Introduction, and question about power supplies.

[docz]

Hello everybody, I'm new to this forum and new to this wonderful world of electronics. I got hooked after I took it upon myself to restore my dads old Teisco 10 tube amplifier from the 50s. After a lot of great help and effort I managed to fix it and restore it to it's original state. So now I got the taste for electronics. Since tube gear is extremely expensive, I started my next project which was building a Ruby Amp. It souds great! A pity it is not loud enough to work as a full band amp.

So I thought I would be able to use the LM386 as a preamp and then get something more powerful to power it. I bought a TDA2030 amplifier board on Ebay, my idea was to use it in a speaker to make it active. And see if it would be good enough to use as a surround speaker. Anyways I ended up getting three boards with a total of six TDA2030s because the first two boards got damaged from shipping.

My idea was that maybe I could bridge a couple or more of these chips to get the power I need to power a 2x12 cab and get the great sound of the Ruby out to the masses. But my first bump in the road is a power supply. This thing needs +15V and -15V as well as 0V. The only transformers I can find with 2x15V and 0V are really expensive! About the same prices as the high voltage transformers used in tube amps. My question is then, is there a cheaper solution to this? If so what can I use? Can I use two 15VDC wallwarts in series to get 15-0-15?  A 15V 4A laptop charger costs like $2 on ebay, compared to the 2x15 toroid that costs $80 it is quite tempting to try it out! But since I have no idea if this will work, I thought I'd ask you guys to see if this is a stupid thing to do.

Cheers,

DocZ

[J M Fahey]

Start with one TDA2030 to practice (anyway 15W are more than enough for the garage), search for a 12+12V, 25VA to 50VA, that's to say 12+12V , from 1A to 2A.
That *can't* cost $80 !!!
The 12+12VAC will give you 16+16VDC , which are fine.
Those Laptop chargers sound interesting, but are weird pieces of equipment and doubt you can really get them for $2, at least the working kind variety.
Shadowy characters can sell you a "charging brick" and send you .... a finely wrapped *real* brick. :trouble , if you get what I mean.

[docz]

I do have a couple of 12V 1000mA wallwarts. I used one for B+ on the Ruby amp. Can I hook those up in series for positive, negative and ground?

I am from Norway, and the only place that sells these kinds of things I have found, charges $50 - $100++++ for transformers. The laptop chargers cost $2, but shipping is $10, my guess is that the seller ramps up the shipping charge to compensate for the low product price, this is quite common on Ebay. But it might be real bricks as you say

Thank you for your reply,

DocZ

[Koreth]

Do the wall warts put out 12VDC or 12VAC? 12VAC, after being put through a full wave rectifier and a couple smoothing caps is closer to 16 or 17VDC. 12VDC has already been rectified and is just that, 12VDC. You an run a TDA2030 on 12VDC, but you won't have as much headroom or power output than if you gave it a higher supply voltage.

[docz]

Do the wall warts put out 12VDC or 12VAC? 12VAC, after being put through a full wave rectifier and a couple smoothing caps is closer to 16 or 17VDC. 12VDC has already been rectified and is just that, 12VDC. You an run a TDA2030 on 12VDC, but you won't have as much headroom or power output than if you gave it a higher supply voltage.

They are 12VDC, I thought I could wire two of them in series, with a center tap for 0V

DocZ

[Koreth]

It sounds to me like that would work for a quick and dirty but functional power supply. Connecting the -12V from one transformer to the +12V from another sounds like it should work for a virtual center tap/common/neutral/whatever the appropriate term is.  However since I'm still in the learning the theory stage of power supply design, I'd sooner take the advice or opinion of someone who has actually designed and built a power supply over my own.

[J M Fahey]

If you already have them, try them  , what can you loose?.
Power a TDA2030, hook a speaker and some preamp, even a 1 transistor job will do, or an LM386 used as a preamp, don't remember the project name but somebody will post it ..... and have fun ....
Watch/smell for smoke/melting varnish though, just in case.
After 1/2 hour practice at high levels, you can trust them.
Don't you have a mail order electronics shop in Norway?
Can't you buy from the UK or France , Holland, Belgium, Italy?
What's the E.U. useful for?
Post any shop links you have, and good hunting.

