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Noob trying to build a small guitar amp

N

ngdbud

Jan 1, 1970
0
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) http://www.aaroncake.net/circuits/amp.htm
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!
 
M

mc

Jan 1, 1970
0
ngdbud said:
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) http://www.aaroncake.net/circuits/amp.htm
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.

Follow the diagram just below the schematic. It shows the IC as seen with
the label toward you.
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?
Yes.

If so, does it matter which wire I put where since sound travels
as AC waves?

Ground the cable shield rathe rthan the center conductor.
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?

Not sure. There should be an LM383 data sheet at
www.nationalsemiconductor.com 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).
 
N

ngdbud

Jan 1, 1970
0
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?
 
P

Pooh Bear

Jan 1, 1970
0
ngdbud said:
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) http://www.aaroncake.net/circuits/amp.htm
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.

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 ). http://www.national.com/pf/LM/LM383.html

2) Only one wire is labled input. Does this mean I attach one wire to
this input

The tip of the guitar's jack plug is the input signal.
and the other to the same ground used for the negative
power?

The screen/shield goes to ground.
If so, does it matter which wire I put where since sound travels
as AC waves?

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

Good practice in case you 'overdrive' the amp for example.
and which would give me better or louder sound, a 4 or 8 ohm speaker?

The impedance will make no difference to sound quality as such but 4 ohms
wil be abit louder.
I've had enough minor experience to understand the rest of this
circuit.

Good luck !

Graham
 
P

Pooh Bear

Jan 1, 1970
0
ngdbud said:
so is it...
pin 5 = 12v + ( the positive supply volts )
pin 4 = the wire connecting between r3 and c4 ( output )
pin 3 = 12v - ( in your case ground )
pin 2 = connects to the positive end of c2 ( feedback )
pin 1 = connects to the negative end of c1 ( input )

????

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

Yup.

Graham
 
P

Pooh Bear

Jan 1, 1970
0
mc said:
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).

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
 
P

Pooh Bear

Jan 1, 1970
0
ngdbud said:
I was thinking of putting this marshall tone control schematic in there
http://users.chariot.net.au/~gmarts/ampbasic.htm you have to scroll
down a bit to find it. would put this right after the input or right
before the speaker?

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
 
N

ngdbud

Jan 1, 1970
0
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.
 
N

ngdbud

Jan 1, 1970
0
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
 
P

Pooh Bear

Jan 1, 1970
0
ngdbud said:
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.

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

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.

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
 
M

Mike

Jan 1, 1970
0
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.

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
 
R

Rich Grise

Jan 1, 1970
0
I have an electronics book with an active tone conrtol schematic in it,
it has treble and base adjustments but no mid range.

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

Good Luck!
Rich
 
N

ngdbud

Jan 1, 1970
0
A single powersupply would be nice... it's a first, I'd like to keep
things simple.
 
L

Lionel

Jan 1, 1970
0
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).

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

Phil Allison

Jan 1, 1970
0
"Lionel"
No, guitar pickups have quite high outputs. More than enough for
standard line levels.


** 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
 
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