LUCKY 7 MOSFET OVERDRIVE

[Dragonfly]

Here's a project I was working on, but haven't had time to "complete". MartyMart did some initial testing for me, and had a few suggestions. It needs some filtering / tone rolloff at the end of the circuit to calm some of the high end..probably something similar to what the ROG circuits use. But its a really good "starting point" on a nice mosfet overdrive.

AC

[WGTP]

Looks good.  Just needs one more stage...

[BDuguay]

I hate seeing '0' replies and good work unnoticed.
Keep 'em coming!
B.

[Mark Hammer]

OK.

My preference is to "spool out" the high end in cascaded gain stage circuits, so that early stages have more treble cut than later ones.  Othersie you end up with harmonics of harmonics of harmonics.    With that in mind, the suggestion is to tame the first stage so that the second one is driven by a "warmer" signal.  With that in mind, sticking a small-to-medium fixed resistor (e.g., 10k-47k) in series with the input of the "Gain" pot, and a cap to ground (in order to roll off some high end) might not be such a bad idea, and ought not to jeopardize the drive capabilities of the first stage that much.

[slacker]

looks cool. I've been playing around with some multiple gain stage ideas recently and the tone shaping does seem to be the trickiest thing to get right.

[MartyMart]

Nice to finally see it Andy !! 

I think that I remember using a 1M gain pot and a dual 12k/1nf pair of roll off sections at the end.
I also ( as mark suggested ) have a 470k with a parallel 470pf cap, pre-gain pot from Q1.
Q2's drain cap ended up as another 22n (0.022uf) just like Q1's

Here endeth my "tips for the day"

MM.

[Dragonfly]

Nice to finally see it Andy !! 

I think that I remember using a 1M gain pot and a dual 12k/1nf pair of roll off sections at the end.
I also ( as mark suggested ) have a 470k with a parallel 470pf cap, pre-gain pot from Q1.
Q2's drain cap ended up as another 22n (0.022uf) just like Q1's

Here endeth my "tips for the day"

MM.

I got so busy I havent had time to play with it !  I figured "why just have it sitting in my archives" when I can post it and let paople mod it to their liking ?

IIRC, I did a layout that incorporated your mods. I'll see if I can find it.

AC

[Barcode80]

hmm, i've been looking for a good od, i built the tubesound overdrive a while back and never could get the high end tamed down without killing the drive on it no matter what input or output cap i used, and unfortunately i'm just not advanced enough to start with major modifications. maybe once this has bounced around a while i will give it a shot!

by the way, what does IIRC mean?

[Dragonfly]

by the way, what does IIRC mean?

"If I remember correctly"

[Dragonfly]

Layouts for the Lucky 7 Mosfet Overdrive

...UNTESTED....

IIRC, these have some of the mods MM and I came up with to tame some high end. MM compared it as "similar" to a Blackstone OD, I believe...I may be remembering incorrectly though, as I've slept since then ! 

AC

[Barcode80]

i'll try to put up a vero as soon as i get home.

[WGTP]

http://www.diystompboxes.com/analogalchemy/sch/obsidian.html

A little more to chew on, for those unfamiliar with Mosfet distortions, which I higly recommend.   

[Barcode80]

on that obsidian, could you not just use 10k trims for the bias instead of breadboarding and swapping resistors?

[electrictabs]

looks great guys
any clips coming?

[Barcode80]

dragonfly, i think you told me once that correct dimensions on printing your pcb layouts is about 60% reduction... is that right?

[Gus]

Trim on the DRAIN leg with an enhancement mode MOSFET?

Some help

Calculate whatever your wanted drain voltage is at what ever drain current you want

Use Ohms law and pick your drain R

Adjust the 4.7megs for the drain voltage wanted

Wipers of pots don't like DC current, so put your trim at low current sections
better yet if it is going to be fixed replace the pot with resistor(s) of the pots value.

Cookbook mosfet gain stages

[MartyMart]

Drain resistors of about 3k9 to 5k1 should work for between 4.5-5.5v at drain, it doesn't need to be too "futzy"
like a jfet...

[markm]

Looks like a great job Andy, thanks for the mail too!!
Here's a look at the enclosure artwork I made for Andy when this circuit was in development;

[Dragonfly]

Looks like a great job Andy, thanks for the mail too!!
Here's a look at the enclosure artwork I made for Andy when this circuit was in development;

That box looks AWESOME...hopefully I'll have time to "stuff" it soon... 

AC

[markm]

That box looks AWESOME...hopefully I'll have time to "stuff" it soon... 

AC

I'm almost ready to stuff my Creampie Box 
sorry but, that's all the details you guys are gonna get for now!