Help: Sunn Beta Preamp Mid-Freq Mod

[wildhog]

I’m looking to build an EffectsLayouts Sunnbeam (Sunn Beta preamp) and want to add either a pot or switch to control the mid frequency. Can someone help identify which capacitor(s) control the mid-range on the attached schematic?

Also, a switch to select between 3 fixed frequency centers is a bit more straight-forward, but how would I go about using a potentiometer instead?

Any help would be appreciated!

 

[YourGuitarist]

Continuous mid adjustment would be done via a capacitance multiplier.

Look under variable capacitor here:

C20 would be my first guess. Very complicated EQ, I'd have to simulate. Stick a multiplier in place of C20.

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[eh là bas ma]

I’m looking to build an EffectsLayouts Sunnbeam (Sunn Beta preamp) and want to add either a pot or switch to control the mid frequency. Can someone help identify which capacitor(s) control the mid-range on the attached schematic?

Also, a switch to select between 3 fixed frequency centers is a bit more straight-forward, but how would I go about using a potentiometer instead?

Any help would be appreciated!

I m not sure i understand.

There is a Mid control already in this circuit. It's mentioned in the build doc ?

You want a second Mid control ?

Edit : ah nevermind... i think i got it. You want to control what mid frequencies are cut or boosted by the mid control.

Good idea !

 

[z2amiller]

Edit : ah nevermind... i think i got it. You want to control what mid frequencies are cut or boosted by the mid control.

Would you call that a Mid Control Control?

 

[wildhog]

I m not sure i understand.

There is a Mid control already in this circuit. It's mentioned in the build doc ?

You want a second Mid control ?

Edit : ah nevermind... i think i got it. You want to control what mid frequencies are cut or boosted by the mid control.

Good idea !

Yeah exactly -- basically looking to add a mid-frequency control in addition to the mid level control. A pot like what's on a Boss Metal Zone would be cool but I think a switch like on an Ampeg V4 or 2nd gen Sunn Model T would be easier

 

[Blackboarcult]

Since the mid frequencies rely heavily on the corner frequencies of both bass and treble circuits (at least for the "cut"), there is no *easy* way to implement a mid shift on the Beta. It would quickly become a nightmare of switches and dual pots for it to be somewhat effective. An alternative is to replace the tonestack altogether with something that already comes with a mid shift (E.g. Peavey VTX series, Blackstar ISF, Metal Zone, umpteen bass amps...) but then you would lose a lot of the uniqueness of the Beta. Sunn had a lot of weird tone stacks that imparted their own character to fairly flat preamps, for good and for bad

 

[eh là bas ma]

Would you call that a Mid Control Control?

i would if i wanted to be perfectly clear, but it's a bit too long. The Mid's pot's pot feels easier to use in a sentence.

An alternative way to have some mid frequency options, easy to do and close to the original circuit design, would be a toggleswitch inspired by the changes for the guitar/bass versions.

On my build i used two 4pdt switches to change the values of the 7 components needed to recalibrate the EQ for the bass version.

I didn't think much about it, i just put all resistors on one switch and all the caps on the other.

I guess it's possible to experiment with the values of the components near the Mid control on the schematics.
R27, C14 and C18 have a good chance to have a significant impact on the mids.



Edit : These two circuits being stompbox adaptations of another circuit, your schematics are different from Aion's project around the Mid control.

I'd say on your schematics it would be R32, C19 and C20.

Based on Aion's modifications, increasing these values will probably lower the mid frequency range, and vice-versa.

 

[comradehoser]

there's always equalizer pedals you can run in tandem with the Sunn to boost specific mids, or things like the acrobat and harmonic energizer that you could rock with as well. You might just put everything in one enclosure and call it a day.