Power jack implement

[tomtom]

Despite playing with many stompboxes , I still use batteries... for all of them...so I check with my dmm !
  Current needs are quite low however (diy simple projects !).

  I have to put power jack on them !

  Power supplies units (or wall wart) seems a more noisy way to go when power outputs are not isolated (daisy chain). It sounds like it may need some extra filtering just in case.
   I was thinking about a resistor (100R) in serie from power jack to circuit power and a cap (100µ?) plus the classic protection diode.

   Any idas ? I'm in the dark !

   Tom

[gez]

I was thinking about a resistor (100R) in serie from power jack to circuit power and a cap (100µ?) plus the classic protection diode.    

It's probably wise to measure the current draw of your effect before you decide to slap a simple RC filter in there.  If the effect is a bit of a current hog the 100R will limit the available headroom, which may be undesirable.  15mA will generate 1.5V across a 100 Ohm resistor, which is quite a chunk out of a 9V supply and not an unrealistic amount of current draw for some effects.  

Having said that, most of the effects I build have this set up and I get round any headroom issues by using op-amps with a CMOS output and trying to keep current draw as low as possible.  

You said your effects don't use much current so you shouldn't have a problem.  Whether you need additional filtering will depend on your supply - buy a decent adaptor.

Edit: P.S.  If headroom IS an issue, a lot of the time just a cap across the rails will do.  Also, using a Schottky diode for protection will help matters (less forward drop).

[tomtom]

I may found a well built pw supply but my friends won't. They just play and go cheap when power supply is concerned !

 That's why I want extra filtering ! But if a cap works ! (I use sometimes two leds so...).

 Thanks for the diode tip (any schttky will work ?)

 Tom

[gez]

But if a cap works ! (I use sometimes two leds so...).

 Thanks for the diode tip (any schttky will work ?)

 Tom

You don't need filtering for the LEDs     If the audio part of your circuit has a low current drain then you could probably stick a small value resistor in there, separate to the LEDs posistive supply.  It WILL improve things, but often you can just get away with a large value cap across the rails (upwards of 100u).

There should be some stuff at GEO about protection diodes etc.  I tend to use normal Si, but if you want to use Schottky more or less any should do.  There are slight differences in forward drops, but not much; at the current levels we're talking about the drop should be less than 0.4V.

[gez]

http://www.muzique.com/lab/hum.htm

http://www.muzique.com/lab/filter.htm

Says it better than I ever could...

[tomtom]

thanks !
thanks !
thanks !

[tomtom]

I've just found something at 4ms, they use an LM7809 instead of th resistor (with 100µ cap too), it sounds interesting, no?

 Tom

[gez]

I've just found something at 4ms, they use an LM7809 instead of th resistor (with 100µ cap too), it sounds interesting, no?

 Tom

A few things to bear in mind.  Firstly, to get 9V out you need a input voltage a few volts higher - at least 12V.  Secondly, many regulators have 'high' quiescent current, in this case I think it's around 5mA or more.   So, if you still want the option of running your effect off a battery none of this is good news.  

You can use micropower regulators which are low-dropout and use a miniscule amount of current, but that's no guarantee that you still won't need a RC filter at it's output (the ones I use produce a swooshing sound unless filtered).  Also, from a 9V wall-wart, you're going to end up with limited headroom (assuming that you're using a regulator with an output lower than 9V).

[tomtom]

I have tried 100R and 100µ and it works great, I wonder if that change the sound, it sound silly I know but, for exemple, tube circuits tends to be picky about filter capacitors values.

  100µ is enough ?

 One great GEO tips (one more !) lies in using a mosfet for polarity protection w/o voltage drop, it's fine but it's one more component !

 Tom

[gez]

I have tried 100R and 100µ and it works great, I wonder if that change the sound, it sound silly I know but, for exemple, tube circuits tends to be picky about filter capacitors values.

  100µ is enough ?

 One great GEO tips (one more !) lies in using a mosfet for polarity protection w/o voltage drop, it's fine but it's one more component !

 Tom

Shouldn't think it'll make any difference in sound, unless the filter is limiting headroom and your circuit is an overdrive (in the true sense), in which case it might sound better!

If the filter is working then 100u is enough - simple as that!

The GEO tip is another good approach.