Super Low Watt Guitar Amp

[kevinng]

Hi, I'm looking to build a super low watt guitar amp that runs on batteries.

1W is too big for me. Preferable something 0.5W or less. Just enough to hear yourself (e.g., like listening to the audio on the smartphone).

What size (inches, watt) speakers should I look for? What types of speakers will work for a guitar amp?

Are there existing amp designs I can use?

I have looked at the honey and ruby amp design - they seem to work for speakers up to several watts. If we can have something smaller and more efficient that'll be better.

[Elektrojänis]

One important thing to remember is that a watt is not a unit for loudness. The watt-rating for a speaker does not tell how loud it is either... It just telss how much electrical power it can handle from the amp.

The important figure in speakes specs is sensitivity. (In other words efficiency.) The annoyng thing is that most speaker manufacturers dont really tell you how they measured it. dB/Watt at one meter is usually assumed but even that isn't actually stated too often. And no one seems to mention what frequency they used or what kind of box they put the speaker in or how long and how much power they actually used for the test.

All that said, bigger speakers are usually more sensitive so they are louder for the same amp power. I once tried my little LM386 amp (running on 9 volts, so about 1/2 watt) with a good 2x12 cab and it was actually quite loud for overdriven sounds.

Oh... A half watt amp can drive speaker rated for 100 watts just fine.

[PRR]

1 whole Watt in most non-teeny speakers is 85 or 90 dB SPL, and it is hard to talk over that, and annoys the family, even the next-door neighbors.

You maybe can be looking at 1/10th Watt.

Since there are no readily available amps that small, and the power waste is trivial, and guitarish speakers like some series resistance, you can try a 10Ω to 100Ω 1/2W resistor in series with the speaker, waste-off some electrical power. Get a 6-way switch to try many series Rs from zero (mid-day) to a few hundred Ω (baby napping). (Ordinary pots won't take the abuse for long.)

[Rob Strand]

The annoyng thing is that most speaker manufacturers dont really tell you how they measured it. dB/Watt at one meter is usually assumed but even that isn't actually stated too often. And no one seems to mention what frequency they used or what kind of box they put the speaker in or how long and how much power they actually used for the test.

Some are a bit sneaky and quote at 0.5m to give higher figures.    The standard allows different test distances but you have to state it.

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.

A loop-hole is you are allowed to test without a test baffle provided you state it.

So following the standard there's no test frequency.  The only thing pinning down frequency is the operating frequency range.

[Vivek]

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

[anotherjim]

A quiet amp can be annoying - it becomes overpowered by the direct acoustic sounds from the guitar - it's time to move to headphones.

[cab42]

A quiet amp can be annoying - it becomes overpowered by the direct acoustic sounds from the guitar - it's time to move to headphones.

Exactly for that reason, I am building Dead Astro's Astrosim as it having headphone out

[EBK]

If you want something low power that runs off a battery and sounds good, I recommend a Ruby with a 5-inch Jensen speaker.  I have built two of them in cigar boxes, and I love them. 

http://www.runoffgroove.com/ruby.html

https://www.jensentone.com/mod-series/mod-5-30


Welcome to the forum!


Not the greatest demos of the amp, but I used one of my cigar box amps for my recent Creaky Floor pedal demos (this post and the two demos after it in the thread all use the same amp):
https://www.diystompboxes.com/smfforum/index.php?topic=121805.msg1230568#msg1230568

[teemuk]

What size (inches, watt) speakers should I look for? What types of speakers will work for a guitar amp?

IME, anything smaller than 6.5" will sound overly bright, thin, boxy and anemic. Unless you play acoustic you also should be looking at speakers that start to roll off around 5 kHz.

Also, IME, any decent-sized speaker will be inconveniently loud even with very low power amp. My "little" LM386 1/2W combo (which puts out maybe 0.12 watts to 16 ohms) sounds great through an external 16-ohm 4x6.5" cab...
...but cranked it's then loud enough to hang with a drummer and way too loud to use in apartment. Through its smaller internal 2x2.5" speakers it's still too loud, (though not as loud)... ...and also anemic and thin sounding. Thankfully, none of my practice amps rely on power stage distortion for overdriven tones. Not even the half-watt LM386 amp.

So.. truthfully, the output power is no issue as long as the amp has a good master volume. My other practice amp at the moment is s 30-watt Peavey with a 10" speaker and it can be easily dialled down to quiet volume levels. But at those conversation volume levels I'd just rather use headphones because of afirementioned clean guitar bleedthrough.

[kevinng]

Thanks guys.

Any tips on the type of speakers I should get? I'm looking at 2 inch size, and likely off Aliexpress.

Would 'any' speaker work?

This is for a guitar amp.

How do I pick the best sounding 2 inch speaker for such an amp?

[EBK]

If you want something that sounds like a guitar amp, I wouldn't recommend a 2-inch speaker.  I built an amp with two 3-inch speakers, and even that doesn't sound very good. 

