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Old 4th July 2013, 04:56 PM   #1
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Default Hey Everybody (DIY Acoustic Amplifier)

Hi everybody

Just a quick one,

I'm looking to do some gigs in some small venues (just me, a mic, and guitar) and wondering if anybody can point me in the right direction for building a combo amplifier with a mic input and controls...

I like to think of myself as a handyman when it comes to diy....

Bearing in mind this will be my first project of this sort but could be the start of many to follow!

Thanks for reading/listening

Jack
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Old 4th July 2013, 05:03 PM   #2
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I.E ...schematics/bill of materials/or another structure i could clone???
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Old 4th July 2013, 05:37 PM   #3
Minion is offline Minion  Canada
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Do you need a mic input and a guitar input ??

If so you could use a mic preamp chip like the INA217 for the mic input and use a opamp configured with a high input impedance for the guitar input , then use a inverting opamp in a mixer configuration to mix the the signals and then go into a LM3886 chip amp , you could even add a small 3 band eq if you wanted ......

Though it would probably be easier and maybe even cheaper to find a small cheapo mixer for the mic and guitar and build or buy a small power amp and connect them together .....

Cheers
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Old 8th July 2013, 11:17 PM   #4
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When you say yourself, a microphone and a guitar, is this an acoustic with a built in pickup and you singing into the mic (in which case is the guitar output preamplified, low impedance or a piezo direct), or the mic in front of the guitar while you play it? It doesn't change much, but, in the first case it may be worth you considering a simple reverb/fx unit for when you play in very absorbent spaces. Do you know what microphone you're going to be using? If you're thinking of a phantom powered condenser, it might well be easier to use a small commercial mixer (but 'easy' isn't the point, is it?)

Let's move to the other end:- the speakers. Normally, an eight or ten inch LF driver will handle the lowest resonances from a guitar's body, and I assume you're not going to try for rock and roll levels; if you want loud, youll probably need two. Probably a ported enclosure, and a tweeter for the clarity and directionality; I'd use a horn (because I've got some, and like how they sound) but a small cone, a dome or even a slot radiator would work too, we're not aiming for massive efficiency; I just have a long-term crush on horn loading. I'd horn load the bass drivers too, but I'm assuming small size and reasonable weight, general portability are definite sales points. Although a small speaker always needs to be put on something; a stand (though that's extra weight to transport) the bar, hung from the ceiling (though that's a nuisance to derig after a couple of drinks) even a chair, otherwise all the clarity is lost into the floor, so a tallish cabinet isn't that bad an idea. After all, you've got to have space in your car for a hard case for an acoustic. Handles, and a tall case, chamfer off the bottom back corner and screw on a couple of furniture casters

How I'd do it would be a single two rail power supply, an electronic crossover at about 3kHz, and separate volume controls for HF and LF amps. Bridge two amps for the lows, a third for the high frequencies. Probably chip amps, but there are plenty of discrete circuits offered on this site. You'll need more power for equivalent level than an electric – keeping under distortion levels, but generally you're aiming for lower levels, and much less continuous power. When designing the cabinet, try and put a closing, rattle-free compartment big enough to hold the microphone, a mic cable, guitar cable, power cable (that's the mains lead), spare picks and maybe a stomp box.

Oh, plenty of people will disagree with me - and we haven't even got to the tone controls yet. Basically I'm thinking of a teeny PA system, while you could go dual channel guitar amp style, or basically HiFi with tailored input sensitivity. And I can't even do sketches right now.
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Old 9th July 2013, 02:23 AM   #5
Enzo is online now Enzo  United States
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There are ready made solutions. Any number of speaker manufacturers make powered speakers with very basic mixer inputs. For small venues, one powered speaker should be plenty, and with a mic input and often a line level input or two, you can set it down, plug in your mic, and play.


If you are looking for an actual guitar amp with microphone input as well, then look at any brand of "acoustic amplifier" which meets that description. Most amp makers make them, Peavey, Crate, Fender, Behringer, Trace, etc. If you really want to build it, then look at schematics for any such product and clone away.

