1986 Marshall Bass Sound from Super Bass

[bmcash]

Hi Everyone,

As the title indicates, I am venturing out and wanting to mod a standard 100 watt super bass (ceriatone) to sound more like a 1986 50 watt bass. Is this even possible? I know there are difference in mains filtering; ie, I would need to change the 100 watt super bass to 100 uf mains can. I would think this would make the amp far too stiff though.

Any suggestions?

B$

[M Fowler]

Compare the 68 SB 100w layout and the Plexi 50w Bass layout for suggestions.

[bmcash]

Thanks. To me, the preamp is mostly the same with the exception of the 50/50 electrolytic on the 50 watt compared to the 32/32 found in the 100 watt.

The B+ are different too.

I think that if I change the mains filters to match the 50 watter, the amp would be too stiff, and I dont want that.

Any ideas?

[Littlewyan]

1. Remove the bright cap
2. Change the NFB resistor to 47K and attach it to the 8ohm lug on the impedance selector instead of the speaker sockets.

The filtering might make it a bit more stiff but would also help with lower notes.

[bmcash]

Should I consider changing the dropping resistor on the super bass to match the 1986 voltages?

[Littlewyan]

If you mean changing the 8K2 to a 10K then you won't notice any difference. It will only drop the voltage by roughly 9/10V. Although it will make the amp a bit kinder to the Cathode Follower in V2.

[bmcash]

Thanks. So you think changing nfb resistor and attaching to 8 ohm lug would be best bet? Anything mods to tone stack? What exactly does attaching to 8 ohm lug accomplish?

[Littlewyan]

Tone stack is the same in both amps so you're fine there.

Basically when the NFB is connected to the speaker socket the amount of NFB varies depending on what the impedance selector is set to. So if you used a 16Ohm cab you'd have more NFB than if you used a 4Ohm Cab. Putting it onto the 8Ohm lug will mean you'll have the same amount of NFB no matter what you set the impedance selector to.

Maybe just try changing the NFB first and see if you like it. I'm guessing you heard a 50W Marshall Bass Amp and you preferred it to your 100W 68 Superbass?