Spyder related question

[simonkibble]

Hi

My foray into DIY building is going well - saved a load of money by building myself an FS300 clone and have the bits on the way for a GGG IC buffer that I am looking forward to building. I even found a unibit for drilling the enclosures in my toolbix which saved me going out an buying one...

Anyway, I am now planning on building a Spyder using the weber transformer, with the 8x11V secondaries. I have a plenty of skilled electronics buddies who will make sure I am 100% safe on the mains electricity side of things so I am not worried about killing myself (one of them works for one of our electricity supply companies installing and maintaining power systems - so he really does know his stuff!)

My question is connected to the regulators that can be used with the secondaries. The spyder circuit diagram at Geofex shows the circuit with a 78L09 regulator, which as I understand it can deal with up to 100ma current draw. But I have also seen people build the circuit with a 7809 regulator, which, if I've understood the spec sheet right, can deal with up to 1A of current draw.

Questions are.... if I use the 7809 regulator do I maintain the capacitor values that are shown for the 78L09, namely a 220 microfarad and a 10 microfarad, or would they need to be changed? Secondly, although the 7809 can cope with a 1A draw, are the weber transformer secondaries about to supply 1A to each circuit? I haven't been able to find the detailed specs for the transformer but I see the 9V AC secondary supplies it's current at upto 2A - what can the secondaries designed to be rectified to DC deliver? I hope that isn't too stupid a question.

Would I be better sticking with the 78L09 regulator, given that the pedals I am powering are unlikely to draw anywhere near that current, or is it wiser to go for the 7809, given that the parts are so cheap anyway?

Simon

[simonkibble]

Ok - idiot number 1 here... for some reason I had temporary blindness while on the weber site and missed the link where it said... click here  for specs -so now I know that the 11v secondaries are 300mA! Given that knowledge does that mean it's better to go for the 7809 regulators rather then the 78L09???

[R.G.]

It depends. Most pedals are in the 10-20ma range, mostly the current for the indicator LED. 100ma is actually plenty for any individual pedal, except a very few, mostly digital delays and other digital types.

The 7809 will go up to 1A, which means you can wring all the 300ma out of each winding you like - except that kind of flies in the face of wanting an isolated winding per pedal. The 78L09 is mostly OK, and will protect the transformer winding in the odd case of a shorted output or something similar - which almost never happens, so it's probably not a huge consideration.

I personally would use either one based more on how much space I had in the box and how easy they were to mount, rather than the current they can supply.

[simonkibble]

Thanks R.G.

Can I ask about how the capacitor values are calculated? I've seen some people use up to  1000 microfarad capicitor in their builds and wondered why - is there any advantage to this, is it something to do with trying to lower the ripple of the rectified current?

Simon

[R.G.]

11/15/01, Power Supplies Basics, http://geofex.com/Article_Folders/Power-supplies/powersup.htm