The Fetzer Valve is a FET booster which emulates the input stage shared by many Fender tube amps. Check it out!
Article, schematic, and perfboard layout: http://runoffgroove.com/fetzervalve.html
...."New at runoffgroove.com"... such a beautiful sentence!
Many thanks!
like mentioned in the article, the equivalent tube-circuit is a well-known basic standard, that has been in use simce ~20 years before Fender...
Do you know where it was first commonly used? We'd like the write-up to be as accurate as possible.
dunno, needs to be researched - just looked it up in an old 1939 radio/audio book to be sure it`s been there...
I've seen it in an RCA manual, if I recall correctly. I think the schem I saw was pre-war. It goes back a long way. I'd like to see if cavemen were using this circuit, if anyone knows off the top of their head. I'll bet RG knows.
Yeah it's old alright. Personally for me, I like the series resistance to the gate to be as low as possible. Even on my Fenders, changing it to as low a value as possible really affects the sound.
It should be noted that the famous Trainwreck circuit has no series resistance and boy can you hear it!
I remember Jack putting out a value like 33K and it's worked for me pretty good for some circuits.
BTW: to me Jack's "Marshmallow" and Mini-Tubes was the first widely published example of Tube Amp emulation using JFETs. He sure deserves a TON of credit for putting that circuit out there.
If you guys recall, it switched between Fender and Marshall and came with a matching speaker sim circuit to boot!
Alas it's on his CD, but before that, it was a ground-breaking idea and well done.
Thanks for continuing the tradition!
The Marshall 18W combo is another example of no series resistance to the first grid.
Mr. Orman is a man of legendary status. He, like the other forum "elders" deserve all the thanks we can give them and then some. I'd like to see him around here more often.
that grid-stop resistor forms a lowpass filter with the grid/plate and/or grid/cathode (parisitary) capacitance (Miller).
It reduces the risk of unwanted oscillations, and the chance of "receiving" radio stations.
In tube-circuits, it should be mounted as close to the grid, with as short a lead, as possible.
Absolutely! I'll never forget the two miniboosters circuits, and hearing them for the first time. Wow! Tube sound in a box! Fantastic! I'm forever grateful for that sound. Opening my eyes to FET's.
Jered
Brian, Gary: pace yourselves, guys - the rest of us can't keep up!
If you take the TWO input Fender amps mentioned and trace out the circuit connection for the Hi impedence input then I believe you will see the 1 Meg resistor to ground first then the parallel resisrance of the TWO 68k (34k)resistors connected to the grid. This gives a different sound again from the connection shown. In my clones I usually have one input jack connected as I have just discribed and the other as shown. A toggle switch can do the same thing.
John G
Mmmmmmmm....it would be possible to continue this and make a fet emulator of a fender amp no?
OF Course....
Nice build! Great Sounding Jfet boost.
Without the right trimpot, I had to do some diddling before it turned on..starting with a 47k trimpot + 22k seriesed, I ended up at around 6k8 for total bias resistance.
Cool idea with the gate resistor, it could be parallelled with another [?68k] resistor & switch for preset boost. Or an input gain pot...of course.
Was havin' trubbles with getting the Bazz Fuzz part of the "Wasp" to work and decided to take a break and build this one !!! I cut a small piece of perf off another circuit, the board is 'petite'.
Looks like it could be a good candidate for Aron's next 'beginners project' to me. :)
Q: Does it impart the characteristic Fender 'twang'?
Quote from: Lucas GrijandeMmmmmmmm....it would be possible to continue this and make a fet emulator of a fender amp no?
Already in the works. I've built the prototype's board last night. I hope you like simple and "tweedy"...
I built one of these today. I put a 100K pot on the input and plan on playing around with it to find the sweet spots, hopefully tonight. I will mark the 68K first and then go from there. I put a picture up on another post "Plastic enclosures Pedal Pictures".
Peace!
Arn C.
Its all ball bearings these days.
Quote from: MarkDonMelIts all ball bearings these days.
http://runoffgroove.com/prepare.mp3
HAHAHA