Transformer for Gainclone

[Painkiller82]

Hi,

I'm new here, but it seems like a great forum.

I'm going to build my first hi-fi amp now, and I have been looking at the Gainclone. Is this a good schematic?: http://www.shine7.com/audio/gainclonev1.htm

But I'm not shure what transformer would be good. I'm going to build a stereo amp, and I have been looking at this: http://www1.schukat.com/schukat/schu...256D7900261D0A

Will that be ok? Will there be any advantages in using a bigger transformer?

Espen

[gmilitano]

225VA should be fine for a stereo implementation.

My LM3886 ChipAmp does fine with 160VA.

[Painkiller82]

Thanks!

Your amp looks great! I found that Hammond chassis that you used now, so I think I'll go for that one. Maybe the 1444-28, which is a bit smaller.

[Painkiller82]

What about bridge rectifiers. How much current do they have to handle?

Are any of these ok?:

http://www.banzaieffects.com/Bridge-...c-522-p-3.html

[gmilitano]

Originally posted by Painkiller82
Thanks!

Your amp looks great! I found that Hammond chassis that you used now, so I think I'll go for that one. Maybe the 1444-28, which is a bit smaller.

The Hammond chassis are good and very reasonably priced. Yeah, if you look at mine, you will see a lot of unused real estate so you can easily go smaller.

Cheers,
Gio.

[AndrewT]

Originally posted by Painkiller82
What about bridge rectifiers. How much current do they have to handle?

Are any of these ok?:

http://www.banzaieffects.com/Bridge-...c-522-p-3.html

Hi,
the peak current and the average current through the rectifier is determined by the design of the capacitor input filter hung on the end.
8ohm speakers need +-20mF/channel for deep bass but, almost all chipampers believe this to be balderdash. I stick with this recommendation.
Reduce the smoothing to +-4.7mF/rectifier and your 10A 280V version will survive without any added resistance to reduce peak current.
If you go for +-10mF then, 10A may run too hot.

[troystg]

Steve has the perfect transformers for the LM3886 for a great price.

You can build true dual mono for this price.

http://www.apexjr.com/miscellaneous.html#Transformers

XFM-D0012 is the part #.

http://www.apexjr.com/images/AdireToroid.JPG

[markiemrboo]

Originally posted by AndrewT


Hi,
the peak current and the average current through the rectifier is determined by the design of the capacitor input filter hung on the end.
8ohm speakers need +-20mF/channel for deep bass but, almost all chipampers believe this to be balderdash. I stick with this recommendation.
Reduce the smoothing to +-4.7mF/rectifier and your 10A 280V version will survive without any added resistance to reduce peak current.
If you go for +-10mF then, 10A may run too hot.

Is that assuming a single 10A rectifier per channel?

For what it's worth I am using 20,000uF and two 8A 1000v SIL rectifiers per channel, one rectifier doing the positive side and the other one doing the negative side. With a pair of 8 ohm speakers at near full volume, playing music, the rectifiers on both channels are not even warm to touch, without any heatsinking. Same thing with a pair of "4 - 8 ohm" speakers I have.

[Painkiller82]

Thanks

I have already ordered the parts, and I ordered these rectifiers:
http://www.banzaieffects.com/KBU1006-pr-24042.html

Will they work ok?

I bought the parts based on this schematic:
http://diyaudioprojects.com/Chip/LM3.../LM3886_CA.htm

The smoothing caps are here 10mF, but does that mean that I might burn the rectifiers? I'm going to use 4 Ohm speakers, at least for now.

[markiemrboo]

As above... If my experience is anything to go by then I think you should be totally fine with that power supply schematic and those 10A rectifiers.

I use the 8A version of those in the same configuration, though I would have used 10A if I could find them at the time, and they don't even get warm. I do have a separate supply per channel though (i.e a total of 4 rectifiers). I think even with a single supply for both channels (2 rectifiers in total) would work fine.

I wouldn't worry about it.

Be sure to use a 100W-ish light bulb in series with the mains live before the transformer when testing the amplifier. It can help protect against some faults faults and, I believe, possibly prevent damage. The light bulb should light up brightly for a second or two while the supply capacitors initially charge and then go dim / not lit up at all. If it stays bright then something is wrong.

Also, don't have your face too near the thing incase you have accidentally wired a capacitor reverse polarity etc and things explode! Might even be worth wearing safety goggles. I've got the supply reversed before on a tiny little opamp (NE5532) and you'd be surprised how violently they can explode. The chip's top flew up to the ceiling with a very, very loud bang!