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Old 1st March 2011, 05:27 PM   #1
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Default Help getting started!

Hi everyone!

I've moved a lot in the last couple years and am finally settling in to stay in one place for a while, only to discover I no longer own a fully functional amplifier. All I do have is an old Koss stereo tuner / amp that I bought with my first pay check from my first job a couple decades ago. It works for a few minutes then loses power. Rather than try to fix it or spend money on a new one I decided, why not build something from scratch?

I've been lurking these forums off and on for years while pondering headphone amps, and have a lot of diy experience with making things other than amps, so have a fair idea what goes into it. Now I'm at the point of designing it so that I can start acquiring the right parts and get to work!

Here's what I've got to work with...

Design goals:

2CH: The initial version must be at least 2ch and able to support two 8ohm speakers. Maybe my next will attempt 6ch analog surround but for now I'm happy with being able to play mp3s off my laptop.

DC: I prefer DC power because it's easier for me to work with, and because I'd like it to be optionally battery operated eventually (it is for my laptop after all).

Sound Quality / Small Size: Being in an apartment sound quality is more important than loudness. Likewise small space footprint is also important. The smaller the better. I imagine something the size of an internet router.

Recycled Materials: Lastly, I want to keep costs as low as possible and recycle as much as I can from existing materials. I've got countless boxes of computer parts to pull components from, as well as several DC adapters of various sizes and outputs. I own a soldering iron and several metalworking / jewelry tools that will probably be useful. I also have some opamp chips around here that came out of my Auzentech X-Meridian 7.1 sound card when I upgraded it.

This project does not need to handle more than one input, does not need a tuner, or any other functionality than one 2ch input, amplifying it, and sending it out to the speakers.

With that all said I have some questions for you...

Being relatively new to this kind of technology I have no idea what to even google to find blueprints or tutorials. Could you recommend any?

Are there any particular technologies or methodologies that you'd recommend for this sort of project? What are some of your personal preferences that you think might be similar to what I'm looking for?

And assuming this has already been done many times in the past can you point me at some projects that are similar so I can see how it was done?

Thanks!
Kris
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Old 1st March 2011, 06:33 PM   #2
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Well, building an amplifier may be an easy task, depending on what You want.
My cheapo and small (but absolute not high quality) amp is a single chip.
Google Tda1557q datasheet, this was ment to be for car radio's.
You will need 4 capacitors soldered to the IC, and You get a 2x 20 ish watt amp (at 4 ohms load) amplifier, that can run from dc ~9 volts up to something 16-17 volts. (and best would be to keep it to somethingn close to 15 Volts...)

Notice, volume controll and other controlls are not a function of this chip.
Only the mute function.


If you are looking for cheap quality, do the Tda2050. The datasheet gives you a nice PCB too to, and so on.
But, that is rated to dual powersupply, 22 volt rails. Battery operation is possible, but you need at least 2x12 volts of battery power to make it worthy.


If you must have battery operation, maybe some rechargeable 9V batterys would be the way to go with thatone.

Based on mistakes i have done while building my ultra cheapoo amp, i would strongly suggest that You first and foremost look around, and make a proper powersupply.
Example, while the tda1557q could run from a computer psu, i myself have killed a handfull of them just to learn you need a good quality computer psu to get away with that.

For volume/balance and tone controlls you may want to try an Lm1036 chip.

Actualy none of the above are high quality chips.
On the otherhand, you can mout them on heatsinks from computers, as an example.
The size of 2 pc dvd drives on top of eatch other would offer enough space to fit a pair of Tda2050 chips and psu, along with the Lm1036.
Actualy you can find these chips for dirt cheap. Around 4 euro for the Lm1036 and same for tda1557q, 2 euro or so for the tda2050.
These inexpensive chips are allso sold in kits too, very beginner and diy friendly.
If you are on a tight budget i would suggest these.

