MOsfet Booster not working

[ranchak]

I just finished the AMZ Mosfet Booster. It's not boosting.

  Re: AMZ Mosfet building problem
« Reply #2 on: September 15, 2006, 06:38:59 AM »   

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1.What does it do, not do, and sound like?
Sound geos through the pedal, but there is no boost

2.Name of the circuit
Amz Mosfet Booster

3.Source of the circuit (URL of schematic or project)
http://www.generalguitargadgets.com/diagrams/ge_boost_lo_amz_mosfet.gif

4.Any modifications to the circuit?
No

5.Any parts substitutions? If yes, list them.
Yes, a 68k resistor for the 62k resistor
I didn't have a 5k pot so I took a 100k pot and used resistors to bring the resistance down to 5k.
J201 instead of BS170


6.Positive ground to negative ground conversion?
No

9.3v battery

D     5.19
G     2.818
S     4.041

Am I making a mistake with adding resistors to the pot?


I checked the pinout on my tranny and it is inserted correctly. I did use a

[boogietube]

My 2 cents- I found that I had to replace the drain resistor with a 100k trimmer to get it to work.

[boogietube]

Oh ya I also tried the resistor / pot thing. I tried several things  , but the pot thing didn't work for me. I had to use the 5k pot - I was searching for a better taper. The 5k bunches up the boost in the last 25% of the pot. Apparently, SmallBear will have the reverse audio 5k pots available in the new year. I can't wait.

[Laus]

I don't think you can replace a BC170 with a J201. Should try it in mine anyway.

[$uperpuma]

nope ones a jfet, ones a mosfet...

[burnt fingers]

A j201 is a Jfet.  It is not interchangable with the BS170 which is a MOSfet.  Different pinouts, different specs.  You'lle have to get a BS170 or a 2n7000 MOSfet for this circuit.  There are plenty of cool boosters you can use a jfet with.  Check out the layouts gallery
http://aronnelson.com/gallery/album18/ROG_FETZER_VALVE_VERO
http://aronnelson.com/gallery/album18/DOD_201_JFET_PREAMP_VERO

[ranchak]

You guys were right, I got a BS170 and now it works. One thing I noticed is there is not a lot of boost at low volumes. I almost thought that it wasn't working until I turned my amp up. I can hear the difference at louder volumes. I removed the pot from the circuit and picked up a bit more boost. Sounds good for rhythm or a slight blues sound. Any ideas on mods for this for more clean boost?

[$uperpuma]

most of the boost on that one is toward the end of the pot range... do a search about these and you'll find all kind of cool info....maybe try a different taper?