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Old 6th November 2010, 06:14 AM   #1
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Question New to Pro Audio

Hello, I am new to the pro audio stuff, and I am trying to make an amp that is for a bass. I am usually dependent on one being in the store that I want, but i cant find it cheeply.

I want to build a multi-speaker bass amp, that can be built into a flightcase, so it can be transported. I am also comfused how airtight/open amps are different, and the circuts or amp heads I would need to buy or build to get this to work

I have worked with electronics, so I know about circuts, and I know how to play guitair.

Is there the possibility of switching from bass to regular speaker output?
how should I wire multiple speakers (posibily 4), and can I have a few cases hooked to different outputs out of an interface.

I love the do it yourself, but i cant find a lot on bass stuff, but much on the guitair. I cand get anything for a reasonable store priced item with what I need
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Old 6th November 2010, 01:48 PM   #2
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What are you trying to end up with as far as power out, as in speakers and watts from the amplifier? If you could afford a store bought amp what would you buy?
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Old 6th November 2010, 06:23 PM   #3
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I would get sonthing like the ibanez is412c 4x12 guitair speaker cabinet, but for the bass input. and a amphead to go along with it
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Old 7th November 2010, 01:50 AM   #4
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So you want to use a guitar cab for bass? Are you planing on playing loud or not? How much power do you think you need?
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Old 7th November 2010, 09:28 AM   #5
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Default cheap sound

If you want to play loudly, the semiconductors and capacitors are not too expensive new, but heat sinks, and power transformers are pretty pricey.
The cheapest way I have found to get heatsinks and power transformers is to buy blown up PA amps on craigslist.com off the music instrument part, then repair them. There are schematic available online for Peavey, QSC, Crown equipment. Not for Behringer. I don't know about Mackie. When you buy a non-functional PA amp, make sure it doesn't stink powerfully of burned paint or chemicals, as this means the power transformer may be bad. I recently scored a blown up PV1.3k for $65, but I had to watch 4 months to find it. That's a little hot for 4x12's, you'd do better with a 400 or 800 watt amp at 4 ohms rating.
Blown up 4x12 Speaker cabinets are a little more pricey, about $100 sometimes, but worth it unless you want to experiment with woodwork cutting round holes. You can get new Jensen or Peavey speakers online at tubesandmore.com in Phoenix, or another online shop in Washington DC or others, you can google search. Save on shipping, buy close, on heavy speakers.I've used tubesandmore, they are okay. Match your speakers to ones you have in the speaker that are don't have ripped cones or burned coils. Usually there are 4 ohm speakers, two in series (+-+-) and two series pairs in parallel (+ to +, - to -) to make a total of 4 ohms. PA amps like 4 ohm loads.
When you've found a dead amp, search on here for a repair thread about it, or start a new one.
There are actuall integrated guitar-bass-keyboard amps available on craigslist broken, but they go for more money for some reason. To turn a keyboard amp into a bass amp, install a high filter on the input and maybe some tone controls, and remove the tweeter to save weight. Many instrument amps have clipper circuits for that distorted tube sound, that can be builts for about $4 for the switch and $1 for the zener clipper diodes.
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Old 9th November 2010, 04:21 AM   #6
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I may want to use the cabinet to practice (showing off) so it needs to be quiet, but if I evet neet to use it at a show or whatever, I would need loud. I would like varying volumes. Could i have a reverse phase on the cabinet. In case I need it.

I have some experience as a woodworker, but closed cases might be difficult. Would it be worth it for me to try??

What is a resonable price for a blown amp?

And is it fesable to have all the electronics on the outside of the cabinet, like on an external amp head, so it makes for one one hole for the input.

I am thinking to hold off on the speakers until i have the case built. Plan to make the hole for the speaker a little small, so it can be sanded.

What kind of parts do I need (compasitor voltage, ect)

I have a blown out pre-amp for a home theater system. Can this be used?

Thanks for all the help. I have a lot of questions, but, i try to learn
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Old 9th November 2010, 06:46 PM   #7
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Blown PA amps $50-100.Obsolete monaural amps can go $75 working or $20 blown. Blown guitar-bass amps $100-$400 (if a cherry brand).Tube amps are more. Yes, you can put the amp in the speaker case, especially if you have fan ports in and out. You can set up gain loud and soft. Reverse phase is one switch. 4-12" plus an amp is heavy, is why the "head" as they call a mono amp, is sort of separate from the speaker part. Most stereo PA amps can be "bridged" mono for more power. Look up in speakers for how to port or not port your speakers for best effect, there are specific plans for sawing & glueing on some projects. Some 4-12"s are bass reflex with a port on the front from the back of the speakers, some are sealed. You can reverse the polarity with one switch, although most pro-PA speakers have two different jacks for the different polarities.
There are prople that buy up blown amps and fix them for a living, so if you find one on craigslist reasonably priced you have to be quick. Being unemployed or retired helps. Bad spelling in the ad or a lousy description can help you score, but you may waste your time too on junk. Look up the model number before you buy, some amps like B********* don't give away schematics.
Bass guitars don't need much of a preamp, so your home theater system may not be much help. The tone controls that bass guitar players use are unique to the performing world. Modern home theater systems don't even have a power switch or fuse, just a rubber strip for the controls to go to the D/A converter input.
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Last edited by indianajo; 9th November 2010 at 06:56 PM.
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Old 11th November 2010, 05:25 PM   #8
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Not to be a spoil sport but from the sound of it you do not have too much experience with electronics or speakers. While I commend anyone to get their hands dirty and play around with the stuff I do not think it would be in your best interest.

I take it that you want to put together an amplifier/speaker combo to save money. I can not see this happening in a reliable package. Instrument amps and speakers need to be more robust and tolerant of abuse than hifi equipment. Not a simple thing to achieve at high power levels in a band situation.

My suggestion is to find a used working amp and speakers. It may not cost you much more than if you put together an equivalent system yourself and it will be much more reliable. The last thing you want when playing out with people is for your amp to stop working.

Now if you were building a practice amp bass or a 20w or less guitar amp I would say go for it. Something that you do not need to take along in a flightcase, just a regular head or speaker combo. Actually that would be a good stepping stone on the way to make a higher power amp. You can make your mistakes on it and learn the ins and outs of building instrument amplifiers.
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Old 10th December 2010, 03:08 AM   #9
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Printer2 is right. I have seen speaker cabinets for guitar built in to flight cases but they didn't do that with the heads. Basically for playing live you can either have easy mobility or good reliable sound but both is almost impossible. If you are being paid to play you can't have your equipment crapping out on you. The people paying you won't care if it is your fault or not. You will be held responsible even if the problem is with the equipment. When the word gets around nobody will hire you.
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