That is, if You do not mind dong an IC based amp.
There are other questions You should ask Your self about too.
What is Your budget, for example.
Class AB, class D, what You prefer?
Should it be Ic based, or other technology? (like single transistor class A, or something like that)

If you are unsure, as a first project the tda1557q in a kit with lm1036 in a kit,
and foremost a proper powersupply rated to 12-16 volt DC at 60 VA or so should be quite a lot of fun, and tight on budget.
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Old 1st March 2011, 07:08 PM   #3
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What speakers are you trying to drive? Expectations in terms of level & quality? Budget?

There is a wide variaty of projects for a 1st time build, gain-clones, lots of Pass amps, and many other SS. Tube stuff galore.

Myself, i couldn't live long without tunes. I'd 1st look to canabilizing the dead unit, and bolting in a couple chip amps. Cheap, decent, and hard to get wrong.

dave
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Old 1st March 2011, 07:42 PM   #4
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Welcome to the forum.

Your DC power idea will limit you if you're looking for high quality and more than a couple watts.

The MyRefC chip amp is the only thing that comes to mind that I can recommend personally, but it also requires dual rails. It sounds waaay better than it has the right to. I'm not even sure PCBs are still around but the artwork is.

The ESP website www.sound.westhost.com is a great place to bone up on stuff, it has a more non-technical nature if that's where you need to be at this point.

There's plenty of help available to you right here if you do your homework first. The Forum search engine works pretty good these days also.

Best, Bill

Last edited by Bill Fuss; 1st March 2011 at 07:46 PM.
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Old 1st March 2011, 08:21 PM   #5
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Thanks for the replies, you've all given me a LOT of new search terms to look for!

I will definitely be doing a chip opamp for this first time around. I am fairly certain I already have 100% of the components I'll need to at least get a steady sound out of my speakers without it shutting itself off every few minutes, which is more than I've got right now.

I have three chips made by AUK labeled S4580P that came out of my old sound card:

http://www.datasheetcatalog.org/data...auk/S4580P.pdf

I don't mind if I burn, melt, or explode these chips so that gives me three attempts with them before I start looking for a specific, better chip out there.

@Arty: What you've described is pretty much exactly what I had in mind! So far the closest project I've found online is this one: Nanoo - LM3875 Non-Inverting Chip Amplifier (Gainclone)

Your idea of using PC power supply is a great one. I've got several old PCs laying around most of which have at least halfway decent power supplies in them. That gives me a good set of 12v rails I could use to power this thing.

@planet10: I've got a few speakers to choose from but the most likely will be a pair of old Polk Audio r30 front speakers. Data sheet here: R30 Specs Page : Two-way floor-standing loudspeaker : Polk Audio

I also have a center that matches them:
CSi40 Specs Page : High Performance Center Channel Speaker : Polk Audio

and a sub
PSW202 Specs Page : Powered Subwoofer : Polk Audio

Right now I'll be happy to have just mono sound over the center as it gets the best audio of the lot, but I'm not too picky as any music is better than none!

The important part is that I need 20W to 150W (the latter would probably be much too loud for my apartment) and 8ohms.

@Bill: Thanks for the info, I'll look into it! The MyRefC amp looks a bit out of my price range but still looks like good info!


My next question for all of you is, will the S4580P opamps work for powering the speakers I already mentioned?

Now for doing some homework to figure this stuff out! Thanks again everyone!

Edit: I should also mention that at this point I'll be happy with sound that's better than comes out of my laptop speakers and doesn't have the power problems my current (mostly dead) stereo does as mentioned already. I don't need this first attempt at an amp to be "high quality" as long as it works.

Last edited by KrisWood; 1st March 2011 at 08:29 PM.
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Old 1st March 2011, 09:12 PM   #6
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Also look at the TriPath class D amps over in the Class D forum. Plenty to choose from, compact, quite cheap and can be very nice sound. Many of them run from a 12v, single-rail supply. Look for the 2020 or 2021B chips. 41Hz.com (kits) and on eBay, arjenhelder (assembled) have decent reputations. Others seem to be OK as well.

