Help with a quick question in the bb preamp layout

[Belanger]

If I wanted to use A electrocylic for capacitor 2 what way would I put the negative side (I'm new at this). Also could I use bc109 trannies on this instead of the 2n5088

[bluebunny]

Just glancing at the layout you posted, it's not easy to tell how an electrolytic C2 would be oriented.  You need to find and post a schematic, which will tell the whole story.  You may be able to substitute BC109s, but check the datasheets first to see if their characteristics are similar (probably) and for the pinouts (which surely differ).

[samhay]

It looks like it should go with negative side to row f ('down'). However, without a schematic, I'm guessing/error-prone.

The safest approach is to build it without C2. Measure the voltage at the point where each lead connect, then orient with the negative lead to the more negative point.

[Mattnezz]

C2
There is a bit of logic to it.
C2 is between Q1's emitter and IC1's +input.
Q1 gets V_ref at its base via R2. There is a small drop across R2, depending on hfe not worth mentioning yet.
So its emitter is approx. : V_ref - 0.65V, the drop caused by forward biasing the BE junction.
IC1/pin 3 is connected to V_ref via R4(10k). Since this highZ input doesn't load the the resistor too much, the drop across the resistor is almost zero.

So I expect a small potential-difference between the two.
d2-point at 4.5V
f2-point at 3.85V

This is a standard Tube-screamer input section, and because the potential difference is so small you see non-polar C's in the old TS808's and film-types in the newer ones.

2N5088>BC109
There seems no problem, both are just buffers. But it might change the input impedance a bit, some like the lower-hFe trannies for their darker sounding buffers. Where a high hFe (BC550C or 2N5089) usually adds brightness.
With lower hFe for Q1, the voltage drops more significant across R2. (as R2 forms a divider with appr. Hfe*R3)

[antonis]

Besides of any analysis, you have many options:

Use a Poly 1μF which isn't polarized..

Use an electolytic Non-polarized 1μF..

Use 2 parallel 470nF or even 3 X 330nF (there is enough space on layout)..

[Belanger]

It looks like it should go with negative side to row f ('down'). However, without a schematic, I'm guessing/error-prone.

The safest approach is to build it without C2. Measure the voltage at the point where each lead connect, then orient with the negative lead to the more negative point.

BRILLIANT. why did I not think of that!   Of so where would I wanna set my multi meter to( this is my 4th build this week/ever so I'm reading as much as possible all the time and literally just diving in head first. If it wasn't for being able to ask you guys questions I think I'd still be trying to figure out my first build (blue collar od).  Here's how it looks so far

[Belanger]

C2
There is a bit of logic to it.
C2 is between Q1's emitter and IC1's +input.
Q1 gets V_ref at its base via R2. There is a small drop across R2, depending on hfe not worth mentioning yet.
So its emitter is approx. : V_ref - 0.65V, the drop caused by forward biasing the BE junction.
IC1/pin 3 is connected to V_ref via R4(10k). Since this highZ input doesn't load the the resistor too much, the drop across the resistor is almost zero.

So I expect a small potential-difference between the two.
d2-point at 4.5V
f2-point at 3.85V

This is a standard Tube-screamer input section, and because the potential difference is so small you see non-polar C's in the old TS808's and film-types in the newer ones.

2N5088>BC109
There seems no problem, both are just buffers. But it might change the input impedance a bit, some like the lower-hFe trannies for their darker sounding buffers. Where a high hFe (BC550C or 2N5089) usually adds brightness.
With lower hFe for Q1, the voltage drops more significant across R2. (as R2 forms a divider with appr. Hfe*R3)

Thank you very much for sharing that info with me.   That will help me out in future builds for sure as well. 

[Belanger]

I'm now just taking that little electrocylic out and putting in a 1uf Panasonic film cap