need help with a Fat Boostered

[rotoghost]

I'm building the "Fat Boostered" off www.GeneralGuitarGadgets.com

Ok, here goes:  I've checked the offboard connections many times, checked the parts layout, tested as many part values as I could with the parts still soldered in place... but when I turn it on, I get a loud pop, and then the singal level comes through at just about the same level as when it was off - but the controls do function (it has volume, gain, treble and bass, which all seem to do their job).   I did double check the pinouts on the Qs, and they were right... I just don't know where to go from here.

Power supply noise/hum does come through to the amp when it is turned ON.  When I use a battery it's dead quiet, but when I use a lousy wal wart with no filtering I get an AC hum.

Anybody have any thoughts?

[Paul Marossy]

Are you saying that you get a popping noise when you engage the circuit (turn it on from bypass mode)?

For the hum, you could add a 100uF filter cap for when you're using a wall wart. Most wall warts suck when it comes to a clean (ripple free) power supply...

[Jered]

Can you post the voltage readings your getting? Test each lead on each fet and post the votages. That will usually get most problems solved pretty quickly.
Jered

[rotoghost]

Ok, voltages are as follows:

Q1:
D 0v
S 65.5mv
G 2.3V

Q2:
D 2.16v
S 2.32v
G 4.5v

Q3:
D 2.86v
S 3.42v
G 4.5v

Well, there they are... I'm not sure what typical voltages in this circuit are supposed to be, so I don't know how to interpret these results...

On the POP:  I get the pop when I go from bypass to FX ON, yes.  Also, for the hum (and here's something else I find odd) I have a pi filter after the supply... 2200uf to choke to 100uf.  Still get a hum, but only with this board (I've used the supply on another board without that hum)

[RDV]

Pinout?

RDV

[rotoghost]

The pinout of the Qs?

They are TL072, looking at them from the bottom (as a D)

Drain
Source
Gate

[rotoghost]

sorry, too many projects in my head at the same time...

the Qs are J201 fets.

TL072, obviously an opamp from another project...

[Paul Marossy]

I think RDV was asking if you have the pins of the FET connected to the circuit properly...  

[rotoghost]

Ah, ok.  I double checked the pinout to make sure they were hooked up right at first... later I did find some J201s with a pinout that were different on Mouser, so I reversed all of them - there was no sound after that... so I switched them back.