Turning a guitar combo into a bass combo

[Alex Masters]

Open baffle speakers can certainly work well. The main issue you have with them is that bass response will be weak as your baffle isn't wide enough for low frequencies due to the long wavelengths involved.

You can calculate the frequency response you will get using a tool like this Invalid Link Removed . You know the parameters of the driver you're using and the size of the cabinet.

Anyway, good for you for trying something new. I heard a pair of DIY open baffle speakers using two eminence 15 inch drivers in a hifi context. It sounded pretty awesome and the freedom from box boof was quite attractive.

 

[TonH]

Open baffle speakers can certainly work well. The main issue you have with them is that bass response will be weak as your baffle isn't wide enough for low frequencies due to the long wavelengths involved.

You can calculate the frequency response you will get using a tool like this Invalid Link Removed . You know the parameters of the driver you're using and the size of the cabinet.

Anyway, good for you for trying something new. I heard a pair of DIY open baffle speakers using two eminence 15 inch drivers in a hifi context. It sounded pretty awesome and the freedom from box boof was quite attractive.

Thanks! Interesting website. I will look into that.

 

[BuffaloBill]

Why is there always so much negativity when folks do things like this!? You would think no one is ever allowed to try anything different. Ever.

How do you think new tones have been invented over time?

- John

So people with knowledge and experience can't suggest a better way to do things?
You talk like a science hater.

 

[khutch]

Why is there always so much negativity when folks do things like this!? You would think no one is ever allowed to try anything different. Ever.

How do you think new tones have been invented over time?

- John

You are falling prey to the modern politically correct misconception that to disagree is to hate, to be an -ist or a -phobe. Sometimes disagreements are just disagreements and sometimes disagreements are grounded in facts that one side is ignorant of. Open back bass combos have been tried in the past and most people found them to wanting for several reasons. You can re-visit that topic in the hopes that you will see something that no one else has ever seen. It does happen occasionally. But the odds are against it in this case because the physics of speaker cabs has been very well studied at this point in history. Back when people tried open back bass enclosures it had not been studied nearly so well and they were/are successful for guitar amps so it seemed reasonable to go that way for bass amps. And yes, it will work. I used to play bass through my father's open back Fender Tweed all the time. At the volume levels my parents would tolerate it simply was not an issue at all!

Personally I have thought about buying a cheap open back guitar combo to use as a bass amp. My plan was to seal it up and port it. There are good reasons why bass cabs are built the way they are, but it is your amp and your money so do as you wish. These folks are just trying to steer you away from a course that they feel with good reason is going to disappoint you. If you enjoy the journey even when it leads to disappointment then there is no reason why you should not take it. Just do pay attention to what has been said above about speaker excursion if you want to still be able to use your new driver after you prove to yourself what everyone has said above about the results you will get.

 

[JKos]

Hi Folks,
Please don't get me wrong. If the OP had come in saying he had hooked up his Marshall 2555X Silver Jubilee 100W Reissue head to a 5" speaker laying on his coffee table, my response would have been much different. I'm only saying that in this case, the OP is using a low-ish wattage amp and is cognizant of the necessary volume limitations of his experiment. If the OP enjoys the tone that he is getting, then none of us can argue with that. If the OP plays within the limitations of the given system, then no harm done. Correct?

My other point is that many tones/sounds we know today were achieved via methods that were deemed unorthodox or down right wrong at the time they were done. Again, if the OP likes the tone and plays within the bounds, why should we judge his opinion of that tone? Even with TB-approved bass equipment, you may not like my tone and I may not like yours.

Thank you,
John

 

[vindibona1]

I hope not to hijack the thread, but I'd asked a similar question months ago and got similar answers. But in light of this thread I want to revisit this again...

For the most part, when I'm playing at home in a small condo. I've been playing through my old Line 6 Spider II 75/12 amp, and frankly at acceptable volume levels it sounds as good or better than any of the "practice" bass amps out there (Rumble 25/40 or the smaller Ampegs). While I know the my Line 6 won't be truly gig-worthy, can I make acceptable for informal jams where I will need the kind of volume that 75 watts might produce? I can get an Alpha 12A for $65 and even board up the back of the amp it needed (would that even help with a Alpha 12A?).

Or... Should I just keep practicing on my Line 6 and hold out for something like one of the TC Electronic BG-250 configurations for stuff down the road?

 

[Stumbo]

I hope not to hijack the thread, but I'd asked a similar question months ago and got similar answers. But in light of this thread I want to revisit this again...

For the most part, when I'm playing at home in a small condo. I've been playing through my old Line 6 Spider II 75/12 amp, and frankly at acceptable volume levels it sounds as good or better than any of the "practice" bass amps out there (Rumble 25/40 or the smaller Ampegs). While I know the my Line 6 won't be truly gig-worthy, can I make acceptable for informal jams where I will need the kind of volume that 75 watts might produce? I can get an Alpha 12A for $65 and even board up the back of the amp it needed (would that even help with a Alpha 12A?).

