biasing bsiab2 ( gaussmarkov layout)

[dorothegreat]

hi!

recently finished populating my board (from  gaussmarkov  site).

im at a lost in biasing the trannies, im confused with labels (Q1, Q2, etc.) of the different posts here.
im not sure which is which, i used  gaussmarkov  layout and it would be a great help if you guys could point me
to right direction.

thanks!

[Quackzed]

Q is short for transistor,usually numbered left to right, so Q1 would be the leftmost transistor.

 

                                                                                           

[bigandtall]

Any quick tips on how to bias a transistor? I'm about to build a Runoffgroove Flipster and will need to bias the trannys with trimpots. I'm just starting to look around to figure out how to do this.

thanks!

[dorothegreat]

Thanks for the reply Quackzed.

But what i was trying to say is that Q1 Q2 Q3 Q4 Q5 labels on the GGG site is different from that
of gaussmarkov's layout. Another thing is that i cant seem to figure as to what tranny is supposed to be
affected by the 100k trimmer.

thanks!

[waltk]

Only one transistor on the BSIAB2 is biased.  On the GGG layout the transistor is Q5, on gaussmarkov's layout it's Q3 - same transistor, just named differently.  To bias it, hook the negative (black, or common) lead on your voltmeter to ground - the negative battery terminal for example.  Hook the positive lead (red, +) the the drain lead on the transistor (this is easiest if your trasistor leads are long, and you have alligator clips on your meter leads).  You should be able to measure the voltage with these connections somewhere between 0 and 9 volts.  Your goal is to have the meter read 4.5 volts, and this is adjusted by turning the trimpot.

[kungpow79]

Your goal is to have the meter read 4.5 volts, and this is adjusted by turning the trimpot.

Hmm... I'd say your goal is to have it sound good.  Adjust it by ear!  :icon_biggrin:The 4.5V volt is just an estimate.  It should be around that value, and likely in the 3.5-4.5 range.  In fact, on JDs site, in the kit instructions its mentioned they adjusted one to like 3.4 and it sounded great. 

Too low and its too quiet, too high and the note decay is thin and crackly.   Use your greatest tool;  your ears!