Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

March 28, 2024, 09:25:20 PM

Login with username, password and session length

Recent Posts

 

Fet version of the Sharp channel of the Bogner Triple Giant

Started by KMG, February 01, 2011, 04:54:32 AM

Previous topic - Next topic

Steve Conner

The LND150 is a great device for this kind of application. I've seen people substitute it directly for a tube. I managed to get some samples recently, but I've not tried them yet.

rowdy_riemer

I've actually got 5 of these from Mouser a while back but never got arround to playing with them.

rowdy_riemer

Quote from: J M Fahey on February 02, 2011, 07:37:00 AM
Sorry, didn't want to hurt anybody, all the contrary :(
Beyond that, we are on a technical forum here, and if somebody says 2+2=5, hurt feelings or not, I'll state the result is 4.

As of ROG projects, seeing a typical one gives me headache, the same kind I get when I hear somebody singing absolutely out of tune or playing very fast, missing 80% of the notes.
Let me explain that:
The Fetzer itself is the only serious part, and I was not referring to it.
Its designers know the triode curves they wish to approach, know what they actually have (pentode-like Fets), know all the theory, how things work, do whatever's needed to bend one into the other, brilliant !! :tu:

*But* cloning a tube design , and finding there a typical 1/2 12AX7 with 1K5 on cathode, 100K on plate, 260V B+ , 160V on plate, and substituting it with a Fet, using 1K5 on source ..... (why 1k5 ?).

There's 3 possible answers I can hear:

1) "because I decided I want that FET to pass 1mA and, look at the curves, this particular one passes 1 mA with any drain voltage between 3 and 30V and 1.5 Vgs , so [1.5V/0.001A]=1500 ohms".
*That* is the "serious" answer and the one I expect  :tu:

2) "Duh?? :o"
Even this one is somewhat acceptable, sort of.  ???
Nobody was born knowing, but studying or experimenting anybody can learn and advance.With some care it may end up good, in a near future

3) "Because Fender uses it"  :duh
C'mon, you are kidding, right? This is magical thinking of the worst kind.
Why the worst? Because to the uninitiated it "sounds" logical, even powerful (Mojo) , pure pseudoscience.
Add this to the power of internet, and another impossible to erradicate myth is born and spread. :duh
I repeat, I find *good* design work the Fetzer approach and the work of all others who took it seriously, such as KMG, Lab Series, Mensur, Trace Elliott, Yamaha, Roland, Univox (Westbury) and the granddaddy of them all: Randall.
1K5? 9V? Forget it !! (unless you buy 100 fets to farm the 5 to 10 amongst them which might be happy with that value)
*None* of the above mentioned established manufacturers uses anything even approaching that Fet-unfriendly combination.

....

No doubt your criticism of their typical biasing scheme is well founded.

KMG

QuoteI managed to get some samples recently, but I've not tried them yet.
While waiting you can try them in simulator, SPICE models you can download there
http://www.supertex.com/spice_models.html

J M Fahey

This is what I love about this Forum, the constant brainstorming in a good way.
Thanks to all.

joecool85

Quote from: J M Fahey on February 02, 2011, 03:42:26 PM
This is what I love about this Forum, the constant brainstorming in a good way.
Thanks to all.

:tu:

This place has really turned out well.  Makes me smile thinking about it.  I never would have thought 5 years ago when I started this place that it would be so successful.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com