Bass and Guitar Amps

[DreamSeller]

Everyone has told me that pluging a bass into a guitar amp can damage it, Is this true and if so why.

What makes a bass amp and a guitar amp so different and can a bass amp be modded into a guitar amp?

-Dream

[teemuk]

Amplifying low frequencies requires more power to obtain undistorted output. When you use a modestly low power amplifier (many guitar amps) to amplify bass frequencies the power amp has to work harder and dissipate more heat - this can be harmful. Also, the distorted signal is most often clipped and a severily clipped signal is essentially DC. An excessive amount of DC current will burn your voice coils.

So, the difference between the two amps is mainly that bass amps are usually more powerful. Guitar amplifier also use lower decoupling values between gain stages, which attenuates frequencies that guitars are not considered to produce. A bass through guitar amp might sound thin. Bass amplifiers have a broader bandwidth. Also, i guess that their tone controls are suited for a bass guitar. It should be easier to convert a bass amp to a guitar amp than opposite way around. The bass amp already has an adequate (some might say overkill) decoupling and probably a higher power as well. The amp would be voiced for a very clean tone. Some jazz guitarists prefer bass amps for the same reason.

[DreamSeller]

I ask because I really like the Ampeg SVT, Is it worth it to mod it to a guitar and can it be done.

-Dream

[el mo]

probably depends on your style of playing, have you tried it once?

[DreamSeller]

Yeah and it sounds pretty good, I primarily play metal and heavy rock and I like the slightly bassier tone.

-Dream

[joecool85]

If you like the heavy tone of it, go for it.  For a while I was playing on a 30w Fender Bass amp and loved it.

[el mo]

if you decide that you really want to mod it, the easiest thing to do is to experiment with different valves
in the preamp. you may get some more or less gain that way and some different coloration to the sound.
it may also be advisable to tweak the tonestack a little in order to suit the frequency range of the guitar a little better; that's the point where it dangerous, however, as you need to work inside the chassis i.e. in
the vicinity of parts that may carry high voltage.
a very inviting mod would be to convert the cathode follower to a second gain stage, possibly with extra gain pot.

[joecool85]

You could just set it to flat and make a simple tone stack as a pedal to go in front of the amp.  That way you get tweak it the tone better without hurting yourself, and without a permanent mod to the amp.

[DreamSeller]

Thats what someone I know has done, He uses a bass eq.

-Dream

p.s. What are chip points?

[joecool85]

Chip points are a way of showing how credible someone is.  If someone thinks their post is good, they can rate it good or bad.  Then later if they post something and they have a chip points rating of 100, someone will believe them, if they have a rating of -10, no one will believe them.

[Bob N]

A Fender Bassman has been used for many years by many pro guitar players looking for that deeper tone that you are talking about. The SVT, if memory serves correctly, has a pretty large output transformer with pretty heavy windings inside. The larger the wire inside the transformer is, the deeper the tone. A perfect example of this is my homebuilt firefly amp. With the Hammond 125A transformer that the original schematic called for the sound was quite bright and less than stellar for my style of playing. I changed out the output transformer to a 125D (which is rated for higher power with very similar specs) and the bottom end filled in quite nicely. There's no more sound volume with the "D" versus the "A" but the "D" is much beefier with heavier windings to support the higher potential output power.

While this works for guitarists plugging into bass amps, plugging a bass into a guitar amp is a much faster track to a dead guitar amp for the reasons that teemuk has already described.

[Ge_Whiz]

Playing a bass through a guitar amp is unlikely to damage it. The usual problem is the possibility of damaging the speakers. Symmetrical clipping does not introduce any DC component, and anyway, there is usually a big output capacitor to filter it out.

Modern guitar speakers are much more robust than they used to be. 30 years ago, people would have laughed at the idea of playing a bass guitar through 10" speakers. Playing a guitar through a bass amp is a completely different bucket of prunes - I always used to play my guitar and bass through a general-purpose SS amp with a 15" bass speaker in a big bass-reflex cabinet. Great tone. I've recently purchased a new 15" PA cabinet to re-visit that tone.

[teemuk]

Symmetrical clipping does not introduce any DC component, and anyway, there is usually a big output capacitor to filter it out.

Well, unfortunately the bigger the capacitor the more lower frequencies it will pass. If the amplifier clips a signal with low enough frequency the clipped portion will essentially have the same effect for the speaker's voice coil as pure DC current - although the signal does not have a DC component in technical sense. The clipped portions will mainly just heat up the voice coil since DC can not act as a magnetizing motor. Naturally, a bass signal will more likely contain lower frequencies than a guitar signal. A lower frequency signal causes more supply voltage sag than a higher frequency, therefore resulting into heavier clipping. Bass amplifiers need that huge power and supply capacitance for reason: Clipped low frequency output signal is lethal for any speaker! Guitar speakers are quite sturdy but also fairly expensive and I wouldn't be too happy of stressing them too much with bass oriented signals. Another aspect is that the low frequency may force the speakers cone to travel too much and eventually break it.