BSIAB take 4

[Storing!]

I build 3 BSIAB already. 2 for me one for my boy. The fact that they all sound different doesn't need an introduction  
Well I got hold of a set of different JFETS and decided to breadboard #4, just to experiment with the various fets. Until now I tried combo's of J201, 2n5457. bf245 (a,b,c) ans 2n5952, . The best sounding to my ears until now are J201 and5457 in various combo's. The BF245 differ a lot from a, b and C. Now 3906 and mpf102's enter the stage.

A lot has been written in these pages about that. So I started digging for all the info I could find and started to experiment with the breadboard.
What did I find:

1) The first stage isn't to critical. When altering it, it has only a minor change. So using not to high gain fets gives a somewhat more tighter feel (I can only distinguish this at low gain settings).  eventually I settled for a pair of MPF102.

2) The second stage is interesting. different fet's give an altogether different feel. j201 give a high gain drive MPF102 and 5457 a more low gain feel. The 245 and 3906 I were in between but were a bit shrill. I liked the difference betwen 102 and 201 do I decided to use both and make it switchable. (There's a subtle difference between various fets takes time and titing ears to select them.)
Making it switchable is easy a DPDT switch after C6 and before c12 does the trick so 2 second stages will be there.

3) looking at other mods. Using a switchable second stage means u can tune C7. It makes a difference, I settled for 0,1U for the 201 and 0,068U for the 102's. This isn't calculated, just my ears.

4) the third stage is As interesting. lots of changes using different fets. I choose one in the middle ground  (a mpf102). Could have made it switchable but the trim had me decided not to. A 201 gives a lot more staturated tone. the BF245 is a bit harsh. bit then again its all about taste.

5) I found a mod I really liked. a C-r couple over r15.
http://www.diystompboxes.com/smfforum/index.php?topic=41148.0 check out #4 check out nr 4.
A 1U cap with a 5K trim made switchable. It gives extra distortion but a nice open sound.  From the stuff I tried I liked this one very much.

So what does this give. A BSIAB with a switchable 2nd stage and a AC bypass switchable for R15. Well this is the experiment for now. Maybe my ears are tired, so other mods have to wait. It's going to gt a gruelling tryout with my band.

I used sockets for all fets as I know I will be tweeking.

Here some pics.


The first stage. This uses mpf102



The second stahe doubled The first are J201's  the second 102's U can also see the sockets for the fets in the first stage.

Finished board 1



Finished board 2



Then finanly box it. I dismanteled my first BSAIB and put this one in (motice the small millenium board on the left.



And the boxed set



One switch to select the 201 or the 102
one switch for the AC bypass.

Makes a lot of nice combinations.

Curious how it holds up to my second bsiab thats in my pedal board.

Enjoy. E

[Hupla]

Very nice,

just looking at your wiring there and wondering if you had any oscillation problems?

[Storing!]

Hi

No oscillation problems at all.
Must admit was afraid it would. But it's really clean.

[alfafalfa]

Hi Eric,

Nice work you did there.
So far I've built 4 BSIAB's : one version 1 and three version 2 and I like the design very much.
Besides it's a great platform for some individual tweaks. The sort of caps you use can make a big difference.
And of course the transistors. Mine all sound a bit different.
What you did with the switchable transistor is an idea I had yesterday (talking about coincidences).
Could tell a bit more about how you accomplished that ?

Did you put the transistors paralel ?

Alf ( as it happens a fellow countryman as well as living in the same town)

[Storing!]

Hey Alfa

Same town, Rock City!

The switching was done by duplicating the parts R10,11,12, c7 and of course Q3,4.
Then with a dpdt switch, connected before the gate of Q3 and before C12.
This way the while midsection becomes switchable.

I used sockets for the fets because it pays to try several combi's. Some j201 for example sound better than others.

[alfafalfa]

Thanks Eric for revealing "the secrets".

I'm gonna to try that when I build yet another version.

Alf