BSIAB II ? can I add a switch to use as a low gain/ high gain switch?

[rosssurf]

I really like my BSIAB( could use a little more low end though)
Anyway, I would like to have the ability to switch it from high gain to low gain settings. I would like to make it switchable so that the full rotation of the gain pot would cover only about the first two hours on the dial in high gain mode. This would enable finer tuning of the gain in Low gain mode>
How might I accomplish this?
Does this question make any sens? I hate puytting this stuff into words

[zeta55]

Hmm, maybe as simple as switching in/out a resistor in paralell over the gain pot.

/Krister

[Phorhas]

I'm sure that there are many ways that I haven't thought about, but here are a few suggestions:

1. Make the 120Ohm Source resistor on the second gain stage switchable: connect a larger resistor in series (could even be a trimmer to fine tune your "low gain range"). The switch shorts out this larger resistor to go to "high gain mode"
2. Breaking the connection between the Source of the of the first gain stage and the Source bypass caps: this way will both lower the overall distortion (although not as much as the first suggestion) and mellow out the high frequency content with will make it sound a bit "creamier"
3. Add a switchable resistor in series with the 470k/470pf pair: this will make things similar to suggestion #2



Dan

[Bucksears]

How about toggling 1/2 (or so) of the value of the gain pot?

(Please, someone correct me if I'm wrong, because I'm about to do the same thing and will do something differently if this won't work)

I am working on a four-knob, three footswitch BSIAB II in the following config:
CONTROLS: Gain1, Gain2, Tone, Volume
FOOTSWITCHES: On/Off, Gain1/Gain2, Boost

The Gain1 & 2 pots will be 250k, independent of each other, so I will toggle between two different gain settings. The stock BSIAB II gain pot is 500k, so each of my gain pots will be half of that.
The 'boost' is a (footswitchable) 250k resistor in series with the 250k pot(s) that, when engaged, should act as the remaining portion of the original 500k gain pot.
So, assuming that the gain maxed out on a 500k pot would = 100%, the available settings will be:
1) 250k Gain1 at 50% = 25% total gain
2) 250k Gain2 at 100% = 50% total gain
3) Gain1 + 250k boost = 75% total gain
4) Gain2 + 250k boost = 100% total gain

If there is a problem with this scenario, please chime in. I have a case ready that I'm going to use on this one.
Thanks,
Buck

[Bucksears]

bump

[Morocotopo]

Use a pot half the value of the original (example: if 500K, use 250K) and switch in/out a resistor of the same half value in series with the pot, and you get double the pot travel for the gain range.
Or, use a multiturn pot.

Morocotopo

[Bucksears]

Use a pot half the value of the original (example: if 500K, use 250K) and switch in/out a resistor of the same half value in series with the pot

Should the resistor be in series before or after the pot? I'm assuming it would connect to the 3rd lug if before, or connect to the 2nd lug if after?
Thanks again,
Buck

[John Lyons]

Buck
Your modifications seems fine to me.

The resistor would either be lug 1 or lug 3.
You are just limiting the range of resistance to ground. More resistance = more gain.
If the resistor is in series with lug 1 you are adjusting the higher gain range with the pot.
If the resistor is at lug 3 you are adjusting the lower gain range.

John

[Bucksears]

Thanks man.
I'm waiting for the dust to settle on the 'final' Dr. Boogey before I restart that one.

- Buck