply as I can get by with.)

So my question is, how much do I need for the filter caps(assuming 400va and 5 lm3886's), and is this setup advisable? I found a previous post on parallel transformers, but with 2 amps instead of 5, so I thought I would repose the question. Also, I am not using torridals, so do I need to shield them massively from each other?

One other quick question. I use a Pioneer SX-1280 for my main amp which will pump a lot of power. I am worried the lm3886's may not keep up (especially on the center channel) without me dropping the gain on the mains quite abit. As such, I thought about bridging two 3886's for the center, since I suspect it will be the one doing the most work. However, since I only have about 400 watts, I suspect the current pull will be a little high and I may not really need to add more power to the center anyway. My center is a homemade sealed 3-way sealed box, and is fairly ineffcient. I have never calculated the baffles in the crossover, so there are probably a few frequecies which will require MUCH more power. I know, fix the speaker! :-)

Long story short, would 400watts be enough for 4 surrounds at fairly low draw, and one bridge setup?

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Old 22nd September 2006, 09:36 PM   #2
owen is offline owen  United Kingdom
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Join Date: Mar 2004
Location: Shilton
It would be fine for a class T set-up, but in this configuration, I'd go for a 600 or 800 VA transformer, to provide plenty of current reserve for the centre - yes the peaks may *only* be 200w, but, the energy transfer of the chips is nowhere near the 90% or so a class T amp has.

That means heat. Lots of it, at high levels, but not unmanagable. It also means that for your 200 w output centre, you should allow 400 W (or VA, they're pretty much the same thing), just for that channel, or risk diminished dynamics etc that an undersized transformer would bring.

But, if you've found a deal on 400 VA transformers, and can get 2, then you'll be in hog heaven, with a complete overkill PSU!

This would be the route I'd take...

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Old 23rd September 2006, 01:05 AM   #3
Kevinwil is offline Kevinwil  United States
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Join Date: Sep 2006
Thanks Owen,

It sounds like I will just try this out with no bridge and run 5 strainght 3886's. So how much smoothing should I do? 10,000-20,000mf?

I usually just put about 10,000mf in there or so (depending on what I've gutted laterly). Right now, I only have 2 6800mf caps that are even at the proper voltage rating, but I suspect with 5 3886's that may be not enough.

Any thoughts, and I will start soldering. :-)

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Old 23rd September 2006, 07:51 AM   #4
Williams Audio is offline Williams Audio  Jamaica
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Join Date: Apr 2004
Location: far away
Default hi kevin, calculus

is not too difficult to calculate.
each ch. will be able of 60watts@8omhs and about 100watts @4omhs. that gets you to peak current 100=i^2*4, i=5amp rms 5*1.4=7amp peak for max pwr ever from each ch.
7*5=35amp peak for 5 ch amp; 400va=i*v, 400/35=9.8v for max peak current.
so calculating this way you wouldn't be able to drive none the voltage will drop to low, but
in home cinema audio programs i think there is not such a sound track that will drive all ch to max pwr at one long time??
a nominal calculation is depending of time to drive the 5 ch.
if you are interested i can help you with the calculus, write to my email directly.
best regards
williams audio
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Old 23rd September 2006, 11:31 PM   #5
MyNameIsJake is offline MyNameIsJake  United States
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Location: Arizona
You want a movie that will drive your amps to peek? Watch "Twister"

That will do it.
“We are no longer the knights who say ni! We are now the knights who say ekki-ekki-ekki-pitang-zoom-boing!”
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Old 27th September 2006, 05:24 PM   #6
Kevinwil is offline Kevinwil  United States
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Join Date: Sep 2006
Thanks everyone. I found some 80v 47,000mf caps for $17.50 each on apexjr.com, and I think I will go that route. I will try out the xformers I have for now, and I can always upgrade if they don't work out. :-)

My budget was unexpectedly increased thanks to the Goodwill store! My favorite place to buy vintage audio. I found a Sony TA-N731 amp for $10 that I think I can get 75-80$ for on Ebay! ;-)

I know it's off subject, but I wanted to share some of my finds @ thirift stores over the last few years.

1. AR5 pair in AWESOME condition - $10 for the pair. I wired around the brass wirewound LPads, and they work like new. Someone had even repaired the surround on the woofer relatively recently. I will never sell these speakers as they simply have the best midrange I have ever heard. (Now in my bedroom with a 280watt Yamaha Natural Sound Amp. This is also where my laserdisc, CED, and beta player are hooked up!)

2. B&O Beovox M100 - $24 for the pair. Recent purchase. Not my favorite speakers, but they do sound really good. They have a wider sound stage than the AR-5's so they fill my living room better. They also have really good bass, so I quit using my homemade sub for now. But I honestly think the mids are a little lacking. One tweeter is gone, which is a problem. I had to resurround the mids, but the woofer (Seas I think) has a rubber surround.

3. Pioneer SX-1280 high-powered receiver, Teac AG-6300 10.5 in reel to reel, and a Highend Pioneer turntable whose model aludes me - $599.00 for the three. A bit higher than I would normally spend, but I really wanted the Teac reel to reel and I was planning on selling the receiver to recoup costs. Now, this amp is driving my mains, the B&O's, WELL over their clippling limits. (Fortunately, they have protection circuits which kick in somewhere between 75 and 100watts. ) Now I'm looking to sell the reel to reel to buy a new preamp. Anyone interested? :-)

I have found many other misc amps/speakers, etc which for the very least are good for parts and project boxes. My Gainclone will use a Nakamichi tape deck box, and an old Sansui receiver box more than likely.

Long story short, hit the thrift stores people! Unless you live in Texas, then I want you to stay out so I can make all of the finds. ;-) I visit a circuit of stores a few days a week on my lunch break and I am simply amazed at the stuff I find. I tend to buy quite a few records while I'm out as well! I suspect it won't be too many more years when you won't find records anywhere.

Ok, I've diverged from the topic quite enough, thanks again everyone for your help. I am ready to go electrocute myself! :-)

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Old 5th January 2007, 04:03 AM   #7
clearwaterms is offline clearwaterms  United States
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is this amp completed? how did it turn out?
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