TILLMAN: HOW TO INCREASE OUTPUT LEVEL?

[slacker]

Welcome to page 10 

[gez]

Boof...back of the net!

[Renegadrian]

I started breadboarding today, and the Tillman was an easy one to begin...Well, I tried to add some el.caps in it, as suggested, parallel to the source resistor...I put a 4.7µF , 10 too, but found some kick with a 33µF. Tried to replace the source resistor too, but no significant change to my ears,,,
The same poor result changing the C1

Also, I found a lil' difference between those 2 layouts

The one I used and Another layout

The second lacks the 10µF cap - Being spread between + and -, I think it's like a power filter??? Am I wrong?

ATM, it seems that adding that source cap parallel to the resistor does give some (but not much) extra level...

I Just couldn't use math theories, adding, dividing and so on, after all I can only count to 4 (it's what I need for Rock n' Roll!!!) 

[Renegadrian]

My breadboard experiments continues...Swapped the j201 for a 2n5457...Instant volume raise!!! 
have to fiddle a bit to find the right cap value, with the 2n5457 you get more gain, so it distorts more easily...
So while I went up to 33µF with the j201, I believe a 4.7 or even a 3.3µF are enough for the 2n5457.
Was thinking to let my man audition the breadborded circuit, maybe i can throw in a "gain" switch (spdt (?) tied to that cap).

[Renegadrian]

http://till.com/articles/GuitarPreamp/index.html

It's always useful to read what its inventor explains...So I was right about C2, the cap between + and -
It's like a power filter.

My original design used a Motorola 2N5457 N-channel JFET, which also works well, but the J201 is a lower noise device.

R1 determines the input impedance and, for the case of open inputs, capacitively coupled inputs or piezoelectric pickups, references the FET gate to ground.  R1 can be almost any value, and in some cases, such as if the preamp is connected directly to an electromagnetic pickup, can be eliminated entirely.  I originally used 10 Mohm for this resistor, but more recently I've been using 3.0 Mohm so that there's less noise during switching transients.

R2 biases the FET at around 0.5 mA.  This can compensate for some variation in FET characteristics -- if the FET is conducting too much current, the voltage across R2 will rise making the FET gate more negative with respect to the FET source, and thus reducing the current in the FET.

R3 is the FET drain load resistor.  The value is chosen for roughly 6.0 volts at the FET drain.  The value of R3 also determines the output impedance.

C1 is a coupling capacitor to remove DC from the output.  R4 references the output to ground, and keeps the output from floating positive if left unconnected.  C2 isn't really necessary, but depending on how the power supply is rigged it can reduce power on/off transients.