Fundamental Differences between Bass and Guitar Amps

[Wheeman]

I've been meaning to ask this question for awhile.

What is the fundamental difference between a bass amp and a guitar amp? I know that there is a different quality of speaker used, but what about the discrete circuitry?

I also realize that there is a difference in the frequencies that are attunated.

What else is there?

Again, this is one of those things that have been bugging me in the back of my mind...

[suttree]

well, typically a bass amp will have a tweeter, which a guitar amp won't have, and typically a bass amp has a larger, heavier duty speaker.... bass amps also need a lot more power, because they're trying to reproduce a clean(er) sound at volume than a guitar amp is. what it boils down to is that a bass amp is generally intended to have a fairly flat acoustic response across a fairly wide section of the audio spectrum, where a guitar amp is specifically designed to reproduce only certain frequencies (those that we associate with a guitar's tone)... of course there are exceptions, like the fender bassman amp, which was more popular with guitarists..

[Wheeman]

So, could I -- in theory at least -- take a guitar amp and modify it for use as a bass amp? It wouldn't be much more than changing some caps, resistors and the speaker, right?

[sliberty]

The primary differences between a guitar amp and a bass amp are the transformers and the caps. Often a bass amp will use larger value caps for cathode bypass and coupling to accentuate the lower frequencies. For example, a JTM45, whcih is really bass amp (Fender Bassman) uses a220-330uF cathode bypass cap, while a Plexi uses a .68uF cap. The transformers on bass amps are also generally different, sometimes being ultralinear, while "most" guitar amps don't use ultralinear trannies, or if they do, they ignore the ultralinear taps (Dr. Z is one notable exception). Bass amps primarily use the bigger tubes too. You will rarely, if ever, see a bass amp using EL84's, or 6V6's. Instead, they will use 6L6's, EL34's, 6550, etc. Bass needs more power in general. Sometimes the tone stack is tuned differently for a bass too.

One can certainly change out the larger caps to "guitar" values instead if doing a conversion, and there is probably no need to do anything about the trannies or tubes. If the tone stack is tuned specifically for a bass, a few small part changes will revert it to being more guitar-like.

Or, just play the bass amp as is. It has worked for many of us ever since the 58 Bassman came out.

[Hamm Guitars]

As far as tube amps go, I would suggest asking someone who knows.

But here is my 2 cents.

A bass amp will work as a guitar amp with varying results. However, a guitar amp will make a pretty crappy bass amp in most cases.

Bass amps require more clean power and a tuned cabinet. Most guitar amps are usually less that 100 watts, and the cabinets were never designed to deliver low frequencies that guitars don't produce. The speaker in a guitar amp is usually one that is designed to break up, which is not really something you want in a bass amp (at least not something I would want). Also the tone controls for a bass would have different ceter frequencies than that of a guitar amp.

[Wild Bill]

As far as tube amps go, I would suggest asking someone who knows.

But here is my 2 cents.

A bass amp will work as a guitar amp with varying results. However, a guitar amp will make a pretty crappy bass amp in most cases.

Bass amps require more clean power and a tuned cabinet. Most guitar amps are usually less that 100 watts, and the cabinets were never designed to deliver low frequencies that guitars don't produce. The speaker in a guitar amp is usually one that is designed to break up, which is not really something you want in a bass amp (at least not something I would want). Also the tone controls for a bass would have different ceter frequencies than that of a guitar amp.

Good points all. I would add that the output trannie for a tube bass amp needs to be a LOT bigger and heavier than for standard guitar! Bass notes have more energy and for the trannie to handle it you have to dump in about 30% or more iron.

I see this a lot when someone brings me a SLO-100 or whatever and complains that it's "muddy". First thing I ask is if they're playing in one of those super low open C or whatever tunings, where the strings are ready to fall off. Sure enough, that's usually the case. I gently explain to them that the poor output transformer is just not big enough for the job they're asking. They should be using a bass amp for those tunings.

:food-smiley-004: