<Community Design Project> Boutique Mosfet Madness

bajaman · Post by **bajaman** » 26 Nov 2007, 01:28

how about MJ2

(one mosfet and two jfets)
bajaman

soulsonic · Post by **soulsonic** » 26 Nov 2007, 01:49

I haven't checked this thread in a few days.... it's really turned into something interesting! Good job guys! I really like the ideas for the Tone and Bright controls.

pz · Post by pz » 26 Nov 2007, 17:09

bajaman wrote:how about MJ2
(one mosfet and two jfets)
bajaman

I like that!

Ok, here's my schem with all add-ons:
Schematic
I added something, mainly because i like to use all the available place on the pcb, and while the dimensions are determined by the pots and enclosure...
Another goal was to desing a pcb that will be universal for a lot of variations of this pedal. So the add ons, including the previous ones are:
1. Switchable Gain Boost in the second stage. Rx sets the gain boost, 0R (jumper) gives max boost. Good idea would be to solder there a 10k-47k trimpot, set the desired boost by ear, desolder trimpot, measure the resistance and put there a fixed resistor.
2. A driver for Boost LED. It's a basically an BJT inverter. A SPDT switch can be used for BOOST function (cheaper maybe than DPDT... or the second section we could use for another feature, like maintaining the constant output volume)
3. An additional, optional output buffer. The type of the output (buffered/unbuffered) is selected with one jumper.
4. An additional, RC filtered power to drive LEDs and minimize the clicks.

After adding all this to the pcb design i still had some spare place, so for those that would like to use a 2PDT bypass footswitch i added a RG's Millenium Bypass. It is powered from the filtered LED supply.

When designing the pcb (one layer, only two longer jumpers) i tried, more or less to follow the star grounding methode. Each stage has is own "semi" local ground point, just like it is done in tube circuits to minimize the hum.
In case of out circuit probably the hum wouldn't be a problem, but since it's doable, and technically correct, then why not?
I think that when i finish the pcb project i will add a description like:
"If you dont need a X feature, do not mount listed here components...."
We could also write some "recipes" for newbies, how to tune the circuit to own expectations (more lows, more attack, less bright etc)

Piotr

DougH · Post by **DougH** » 26 Nov 2007, 22:00

bajaman wrote:how about MJ2
(one mosfet and two jfets)
bajaman

Michael Jackson 2?

pz · Post by pz » 29 Nov 2007, 14:03

here's the pdf with schem and pcb project of my version:
Freestompboxes.org OpenSource OD

gnognofasciani · Post by **gnognofasciani** » 29 Nov 2007, 18:04

Skreddy wrote:Looks like PZ's design could take over as the better version, but here's my latest revision
-Removed the cap and bias resistor from between the gain pot and T2
-re-did the layout a bit more compact and filled in the ground traces
http://marc.happybob.com/circuits/what/schemo5.gif
http://marc.happybob.com/circuits/what/copperV5.gif
http://marc.happybob.com/circuits/what/partsV5.gif

You should avoid 90° angles, I was told by a wise friend of mine that they can introduce noise

marshmellow · Post by **marshmellow** » 29 Nov 2007, 18:58

Believing this guy or more precise his layout tutorial this is more of a myth. 45° are only preferred for the aesthetics.

Besides, the tutorial is some good lecture. You probably would do most things intuitively, but who knows...

bajaman · Post by **bajaman** » 29 Nov 2007, 20:05

nice work folks

Modman - perhaps we should move pz's pdf project file to the DIY projects section of the forum

cheers
bajaman

Sock Puppet · Post by **Sock Puppet** » 05 Dec 2007, 15:11

Hi, I've just found this thread and had a thought about the pregain stage.
Couldn't the 5k pot become the source resistor with C9 (looking at schemo5) to ground on the wiper (like a FF), to get rid of R5 (larger C9 for bass?) with R2=5k or both pot and R2=4k7.
Also, does it need an R.F. path to ground (or does C6 accomplish this) and why not a higher input impedance (R8).
R1 has me puzzled though, what's it for?

S.

Sock Puppet · Post by **Sock Puppet** » 05 Dec 2007, 15:50

A couple more things (excuse my newbeeness) -but how many are breadboarding this? Can R4 be replaced with a fixed resistor, R11 does nothing, R16 - just seems to increase the supply impedance etc...

Also, I thought there could be two filters to push bass and treble bands into two separate distortion stages, which may not be the same - with a blend, naturally.

So clean out the breadboard it is then, near Christmas or not.

S.

MoreCowbell · Post by **MoreCowbell** » 30 Dec 2007, 20:12

Any further progress and / or build reports ?

~arph · Post by **~arph** » 22 Jan 2008, 16:38

So how many pedals are out there on the market now that are actually this design?

Anyone got as far as making some soundsamples?

premiumplus · Post by **premiumplus** » 03 Mar 2008, 10:37

Revival post... this is a great forum and I'm so glad that I found you.
Great thread, everyone.
I'm mostly watching and being quietly respectful of you all. We are peers and this forum is terrific. Thank you for being here.

Has anyone built/breadborded this yet?
I'll be experimenting with it as soon as my parts arrive. I just restocked and rebuilt my shop after a nasty divorce and 4 year hiatus from building. Only $200 to start!

-Dave

bajaman · Post by **bajaman** » 03 Mar 2008, 11:56

Welcome aboard Dave

- lots of good things happening here - feel free to contribute or just lurk - no worries mate

bajaman

premiumplus · Post by **premiumplus** » 03 Mar 2008, 21:44

bajaman wrote:Welcome aboard Dave - lots of good things happening here - feel free to contribute or just lurk - no worries mate
bajaman

Thanks bajaman,
I just finished doing the mods to my old Dunlop wah that you suggested and it sounds great.
I never knew that wahs are supposed to peak from 440 to 1760, and after I did the mods I hooked up my function generator and scope and set my pot to work around those values. Mine actually goes from around 420 to 1.9kHz...

You rock!

bajaman · Post by **bajaman** » 04 Mar 2008, 02:53

thanks
bajaman

briggs · Post by **briggs** » 04 Mar 2008, 10:18

No sound samples as of yet. The L'Overdrive de la Revolution Deux project (on my blog or in the Ready to build project forum) has a similar circuit structure and I can confirm that sounds:

Kind of Marshall meets Mesa. If you play with the tonestack your can get many different sounds too...

Welcome to FSB.

premiumplus · Post by **premiumplus** » 04 Mar 2008, 11:08

briggs wrote:No sound samples as of yet. The L'Overdrive de la Revolution Deux project (on my blog or in the Ready to build project forum) has a similar circuit structure and I can confirm that sounds: Kind of Marshall meets Mesa. If you play with the tonestack your can get many different sounds too...

Welcome to FSB.

Thanks briggs,

I'm looking for a "Marshall meets Fender" sound. I sold my boogie years back

-Dave

dap9 · Post by **dap9** » 28 Mar 2008, 02:13

Man, I can't believe I didn't find this thread earlier. Great stuff!! I have two questions:

1. Has anyone done sound samples of this circuit?

2. What books do you recommend to help me understand the theory and whatnot that you guys are talking about. I have a very basic understanding at this point, but don't know where to go for "the next step" in learning about electronics.

Thanks to everyone for such a cool community!

MoreCowbell · Post by **MoreCowbell** » 09 May 2008, 22:31

One of us needs to eventually build this beast !