PROBLEM WITH AMZ MOSFET BOOSTER

[grani79]

HI!

I built an AMZ MOSFET BOOSTER from:
http://www.generalguitargadgets.com/index.php?option=content&task=view&id=118&Itemid=162

I used the right component. The effect seems to work, but after some seconds it start to do a lot of "scratches", "pop" and "noise" when I play the guitar. I tried different transistor (all BS170), I tried to replace the two elec. caps .... but the problem remains... some helps?

Thanks

Grani79

[Michael Allen]

Check all your connections. Try redoing the battery connection.

[Darren N]

It seems this circuit is susceptible to "battery microphonics". Tap the battery to see if that's where your noise is coming from.  If this is your problem try a different type of battery.

[Phorhas]

what are the pin voltages?

look for cold solder joints

[grani79]

VOLTAGE:

S: 3 Volt
G: 0,5 Volt
D: 6,4 Volt


Keep in mind... it happens after few seconds! It' not always present. It scratches on the speaker after few second I use it.....

[grani79]

no help for me?  

[petemoore]

I don't know where to look for reference voltages for that transistor pin.
 But, one of us should go to GEO, and read all about how to bias a Mosfet..I just can't recall offhand...go there...it's all typed out concisely.
 The Source at 3v looks high to me, a good portion of the swing is eaten up here since your starting with 9V to work with.
 Transistor pin orientation
 Electro caps orientation
 Drain bias resistor...I used a 100k pot as a V/R, connected for this resistor, after biasing it was replaced by a fixed R value, close to equal R value to what the pot was set at during biasing. Just don't turn the potshaft while removing and checking it's resistance at that' setting.
 I had troubles with this build a couple times...it has to work when it's 'right'.
 The MOsfets are reportedly quite static sensative, and can be blown by handling if a charge is discharged into it....I always handled mine...don't really know how to use it without handling it.

[Gringo]

Take a look at this:

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=19014&highlight=bias+amz+mosfet+boost

HIH