Cheap DIY Amplifiers

[luke10050]

I got this cheap amplifier kit from a Design and Technology Teacher from my school (workshop teacher) and i assembled it today, it sounds pretty damn tinny, that said the speakers are only 8 ohm 0.5W and unbranded. Also comes with some Hitano caps. Any ideas on how to improve the circuit? my first idea was to pop some panasonic FC or FM capacitors in it but i figured i'd ask you guys

The Kit: http://www.kitronik.co.uk/products/p...amplifier-kit/

[mariushm]

Re: Cheap DIY Amplifiers

Well, it sounds tinny because it's only 1w amplifier, in ideal conditions, and those speakers are lousy.

The amp can work with voltages from 1.8v to 15v but the higher the voltages, the more power it can output.

Here's the datasheet: http://www.datasheetcatalog.com/data...TDA2822M.shtml

With 8 ohm speakers it can do up to this much but with 10% distortions,

RL = 8 ohm

VS = 6V 1350 mW
VS = 4.5V 700 mW
VS = 3V 220mW

RL = 4 ohm

VS = 4.5V 1000mW
VS = 3V 350mW
VS = 2V 80mW

If you don't want more than 1% distortion, you're limited to about 350mW at 6v (notice that it can actually do about 1350mW with 10% distortion) and about 800mW with 9v input (page 5, figure 10)

Now note that this is in TOTAL, both speakers... so realistically with 9v battery you can do about 0.5w per speaker.

But then if you go to datasheet and look at page 6 figure 13 you have a graph with total power dissipation compared to output power... so you can see there that with 9v input, it can output 1w in total but uses 2w to achieve that.
Now 2w at 9v is 220 mA ... good luck pulling that much from a 9v battery for more than a few minutes.

My advice, replace 9v battery with 7.5v-12v power brick from something and maybe use a bit better speakers (use 4ohm ones) and it might sound better. But capacitors won't make it sound better, it's just a weak amplifier.

[luke10050]

Re: Cheap DIY Amplifiers

ive been using a 12v 1.5A power brick, i think its not so much the amp as the speakers, connected it up to a sony 8 ohm cabinet i have around and it sounded a million times better, so i really dont know. are there many other amplifier IC's like this, or is it a step up from here into different design?

[ben7]

Re: Cheap DIY Amplifiers

P.s. It will sound better if your speakers are in an enclosure of sorts.

These silly "amps" are usually set for full gain ... which makes loud sound, but realllllllllyyyy distorted.

I have a home-designed class AB amp circuit, will have to post it later when I get my computer back. It has about 20 watts output. Not sure about the THD, but it sounded great to me!

P.S. DON'T get into that hifi s$!t - they are idiots who think a wooden knob instead of a plastic one makes an amp sound better. They are called audiophiles.

[lti]

Re: Cheap DIY Amplifiers

There isn't much you can do with the speakers included in the kit. They might sound better in an enclosure, but don't count on it.

[Heihachi_73]

Re: Cheap DIY Amplifiers

8 ohm 0.5W unbranded speaker = PC speaker. Not worth worrying about.

[Logistics]

Re: Cheap DIY Amplifiers

If it were me, I would replace the 470's with bipolar Panasonic SU's, the 10uF with an FM, and absolutely chuck those 100nf (0.1uF) ceramics and get metallized polypropylene films. Also bypass the 470's with .1 or .01uF films. Any resistors I would replace with wirewound and hurl the carbons it probably comes with.

[lti]

Re: Cheap DIY Amplifiers

A TDA2822M isn't good enough for different caps and resistors to make any difference in sound quality.

Could you explain how using bipolar coupling caps will help? Those caps will have half the power supply voltage across them.

[budm]

Re: Cheap DIY Amplifiers

I will not use wire wound resistor unless they are non-inductive wire wound type. Same with Polyester film, make sure they are non-inductive type also.

[ben7]

Re: Cheap DIY Amplifiers

A TDA2822M isn't good enough for different caps and resistors to make any difference in sound quality.

Could you explain how using bipolar coupling caps will help? Those caps will have half the power supply voltage across them.

