Red Llama Diode Question

[remmelt]

http://aronnelson.com/gallery/SteveC/llama2?full=1

The diode in the bottom left corner is there for protecting the circuit from power the wrong way around, right? Against sticking the battery in the wrong way? Can I place the diode BEFORE the 1K resistor (shown in the right bottom)

That way, I can save some pcb real estate by adding it to my home-made battery snap (thanks Mark Hammer) under the hot glue. Sounds like a plan, right?

[puretube]

yes, can be moved there,
BUT: at the risk that the diode may fry,
and the battery may drain very fast,
when (unattendedly) mis-polarized...

[remmelt]

Right. Thanks!

[Stevo]

does just about any 4049 type IC work in this circuit or are there some good ones...Maybe a mouser # would be cool :lol:  I have NTE 4049 they are extreme in the gain :?

[Peter Snowberg]

You need an unbuffered version which is called the 4049UB.

There will be characters in front and behind too, but as long as you have the 4049UB in the part number it's the one you want.

Go to mouser and search for 4049UB. The first 7 items on the list are them.

If you want DIP packaging, look at numbers 2,3,5, & 6. #2 is a Pb Free package, so for leaded chips, you have Fairchild, TI, & STM devices in rows 3, 5, & 6.

I would stay away from NTE devices because I don't trust the cross-match to be the unbuffered version.

[Stevo]

Thanks Peter     ..I think the NTE4049 is the unbuffered if I remember right but I want to get something different to see the sound sometimes NTE is way off!!

[brad]

I can't wait for some more Way Huge schems to surface...because they sound great!  The Purple Platypus is a Red Llama with some extra stuff attached if I remember correctly.  However, I think the Green Rhino was an exact copy of the TS808 except with an LF353L for the opamp.

[guitar_199]

Remmelt

Just to fill in the "why" on that diode move.......

The components are in there that way because.... when you put the battery in backwards.... the diode is what we call "forward biased"..... ie... it tries its best to act like a solid state "short circuit to ground.  It will only allow about a half a volt to be passed on to the circuit.  When it is forward biased like this it will take any and all current that comes out of the battery up to the point that it self destructs.  The resistor is put in there so that, if the battery ever IS put in backwards... the resistor will limit the current flow and "soak up" all the rest of the battery voltage.  If you move the diode in front of it.... that "protection" of the diode is lost.

BTW....when the battery is correct.... a diode acts like an OPEN circuit... i.e.  like it isn't even there.... so it passes all the voltage to the circuit.

[remmelt]

Thanks for the explanation! One thing I don't understand though.

I get what the diode does, and I see that it still passes about .7V to the circuit when the battery is in the wrong way around ( I tested this without the actual circuit attached! See? I'm learning! )

What you are saying is that that .7V is soaked up by the resistor that's there. That's indeed what I want to happen.

What I don't understand is that with the diode BEFORE the resistor, -.7V (in my case) hit the resistor, with virtually nothing left behind the R to inflict any damage on the IC (the IC is rated from -.5 to +20V). Looks OK.

The other way around: -9V hit the R, let's say that about -7V goes through (Ohm's law, but I don't know the I off the top of my head), the diode opens up and will still send -.7 or so to the IC! This is NOT what I want, right?

Any holes in my argumentation? Not saying you're wrong, I honestly don't get it!

Thanks again for explaining!

[Stevo]

This is not a good reply but the diode is directioned to shunt voltage opposite of the norm and allow voltage in the direction it is suppose too...I wanted to say something


How can this circuit really handle another stage it has so much drive for me..I mean the tube sound scheme which is the same!! :?

[guitar_199]

Hey remmelt,

The resistor is not soaking up .7 volts......  the resistor gets 9v - .7 v.

Look at it this way.... when the battery is put in backwards... the diode is forward biased and as such will show .7 v across it's terminals.   The battery has a total of 9 v..........   the diode is dropping .7 volts..... so the remaining 8.3 v has to be somewhere...and that is across the resistor.

Now...... looking at what you say....  it is true.... if you move the diode ahead of the resistor.... the diode will STILL only drop .7 volts.   BUT......  in that configuration....the resistor is not there to drop the other 8.3v.... so... the battery will dump all the current it can through the forward biased diode.... which, if it exceeds the maximum current for the diode.... will quite literally pop it!!!  I mean....... explode-o !!!!  Like.... littlechips of glass, or burned melted plastic depending on the diodes case. To add to this.... if the diode pops fast enough.... it will stop pulling the voltage down to .7 v.... and the full "wrong" polarity will be fed to the circuit...and something in there might smoke......

So it takes the two of those working in concert.... to give the protection.  

If you put the battery in backwards.....

1) the diode will go forward biased and will drop .7 volts across the terminals of the diode, and

2) the remaining 8.3 volts will be dropped across the resistor and ohms law says that only 8.3/(resistance of the resistor) current will flow.  If it is properly chosen...that current will be below the max current for the diode and it will sit there like that until the faux pas is discovered....or the battery dies.

[Stevo]

I did the llama like the tube sound fuzz little better tone I think but this sound is quite addicting on a solid state 10watt cheap amp have to use the headphones today the neighbors you know with the tube amp want to stay friendly :lol: ,,,It is fuzzy yet is transparent enough to allow your picking tone to break through the distortion..This is a very cool sound.... FETS right tubelike :shock:...A very addicting sound set at around half throttle