Suitable small amp for self-powered speakers. - Page 1
Forum section: electronics / beginners

author: LEDAero
author_rank: Regular Contributor
timestamp: January 19, 2015, 06:55:56 am
content: Now that my CNC machine is up and running, I am thinking of making some small bookshelf speakers for the workshop using a bluetooth audio board I have lying around.I was going to use Apple Airplay (via an open source unix hack), but I've got dozens of Arduino's about the place and I should probably use some of them before I go buying more MCUs (my wife agrees! >.< ) - but of course, with thisI wanted to make someFostex 800EorAuratone 5C-type clones and put a good, clean, small amplifier in with the bluetooth module.So, bearing in mind I am new to all this electronic chicanery and I've heard that building an amp is a good project for n00bs, any recommendations on the kind of amp I should look at for my first from-scratch project? I am not averse to a kit, but have enough protoboard, etc. lying around that I can make something from components.And speaking of components - they are short on the ground where I live - I have a few transistors round the place (1N4001, 1N4002, 1N4004, 1N4007) and a bunch of electrolytic capacitors, 1/4W resistors and some diodes, but not much more than that - everything I build will either need to be built from scratch (cabinet, etc.) or imported.Of course I could go down to the shops and buy a 12V car-audio amp and stick that in, but where's the fun in that?I guess I am looking around 10-15W. I mostly listen to jazz and acoustic stuff - not a head-banger - and not that loud, either. If they work out OK, I would make a pair for my wife's classroom, too. She has some awful plastic horrors that buzz and spit and generally sound like they have the mange.Any advice gratefully received.

author: LEDAero
author_rank: Regular Contributor
timestamp: January 19, 2015, 08:37:38 am
content: Further...I have been seeing a lot of Class T (tripath) amps around the place - are they something worth investigating, or do they take all the fun out of it?

author: diyaudio
author_rank: Frequent Contributor
timestamp: January 19, 2015, 08:46:15 am
content: Quote from: LEDAero on January 19, 2015, 06:55:56 am12V try this.http://www.ti.com/product/tpa3100d2Quotethere are far more fun areas in DIY sound, than amplifiers, signal processing is one of them.

author: LEDAero
author_rank: Regular Contributor
timestamp: January 19, 2015, 12:12:51 pm
content: Quote from: diyaudio on January 19, 2015, 08:46:15 amThanks, but I'm not sure how how that helps me learn about amplifiers - it's a link to an SMD IC that seems to be a complete amp on a chip. I'm also not sure how I am going to fit that on some protoboard - it looks to need a decent heatsink to work properly.If I read the product sheet correctly, I can just connect power, audio + and -, connect a couple of caps to the outputs and drive some speakers?I would probably have to understand what signal processing is before I venture into those areas.Perhaps I didn't make myself clear - I have never made a circuit for myself, other than to connect a sensor or transceiver to an Arduino or Pi or similar.I think you are either over-estimating the abilities of someone that has only just started the section on diodes in Electronics for Dummies, or didn't understand what it was I wanted to do.

author: dannyf
author_rank: Super Contributor
timestamp: January 19, 2015, 01:09:46 pm
content: TDA2030, or things like that.

author: macboy
author_rank: Super Contributor
timestamp: January 19, 2015, 01:23:15 pm
content: I would go with something affectionately known as a "chip amp". This is basically a power op-amp, optimised for used in the audio region. There are many varieties, with the most common from ST, Toshiba, and especially National (now TI). For your power range, I would suggest a TI LM1875. This is a very simple and cheap 5 terminal, TO-220 package device (+/- power, +/- inputs, output). Being just an op-amp, all you need to do is give it +/- power, configure for a gain of at least 10 (>=10 required for stability), feed it a signal, and connect to speakers. Little else is required. I would use the RC snubber at the output (see datasheet), AC coupled input (DC blocking capacitor), and good power rail decoupling. Do that, and your chances of success are quite good.I have powered these from as little as a single 12 V (+/- 6) supply but you should aim for +/- 15V to +/- 20V. The sweet spot depends on your speaker impedance and wattage needs. A higher supply means a hotter device, so don't do that just to get "MOAR POWER!", as you may regret it.If you want to get creative, use an active crossover and a separate amp for woofer and tweeter. Standing out from all the audiophoolery and noise, this is one upgrade that will genuinely increase the sound quality.

author: LEDAero
author_rank: Regular Contributor
timestamp: January 20, 2015, 12:41:10 am
content: OK- so maybe it's me that didn't understand what he wanted to do...Has it gotten to the stage where small amps are just off-the-shelf ICs? Give it a suitably balanced input and some volts and it's as easy as wiring up some speakers?Well that's taken all the fun out of it!I was hoping for something a bit more esoteric, but given I will be sourcing content from an iPod, it's silly to go all audiophile when I have a bluetooth path shuffling lossy bits about.I guess I will buy a couple of ICs and see what it sounds like.Thanks guys - in one way I am kinda let down, in another I can now spend my time on woodworky things, rather than circuity things.

author: macboy
author_rank: Super Contributor
timestamp: January 20, 2015, 01:35:10 pm
content: Well, if building an amplifier from a single IC and a handful of passives sounds like no fun, then head over toRod Elliot's websiteto find some very nice discrete transistor designs that have been built successfully by many many people. He also has active crossover designs and many other audio related circuits.

author: lutkeveld
author_rank: Regular Contributor
timestamp: January 20, 2015, 03:41:05 pm
content: https://www.eevblog.com/forum/buysellwanted/fs-%28uk%29-some-more-really-small-50w-amps/Small amp, big sound

author: Zero999
author_rank: Super Contributor
timestamp: January 20, 2015, 08:22:09 pm
content: Quote from: LEDAero on January 19, 2015, 06:55:56 amThe 1N4001, 1N4002, 1N4004, 1N4007 are diodes, not transistors.

author: LEDAero
author_rank: Regular Contributor
timestamp: January 23, 2015, 12:57:20 pm
content: Doh! Of course they are... I just went back to my Aliexpress order and cut and pasted without really looking.The transistors I bought were TIP102s - that's all I have. I had a reason for buying them when I did, but it eludes me now

author: LEDAero
author_rank: Regular Contributor
timestamp: January 23, 2015, 01:00:43 pm
content: Quote from: macboy on January 20, 2015, 01:35:10 pmYou're a star! That's exactly the kind of thing I was looking forThank you!I am trying to learn Eagle and it's much easier when you have something to actually build (as it were) - as well, it's a good learning curve for general electronics.

author: KM4FER
author_rank: Regular Contributor
timestamp: January 23, 2015, 01:28:54 pm
content: LedAero,So you want to build an amp from scratch. Good for you.Here's a couple of videos on design of transistor audio amps by SignalPath.Tutorial on the design of a single transistor amplifierTutorial on the design of a Class AB amplifierAnd, from W2AEW#113 Basics of transistor bias point and class of amplifier operationThese should get you started. Then come back here with questions on what you need help with.earl...

author: LEDAero
author_rank: Regular Contributor
timestamp: February 18, 2015, 09:35:24 am
content: Thanks Earl.Sorry it took me so long to say it - it's been a busy time round here...I'll look at those vids shortly.