Super Low Watt Guitar Amp

[Puguglybonehead]

To make something pedal-sized, you're probably best off building a Ruby or something similar. As for sounding decent, as others have said, that really comes down to your speaker. True instrument speakers start at 4 inch and up. (look for second-hand speakers that have been pulled from broken practice amps) You're really going to have to decide if you're willing to compromise sound for size or the other way round.

Honestly, if you want something tiny and battery powered, Joyo, Fender and many others have ready-made tiny battery amps. You will probably not be able to make anything that small that will sound any better than those. I'm currently planning a battery amp for busking but I'll be using an 8 inch speaker and likely a different (louder) circuit.

[davent]

I know little beyond this kit other than has been around for a number of years now so should be lots of info, demos and informed opinions on it's worth, a 2.5" speaker.

https://www.thejamjaramps.com/info

Edit, first youtube video review to pop up in when searched...

[PRR]

> What's wrong with building a 1W Amp and driving it with less signal with a volume control ?

Try it. Clipping is a key tonality in modern (post 1938) guitar sound. E-guitar lacks the timbre "break" at raised level, the way brass and voice shift from "sing" to "scream". We rely on the amplifier to provide that emphasis. If you turn-down a e-guitarist he will play louder until it breaks on the accent notes. If you turn-down too much he will just say the amp is lame and not use it.

I discovered similar in planning record playback systems for dance studios. They do not have to be HIGH power as long as the IMD would go over 5%. By using "bad" (for hi-fi) speaker techniques the bass would flubber the midrange, give an enveloping "phatt" sound.

> ...reduce the response in the amplifier itself where you are in control of the lowpass characteristics.

Part of that treble is amplifier distortion. Traditionally in the last stage. No simple trick will give the sharp high-cut needed for strings or electronic distortion. The crappy top end of old-school cone speakers was a blessing to e-guitar.

Our ears "know" the size of a single sound source, by wavefront arrival, and "know" that a 2 inch hole in a box is not a guitar. 10" or 12" speaker is much less un-convincing. A half-Watt in a Half Stack "sounds big" not just by improved efficiency, but because your ear knows the source is as big as a donkey.

There's no good answer.

[stallik]

because your ear knows the source is as big as a donkey.

There's no good answer.

Oh I dunno Paul, that sounds like a good answer to me

[Elektrojänis]

FYI, there is a standard for the measuring sensitivity.    The simplest form is:
The manufacturer must first state range of operating frequencies.  Once that is stated a test signal is formed by passing pink noise through a band-pass filter with 24dB slopes and cut-offs corresponding to the range of operating frequencies.   The rms voltage of that signal is measured.  You then feed the band-limited signal through the speaker and measure the rms pressure.    From that you compute the sensitivity.    The input power is the band-limited pink noise level feeding into the nominal impedance.

That's good info... A lot I was not aware of half of that. I knew there was some kind of standard, but I generally don't really trust any manufacturer to follow those unless they actually state it. (And mostly they just give you a number with maybe dB thrown in after it.)

> What's wrong with building a 1W Amp and driving it with less signal with a volume control ?

Try it. Clipping is a key tonality in modern (post 1938) guitar sound. E-guitar lacks the timbre "break" at raised level, the way brass and voice shift from "sing" to "scream". We rely on the amplifier to provide that emphasis. If you turn-down a e-guitarist he will play louder until it breaks on the accent notes. If you turn-down too much he will just say the amp is lame and not use it.

You could create the distortion in the preamp. That won't be poweramp clipping, but not everyone prefers it anyway even on tube amps, and even less so on solid state. I know a lot of people seem to like the way LM386 clips, but not everyone.

Anyway... The best small speaker I have found was way back on old Compaq desktop/tower computers. Like this:



It works nicely for distorted tones, but for cleans it tends to be too dark, at least in the small LM386 based "combo" I used it in. It's quite a bit bigger than pedal sized though.

[Rob Strand]

I generally don't really trust any manufacturer to follow those unless they actually state it.

Audio is good for having standards but bad in that too many manufacturers don't follow them.
For safety standards you can't sell unless you conform to standards.

Anyway... The best small speaker I have found was way back on old Compaq desktop/tower computers. Like this:

It works nicely for distorted tones, but for cleans it tends to be too dark, at least in the small LM386 based "combo" I used it in. It's quite a bit bigger than pedal sized though.

+1
Those things did sound pretty good for guitar.    Highs were good, no nasty zing in the top end.
A few manufacturers used them say back in the late 90's early 2000's.