Or... Should I just keep practicing on my Line 6 and hold out for something like one of the TC Electronic BG-250 configurations for stuff down the road?

Add some insulation, change the speaker and close up the back. Might work.

 

[waveman]

Add some insulation, change the speaker and close up the back. Might work.

And what effect would that have on the tubes it is enclosed with? Just wondering, because I would think that extra pressure wouldn't be good.

BTW, to the OP, I have thought of doing the same thing with a Peavey Bandit or Vox Pathfinder for low volume playing around, but I keep coming to the same conclusion: I would be better off just running the power amp to small 10"bass cab, or just buy a cheap 10" bass combo. If I didn't like my Pathfinder so much, I would just make a head out of it and use whatever kinda cab I needed.

And, if it sounds good and works for you, who cares what the proper thing is to do scientifically. It's not saying science is wrong, but saying it's ok to not follow the scientifically most proven best path if you like where you wound up

 

[Stumbo]

And what effect would that have on the tubes it is enclosed with? Just wondering, because I would think that extra pressure wouldn't be good.

BTW, to the OP, I have thought of doing the same thing with a Peavey Bandit or Vox Pathfinder for low volume playing around, but I keep coming to the same conclusion: I would be better off just running the power amp to small 10"bass cab, or just buy a cheap 10" bass combo. If I didn't like my Pathfinder so much, I would just make a head out of it and use whatever kinda cab I needed.

And, if it sounds good and works for you, who cares what the proper thing is to do scientifically. It's not saying science is wrong, but saying it's ok to not follow the scientifically most proven best path if you like where you wound up

Forgot about the tubes.

Put an HPF in your signal chain and be done with it.

 

[waveman]

Forgot about the tubes.

Well, if we are still referring to the OP's setup, and you fully enclose the amp, you could run into heat issues and I suspect vibration issues. No?

 

[vindibona1]

...I have thought of doing the same thing with a Peavey Bandit or Vox Pathfinder for low volume playing around, but I keep coming to the same conclusion: I would be better off just running the power amp to small 10"bass cab, or just buy a cheap 10" bass combo...

You know, I'm not sure why I ignored this solution- running the head to a cab. The Line 6 has an open back with the speaker wires connected to slide-on terminals. I've been demoing cheap bass combos and at lower volumes I like what I'm getting out of my unaltered Line 6 better than the cheapie bass amps.

 

[JimChjones]

Or... Should I just keep practicing on my Line 6 and hold out for something like one of the TC Electronic BG-250 configurations for stuff down the road?

Or... you could keep your eyes open in the local secondhand market for a really cheap small bass cabinet, and plug the line 6 into that. In my early days I used an HH transistor guitar head as my bass amp, and I was basically happy enough with the sound into a 1*15.The tone controls aren't voiced ideally, but if you have a fairly flat sound it won't worry. And if you luck into something like a half decent 1*15 or 4*10 you can then keep your eyes open for a bass head next time the money tank has filled up a bit. I've seen a couple of decent looking cabs go through the local sadbook sales groups at very reasonable prices.

 

[David Jayne]

Well, if we are still referring to the OP's setup, and you fully enclose the amp, you could run into heat issues and I suspect vibration issues. No?

Not likely to be an issue given the very low power of this amp. I wouldn't be the least concerned.

 

[TonH]

You are falling prey to the modern politically correct misconception that to disagree is to hate, to be an -ist or a -phobe. Sometimes disagreements are just disagreements and sometimes disagreements are grounded in facts that one side is ignorant of. Open back bass combos have been tried in the past and most people found them to wanting for several reasons. You can re-visit that topic in the hopes that you will see something that no one else has ever seen. It does happen occasionally. But the odds are against it in this case because the physics of speaker cabs has been very well studied at this point in history. Back when people tried open back bass enclosures it had not been studied nearly so well and they were/are successful for guitar amps so it seemed reasonable to go that way for bass amps. And yes, it will work. I used to play bass through my father's open back Fender Tweed all the time. At the volume levels my parents would tolerate it simply was not an issue at all!

Personally I have thought about buying a cheap open back guitar combo to use as a bass amp. My plan was to seal it up and port it. There are good reasons why bass cabs are built the way they are, but it is your amp and your money so do as you wish. These folks are just trying to steer you away from a course that they feel with good reason is going to disappoint you. If you enjoy the journey even when it leads to disappointment then there is no reason why you should not take it. Just do pay attention to what has been said above about speaker excursion if you want to still be able to use your new driver after you prove to yourself what everyone has said above about the results you will get.

It is good to read that folks are worried about me blowing up my new speaker.

