Power Supply beginnings (problems) (spyder)

[carrejans]

Hi All,
I'm going to build a power supply for all my pedals. I'm going for the Spyder design of RG Keen, with all the seperate transformers.
But I have some questions; hope you guys could help me further.
- All those commercial pedals, specify the exact adapter you should use. Most of them 9V, but different amperes. Isn't this important?
- I read the datasheet of the 78Lxx serie. They all have an specified Vin. Is this the exact Vin that is needed for them? Or may this be a little higher, or even lower?
- Some pedals use positive ground. How do I have to achieve this? Is it just reversing the + and - connection of the DC-out-jack of my powersupply? Is there a possibility of using a switch, so I could select pos/neg ground?
- Will there be any problem, if I connect a fan at my 12V output? Will this affect the sound?
- In my drawing, which capacitors should I use?
- And which transformers should I use? I calculated the output voltages that the transformers should have. (see my drawing) Does it need to be these exact values?
Any usefull between these:  http://www.banzaieffects.com/Xicon-TMxxx-c-567.html


My drawing:
http://members.lycos.nl/carrejans/temp/PowerSupply.jpg


Thanks for all the help.

[R.G.]

- All those commercial pedals, specify the exact adapter you should use. Most of them 9V, but different amperes. Isn't this important?

If the pedal says 9V, it can use any 9V supply that will provide at least as much current as the pedal says it needs.The pedal will take only as much current as it needs. It is unusual for this to be a problem.

- I read the datasheet of the 78Lxx serie. They all have an specified Vin. Is this the exact Vin that is needed for them? Or may this be a little higher, or even lower?

It may not be lower. It may be higher, even quite a bit higher. The 78Lxx series are regulators. That means they take an unregulated (and that means varying) input voltage and turn it into a lower and constant voltage. The only limits are (a) there is a minimum voltage they need to work. For the 78Lxx series this is usually 2.0V. So a 78L09 needs 11.0V minimum. A 78L05 needs 7.0 minimum. The maximum voltage is the voltage which causes the device to get too hot, or to fail catastrophically. I believe this is 40V for the 78L series. I know it's 40V for the 7800 series.

- Some pedals use positive ground. How do I have to achieve this? Is it just reversing the + and - connection of the DC-out-jack of my powersupply?

Yes.

Is there a possibility of using a switch, so I could select pos/neg ground?

Yes.

- Will there be any problem, if I connect a fan at my 12V output? Will this affect the sound?

Acoustically only. You can hear the fan run. You should not hear any effect caused by the electric wiring.

- In my drawing, which capacitors should I use?

See my article on power supplies basics at GEO.

- And which transformers should I use? I calculated the output voltages that the transformers should have. (see my drawing) Does it need to be these exact values?

See my article on power supplies basics at GEO and the answers above.

Any usefull between these:  http://www.banzaieffects.com/Xicon-TMxxx-c-567.html

Those are all audio transformers not power transformers. THEY ARE NOT SAFE TO USE ON AC POWER!!!!! Use only transformers that are specified for AC power line use.

In fact, I worry about your ability to wire up the AC power line part of this project safely. Unless you already know how to wire AC power safely, do not attempt to do this on your own. It's not worth dying for. Get someone experienced and capable with AC power to help you do the wiring safely.

[carrejans]

Sorry for the late reply. (been away for a few days)
Thank you for your explanation RG.

- In my drawing, which capacitors should I use?
See my article on power supplies basics at GEO.

Yes, I read your article. But in the datasheet of the 78Lxx serie, the C0=0,33uF and C1=0,1uF. You use C0=220uF and C1=10uF. Why this difference?

- Any usefull between these:  http://www.banzaieffects.com/Xicon-TMxxx-c-567.html
Those are all audio transformers not power transformers. THEY ARE NOT SAFE TO USE ON AC POWER!!!!! Use only transformers that are specified for AC power line use.
In fact, I worry about your ability to wire up the AC power line part of this project safely. Unless you already know how to wire AC power safely, do not attempt to do this on your own. It's not worth dying for. Get someone experienced and capable with AC power to help you do the wiring safely.

Sorry, I pasted the wrong link. I meant this: http://www.banzaieffects.com/Transformers-c-299.html
Yes, I know everyone should be carefull with AC. I had several safety instructions in my school (I study Industrial Engineering). These first two years were very theoretical; so now I want to try some DIY, to understand more of all the theory.
But before I plug in the electrical cord; someone who knows a lot about it will check my build. Don't worry.

[carrejans]

- I read the datasheet of the 78Lxx serie. They all have an specified Vin. Is this the exact Vin that is needed for them? Or may this be a little higher, or even lower?
It may not be lower. It may be higher, even quite a bit higher. The 78Lxx series are regulators. That means they take an unregulated (and that means varying) input voltage and turn it into a lower and constant voltage. The only limits are (a) there is a minimum voltage they need to work. For the 78Lxx series this is usually 2.0V. So a 78L09 needs 11.0V minimum. A 78L05 needs 7.0 minimum. The maximum voltage is the voltage which causes the device to get too hot, or to fail catastrophically. I believe this is 40V for the 78L series. I know it's 40V for the 7800 series.

So they need a minimum of 2V above their output voltage. The voltages suggested in the datasheet are:
78L09: Vin=15V
78L12: Vin=19V
78L15: Vin=23V
Are these suggestions for best performance?
Or is the minimum of 2V that you said, the voltage before the diode-bridge maybe? (V=(15+1,4)/sqrt(2)=11,6~=9+2)

[carrejans]

So for the 9V, I should use transformers with a secondary off 12V
And for the 12V and 15V, I could use one with a secondary off 18V


What should be the power rating of the transformers?

[OG]

Jan,

Here are 3 interesting links that could be helpful :

http://www.kpsec.freeuk.com/powersup.htm

and if you speak french (better than me by the way because I don't speak dutch   ):

http://kudelsko.free.fr/articles/alimentation2.htm

http://perso.orange.fr/e-lektronik/LEKTRONIK/RP2.htm

RG is right, be careful.

Olivier