[GibsonGM]

That's the deal I was making into a little jam amp...kept the speakers of course.    Running the amp for THOSE into an 8" practice amp cab w/JFET preamp.  Not done yet tho      I 'jammed' thru them via my PC since yup, 2000.

[R.G.]

Mother Nature will generally (that is, every cotton-picking time) intrude on speaker size discussions.
There is a reason that speakers that make more audible bass are larger. Actually, there are several reasons.
Making bass frequencies audible in the face of the declining sensitivity of the human ear requires moving a lot of air. The smaller the speaker, the more it has to move front-to-back to move as much air as a bigger diameter speaker. You rapidly get into needing to move the cone of a small speaker in and out by its own radius, or more.
This is why tweeters can be at the same time loud and small. The sound frequencies are higher and the wavelengths are shorter.
A 1.5" to 2" speaker that will fit in a pedal enclosure will have a "bass" cutoff way up in the human midrange. It just can't move enough air to be loud down at 80hz. Sure, if you put your ear right up next to it... oh, wait! That's headphones.
So "decent" is going to have to be the escape valve.

I'm wondering - why isn't a set of headphones driven by something like an LM833 or an LM386 the answer?
(I -do- still have a functioning Pignose.     )

[EBK]

A 1.5" to 2" speaker that will fit in a pedal enclosure will have a "bass" cutoff way up in the human midrange. It just can't move enough air to be loud down at 80hz. Sure, if you put your ear right up next to it... oh, wait! That's headphones.

Yep.  We are certainly approaching that reality from several angles here. 

[Rob Strand]

Yep.  We are certainly approaching that reality from several angles here. 

There's a new reality inside a speaker box or in a cavity.  The acoustics all changes.

You can get 120dB from a tiny little speaker with very little power,  (the level isn't only because you are close, the sound doesn't radiate)

https://www.kennards.com.au/sound-level-meter-personal-calibrator.html
https://www.mvaudiolabs.com/diy/1khz-microphone-level-calibrator/

[kevinng]

Thanks so much, especially for the Youtube video of the small cigarette box amp.

[FUZZZZzzzz]

Ive build the Ruby Noisy Cricket with a pcb from pedalparts:
https://shop.pedalparts.co.uk/Ruby__Noisy_Cricket_Amp_-_Board-mounted_controls/p847124_13914421.aspx

I like it a lot. I even record it with a mic on some suitable songs.

[Vivek]

Oh I just remembered

About 20 years ago, I wrote a program in Visual Basic to plot  the effect of speaker cabinet size on frequency response

I suppose it still lives on the internet somewhere

I had called it ABACUS

from A Box and Cone User Simulation

Or something like that

[rx5]

could we consider using SUB bass speakers (2.1 ch) found on PC?

[Rob Strand]

I had called it ABACUS

from A Box and Cone User Simulation

I remember that name.



Edit:
It's here,
http://tehnomagazin.com/Software/Loudspeaker_box_design_program.htm

I've tried most of those at some point.  These days I tend to use WinISD.

[kaycee]

I'm also going to punt Dano's Noisy Cricket. I've had one for many years as a bench amp, but will also often plug into it if i fancy a quick noodle and don't want to run the little Laney Cub for 5mins only. I think it sounds great for what it is, takes pedals well and is quiet enough for me to use without getting the 'evil eye' round the corner of the door as soon as I start playing. I sometimes put a cushion in front of the speaker.

Mine has an 8ohm 10watt speaker in it. The cabinet is an MDF replica of a Roberts, Transistor Radio (which graced our kitchen windowsill as a kid).

[bamslam69]

Another nod to BeavisAudio's Noisy Cricket.
Here's mine, with a rotary switch for the extra bass, grit switch, and terminal posts, which are super handy for connection to any old speaker.
Sounds great, and a handy amp for testing pedals on.

For a simple project, I definitely recommend it for other noobs and amateur pedal butchers.

[davent]

Another nod to BeavisAudio's Noisy Cricket.
Here's mine, with a rotary switch for the extra bass, grit switch, and terminal posts, which are super handy for connection to any old speaker.
Sounds great, and a handy amp for testing pedals on.

Looking good! 

Your thunbnails take me to a "Post Image" and not to the larger image. The code in the quoted post looks okay.

[bamslam69]

Looking good! 

Your thunbnails take me to a "Post Image" and not to the larger image. The code in the quoted post looks okay.

Cheers!
Ah, I had to go back through my posts to find the pics. I suppose I could've just gone downstairs and taken a photo of it.

Edit: Photos fixed now.

[kevinng]

Will 8 x AA batteries, 4 in series work for Ruby Amp?

I plan to connect a 1-inch speaker to it. That's 14.8v, will it fry the circuit?