AMZ Fet Booster

[gtudoran]

A stupid question guys... is there any way to use another value for the volume pot on a AMZ booster?... let's say i would like to use a 100kA pot? As far as i see... i have to keep the proportions regarding de source resistor, am i right?

This is the schematic: http://www.tonepad.com/getFile.asp?id=87

Best regards,
Gabriel Tudoran
Analog Sound

[petemoore]

  Without studying it...
  Good amount of room to modify the two resistors.
  A resistor string, the 2 resistors add to the value of the voltage divider.
  These two resistors load the ouput, small resistance from SP to Gnd. means more signal is shunted, the difference between 100k and 1meg in this regard is small, but the HF's tend to get effected by resistors quicker than the LF's.
  100k is a good 'center value' for volume pot on such a circuit.
  1 meg: as it's turned down, soon the resistor in the signal path gets large enough to be...a large resistor in the signal path, again the HF's may have trouble getting past, in such cases where it's deemed', a bypass capacitor can allow a low impedance path across the SP portion of the volume pot wafer.
  <100k or about 50k...you may notice that the signal is getting loaded down.
  For circuits with very low output impedance and where the treble loss is 'in the account' of design, you may see a 10k volume pot.

[gtudoran]

Thank you peter for your answer... i was wandering if there should be a difference regarding the sound (or overall gain) if i modify the 5k pot with a 100k pot on the AMZ Fet Booster (i don't see any voltage divider on that particular schematic, as far as i can see the pot modify the FET polarization).

Best regards,
Gabriel Tudoran
Analog Sound

[petemoore]

100k pot on the AMZ Fet Booster (i don't see any voltage divider
  The 100k pot is 2 variable resistors, they always add to the exact value of the pot, around 100k.
  When the resistance on one side of the pot goes up, the resistance on the other side of the pot must go down by the same exact amount.
  The wiper divides resisance as a result of dividing the pot wafer into two parts.
  A potentiometer with 3 lugs is a variable resistive divider, put a voltage across the pots R wafer and it it's a variable voltage divider.
  If the wiper/knob is near the middle of a 100k linear pot, 50/50 between the outside lugs [each lug is connected to an end of the resistive wafer]m the resistance can be 50k / 50k.
  Audio taper sets 50/50 up higher because the thickness of the resistive wafer the pot divides is 'tapered', hence 'tapered response', one end of the wafer is thicker than the other.

[thetragichero]

only way to figure it out is to breadboard it!
i've had times where i didn't have the 'correct' value, but what i subbed it out with sounded even better!

[petemoore]

  It can be calculated.
  Every one of the circuits has been calc'd in one form or another.
  Frequency, gain at least, usually plus about anything else.
  Those numbers may fly right out the window too.
  Once the circuit tweeker knows 'which way' to move the value of something, the numbers are best used for figuring 'how far'.
  Those exact numbers can then be written.
  Tweeking by ear makes sense, ballpark is where the game is, and since whatever the box is doing Fr or Gain wise, it's multiplied many times by some unknown amounts. These unknown amounts render ugly heads when out of control, such as when my Tube Reamer oscillated because the driveway was packed with thick cakey white stuff and I didn't make it down to RS for the LP Filtercap value I want to try first across the diodes [I tried a too big one already today, cool...
  Time to get to proper Voicing of my new Tube Reamer + I have 2 switches I want installed for just what this topic is about.
  This kind of thing is hard to tell about before, after it becomes semi-readily obvious which Fr's need taming or let grow more, otherwise having values switchable as time and settings and room changes goes by as a way of getting a more accurate barometric average for 'this' value seems to pan out in the long run.
  Meanwhile thinking of how to patch holes in boxes I've 'damaged' by adding then subtracting switches for use as permanent value finders.