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Noob trying to build a small guitar amp

Hey guys, after searching the web for some simple schematics, I found this 8 watt amp that would be perfectfor me as a beginer (based mostly on the number of components)

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There are just a few things that need clarifying for me.

1) The IC doesn't have pin numbers labled and it's beyond me to figure them out. 2) Only one wire is labled input. Does this mean I attach one wire to this input and the other to the same ground used for the negative power? If so, does it matter which wire I put where since sound travels as AC waves? 3) This says it's an 8w amp, but would it be a good idea to plug in a 10 watt speaker just in case? and which would give me better or louder sound, a 4 or 8 ohm speaker?

I've had enough minor experience to understand the rest of this circuit.

Thanks in advance!

Reply to
ngdbud
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Follow the diagram just below the schematic. It shows the IC as seen with the label toward you.

Yes.

Ground the cable shield rathe rthan the center conductor.

Not sure. There should be an LM383 data sheet at

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that will tell you more.

Does your guitar have line-level output? I thought guitars were closer to microphone level, usually, and this won't be enough amplification for them (I don't think).

Reply to
mc

so is it... pin 5 = 12v + pin 4 = the wire connecting between r3 and c4 pin 3 = 12v - pin 2 = connects to the positive end of c2 pin 1 = connects to the negative end of c1

????

I did my best at guessing. Did I get it right?

Reply to
ngdbud

Actually they *are* there in the diagram marked LM383 Pinout. It's rather small though. You can find the data sheet here ( but the part's been discontinued btw ).

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The tip of the guitar's jack plug is the input signal.

The screen/shield goes to ground.

Yes it matters because of how the shield works. The shield must go to ground.

Good practice in case you 'overdrive' the amp for example.

The impedance will make no difference to sound quality as such but 4 ohms wil be abit louder.

Good luck !

Graham

Reply to
Pooh Bear

Yup.

Graham

Reply to
Pooh Bear

It's got a voltage gain of 100x ! That's plenty for a guitar amp, if fact possibly too much.

It really needs a level control before the input.

Graham

Reply to
Pooh Bear

I was thinking of putting this marshall tone control schematic in there

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you have to scroll down a bit to find it. would put this right after the input or right before the speaker?

Reply to
ngdbud

That's a 'passive' tone control i.e. it doesn't use any amplifying device ( tube, transistor or IC ). As such it's affected by the source and load impedances. The source impedance should be low and load impedance high for it to work right. You don't have that. In order for it to work satisfactorily it would need to be 'buffered'.

Try googling for 'active tone control' maybe, although it has to be said the guitar types of circuit are interesting if only for their quirky 'imperfections'.

Btw - I meant to add before .... You do realise that amplifier chip needs a heatsink don't you ? And see the note about stability.

Graham

Reply to
Pooh Bear

I have an electronics book with an active tone conrtol schematic in it, it has treble and base adjustments but no mid range. I'll keep searching. And yes, I know I have to use a heatsink. The way he put it in caps and that this claims to be an 8 watt amplifier while the data sheets on the chip say seven were screaming at me that this can't be avoided. The note about stability... Are you talking about the one that says to build it on a pcb to avoid oscillation? Thats gonna be tricky. I don't have etching solution or clad boards or anything like that. after diging through my junk box late last night I found a 5 watt 250 ohm resistor, is this god enough for R3? keeping in mind that I'm going to swap it with R1 like he says in the notes to make it for guitars.

Reply to
ngdbud

I found an active tone control schematic but it takes two more IC's.

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I can deal with it though.

Reply to
ngdbud

good to know, I have tons of 1/2 watt resistors, i just figured since it was connected directly to the ground of an 8 watt amp i might need a little over kill

Reply to
ngdbud

I reckon after som ethought that the best answer is to use a couple of buffer stages and use the guitar tone controls actually.

Yes.

Hmmm... It seems he thinks then that a guitar amplifer needs no gain at all. I wouldn't do that. sadly this is typical of mny ppl's websites with hobby plans where the info is really not that great.

Just forget that for now !

You really don't need a 5 watt resistor either.

How do you plan to connect it all together then ? Perfboard ?

Graham

Reply to
Pooh Bear

That's the kind of thing - unforunately that design has huge control interaction !

Do you need this to run off a single 12V supply btw ?

Graham

Reply to
Pooh Bear

For stability be sure to follow his note number 7 by adding the .2uf/1ohm components to the output pin of the LM383 as shown in the data sheet. Mount C3 as close to the LM383 pins as possible.

He says you don't need a PCB to build it and he's probably right. Just keep all the ground connections as short and direct as possible.

The 5watt resistor would work, but it's way bigger than you need. I'd go to radio shaft and see if you can find a 220ohm 1/4watt.

I don't understand what swapping R1 and R3 is all about, but that doesn't sound right to me. Maybe someone who knows could clairify that.

The input resistance of the LM383 is 150k, but if that is too low is there any reason the OP couldn't add a simple jfet source follower to the output of his tone control circuit to form higher Z load for the tone control?

Mike

Reply to
Mike

There's no need. To boost the midrange, cut the bass and treble and turn up the volume. ;-)

Good Luck! Rich

Reply to
Rich Grise

A single powersupply would be nice... it's a first, I'd like to keep things simple.

Reply to
ngdbud

No, guitar pickups have quite high outputs. More than enough for standard line levels.

--
   W          
 . | ,. w ,   "Some people are alive only because
  \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------
Reply to
Lionel

"Lionel"

** That is just not true.

The *average* valve or SS guitar amp has an input impedance of 500 kohms and a sensitivity of 10 mV at 1kHz to full power output.

The popular Marshall " Master Model" (an all valve amp) has an input impedance of 1 Mohms and a sensitivity of ** 60 microvolts ** to full power at 6 kHz !!!!

While some electric guitars have pickups that can deliver an "unloaded" output of 500 millivolts or so when crashing a full chord, the level with gently played single notes is only a few millivolts.

Line level it sure aint.

....... Phil

Reply to
Phil Allison

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