The regular polarized capacitors are just fine, as long as you have the polarity correct. (Negative to speaker if the speaker is tied to ground, and negative to amplifier if the speaker is tied to +V)

A better one would be a TDA2050. It will require a higher power PSU, and a heatsink - this is because it has a greater output power capability. You should then use a speaker that can handle the power. The cheap half watt speaker will likely burn out. A switch mode power supply should be avoided because of noise from the high frequency switching.

[mariushm]

Re: Cheap DIY Amplifiers

Here's a tda2050 based amplifier:

http://diyaudioprojects.com/Chip/DIY...hip-Amplifier/

The tda2050 datasheet also has a circuit to make the chip work with single power supply (not + and -) so if you make that you could power the amp straight from a 24-36v DC switching power supply. A switching power supply will introduce some noise compared to a classic big heavy transformer but you probably wouldn't notice the difference with average speakers.

TDA2050 likes higher voltage, it needs a minimum of 9v (+/- 4.5v) to output about 1-2 watts of audio power and about 25-40w at 42-45v (+/- 20-23v) ... less with 8ohm speakers, more with 4 ohm speakers..

See page 8 in https://cdn.badcaps-static.com/pdfs/...31cada06bb.pdf

The IC is cheap enough and easy to put on regular prototyping board (but make good traces with solder and thicker solid core wire on bottom as in the first link) : http://www.digikey.com/product-detai...28-5-ND/634792

[ben7]

Re: Cheap DIY Amplifiers

Here's a tda2050 based amplifier:

http://diyaudioprojects.com/Chip/DIY...hip-Amplifier/

The tda2050 datasheet also has a circuit to make the chip work with single power supply (not + and -) so if you make that you could power the amp straight from a 24-36v DC switching power supply. A switching power supply will introduce some noise compared to a classic big heavy transformer but you probably wouldn't notice the difference with average speakers.

TDA2050 likes higher voltage, it needs a minimum of 9v (+/- 4.5v) to output about 1-2 watts of audio power and about 25-40w at 42-45v (+/- 20-23v) ... less with 8ohm speakers, more with 4 ohm speakers..

See page 8 in https://cdn.badcaps-static.com/pdfs/...31cada06bb.pdf

The IC is cheap enough and easy to put on regular prototyping board (but make good traces with solder and thicker solid core wire on bottom as in the first link) : http://www.digikey.com/product-detai...28-5-ND/634792

I once powered a TDA2005 amp off a PC power supply. Delta brand, with good caps. Lots of hissssssssssss from the speakers! These were cheapo crap speakers too.

[mariushm]

Re: Cheap DIY Amplifiers

TDA2005 is not the same as a TDA2050. It's a class b amp, tda2050 is class ab.

And if you really want to, you can use slightly less than average linear regulators to reject some of the noise from the smps psu. Most linear regulators accept up to 40-50v in, and since they drop only 1-2 volts, 2-3 watts of dissipated power on the linear regulator would not be a problem.

[ben7]

Re: Cheap DIY Amplifiers

TDA2005 is not the same as a TDA2050. It's a class b amp, tda2050 is class ab.

Uh, then please explain why my comment about the TDA2005 is inaccurate.
Still, it is a linear (i.e. not digital) amplifier...

[mariushm]

Re: Cheap DIY Amplifiers

I didn't say it was innacurate, just that tda2050 will not necessarily be just as hissy as your tda2005. It should give much better audio quality.

http://stason.org/TULARC/entertainme...hat-is-Cl.html

I'm too lazy to write my own text so I'm just gonna paste fragments from that page.

Class A refers to an output stage with bias current greater than the maximum output current, so that all output transistors are always conducting current. The biggest advantage of Class A is that it is most linear, ie: has the lowest distortion.

Class B amps have output stages which have zero idle bias current. Typically, a Class B audio amplifier has zero bias current in a very small part of the power cycle, to avoid nonlinearities. Class B amplifiers have a significant advantage over Class A in efficiency because they use almost no electricity with small signals.

Class B amplifiers have a major disadvantage: very audible distortion with small signals. This distortion can be so bad that it is objectionable even with large signals. This distortion is called crossover distortion, because it occurs at the point when the output stage crosses between sourcing and
sinking current. There are almost no Class B amplifiers on the market today.

