JHS Mini Bomb- Gutshots and values

atreidesheir · Post by **atreidesheir** » 28 Jun 2012, 20:01

No, real question. real answer. thanks
How do I find the math for the appropriate diode on one of these?

Jack Deville · Post by **Jack Deville** » 28 Jun 2012, 21:19

atreidesheir wrote:What is the role of the diode in a common source amplifier?

Perhaps it is being used for reverse polarity protection?

atreidesheir · Post by **atreidesheir** » 28 Jun 2012, 21:28

Interesting. I was reading around the web and could not find a reference to the diode.

culturejam · Post by **culturejam** » 28 Jun 2012, 22:03

atreidesheir wrote:Interesting. I was reading around the web and could not find a reference to the diode.

Search on "cathode diode bias" and read up on it. It works the same way with JFETs (or transistors).

atreidesheir · Post by **atreidesheir** » 29 Jun 2012, 00:36

ok I am catching up slowly.

geiristudio · Post by **geiristudio** » 24 Apr 2013, 23:00

Soooo schematic?

aaronmcoleman · Post by **aaronmcoleman** » 25 Apr 2013, 01:32

For a simple boost like this, what are the drawbacks to a common source design? I mean, it's not the most "original" original design, but a simple JFET amplifier can be a pretty nice boost in my experience.

Also, given the ultra low parts count, there are only so many ways this could work 100n input, 22u output (or switched), 100k drain, 5k1 source, 1M volume.

Intripped · Post by **Intripped** » 25 Apr 2013, 12:03

looking at the pics this should be the schem - tested on breadboard and it works

Seiche · Post by **Seiche** » 25 Apr 2013, 17:08

that's pretty fucking basic. What are the advantages/disadvantages in not having an input cap and biasing resistors on the jfet?

Frabbio · Post by **Frabbio** » 26 Apr 2013, 00:15

Nothing, apart saving a quarter for each pedal manufactured.

Seiche · Post by **Seiche** » 26 Apr 2013, 10:16

Frabbio wrote:Nothing, apart saving a quarter for each pedal manufactured.

economics, albeit silly, might have an influence. Maybe they also wanted to cut down on manufacturing time, who knows? But what would be the disadvantages compared to the typical jfet boost topology found here:

Fermusicman · Post by **Fermusicman** » 26 Apr 2013, 23:16

Intripped wrote:looking at the pics this should be the schem - tested on breadboard and it works

actually the pot goes to the input, according to a my diagram draw basing on the photos here.
I built a couple of these in this way and I like the sound.

Fermusicman · Post by **Fermusicman** » 26 Apr 2013, 23:26

By the way, this one also has less pop noise that ep booster or super hard on.

Intripped · Post by **Intripped** » 27 Apr 2013, 01:01

Fermusicman wrote: actually the pot goes to the input

oops, you're right!

nice that it works also in the other configuration, anyway.
tomorrow i'll try this new one and listen to sonic differences: i found that "my" version sounds cleaner than the real one in the demos and i think i would prefer it with a bit more of grit

Dr.Detroit · Post by **Dr.Detroit** » 27 Apr 2013, 21:46

Very likely it is Tim Escobedo's "Duende JFET"

Seiche · Post by **Seiche** » 28 Apr 2013, 17:36

yep, that looks like it. And he probably either matches the jfets or picks a resistor after testing the jfet.

soulsonic · Post by **soulsonic** » 03 May 2013, 05:50

Let's see what happens now that they've stopped making J201s... or any other good JFET....

irmcdermott · Post by **irmcdermott** » 08 May 2013, 01:33

He's already starting to go the the SMD route. He's got the JFETS on the bottom side of the board in his Superbolt

https://www.freestompboxes.org/viewtopic ... 20#p216547

And I think the new Prestige Boost, or whatever it is, is entirely SMD

batteryacidtea · Post by **batteryacidtea** » 08 May 2013, 03:52

I'm a little late do the party, but holy jeebus, his soldering skills are really and litterally da shit!

POTL · Post by **POTL** » 27 Aug 2017, 23:42

Project link
http://www.stewmac.com/freeinfo/i-2150/ ... st_web.pdf
Note
Trimpot 25K can be replace to resistor 5K1 and matched fet.
Its Traced 100%