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.

 

[Fama]

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.

View attachment 100296

Edit : These two circuits being stompbox adaptations of another circuit, your schematics are different from Aion's project around the Mid control.
View attachment 100297
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.

Do you feel like the modification to be able to toggle between the version was worth the effort?

Also curious about what @wildhog ended up doing and if it worked well.

 

[tegendemuur]

Such a knob would be called frequency. The L5 uses a rotary for this (likely the easiest to implement a bunch of frequency shifts, via the available daughter boards on the market). The Bajaman Ampeg SVT circuit is another such case.

 

[wildhog]

Do you feel like the modification to be able to toggle between the version was worth the effort?

Also curious about what @wildhog ended up doing and if it worked well.

I ended up dropping the mid-frequency idea for now and just built it with the lead/bass toggle which was much easier on the EffectsLayouts circuit than Aion's since you only need to change 4 caps so it works with a single 4PDT switch. After playing it for a bit, I'm not sure a mid-freq would add much but I really like being able to toggle between bass/lead. I'll probably even build a second one to be able to run bass and lead in stereo

 

[eh là bas ma]

Do you feel like the modification to be able to toggle between the version was worth the effort?

I think so.

I play guitar and bass but i could probably be fine with only the bass version for both, i think.

I often use the bass version with guitars, i like how it sounds, and i also use a GE-7 at the end of the signal chain, to shape the mids on guitars almost all the time.

On the other hand, having both options is comfortable, i do switch to the guitar version sometimes when i want some specific settings for a tighter sound.

For this mod i used two 4PDT located at each sides of the 3PDT, to be able to keep the circuit in the original BB enclosure.
It's very easy to do, there's only the extra 8 euros for both 4PDT toggleswitches.
I guess it's quite cheap if we want to use the circuit on various instruments, or use the bass version on guitars occasionally.

 

[Fama]

I think so.

I play guitar and bass but i could probably be fine with only the bass version for both, i think.

I often use the bass version with guitars, i like how it sounds, and i also use a GE-7 at the end of the signal chain, to shape the mids on guitars almost all the time.

On the other hand, having both options is comfortable, i do switch to the guitar version sometimes when i want some specific settings for a tighter sound.

For this mod i used two 4PDT located at each sides of the 3PDT, to be able to keep the circuit in the original BB enclosure.
It's very easy to do, there's only the extra 8 euros for both 4PDT toggleswitches.
I guess it's quite cheap if we want to use the circuit on various instruments, or use the bass version on guitars occasionally.

I did order a 4PDT switch to toggle between the two, I've got the Effects Layouts version so only four cap changes are needed (which the one 4PDT should be enough).