If you want something cheap, visit a thrift store and look at their stereos.  You may even find a decent sized speaker already in a box that you can build your amp into.  You could also go to a junk yard and get a 5×7 car speaker.

If you want something that sounds great, I still recommend the speaker I mentioned earlier, but it will cost you around $30.

[Big Monk]

Marshall MS-2 with the resistor on the headphone jack replaced with a 1k pot.

Crunchy and whisper quiet.

[EBK]

I have a tiny cigar box amp that I'm willing to sell if you are interested and in the US.

It has one of these amps, plus a 2.5-inch speaker (I think):
http://artecsound.com/pickups/electronics/sda.html


$20 plus shipping (beer can not included  ).


This is not a good sounding amp.  It works, but the sound is very tinny, toy-like.

[amptramp]

I don't think you are going to get the sound you want with anything under 4 inches.  This is the smallest size I have seen for "full range" speakers that could be expected to reproduce the entire audio spectrum.  A guitar only goes down to 82 Hz so you do not need audiophile or "hi-fi" components but you want something that makes your guitar sound like it would in a system you would use on stage.  The four-inch size is the smallest I have seen that is available with good magnets, a solid frame (to prevent resonances) and a proper cone and surround.  Anything smaller would sound like a transistor radio from the 1960's - no bass at all and even the amplifier stage taking 9 volts at 50 mA can drive it into severe distortion.

[Vivek]

I once attended a private concert by a world famous artist, and he connected his pedal board to a Bose SoundLink Mini II small little thing.

And the quality and volume was kinda sufficient for that 20 guest concert.

[teemuk]

This is the smallest size I have seen for "full range" speakers that could be expected to reproduce the entire audio spectrum.  A guitar only goes down to 82 Hz so you do not need audiophile or "hi-fi" components but you want something that makes your guitar sound like it would in a system you would use on stage.

Yes. But you definitely will not be needing a "full-range" speaker for guitar amp. Yes, the loudspeaker doesn't need to produce bass frequencies below 80 Hz BUT generally we also don't want it to produce higher frequencies above 5 kHz either. Especially distorted tones will sound nasty and fizzy if the speaker reproduces all the high order harmonics. Clean acoustic guitar can sound tolerable.

In my experience the issue with little loudspeakers is not only their limited low frequency response (that makes them sound thin and boxy) but also their broader response towards higher frequencies (that makes them sound shrill and fizzy). The latter is heightened by their broader dispersion of HF: When big speakers may sound ear-piercing in their on axis "beam" the little speakers sound ear-piercing even off axis.
On top of that, some of the little speakers (especially those found from cheap car stereos or ghettoblasters) have dust cap designs that artificially try to to increase the high end response. They are probably the most awful devices ever for reproducing a distorted guitar tone.

[amptramp]

This is the smallest size I have seen for "full range" speakers that could be expected to reproduce the entire audio spectrum.  A guitar only goes down to 82 Hz so you do not need audiophile or "hi-fi" components but you want something that makes your guitar sound like it would in a system you would use on stage.

Yes. But you definitely will not be needing a "full-range" speaker for guitar amp. Yes, the loudspeaker doesn't need to produce bass frequencies below 80 Hz BUT generally we also don't want it to produce higher frequencies above 5 kHz either. Especially distorted tones will sound nasty and fizzy if the speaker reproduces all the high order harmonics. Clean acoustic guitar can sound tolerable.

In my experience the issue with little loudspeakers is not only their limited low frequency response (that makes them sound thin and boxy) but also their broader response towards higher frequencies (that makes them sound shrill and fizzy). The latter is heightened by their broader dispersion of HF: When big speakers may sound ear-piercing in their on axis "beam" the little speakers sound ear-piercing even off axis.
On top of that, some of the little speakers (especially those found from cheap car stereos or ghettoblasters) have dust cap designs that artificially try to to increase the high end response. They are probably the most awful devices ever for reproducing a distorted guitar tone.

I agree that you don't need the high end, but that can be eliminated within the amplifier itself and it has the benefit of feedback lead at high frequencies that tends to stabilize the amplifier.  Trying to get a speaker to not respond at the high end may be a bit futile.  It is best to reduce the response in the amplifier itself where you are in control of the lowpass characteristics.

[kevinng]

Thanks

Actually I'm looking for a speaker you can mount into the pedal-size enclosure.

Sounding good is a plus, but sounding decent is a must.

[j_flanders]

Thanks

Actually I'm looking for a speaker you can mount into the pedal-size enclosure.

Sounding good is a plus, but sounding decent is a must.

Maybe a Smokey/Zinky?
In this video you can hear how horrible the built in speaker sounds at around 1:12.
And also how good when connected to a proper guitar speaker at 2:03.

[EBK]

Thanks

Actually I'm looking for a speaker you can mount into the pedal-size enclosure.

Sounding good is a plus, but sounding decent is a must.

Sounding decent will be tricky, but that depends on your subjective interpretation and how loud you want it.  You may be able to get something ok at a whisper or very low conversation level.