fetzer question

[oneeyedog]

Hi folks, i have just completed a Fetzer build as per this diagram....
http://www.aronnelson.com/gallery/main.php/v/Renegadrian/Fetzer+Valve.gif.html
is works (thanks renegadrian) but when I switch on there is a noticable volume drop... any suggestions as to what I have got wrong?

thanks
john

[newfish]

Hi.

If you've built it 'as-is' from the layout, the first thing to check would be for solder bridges between the copper strips.

Assuming there are none, the 22K resistor that worked for Renegadrian's J201 may not work for yours.

Despite modern manufacturing preocesses, every single J201 will be slightly different in its demand for current etc.

If you have a 100K trimpot to hand, remove the 22K resistor, and replace it the trimpot.  You'll have one spare leg - for the moment, this is OK.  Just make sure that you've used the centre leg of the trimpot for one of your connections.

With the pedal engaged, adjust the trimpot until you get your boost.

J201s sound great, but can be a PITA to bias...

Hope this helps.

[petemoore]

  Fetzer Article, ROG, a related J201 jig/choosing device.
  Then, once a Jfet [2n5457 ?] is chosen for it's
ability to use a small enough proportion of the 9v
for it's operational bias needs, or biases otherwise/somehow.
Put a bias on that,
put yer Fez on and play !
  Otherwise a few more supply volts probably wouldn't hurt to
make the hoggy
Jfet be happy enough to swing +/-, with more way-room
between the rails =ing a less 'delicate' to bias Jfet circuit.

[Renegadrian]

Yes I guess that you have to find your own bias value - I got some 201s that biased good with 22k so I just put that res in instead of the trimmer but yeah it may not work for you - I'd say stick to the trimmer solution and then cheange it ti a fixed resistor if you wish.

[oneeyedog]

thanks people... i dont have a trimpot to hand but i'll get one as soon as and let you know.
cheers
john

[Ice-9]

thanks people... i dont have a trimpot to hand but i'll get one as soon as and let you know.
cheers
john

It doesnt have to be a trim pot, if you have a normal pot to hand use that then measure the resistance setting and replace the pot with the same value resistor.

[oneeyedog]

hi folks, I replaced the resistor and now my output is adjustable (obviously, I hear you say!!!) however it starts to get noisy at a certain point, still noticably lower than the bypass volume, I realise there should be some differencer between levels but I dont think what I have got is correct.....................