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Old 25th August 2007, 08:30 PM   #1
pojk is offline pojk  Norway
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Default Acoustic guitar amp

Hi!

I've been searching the net for plans for an acoustic guitar amp and come up blank... thought this would be the place to ask..

anyone here who has plans for something like this, have built one, or any ideas?

I'd much appreciate any help...
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Old 26th August 2007, 12:49 AM   #2
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Tube or SS? Combo or head unit?
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Old 26th August 2007, 02:07 PM   #3
pojk is offline pojk  Norway
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i'm still learning about all this, so i don't know all the pro's and con's but i was thinkning about an SS combo, for a clean acoustic sound...

also thought that building it myself would be an excellent way to learn.

The main use for this would to plug in my acoustic guitar, but it would also be great if mp3/cd/mic could be plugged in along with the guitar i.e the need for two channels, maybe with phantom power?!?
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Old 26th August 2007, 07:59 PM   #4
Minion is offline Minion  Canada
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the simplest way would probably be use a LM3886 chipamp with a simple Opamp buffer at the input with a Tone stack and then another Opamp with Gain......you could build a few different preamp curcuits (for low impedance and High impedance Inputs) and add a simple summing curcuit before the power amp stage......

This is simular to how I built my Electric Guitar/Bass amp accept I added several selectable overdrive stages and it is only one channel but it goes from very quiet with no overdrive engaged to super crunchy when the OD is engaged.....


Cheers
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Old 26th August 2007, 09:32 PM   #5
pojk is offline pojk  Norway
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i'm confident in my soldering ability and ability to piece together
kits and whatnot. but i don't have the knowledge about all of this to figure out what i need to make a good acoustic amp.

is this a hopeless task for me, or are there people out here willing and able to guide me through?
maybe you have some suggestions for pdf's or something to study?

also i was at the chipamp site, which of the kits there would suit me?

oh, and thanks a lot for the replies so far...
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Old 26th August 2007, 09:37 PM   #6
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Build Albert's Bass preamp and add a chipamp or better still a UCD180.

http://www.albertkreuzer.com/start.htm
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Old 27th August 2007, 09:13 PM   #7
pojk is offline pojk  Norway
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what is it exactly that makes an amp suit an electric or acoustic.
is the main amp the same, is it in the preamp, speakers, or just different crossovers?
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Old 27th August 2007, 11:06 PM   #8
Minion is offline Minion  Canada
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A electric guitar/bass amp has to have a high input impedance as most Pickups are high impedance, so the Preamp has to have a high impedance input......

For a PA system or anything with microphones you would need a low impedance input as most mics are low impedance.....

This all mostly has to do with the pre amp used in the amp...the simplest way to go to build a preamp is to use Opamps , Once you know how to use an opamp you can basicly build an amp with just that basic knowlege, well you still ned to know about supply filtering and calculating Gain for inverting and Non-inverting inputs and Phaze and some other stuff but much of that will be covered when learning about opamps.......

If you go to the National web site or the TI web site there are lots of application manuals that explians much of this stuff, pluss there are a lot on line sites that explain a lot of the Basic principals of electronics.......

Good luck
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Old 28th August 2007, 12:14 AM   #9
pojk is offline pojk  Norway
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ok, i can see i've got a lot of stupid questions, but here i go again...

the "speakerbox" i plan on building for this amp, is going to consist of 2 8" full range speakers and one tweeter that will give an added about 100W 8ohm.

what is it exactly that determines the wattage of the amp?

can i get by with the lm3886 dual kit, and a transformer that gives at least 200VA. (or have i got it completely wrong)
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Old 28th August 2007, 12:53 AM   #10
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Quote:
Originally posted by pojk
ok, i can see i've got a lot of stupid questions, but here i go again...

the "speakerbox" i plan on building for this amp, is going to consist of 2 8" full range speakers and one tweeter that will give an added about 100W 8ohm.

what is it exactly that determines the wattage of the amp?

can i get by with the lm3886 dual kit, and a transformer that gives at least 200VA. (or have i got it completely wrong)
Re the box: if the two 8" are twin cone and reasonably efficient, I'd leave the tweeter out for the moment. Leave space for it, but don't buy it, you may not need it. Also, array the drivers vertically, it'll sound a heap better, as will a well braced open back cab. The last one we built was a rectangular box with 5 sides including the baffle, with 2x12" vertically and an open back. Inside the 'box' was a brace shaped like this # (but square) that held the drivers firmly The tube pre was built into the top and the poweramp in the bottom for balance issues when carrying it. At 17W, with a harmonica cranking through it it's very, very loud.

Power: using one of the chipamps, the output power will be determined by the power supply voltages and the load. Read the datasheets and around here for links about how to do itIf you're ging to buy one of the twin 3886 boards run one to each 8" as I beleive they're not as fond of low impedance loads.
Some useful info here;
http://www.audiosector.com/nigc_kit-users_guide.pdf

As noted above, 100W is a lot for this sort of amp.

I'd still suggest building the Kreuser pre, as it has a bit of distortion to it which will give it a bit of character.
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