Using guitar heads for bass

[Ethan]

So my Ampeg SVT3 Pro is in the shop, waiting for the mosfets to be replaced, and I have some shows coming up where I need an amp. Just for experimentation's sake, I got out my old Mesa Dual Rectifier and plugged it into my Ampeg 4x10 bass cab. It sounded awesome for about 5 seconds, then there was this really strange low-frequency oscillation in the sound that did not go away til I turned the amp off. I tried it through my guitar cabinet for about 30 minutes, no problems. Tried my 20 watt custom made tube guitar head thru the Ampeg cabinet, no oscillation. Any ideas? I really wanted to use this head to see if 100 watts of tube power would be enough for me live, plus the tube sound is my favorite!

[MCChris]

No idea about the oscillation, but can't you just go direct and have your bass coming back at you through the monitors?

[Ethan]

I could, but with this band, I rarely get a monitor...I'd say about 1 in 15-20 shows do I actually get a monitor. That is why having an amp is key for me, so I can hear myself playing. Wish it were different but that is just how it is! I am able to borrow/rent an amp so that is not really the issue, was just wondering about why the Mesa amp would do that.

[gtone]

What kind of pu's are on your bass?

[hardheartedbill]

I played about 25 shows on bass last year, all through a vintage mesa mk I head. Really happy w the growl. Maybe you hit a frequency on bass that set the tubes into weirdness but thats a total guess. Just saying it can be done

[crunchee]

I know nothing about monitors, but couldn't you bring a speaker cab to use as a monitor, and just go direct that way? The purpose of a monitor for you is to hear yourself and make sure you're in tune, right?

[tommy p]

Lemmy does it but I'm sure he doesn't care too much about sound quality or equipment damage.

[JohnnyB]

If you slog through this Wiki entry, you may be able to chase down the problem. The heart of the problem is evidently feedback from output to input. This can happen several different ways including microphonics, possibly your bass pickups capturing the speaker output and putting it back through the amp, a grounding scheme that's not compatible for the three components and the AC supply, a power supply that's trying to do too much, strange paths of inductance and/or capacitance, etc.

My first thought was to check the impedance output of the Mesa head vs. the rating on the bass cab. Also, make sure your bass isn't facing the speaker cab if you try this rig again. It could also be that--even as beefy as Mesa power supplies tend to be--the PS in the guitar head may be insufficient to the demands. For example, if the amp if bandwidth limited to a guitar's range, the octave lower notes of a bass might make demands it can't supply.

[Scottcrud]

I've played fill in bass gigs from time to time. Mind you I am not a bass player and do not own bass equipment. And the bands I've helped out are in the hardcore, old school thrash, death metal variety. That said, I've played bass through a dual recto head with nary a problem as well as a 5150 head.... Never had a problem. Both were hooked up to a 2x15 cabinet. Plenty loud, no oscillation problems....

[blackfbiv]

Used a JCM 800 50 watt combo in a pinch once... no issues except that overall it sounded like a$$... IMHO of course

[Ethan]

Gtone I have a Dimarzio Model P in there. Thanks for the responses guys...head is 100watts and cab is rated at 600 watts (1200 peak), and I ran a 4 ohm load into the 4 ohm cab...the Mesa has lots of options for impedance. I am thinking about shooting Mesa an email on it, we'll see!

[stobro]

Try isolating the head from the cab. It could be vibrations causing the tubes to go microphonic.

[tomteriffic]

Try isolating the head from the cab. It could be vibrations causing the tubes to go microphonic.

That would be my guess too.

[Hamer95USA]

Borrow a bass amp/bass cab or a bass combo amp for your gig. Let the soundman connect a direct box to your bass rig. Or use a Sansamp Bass Driver DI box as a preamp, power amp, & bass cab for your gig, and run direct out from Sansamp Bass Driver DI to the P.A. system. I've done the latter as I was a house bassist for a jam night until I bought my SWR Super Redhead bass combo amp.

Some guitar amps can't handle the bass input signal especially if it has active pickups. It starts to distort and sound broken up. I've seen a guy damage a Fender Hot Rod Deluxe playing his bass through it and blew the speaker up. Plus to top it off, it sounds rough, distorted with no clarity. The opposite of what you want for bass unless you're after that Ampeg SVT kind of sound.

Guitar George

[blackfbiv]

until I bought my SWR Super Redhead bass combo amp.

unless you're after that Ampeg SVT kind of sound.

Guitar George

Redheads are a sweet sounding combo for sure.

and even SVT's don't break up THAT much...

[Jimbilly]

It should be fine to use that amp for bass, -that's an odd problem. I would also suspect a tube, I would try to get it to oscillate again (but quietly) and grab each tube while wearing a glove, and see if it stops.

I've used a couple much older tube guitar heads for bass, and they work great (Dual Showman, and V4). The Mesa should be designed for plenty of low end, enough to handle a bass guitar.

[Ethan]

Well I tried all of the above, and tested it with guitar again and it's fine...my Ampeg has now been mailed out for repair (guy #4). I found an old Mesa D180 used and bought it. Sounds awesome. Problem solved!