Lower gain transistors for my BSIAB 2

[Its been said]

So I really really love My BSIAB 2, but I never find myself turning the gain nob past noon. I was thinkign if I put some lower gain transistors in there I'd get a more usable range. It currently has three 2N5457's and two J201's. I've built a couple of DIY pedals, but I'm still pretty much a noob at the actual knowlege of it past putting part A in hole A and part B in hole B, so let me know if this is possible and which transistors I should use. thanks! 

[Talon5051]

There is a lot of entries on the BSIAB 2 and mods in the forum.  This one http://www.diystompboxes.com/smfforum/index.php?topic=79647.msg657553#msg657553 talks about different Jfets for the box. 

[brett]

Hi
in general you get more gain from JFETs with higher (less negative) Vgs.
The J201 is highest (Vgs of about -1 V), so they are the obvious candidates to change.  Of the JFETs I use, the 2N5484, 5485 and 5486 are sequentially lower gain.  The MPF102 is a classic low gain JFET with Vgs of between -4 and -6 V.  IIRC the 2N5457 is a middle-of-the-road device.
It won't necessarily be easy to get the bias right when you swap JFETs.  But then again, non-centred bias sometimes sounds sweet with JFET gain stages.
cheers

[Ed G.]

Try mpf102 for q1 and q2, 2n5457 for q3 and q4 and 2n5457 for q5. If that's not enough gain, go back to j201 in q3 and q4.

[aron]

> I was thinkign if I put some lower gain transistors in there I'd get a more usable range.

Try swapping out the 500K gain pot for a 250K pot. You may have to adjust the 150pf cap or maybe not.

[liquids]

I love the BSIAB too.  I haven't really gotten my hands on too many JFETs other than the 'three' I see here most - J201, 2N5457 and MPF102s.   The information brett posted is useful, thanks.  

Anyhow, I've found that the J201s and 2N5457s to be more subtle than expected, and closer to the J201 than the MPF102 in this circuit, however, it may be the ticket for you and is for many.

While I'm not really going for 'the brown sound,' but that being said, my current BSIABs builds (which I'm ever modding and tinkering with) have MPF102s for all but Q5.  People say the MPF102s are highly variable one to another (all JFETs are anyhow), but all that I've tried in a mini-boost based circuit they consistently yield less distortion ('lower gain'), better dynamics, feel/less compression, if that is what you are after.  Don't be afraid to compare multiple examples of the same JFET type and compare tpp.

I always say it, but apart from simply swapping JFETs and seeing if you like it more or less, it's useful to breadboard it...a JFET swap may also beg a re-voicing.  Also keep in mind that tinkering with making R10 larger (1k, 2.2k, 3.3k, etc), for example, will also lower the gain, if you keep the same JFETs.