Class AB amplifiers are almost the same as Class B amplifiers in that they have two driven transistors. However, Class AB
amplifiers differ from Class B amplifiers in that they have a small idle current flowing from positive supply to negative supply even when there is no input signal. This idle current slightly increases power consumption, but does not increase it anywhere near as much as Class A. This idle current also corrects almost all of the nonlinearity associated with crossover distortion. These amplifiers are called Class AB rather than Class A because with large signals, they behave like Class B amplifiers, but with small signals, they behave like Class A amplifiers. Most amplifiers on the market are Class AB.

TDA2005 is class B.
TDA2050 is class AB.

tda2005:

thd 0.2% avg. 1% max (f = 1 kHz; VS = 14.4 V; RL = 4 Ω; Po = 50 mW to 4 W

tda2050:
thd 0.02% avg, 0.5% max Vs = ± 22 V, RL = 8 Ω, f = 1 kHz, Po = 0.1 to 20 W, f = 100 Hz to 10 kHz;

TDA2050 will, in theory, distort less.

TDA2005 is designed for car radio aka environments which are subjected to constant noise from driving, engine humm etc, stuff that will hide some of the background noise...
The IC is also kinda designed to work in bridge mode, one IC driving one speaker, not two speakers.
It's also sort of made for 2-4 ohm speakers... tda2050 can work just fine with better 8 ohm speakers etc..
See the supply voltage rejection graphs on pages 13-14 in datasheet, see how it handles high frequencies.... or how it doesn't better put... compare with pages 8-10 in tda2050 datasheet etc etc etc

[lexwalker]

Re: Cheap DIY Amplifiers

For simple and cheap DIY amplifiers, I would usually suggest TDA1517 although its a Class B amplifier.

The nice thing about this I.C is it uses very minimal components, can use single rail supply and lower voltages. For those ingenious enough, can even build one without requiring any PCB or circuit boards.

[Logistics]

Re: Cheap DIY Amplifiers

A TDA2822M isn't good enough for different caps and resistors to make any difference in sound quality.

I disagree. The fact that it is a very inexpensive amplifier should tell one that it can use all the help it can get. Distortion is going to be a large issue for something of this low-caliber so bypassing the electrolytics in the audio stage, even bypassing the power-cap should help eliminate some unwanted noise.

Could you explain how using bipolar coupling caps will help? Those caps will have half the power supply voltage across them.

Audio has A/C characteristics and does benefit from non-polarized capacitors. I've tested this out on cheap amplifiers myself and heard differences, first-hand. In some cases it may not seem better because, for example, you may lose low-frequency extension, but gain high-frequency extension or perhaps a gain in mid-range frequencies. Often times different parts need to be used in tandem to see a beneficial change rather than simply a change.

But if you have any equipment that has small films at the line-level stage, before the amplifier IC, try swapping them from films to electrolytics (polarized or non-polarized) or vice versa and see the huge difference, firsthand.

In any case I would never prescribe to using crappy parts because the amp seems crappy,too.

[redwire]

Re: Cheap DIY Amplifiers

Chip-amps are a bit of work to get lowest distortion. I've used TDA2005, TDA2030, TDA2040 etc. (they're the same family/topology), and the TDA2822 for flea power stuff (its too little for hi-fi), and STK's for bigger amps.
All the IC's sonically benefit from decent capacitors- beefy electrolytics on the rails and outputs (if single supply) and film types elsewhere.

Oddly enough, RF bypass on the rails/input and output inductors makes a huge difference. Chip-amps are very sensitive to RF coming in on the input or speaker wires, usually AM radio.

eBay has tons of Chinese TDA2040/50 amps

[JonathanAnon]

Re: Cheap DIY Amplifiers

Hi guys,

I was about to post about amplifiers earlier this week only I didnt get a chance. I've made a video showing what I have made up at the moment. I dont like those kits made in the original post. I prefer to build from scratch. And this is what I'm working with at the moment..

http://videobam.com/jnDwq#

The schematic is pretty much the same as this..



I just used whatever electrolytic capacitors I had around for decoupling, and one large electrolytic cap to smooth out the DC coming from the battery..

thanks,

[lti]

Re: Cheap DIY Amplifiers

That is one lousy video hosting website.