New at runoffgroove.com: Fetzer Valve

[B Tremblay]

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

[nooneknows]

...."New at runoffgroove.com"... such a beautiful sentence!
Many thanks!

[puretube]

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...

[B Tremblay]

Do you know where it was first commonly used?  We'd like the write-up to be as accurate as possible.

[puretube]

dunno, needs to be researched - just looked it up in an old 1939 radio/audio book to be sure it`s been there...

[Gary]

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.

[aron]

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!

[Gary]

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.

[puretube]

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.

[Jered]

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

[Ge_Whiz]

Brian, Gary: pace yourselves, guys - the rest of us can't keep up!

[John G]

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

[Lucas Grijande]

Mmmmmmmm....it would be possible to continue this and make a fet emulator of a fender amp no?

[petemoore]

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'.

[Ge_Whiz]

Looks like it could be a good candidate for Aron's next 'beginners project' to me.  

Q: Does it impart the characteristic Fender 'twang'?

[Gary]

Mmmmmmmm....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"...

[Arn C.]

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.

[MarkDonMel]

Its all ball bearings these days.

[B Tremblay]

Its all ball bearings these days.

http://runoffgroove.com/prepare.mp3

[MarkDonMel]

HAHAHA