basically take the VA rating and divide that by the input voltage to get close to your max mains current draw, then increase that by perhaps 30%-50%.

The main toroid is a 250VA 25Vx2 transformer. 250VA rates both secondary windings together.

250/120 =

2.1 + (0.4 * 2.1) =

~3A

The other transformer is a 12V 1A (6-0-6) transformer, which makes the VA around 12VA.

12/120 =

0.1 + (0.4 * 0.1) =

~0.14A


Okay so perhaps I was a little off on my calculations.

I think a 3.2A slow blow would do the trick. I'll never be drawing that much under any reasonable load anyway because the speakers that it will be hooked up to will be blown out by then.

 

It's two LM3886s, one LM4780 in parallel, one sub woofer preamp board (2x NE5532), one headphone amp board (OPA2134), and two fans.

Even though it is quite a few things...do you guys think that could ever hit ~380W? =/

 

For a sub that is too low.

But that's just me.

 

Haha...no my sub is a 5.25inch sub. It handles 50W/80W max.

This setup is for my computer. Don't need to become deaf at short proximity.

Are you talking about fuse? Or are you talking about wattage? Wattage I presume.

 

Are u going for active crossover.
Please do, you'll thank me, I promise

 

Are u going for active crossover.
Please do, you'll thank me, I promise

Subwoofer has active crossover, and phase adjustment. It would have cost $100+ for a decent passive sub crossover.

Left and Right channel have passive crossovers. I'm using passive because that's what the speaker design I'm following calls for...so I went for it.

 

Every speaker is design for passive.
It's not a problem to go for active, only difference is tht it will sound far better than you think, since you have LM3886, I suggest that you built atleast 4 amps using these.
Two for low/mid and two for tweeter.

And don't worry about power, what you have got for a transformer is sufficient.
All u need to built in addition to replace the passive xovers is a stereo 2 way active cross over

 

Every speaker is design for passive.
It's not a problem to go for active, only difference is tht it will sound far better than you think, since you have LM3886, I suggest that you built atleast 4 amps using these.
Two for low/mid and two for tweeter.

And don't worry about power, what you have got for a transformer is sufficient.
All u need to built in addition to replace the passive xovers is a stereo 2 way active cross over

I already built the passive crossovers...thanks for the heads up. I'll keep it in mind for next time.

 

bummer !!!!!

 

Hey guys,

Back on topic, sort of. I threw together a dual supply with a 6V and -6V regulator.

The bridge rectifier I am using. (1.5A Vishay W10G-027C)...is getting sizzling hot with no load. But if there's no load, then it shouldn't really get hot at all...right? Is 1.5A still too small or something?

I've checked all of my joints 9 million times...I DMMed the outputs before I added the regulators, and the output voltages were fine, but I didn't really notice it getting hot. After I've added the regulators, it seems to be getting hot....I don't get it.

Thanks.

 

check the smoothing caps for high ESR

 

check the smoothing caps for high ESR

What do you mean?

I don't think I have the equipment for that. I have a 0.01uF ceramic on each smoothing cap. The smoothing caps are Panasonic FM 470uF 25V. I'm also "snubberizing" the bridge rectifier with 4x 0.1uF ceramics. Can this be a problem?

I don't see how since it was just working, sort of.

One thing to add. I had one of the voltage regulators hooked up wrong before...as apparently there is like 12 ways to hook up a 3 pin voltage regulator. Anyway. I had ground hooked up to input and input hooked up to ground.

Could I have like damaged the bridge or something? If anything, I think the voltage regulator would be shot.

Thanks.

 

U might have a damaged the bridge, it is advisable to use the bridge current rating double that of ur load. U do ot need to snubber all the diodes. Just use 2 100n 50V ceramic from each AC pins of the bridge to ground.
That is how I use it.

You should put one 100n across the smoothing caps.

Abt ur problem. Replace the smoothing cap and check the ceramics for shorts plus the bridge. Remove the regs and check for proper voltage at the smoothing cap. After that attach ur Regs.

One more thing, Use a higher capacitance for smoothing

Use appropriate fuse before the bridge. And ur regulator may be damaged

 

U might have a damaged the bridge, it is advisable to use the bridge current rating double that of ur load. U do ot need to snubber all the diodes. Just use 2 100n 50V ceramic from each AC pins of the bridge to ground.
That is how I use it.

You should put one 100n across the smoothing caps.

Abt ur problem. Replace the smoothing cap and check the ceramics for shorts plus the bridge. Remove the regs and check for proper voltage at the smoothing cap. After that attach ur Regs.

One more thing, Use a higher capacitance for smoothing

Use appropriate fuse before the bridge. And ur regulator may be damaged

Thanks for the information. It's only going to be powering a headphone amp but I'll use a bigger smoothing caps.

I think something is just damaged because it was working fine and then after trying to figure out what was wrong with my voltage regulator, I think I killed something, one way or another.

I'll start over from scratch. It's such a simple circuit. I don't know what I did...

---
For the 100nF cap. Are you using two of them? Or one from the positive rail to the negative rail, skipping over the 0V ground?

---
For the snubber caps. That's from each AC pin to the centertap ground, right? Just don't want to blow anything up...

---
However, if there was no load, why would the bridge have even overheated? ....Well whatever. I'll just start over. I know what I'm doing...mostly.

 

Yeah I think I must have messed it up when I put in the regulator the wrong way. =/

 

I remember snubberizing a diode bridge a long time ago, so I can't remember the details, but it was about using the diodes very close to their voltage limits. It's been so long that I was probably limited by the quality of diodes available!

Point is, snubberizing probably isn't very important nowadays. 1000 volt diodes (1n4007, ecg125) are available for only a few cents each. When I saw them at $5 per hundred, I bought the bag of 100 diodes. I haven't been concerned about voltage limits for so long that I'd have to go look it up if you wanted to know the voltage limit for a 1n4004!

 

Perhaps. I was just trying it because I had a bridge that would make it easier to snub it, and I have like 500 0.1uF Kemets...soo....

 

and I had a hundred 1000pf @1kv capacitors.

Hey, you gotta find a use for these things, right?

 

and I had a hundred 1000pf @1kv capacitors.

Hey, you gotta find a use for these things, right?

Of course. I really have to start bulk buying more. I wind up buying the same parts over and over again at the same price (per 1). Spend a few hundred bucks now, save a few hundred bucks later...

Interesting thought. Still trying to convince myself...

 

Don't forget to lurk at surplus stores and websites. I wooda never bought a hundred of the thousand puff caps if they weren't practically free (one or two bucks per hundred).