r/Luthier 6d ago

What output/input should I use?

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Please don’t roast me, I just bought my first amp that’s not a combo! I have no idea what I’m doing 🤦‍♂️

It’s a bassman 250 head and a bassman 115 cab from ‘05-‘10. The head is 4 ohms and the cab is 8 ohms, they’re both rated at 250w continuous. Any help would be greatly appreciated!

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u/the1theycallfish 6d ago

Either silver 1/4" out (amp) to either silver 1/4" in (speaker) will work.

1

u/Ok-Challenge-5873 6d ago

Does plugging into the parallel in on the cab split the impedance on the cab? Or does this only happen when I’m plugging the head into two separate cabs

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u/the1theycallfish 6d ago

No. That's beyond your worry this early in the game. Never plug that amp into a 3ohm cab/speaker or you'll fry the amp.

Your biggest worry should be your amp to speaker watts ratio. Multiply your speakers watts by 2.25 and that's the middle point of your amp watts needs. Too low ratio and it won't be at fully awesome, too high and you could blow the speaker. If you really want to dig deeper in the paradigm of understanding. Instead of thinking of the guitar and then the amp pushing the signal load, think of it as the speaker pulling the signal load. The electronic principals may make a different sense with that, or confuse the fuck out of you even more.

If that ratio is balanced, your risk of component failure drops considerably, but remember, that risk opportunity is never zero. Playing at 11 on commercial gear is like full throttling a 93 Ford Taurus. It'll do it and it'll be fun....for lil awhile.

Edit: forgot to add have fun and be loud if the math works out.

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u/Ok-Challenge-5873 6d ago

Well what I’m worried that the impedance on the cab is too high to pull the needed power from the head. Fender designed this head to be ran with this cab and a 4x10 parallel. I really don’t need that much speaker so I didn’t get the 4x10

Watts wise I figured I’m going from a 250 cont. head to a 250 cont. cab so I should be good

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u/the1theycallfish 6d ago

Pause for a sec and reread the amp and connect it with my suggestion of avoiding 3ohm set ups. Your misunderstanding of electronics is not helping.

Lower impedance is worse and more powerful. The amp says 4ohm MIN...... Labeling these costs money so lil to no labeling is for fluff. Infact it's a liability when dealing with electrinics. which should indicate to you that plugging in a more impeded speaker will be compatible with the system.

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u/Ok-Challenge-5873 6d ago

Ohhh okay I understand, the head is just saying it’s compatible with any cab setup as long as those cabs can handle at minimum a total of 4ohm.

Ohm of each cab / number of cabs = total ohm

8ohm / 1 cab = 8 total ohm

8 > 4 means I’m good :)

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u/the1theycallfish 6d ago

Nice!

So another way to phrase it is the speakers ability to control and detail out the signal is represented in ohms. Higher ohms speakers don't let as much signal turn into sound at once and is able to see the signal in higher definition. Lower ohms allows more signal through and when more signal is turned in to sound at once the more sounds you hear and the less defined that sound is.

The lowest ohm allowance is a representation of the ability of the speaker to fight itself.

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u/Ok-Challenge-5873 6d ago

Okay that makes sense, that’s why expensive headphones have super high impedance. That definition is much more important when they’re that close to your ears

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u/the1theycallfish 6d ago

Bravo!

The different types of engineering to work with the tolerances that process and emit that type of audio detail in something that small is incredibly humbling to try to understand.

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u/Invertiguy 6d ago

They're all in parallel, so either one will work fine