An acoustic amp is really just a small PA system in a combo, contrasting guitar amp which is anything but hifi.

chrispen... makes good points. My suggestion is get a folding speaker pole stand to get your speaker up in the air. You want the horn or tweeter to be above the heads of the audience. WIll there be dancers? Is the stage raised or only a step up? Low frequencies can make their way through the room, but high frequencies tend to be more line of sight. That is, the audience bodies absorbs them. If you cannot SEE the tweeter, your ears cannot HEAR it.

I have to disagree a little. I don't think an 8" speaker makes very good sounding vocals. And frankly, while I like the bite of an 8" speaker for electric guitar, for acoustic, I think it sounds thin. Myself, I'd prefer at least a 10" and more so, a 12".

Be a little more specific in your description.
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Old 9th July 2013, 06:51 PM   #6
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I did say there would be different opinions, didn't I? And I can't entirely disagree – if I were building it, it'd probably have a twelve in it. But if you're not hitting for maximum efficiency you can get decent 50Hz out of an eight (and definitely out of a ten), with a bit more power, and I was picturing the guy with a hard case for an acoustic over one shoulder, a mic stand (and now a speaker stand) in one hand, the amp hanging from the other, pushing through a crowd.

Main reason to go for a combo solution; a separate speaker and electronics rack you can sit on, or put next to you, and adjust without having to get up and tweak, is quite a bit more practical, except for transport.
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Old 15th July 2013, 07:15 PM   #7
JMFahey is offline JMFahey  Argentina
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For reference look at this excellent Peavey battery powered amplifier, with mic and clean guitar inputs (bring your own distortion pedal )

http://www.peavey.com/products/index...3630/Solo%20PA

Click the image to open in full size.

Either get one, new or used, or be inspired by it to see what a (successful) real World example uses.

It may spark a couple ideas.

Last edited by JMFahey; 15th July 2013 at 07:19 PM.
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Old 2nd September 2013, 02:48 PM   #8
teleman is offline teleman  Norway
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I wouldn't dare even dream of designing, ( I've tried many things in my ignorant bliss!)let alone building one,just for one simple reason!
Acoustic amplification as opposed to electric is a totally different beast! I often asked myself why is that almost all electric guitar players are almost content with their lives, we,the acoustic addicts are on a perranial search of either a pre-amp or an amp all ours! The simple reason may be, that,perhaps our utopian dream of reproducing this "pure acoustic sound of our martins, taylors,etc electrically! I am yet to meet an acoustic player including myself who is completely happy with either his/her preamp or amp or both!

Impedance,sensitivty & tonal circuitry are 3 main things things are very critcal in an acoustic amp design & it will definitely frustrate you trying to design one, especially as your 1st D.I.Y project!

I think it's one of the few areas,such as designing an dig. chorus/delay & acoustic amps that I would consider a waste of time & unneccessary. There are some excellent products out there which we would find very difficult if not impossible to better!.

AER,Ultrasonic,Roland,ZT & Fishman are among a few very good ones available! My humble suggestion would be that you should first try the best acoustic amp you can afford if you're happy with your current guitar/preamp setup!
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Old 2nd September 2013, 04:53 PM   #9
tinitus is offline tinitus  Europe
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noticed a raw driver the other day where they said it was designed for acoustic guitar

I suppose you will be able to put a few things together ... but might be more tricky and time consuming than you expect

you could try build a mic amp first
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Old 3rd September 2013, 08:46 PM   #10
teleman is offline teleman  Norway
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The most difficult problem I faced during my numerous attempts in designing a Mic + a piezo disc blender preamp has been,although individually these are quite straightforward to design & implement, yet something seem to go wrong when they are combined & mixed!

Mics,especially the back-electret types akin to Panasonic WM61A sound really good however,are notoriously uncontrollable in a closed environment such as inside the guitar body without proper eq circuit.

UST: terrible sounding when installed under the saddle...making all acoustics
sound the same " quack!"(lol)

AST: Fairly natural sounding, but known to have problems with hum!

Magnetic pu: I don't think these really pick up any soundboard vibrations
or the timbre of the guitar at all, but only the string movement!

Piezo Disc : ironically this 1 doller disc found on greeting cards & musical
toys seem to offer the best sound! The down side is that
these have limited frequency range & have a rather
limited frequency range & have a rather nasty "hump"/bump in
the lower mid range, which can be corrected with proper eq.

One constant complaint i've read very often is that there seems to be an impedance mis-match between most onboard preamps & the guitar inputs!
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