Quick question regarding clean boost

[rockhorst]

I was looking through clean boost schematics today, as one of the things on the 'may be fun n easy to built'-list. I came across the one below. Now, is it just me or are those 2 diodes in there obsolete?

edit: tx for the help. As RG posted something about firestorms below I removed the pic. Seems very similar to any other clean boost though.

[R.G.]

It's just you.

The 1N914 is still available, although the 1N4148 is a more common equivalent.

[rockhorst]

I meant obsolete as in 'unnecessary' (I know, slight abuse of the word's meaning). They don't seem to have any use, esp. the grounded one...or is it just me again 

[burnt fingers]

This is a great little booster.  I built a couple.  The diodes are there for some protection against static discharges I believe.  Might as well put them in as they arn't costly pieces.  Rat shack sells them for a buck or so for 10 of them.

Scott

[Dragonfly]

QUESTION FOR R.G., JACK, AND THE SMART GUYS

Wouldn't it be beneficial to use a zener diode (like in the AMZ mosfet boost) between the gate-source junction in this circuit to help protect the mosfet from static charge damage ?

just wondering...

AC

[R.G.]

Wouldn't it be beneficial to use a zener diode (like in the AMZ mosfet boost) between the gate-source junction in this circuit to help protect the mosfet from static charge damage ?

Maybe. The power supply is presumed to be a low impedance connection between +v and ground, so any transients are shunted from the input to the + or - supply, and the device can't see more than +v or less than ground +/- a diode drop. This is the way that most CMOS logic ICs are protected, except that they have some series resistance to limit the input current. A zener at the gate/source is another way that's about as good.

Without getting into discussions about the provenance of this circuit, I think the designer was of the opinion that a reverse biased diode at the input kept the input signal further out of overload from the diode-conduction direction of a zener  clamp. But I could be remembering that wrong.

Either way works.

There will, of course, be a firestorm here when the designer pops in and sees the circuit.

[Dragonfly]

Wouldn't it be beneficial to use a zener diode (like in the AMZ mosfet boost) between the gate-source junction in this circuit to help protect the mosfet from static charge damage ?

Maybe. The power supply is presumed to be a low impedance connection between +v and ground, so any transients are shunted from the input to the + or - supply, and the device can't see more than +v or less than ground +/- a diode drop. This is the way that most CMOS logic ICs are protected, except that they have some series resistance to limit the input current. A zener at the gate/source is another way that's about as good.

Without getting into discussions about the provenance of this circuit, I think the designer was of the opinion that a reverse biased diode at the input kept the input signal further out of overload from the diode-conduction direction of a zener  clamp. But I could be remembering that wrong.

Either way works.

thanks for the great info...youre always WAY more helpful than any person should be !

There will, of course, be a firestorm here when the designer pops in and sees the circuit.

my thoughts exactly....

perhaps Aron should remove this thread, or at least the schematic in question.

AC

[markm]

Doesn't that schem resemble the Mosfet Boost quite a bit?

[Gus]

It is more the mosfet boost resembles that circuit.

[amz-fx]

It is more the mosfet boost resembles that circuit.

-Jack

[R.G.]

Hmmm...

It seems that there are many, many effects circuits that were just pulled out of application notes and circuit compendiums, I guess.

[amz-fx]

Wouldn't it be beneficial to use a zener diode (like in the AMZ mosfet boost) between the gate-source junction in this circuit to help protect the mosfet from static charge damage ?

The 1N914 diodes are performing a similar function.

regards, Jack

[Gus]

Jack

I meant that in a good way

I have that vmos book I like the 4watt SE amp circuit I have been meaning to wind a transformer for that.

I leave out a lot in my posts sometimes.
  The mosfet boost and the circuit above are more different than some might understand here.

  The mosfet looks more EE designed because of the  non varing input Z and cap coupled gain control that does not effect the bias point of the circuit(DC gate to source voltage stays the same) and.......
I have not built it but I have built other circuits like it, nice and clean.

The other circuit has less than a 5 meg input Z(correct me if I am wrong) (10meg drain to gate feedback kind of like fig 4.1 in the 2nd picture)and as the gain goes up the input drops even more also the gate to source voltage effects the bias point.......
  Sounds good I often tell people that ask for a booster it is a good one to buy.

Like You and R.G. posted some stuff is right out of books I have a number of older semiconductor books (60's and later).

This rasies the question how can one legaly share this information? 

An example I have a book from 1964 that has all the math worked out for the FF type circuit.  It was a common "building block" circuit if I am understanding history correctly.  Then look at an early neve circuit etc.....