BTW, with 12v, you'll be limited to somewhere around 15-20 watts, which, truthfully, isn't much of a limitation, as that kind of wattage can make PLENTY of sound for one room, especially of your speakers are in any way efficient. Ten times wattage = twice the sound level.

--Buckapound
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Old 1st March 2011, 09:24 PM   #7
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Thanks on the voltage info. My opamps on their datasheet say they need 18v. I wonder how I can get that out of a PC power supply... Shouldn't I be able to add some resistors to the 24v rail, or combine a few of the 12v rails together? I guess it's time to read up on some basic electronics theory...

As for the various kits, I'm hoping to spend no money at all if I can help it. We'll see how far that gets me though!
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Old 1st March 2011, 09:35 PM   #8
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Ok on further research it seems like what I want to make is a gainclone. It's the best solution for the kind of parts and money I have to work with. That gives me a plethora of projects to work from. The only question left is whether the S4580P opamp will work in a gainclone and output at least 20w on 8ohm speakers.
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Old 3rd March 2011, 09:13 PM   #9
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hmm.. well, a chipamp is realy a good start.
If you did manage to build a headphone amp, then this should be easy to do.

However, the chip it self may not cost a lot, but a decent powersuply may.
The price of the chip is onyl 1 thing.
You will require a nice transformator, and some large capacitors.
No need for any other IC, a simple dual-gang potentiometer will do fine to controll volume. For a start, that should do the trick.

A bit of comment on your pc powersuppy idea:
do be warned, while many of them are okay to supply an amplifier with, most of them are not going to work.
Example: my first tda1557q did work flawlessly from battery power. A soon as i connected it to a pc powersuply i whent silent, and remained ther for ever.
A pc psu needs a dummy load to power up properly. Noise is not the real issue with them, but the turn on voltage spike is.

Pumping up the voltage can work, simple trim pot in the sense line can do it.
But no more than to boost 12V rail to 15 V.
The psu has capacitors inside rated for 16V.
Even 15 V mod is close to the edge, i would rather not play with it.
Connecting more than 1 pc psu to get 24 volt, or +- 12 volts is possible.
But you would have to modifie one of them, and turn on voltage spike would still remain or be growing as a problem.

Prior building anything or purchasing parts, i would still suggest You to take a look at datasheets of simple chip amps, finde one you like, and can afford to build.
By that i mean, including the cost of a proper powersuply.

Alslo, a bit of advice on power rating of amps.
Given a set of good speakers, the efficiency will be high, and you realy do not need more than say.. 10 watt / channel to make it loud.
Given a pair of not so good ones, powerhandling will be probably no more than 20-30 watts.

Actualy i do not think you would need more than 25 watt / channel for stereo application in a small to medium room.
To demosnstrate why..
Lets say You got a pair of avarage sensitivity speakers. I gona rate them to 87 dBL.
1W -> 87 dBL
2w -> 90 dBL
4w -> 93 dBL
8W -> 96 dBL
16w -> 99 dBL

Lets say Your theoretical amplifier can manage 16 watt with no major distorsion rise.
You got a pair of speakers, so we can assume 102 dBL loudness if you listen to them from 1 meter distance.
Make that 2 meters, and you end up with something around 99 dBL.
Jack hammer at 1 m distance makes approx 100 dBL.

That is quite loud, if you ask me.
And you still have some juice left, as we only estimated 16 watts, not 20-30 watts.
Since You would probably add a subwoofer later on, that unit would have to keep up with the rest of the system.
Since it has to provide the subbas for both speakers in he stereo setup, and most subwoofers are less efficient than midbass units, we can conclude that oone would need at least 3 times the power for the subwoofer amp to be safe.
(at least thats how i usualy find it. one may argue, it does depend a lot on room accustics, aligment, woofer, personal taste, whatever...)

