Is there a way to make a buffer into a boost, simply?

[acehobojoe]

So, the first buffer on. This page seems pretty simple, yes, but is there a way to give it more gain? Maybe I'm just not understanding the buffer/booster question.

[antonis]

A schematic of your buffer should be helpfull..

[acehobojoe]

Haha.... Sorry.
Here we go
http://www.beavisaudio.com/techpages/Buffers/

First one.

[antonis]

TYou can go here: http://www.beavisaudio.com/techpages/HIW/HIW.png and see the  schematic differences between Buffer & Booster..

At your buffer you'll have to bias the Jfet, add a resistor (or trimmer) between 9V and Drain and a capacitor to this junction which will lead to an extra output, selectable by a switch...

[acehobojoe]

Based on what I was reading that seems like the only difference. I'll draw a schematic..

[acehobojoe]

http://i.imgur.com/VuWT2Qtl.jpg
That's what I got. Then I can either switch them or blend the 2 with a pot at the end.

[R.G.]

Good intention. However, the signal at the drain is inverted relative to the signal at the source. A true equal-amounts mix/blend gives you cancellation and no signal out at all.

There was a recent thread where I typed in some thoughts about buffer, boosters, and the differences and overlaps. Might be a good read for you.

[acehobojoe]

So it'd have to be a switch, or perhaps there is a way to phase invert it. Could you link me to that thread?

[R.G.]

So it'd have to be a switch, or perhaps there is a way to phase invert it. Could you link me to that thread?

http://www.diystompboxes.com/smfforum/index.php?topic=109288.0

[knutolai]

You could rearrange the circuit for something similar to the tilman preamp (second circuit under "boosters")
http://www.beavisaudio.com/techpages/blocksfragments/

by substituting R6 for a 50k (or 100k) logarithmic potentiometer you would have a circuit able to boost and dampen your signal. Setting the pot to unity gain obviously would give you a unity gain buffer (though with a slightly worse output impedance than your original circuit).

[acehobojoe]

Yes, I imagine it would be a little worse impedance, do you mean because of the pot?

[R.G.]

The output from a drain of a FET amplifier fundamentally has a higher impedance than the output from a source follower.

Then the pot likely raises this a bit.

[acehobojoe]

Ok, I'll make another schem. Where is your other post?

[midwayfair]

You'd be better off doing this with an op amp. The Microamp is fine for this application:

http://www.electrosmash.com/images/tech/microamp/mxr-microamp-schematic.png\

To make it a buffer simply short the - pin and pin 1 with a switch. It won't matter where the boost pot is set; the gain will be 1.

[acehobojoe]

Would that not be possible with the same transistor schem? Just shorting it? Or it would phase out I guess.

[acehobojoe]

I also want to keep the part count low. For I am using a 1590a

[knutolai]

http://www.diystompboxes.com/smfforum/index.php?topic=109288.20
think this is the thread R.G. was referencing to.

[acehobojoe]

Thanks!

[midwayfair]

Would that not be possible with the same transistor schem? Just shorting it? Or it would phase out I guess.

No. The transistor version you posted is a source follower. You cannot get voltage gain from the source output. The op amp is far more complicated than a single transistor on the inside.

There should be a microamp layout somewhere that will fit in a 1590A. Way more complicated stuff fits.