Quick question, do cheap "amplified speakers" still exist

[Alex Eisenhut]

Like the one I had as a kid in the 1980s

https://www.ebay.ca/itm/224491996441?hash=item3444c40519:g:STkAAOSwCT9gwT2D

Everything now is either some Bluetooth thing or 200-300$ boom box. I just want a cheap and cheerful analog mono thing (20$?) that I can put on my electronics tinkering bench with little to no worries about blowing it up because it's easily repairable.

Something I can use to check audio outputs, or poke around random circuits to get sound with an analog input jack. Battery powered would be sweet too.

I don't want to use my Creative T20s for this... The eBay item is like 80$ with shipping.

[DrG]

https://www.amazon.com/Logitech-3-5mm-Compact-Laptop-Speakers/dp/B003CP0OT2/ref=zg_bs_172471_3?_encoding=UTF8&psc=1&refRID=BXQDSC6FB2YVYWNNZD0Y

[Neomys Sapiens]

Maybe the thing for the task:

[pqass]

If you're up to it, try: https://sound-au.com/project113.htm



I was able to bread-board this circuit in less than a half-hour with junk-bin parts.
I used some random darlingtons for the output transistors (which need to add 2 series diodes for D1L and D2L) and a TL072 dual op amp.
FYI: a LM358 sounds horrible.  Use the TL071 single op amp package for a mono version.
It produces ~3W into 4ohms with a ±12V supply.
The most expensive part was the CA$15 Hammond die-cast case.

[NiHaoMike]

Many cheap Bluetooth speakers also have 3.5mm input.

[james_s]

It's easy enough to build one. I have several little PAM8403 audio amplifier modules, some of them that were only around $2 shipped even have a volume pot. They run nicely on 4 NiMH AA cells or a single li-ion cell. Stick one of those in a box with a speaker and battery and you've got an amplified speaker.

[Zero999]

If you're up to it, try: https://sound-au.com/project113.htm



I was able to bread-board this circuit in less than a half-hour with junk-bin parts.
I used some random darlingtons for the output transistors (which need to add 2 series diodes for D1L and D2L) and a TL072 dual op amp.
FYI: a LM358 sounds horrible.  Use the TL071 single op amp package for a mono version.
It produces ~3W into 4ohms with a ±12V supply.
The most expensive part was the CA$15 Hammond die-cast case.

That's a decent enough circuit, but it's designed for headphones. It won't deliver 3W into a 4 Ohm load. R7L and R8L will drop too much voltage for a start.

It will need to be beefed up considerably, to drive a 4 Ohm load with a decent power level.

[SeanB]

I just bought some $8 USB powered PC speakers, and use them for this. Powered from an old wall wart they will work, just find an old phone charger that gives between 5-7VDC as output and use it, even easier if it actually has a USB socket on it, so that you do not have to cut the wires.

[pqass]

That's a decent enough circuit, but it's designed for headphones. It won't deliver 3W into a 4 Ohm load. R7L and R8L will drop too much voltage for a start.

It will need to be beefed up considerably, to drive a 4 Ohm load with a decent power level.

You're right, I forgot to mention that I lowered the emitter resistors R7/R8 to 2R2.
Also, I lowered the feedback resistor R4 to 20K and base resistors R5/R6 to 5K6.  But this is inconsequential.
See attached schematic of my version.  The power supply is a 24V center-tapped transformer into a full bridge and a pair of 4700uF bulk caps.

Since I've built it a year and a half ago, it has been serving as my main desktop computer amp driving a pair of 2-way bookshelf speakers measuring 3.8ohms.  It can be quite loud a 2ft.  As per the waveforms screenshot attached, it can produce 4.24Vrms into 3.8ohms at just below clipping.  That puts the power output at 4.7W  (V^2/R).  Also attached is a frequency response analysis.

[Howardlong]

Mini guitar amp?

Mine even goes up to 11.

They'll win zero prizes for fidelity, power or much else, but for a little test amp & speaker they're convenient.

PP3 powered, so don't expect the earth to move.

About 6" tall.

The model is MS2 or MS-2,  don't know why but they're a lot more expensive in the US than over here in Blighty.

e.g. https://www.ebay.co.uk/itm/224547206424?epid=3032267910&hash=item34480e7518:g:ubwAAOSwNpFg~aoE

[jonovid]

a LM358 sounds horrible

the LM386 audio amplifier has a bad reputation but if its audio amplifier circuit has the right components, it can be made to behave.
LM386 as its an operational amplifier. so if the  differential input is to ground through a .27 uf capacitor not just grounded, wave clipping can be reduced and.
power increased. if the load its 8 ohm or more like 16 or 30 ohm, Not 4 ohm.

Make the PERFECT LM386 audio amplifier