So if I was You, I would first start to look around what powersuply could I afford, and continue to find a suitable chip for that.
Actualy, does not realy mather what kind of amplifier you have, if the powersuply is noisy or not up to the task in any other way, you will still have a bad system, with terrible sound.

TDA1557Q is not a high quality chip, unlike gainclones.
But, it has the advantage of being :
-> stereo, you get 2 nice amps in the package
-> inexpensive
-> powersuply can be built from transformator used for 12 V halogen lamps, that often can be obtained for a reasonable price of approx 10 euro.

I would say 12 V battery is allso easy to obtain. You wanted something that can be powered from battery too. Notice, a battery has no main line humm, nor any noise from main line, and is pure DC. It is superior to any transformator/bridge/filter and or tank capacior setup.

Size wise chipamps makes no real difference, none of them require a lot of external components, chips them selfs are small, so are the few components needed to make em work.
Heatsinks, and transformator are the bigones.
Naturaly, high power -> big psu.


My suggestion for cheap fun..
Look around, if you have many old junk You may be able to score a powersuply of some kind suitable for a tda1557q chip.
It is low cost, and lots of fun.
And even if You do not, You can still power it from a simple battery.
Actualy for starting project that is not a bad idea, mains voltage and the over +- 20 volts required by the LMXXXX chipamps can hurt.
3 , 4.5 volt cheapo battery packs in series is absolute okay for tda1557q.
even if you sort circuit something you do not end up with as mutch trouble as with mainlines or 40+ volts from secundary of a transformer.
IF You have a better quality pc psu, you can even try to power it up with that.
Just make sure You give a nice 5 watt or so load to the +12, and the +5 rails, and have some delay circuit so that the amplifier does not recive the turn on voltage spike. In that case You can have a stereo amplifier for less than 10 euro worth.
Click the image to open in full size.
This should be able to delay a relay for You, protecting Your mini amplifier from psu turn on spikes.
With different timeing setting You can have a notherone, to protect Your speakers from turn on plop.
Same PSU can power on an Lm1036 pre-amp/volume/toe/balance unit.
// for the basics, a simple dual gang pot will be just more than good.

Choice is Yours, but if You ask me it does not get any simpler than Tda1557q.
It can be usefull anytime, as say.. sorround speaker amplifier, or a portable one, or a car amp, or whatever.
Output power for 8 ohm load is around something 12 watt / channel. (assuming 10 volt swing from 13,5 volt powersuply voltage)
it requires only the
-input capacitors (330 uf min can be anything that is not an elco)
-RF filter capacitors for input (15 pf ceramic ones)
-psu filter capacitor (15 pf ceramic paralell to 100 nf non elco very close to ic, preferably soldered directly on the ic pins)
-psu bypass capacitor (elco, 1000 ufd /25 V, paralell to anything that is bigger than 4700 ufd / 25 V)
-cpu heatsink

a switch is an optinal item, only if you need to mute the amplifier.
The schematic of delayd turn on is needed only fi you want to use it with a pc psu.
In that case You need a relay that can handle 6 A current.
The psu needs dummy load of ~25 ohm 10 watt resistor on +12 rail, and ~15 ohm 10 watt resistor on +5 rail. ( or some small light bulbs.. lol. as power on indicator. whatever is cheaper..)
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Old 3rd March 2011, 09:34 PM   #10
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Thanks for the reply, Arty! I don't have any money whatsoever to spend this month so I'm limited entirely to what I can salvage. Fortunately I have a large pile of electronics so I suspect I can manage something even if it's pitiful.

As I said before I'm intending to use the S4580P opamps that came out of my computer sound card. As far as I can tell they probably won't be anywhere near as powerful as the type used in gainclones but I suspect they'll work for learning purposes.

I haven't actually built a headphone amp before, only researched it. It's probably a good place for me to start though while I'm learning and until I have a little money saved up.

I'm also a bit nervous about working with wall outlet voltages and hesitant to jump to AC power. Maybe I can dig up some old DC adapters for phones, game systems, etc...
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