Rocktron Banshee

[Jered]

  In case you were curious.
http://www.epanorama.rackhost.net/schematicsforfree/Audio/Musical/Products/Rocktron%20Banshee%20Amplified%20Talkbox.GIF

[sixpounder]

Hello guys!

Could somebody explain me please how is it possible to get 14,5V from 9VAC? Is that a mistake?

Sorry for my bad English

[Sanguinicus]

Voltage doubling has been discussed here before. I think there's a thread lower down. I suppose you could get to 18v then regulate to 14.5v. It's not very efficient or elegant though. Why do you need 14.5v?

[Mike Burgundy]

Half-wave and full-wave rectification always "changes" the voltage (it's normal and obeys the rules of physics). Nothing strange there, no need to step up to 18V and then step down, just use an AC adapter or the thing won't work at all.

[slacker]

Using that schematic you can't, it must be a mistake, 9 volts AC rectified as shown will give you about +-12 volts DC. Or perhaps the power supply is way over rated and is actually putting out nearer 11 volts AC.
Thats ignoring the fact that one of the diodes is the wrong way round so it won't work at all as drawn.

[Mike Burgundy]

True (you did the math, I was lazy ;p ), if it really is 9VAC. It would actually probably be a bit lower *edit: from true 9VAC* (a little diode loss) There's quite a bit of variation in wallwarts, and seeing the wallwart specified at 9VAC/2A, and typical max. consumption at just over 1A as per the schematic, I would expect the supply voltage to be higher than the transformer's spec.
Lesson here: it's probably not that important to get that nailed down to half a Volt. Keep the TDA2614 running high enough for mondo output, but low enough so it doesn't melt (datasheet!) and rock. It's specced for a supply voltage of 15 to 42V, so it's not critical.
I must be overlooking something - which diode are you referring to?

[slacker]

Good point about the power consumption I didn't notice that, so yeah the wallwart will probably be putting out more than 9 volts.

D6 looks the wrong way round to me, it should be flipped so the rectifier puts out positive DC.

[Mike Burgundy]

See, I was missing that. I somehow glanced over it and looked real real hard at D7, which I suspected could look odd to some people but was ok. You're so right, D6 should conduct the positive cycle and is the wrong way round. Doh. ;P

[Mike Burgundy]

Wow, max input 9.5dBu? That's 6.5Vp-p!
What kind of guitar are they planning on plugging in there?