So far the experiment is not a disappointment at all, a great succes I would say, and I am enjoying the journey.

When you read reviews/articles about open baffle (hifi) speakers, you notice that those speakers have no coloring of the sound by the enclosure that sealed or vented boxes have. That makes the reproduction of bass different what we are used to. The bass sound is more detailed, clearer. And that is what I also hear with my modified TSA15. There is a lot of detail in the sound of my bass, meaning I can hear everything I do. It is a if you are listening to a recording of your bass directly into a studiomixer, very different from the sound that comes of your normal vented combo/amp.

Because I can hear what I am doing so well, I think I can improve my playing technique.

I will do some more experimenting with the placement of the system.

 

[Alex Masters]

Open baffle Hi-Fi speakers can have reduced box colouration as one of their benefits. There are plenty of disbenefits too, but a reduction in box boof that is a major factor in how many bass cabinets sound is a plus. A big chipboard or half-inch box without extensive bracing and dampening is going to be a big part of how they sound as they play along, smearing the timing and panels resonating sharply at certain frequencies.

 

[vindibona1]

I didn't want to start an entirely new thread but I discovered something interesting today...

I actually purchased a (new) Fender Rumble 100 and brought it home and hooked it up. And to my surprise (almost shock), as a practice amp my Line 6 75w/12 guitar amp sounds as good or better than the Rumble at the levels I would be limited to at home. No, I couldn't even think about gigging the Line 6. But I'm thinking that if I spend money on a bass amp I've got to step up to something better. There is no point in spending $300 on an amp that won't do anything more at home that what I have and won't be adequate for something in the future. So it's going back in a day or two.

I don't see any point in even replacing the existing speaker in the Line 6, but do you think that boarding up the back might help protect the cone from excess movement? Or should I just forget about it, play at bedroom levels as is?

 

[Stumbo]

I didn't want to start an entirely new thread but I discovered something interesting today...

I actually purchased a (new) Fender Rumble 100 and brought it home and hooked it up. And to my surprise (almost shock), as a practice amp my Line 6 75w/12 guitar amp sounds as good or better than the Rumble at the levels I would be limited to at home. No, I couldn't even think about gigging the Line 6. But I'm thinking that if I spend money on a bass amp I've got to step up to something better. There is no point in spending $300 on an amp that won't do anything more at home that what I have and won't be adequate for something in the future. So it's going back in a day or two.

I don't see any point in even replacing the existing speaker in the Line 6, but do you think that boarding up the back might help protect the cone from excess movement? Or should I just forget about it, play at bedroom levels as is?

You can gig the Rumble 100.

 

[DrummerwStrings]

^^^. Where are you going to play the Rumble? Compare it with similar amps, pick the one with the best sound & the most features you need/want.

 

[TonH]

I didn't want to start an entirely new thread but I discovered something interesting today...

I actually purchased a (new) Fender Rumble 100 and brought it home and hooked it up. And to my surprise (almost shock), as a practice amp my Line 6 75w/12 guitar amp sounds as good or better than the Rumble at the levels I would be limited to at home. No, I couldn't even think about gigging the Line 6. But I'm thinking that if I spend money on a bass amp I've got to step up to something better. There is no point in spending $300 on an amp that won't do anything more at home that what I have and won't be adequate for something in the future. So it's going back in a day or two.

I don't see any point in even replacing the existing speaker in the Line 6, but do you think that boarding up the back might help protect the cone from excess movement? Or should I just forget about it, play at bedroom levels as is?

Don't replace the speaker and play at bedroom levels. Boarding up the back would will not improve the sound.

 

[Timpanogos Slim]

Yeah, there is always an awful lot of negativity when people bring up hands-on tinkering of most any kind on this forum. It's weird.

My first thought when i saw the thread title was that, having gone over a lot of schematics, is that at least in the preamp section the major difference between guitar and bass amps come down to the high-pass filter in the first stage of the input. That and some guitar amps introduce specific kinds of distortion that you don't find in most bass amps.

The other differences, in a tube amp, come down to having more power in a bass amp (hopefully) and a beefier output transformer. But beefier here is a relative thing -- the old Fender Champ amps sounded the way they did in part because the output transformer was intentionally severely undersized.

This is a little 15w practice amp. You're not going to hurt the output transformer the way you're using it any more than generations of guitarists hurt the output transformers in their Champs.

As for the speaker itself - the Alpha 12A is designed for a much bigger enclosure. Nothing good could possibly come from closing up the back, no matter what you might stuff it with, no matter what port diameter and length you might use.

Even without fully understanding how to crunch T/S numbers, it turns out that Parts Express did it for us. They calculated the optimum sealed cabinet volume at 6.56 cubic feet. Optimum vented volume at 16 cubic feet.

But since the power handling is rated at 150w RMS / 300w peak, I don't think this 15w amp can really kick it around very hard.