AMZ Mosfet Booster - Questions - Help Needed

[ilcaccillo]

Hi,
I was checking the AMZ Mosfet Booster circuit from jack Orman and have some questions that would like to ask you guys out.

The circuit can be found here:
http://www.muzique.com/schem/mosfet.htm



As the output is taken from the "Drain" of the Mosfet isn't this output signal Polarity reversed ("Phase Inverted") when compared to the input signal?
Doesn't it form an "Inverted" buffer?

Is there any reason for taking the output from the "Drain" instead of from the "Source"?
If the output is taken from the Source of the Mosfet it seems to me it would be "Non-Inverted" so would respect the same Polarity that is presented at the input?
Any reason for this, or am I'm missing something here?

Would the below example of the Non-Inverting work?



Thank you so much for all your help

[idy]

The output at the Drain is inverted, but is also amplified; it's voltage is many times the input.

The output at the Source is not inverted, but it is buffered; it's voltage is the same as the input but it can produce more current and drive a long cable or something. Lower output impedance than your guitar pickups.

Also either one has a high input impedance, making long cables and such less of a problem.

There is another version on AMZ that actually provides both inputs, a booster and a buffer, you choose.

[antonis]

R4 on your second schematic is useless..
(to be more precise, it's harmful from output signal swing point of view 'cause it "restricts" positive waveform headroom..)

[ilcaccillo]

Thank you so much for your kind help and replies

The output at the Drain is inverted, but is also amplified; it's voltage is many times the input.

The output at the Source is not inverted, but it is buffered; it's voltage is the same as the input but it can produce more current and drive a long cable or something. Lower output impedance than your guitar pickups.

Thanks for the explanation.

Actually I don't need the "amplification", I just need to use this circuit as a buffer and Hi-Z to Low Z impedance converter,
also I would preffer the signal to be "non-inverted" so I guess a solution with the output from the source fits the bill

[ilcaccillo]

R4 on your second schematic is useless..
(to be more precise, it's harmful from output signal swing point of view 'cause it "restricts" positive waveform headroom..)

Thanks for pointing that out,
do you advice any other value for R4, or removing it completely?

Assuming that the goal is to make an Unity Gain non-inverted Buffer...

[antonis]

Simply remove it ..

IMHO, you'll have to tweak R5 value in relation to Vr (5.5V here) counting for particular Q1 V_GS for a Source given current..

P.S.
On a second thought, just remove R4 and swim in shallow water..

[ilcaccillo]

Simply remove it ..

IMHO, you'll have to tweak R5 value in relation to Vr (5.5V here) counting for particular Q1 V_GS for a Source given current..

P.S.
On a second thought, just remove R4 and swim in shallow water..

No worries about tweaking R5, I can just fit a Trimpot there and tweak it until Vr=5,5v, is that it?

[antonis]

No...

Vr IS 5.5V (9 x 100k/162k)..
Make R5 4.7k - 5.6 k and measure Source voltage..

[ilcaccillo]

No...

Vr IS 5.5V (9 x 100k/162k)..
Make R5 4.7k - 5.6 k and measure Source voltage..

Thanks,
what Source voltage should I aim for?

[antonis]

In theory, somewhere near mid-supply voltage (4.5V)

In practice, as close to mid-supply as you can, 'cause 1V V_GS (5.5 - 4.5) is lower even than threshold voltage..
https://www.onsemi.com/pdf/datasheet/mmbf170-d.pdf, page 2 - On Characteristics & page 3 - Figure 1..

P.S.
Jack Orman's Booster is biased for serving both for Booster & Buffer (actually for phase splitter due to Source & Drain same value resistors) so its Source voltage is aimed to be about 1/4 of power supply one..

edit: I might confused you, so let R5 be 2k7 and make R1 330k - 470k (ideally 390k)