Booster 2.5 from AMZ ? ...build report LONG !

[MartyMart]

I have a schem with Jack's name on it, but find lots of references in the archives to
this being "aron's" design ?? .... are there two "Booster 2.5's" ??
This also seemed to become the "Sweet Thing" and a few other things, like a BSIAB ....

Anyway, this doesn't seem to get a lot of recent mention, and as "The Mother" of all the
Jfet amp emu's ( sort of, sorry Jack !) was worthy of a build
I have played with MU amp setups before, but wanted to try "The Original" which seems to be
2 x Mini Boosters connected in series with some gain control and Big Muff TC.

The word "Boost" seems odd here, as the circuit doesn't really do "clean" boost, which you
would associate with that term, it's actually quite a serious "Gain Monster"  !!
Jacks schem does mention that using 1k source resistors will reduce gain into the mild overdrive
area, I went with the recommended 100 Ohm - actually 120 Ohm was all I had.

Circuit Layout :
Again, I used my preferred "veroboard" medium and fitted it onto a piece 3cm X 6cm, which will
fit happily in a Hammond 1590B.
As the drain from each MU amp pair connects directly to 9v ( no trimpots ) the layout can be kept
quite small and "neat" - i used sockets and placed each pair ( vertical ) directly 'atop each other.
Poly caps and metal film resistors used throughout, J201's were fairchild's

Debug :
Very quick, I missed one copper trace "cut" which shorted out the input cap to stage two's, drain !

Sound :
Superb sounding OD/Distortion, nice and full tone, with a great "gnarly" mid range hump to it.
The TC takes some fine tuning, I found the lower half of the pot almost useless, just a very
"Boomy" tone with mids/highs dissapearing fast !
Settings around half way towards 2 o'clock were great, keeping enough lows and adding back
the high end, above that and the low mids/bass then get cut quite fast too.
Possibly my TC is compromized, I had to use a 250k B pot with a 270k resistor across the outer
lugs and the 39k became a 33k ( all I had )  ?? - maybe the taper has been shifted too much !

Mods :
I socketted the 100n drain caps and the 100n from the gain pot too, I liked the original tone but
wanted to try it a little "thinner" so replaced all these with 22n poly caps.
Still undecided about this, it's a smaller sound bass wise, but cuts quite nicely, also reducing the
22uf from the source of the first J201 pair, will thin the down down but also reduce gain a bit, so
that's staying "as is"

All in all, I'd give it a 9/10 and can be tweaked to be just perfect
Cheers, Jack/Aron  ?

Sorry - can't link to a schem, as I couldn't find it at AMZ, though my schem states the AMZ address !
Marty.

[amz-fx]

Here's some archived info about the Booster 2, and the mods to make it v2.5, from almost 7 years ago:

http://www.diystompboxes.com/smfforum/index.php?topic=15463.0

http://www.diystompboxes.com/smfforum/index.php?topic=15693.0

[Doug_H]

Here's the schematic:

http://www.diystompboxes.com/pedals/booster25.JPG

Jack's "Minitubes" was actually the mother of the JFET "amp-in-a-box" stuff. It was sort of a 3-stage preamp simulation kind of deal using Miniboosters. Aron combined some of those ideas with an old circuit of Jack's (The Booster 2- which IIRC was basically a 2-stage Minibooster circuit) and created the "Booster 2.5". I subbed a different tone control and called it the "Sweet Thing". Ed Guidry did further modifications and called it the "Brown Sound In a Box". And so on... After that we started fooling with CS JFET stages in place of the Miniboosters.

[MartyMart]

Thanks guy's -- still sounds GREAT after 7 years 

MM.

[WGTP]

Doug, it's time to whoop out the lost "Sweet 16" schematic for those looking for an "over-the-top-scooped-mid-monster" tone.   

[aron]

If you look back at the archives, I had a Booster 3 which was 3 Mini-Boosters cascaded. It would have been a monster had I known about J201. Instead, I used some other brand and it was lacking in distortion because of the weak fets. It had level stages between each booster and I still have it boxed.

What I didn't know at the time was this: "Secret" of stacked stages

http://www.diystompboxes.com/wiki/index.php?title=Simplemods#Simple.2C_Easy_Mods.2FTips_.26_Techniques

See how I give you guys stuff for free 

Anyway, Jack brought out the Marshmallow preamp - which was a complete "preamp simulator" and darn did it sound good! Encouraged by this, I started to tweak a 2 mini-booster design and when I put in the 100 ohm source resistors, I knew I had the gain I wanted. This thing was killer at the time!  I still have it boxed but I haven't used it in a while due to a power supply change in my pedal board.

After that Doug wired the Sweet Thing and I like that tone control better so I used that as well.

[Doug_H]

See how I give you guys stuff for free 

People have no idea about some of the nuggets buried in the stickies and archives around here...