Sunn Beta Lead vs Sunn Beta Bass: Tone Control Stage

[Drummer4gc]

Hi all,

I'm looking for some input from folks more knowledgeable than myself about the differences between the Beta Lead and Beta Bass circuits. Other than the Lead having Reverb, they appear to be identical circuits, other than some component changes in the tone controls. However, the Owner's Manual (https://support.fender.com/hc/en-us/...eta_Series.PDF) and the Service Manual (page 5, https://support.fender.com/hc/en-us/...ice_Manual.pdf) don't differentiate between the Lead and Bass in describing the controls, frequency ranges/cutoffs, etc.

I've snipped the relevant parts of the circuits below - C138, C140, C141, C143 are different. I've seen another schematic with a few additional differences, but these two came from the same service manual so let's stick with this. I've played guitar through each, although at different times, and they both sounded great.

Can anyone comment on any difference in frequency response between the two circuits?

Beta Lead:



Beta Bass:



Thank you!

[Gingertube]

The component changes (capacitor values) in the tone sections are what I would expect. The Beta Bass controls will be all centred approximately 1 octave below the Beta Lead.
Note that the cap values are all approximately doubled for the Beta Bass.

C138 forms a shelf filter into IC107 for mid and treble controls drive (it cuts the bass in that feed).
C140 set the high cut in the mid control feed
C141 may have confused you - IC109 is a "gyrator" or simulated inductor whose "inductance" is set by C141. IC109 "inverts" the action of that cap and makes it behave like an inductor.
C143 sets the frequncies feed to the treble control.

Cheers,
Ian

[nevetslab]

The component changes (capacitor values) in the tone sections are what I would expect. The Beta Bass controls will be all centred approximately 1 octave below the Beta Lead.
Note that the cap values are all approximately doubled for the Beta Bass.

C138 forms a shelf filter into IC107 for mid and treble controls drive (it cuts the bass in that feed).
C140 set the high cut in the mid control feed
C141 may have confused you - IC109 is a "gyrator" or simulated inductor whose "inductance" is set by C141. IC109 "inverts" the action of that cap and makes it behave like an inductor.
C143 sets the frequncies feed to the treble control.

Cheers,
Ian

I couldn't have said it any better!