[phatt]

A quick pic might help,
I used a couple of plugpaks while building several Discrete Poweramps, saves a whole lot extra work if you want to just find out if something works.
Be aware a lot are not well filtered and you may need to add some extra Caps for filtering. Not all are Full wave Rectified this can lead to excess ripple issues.
Phil.

[docz]

Well there are a couple of stores that sell these things online. But they are rather expensive. A toroid 30VA 2x12V costs about $50USD, I can find a 6VA for $12USD but I don't believe that is going to cope with the TDA2030. The datasheet for the TDA2030 says it needs a 40VA supply, and 60-80VA for two bridged chips, those toroids cost over $100. Why are transformers so expensive anyway? Isn't it just a chunk of iron wrapped in copper? Haven't we used those for several decades? One would think that the prices of these devices that are practically inside of everything would drop due to the demand.... oh well...I thought solid state would be cheaper than valve amps because the components are cheaper, but it seems it is the same with any amplifier, the transformers and speakers make up 80% of the cost.

I will try to hook those wall warts together and see if I get a signal. Can I use anything line-level to test it?

DocZ

[pyromaniac_]

Well there are a couple of stores that sell these things online. But they are rather expensive. A toroid 30VA 2x12V costs about $50USD, I can find a 6VA for $12USD but I don't believe that is going to cope with the TDA2030. The datasheet for the TDA2030 says it needs a 40VA supply, and 60-80VA for two bridged chips, those toroids cost over $100. Why are transformers so expensive anyway? Isn't it just a chunk of iron wrapped in copper? Haven't we used those for several decades? One would think that the prices of these devices that are practically inside of everything would drop due to the demand.... oh well...I thought solid state would be cheaper than valve amps because the components are cheaper, but it seems it is the same with any amplifier, the transformers and speakers make up 80% of the cost

Yes, transformers are expensive (copper is expensive and it's also expensive to produce a transformer) but NOT that expensive as you say. That online stores would rip you off that bad? I could get a 2x12 VAC 50 VA toroid for about 250 SEK at www.electrokit.se. Don't know if they ship to Norway but you could ask, anyway keep looking 50 USD for a 30 VA toroid sounds even more than it would cost to get one from www.elfa.se (which I think do ship to Norway but are very expensive anyway). So keep looking, 50 USD for a 30 VA toroid is way to much if you ask me.

[J M Fahey]

Hi docs.
Out of curiosity I searched a little, can't believe you must pay those incredible prices, maybe you got a little confused with exchange rates.
DigiKey NORWAY offers in its page :
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=786735&k=transformer%2024V%2030VA
eight transformers, all dual primary (115/230) , 24V center tap secondary, from 30VA  11.5Euro , 36VA 13.6Euro, 43VA 15.25 Euro, and so on, up to 175VA 32Euro. 1 Euro approx. 1.20U$S
The transformers are exported from US warehouses, but *they* pay all Customs duties, you have to pay VAT (like on a Norsk product) which I guess will be around 10%.
Shipping is free on orders over 65 Euro, it shouldn't be that expensive for your order, unless you ask for express next day delivery.
What strikes me as odd is that if you can have a Canadian made highest quality transformer (Hammond), shipped all the way from the US, for such a price, a Norwegian supplier can't charge you more than that.

[Koreth]

Maybe part of the problem is that you're looking at toroidal transformers? An EI core transformer, while bulkier, is easier to make, and thus costs less. Yes, a toroidal transformer is smaller and leaks less EMF noise, but they also have higher inrush current, and thus all other things equal, are more likely to blow fuses on power up than an EI core tansformer.

[docz]

I just built the power supply, hooking them up in series does indeed produce +12_0_-12V My main concern is the current. What will happen if the power supply cannot supply enough current? Is it just that it will not be as powerful as it can be? Or will it overload and burn up the transformers? I read somewhere that this chip needs a 40VA power supply, do I calculate that from the input or output?

DocZ

[J M Fahey]

Hi docz.
Now that you built it, just play.
Watch for funny smells, smoke, too hot cases, do not wait for molten plastic.
Touch them every 5 minutes.
If you find them unbearably hot, forget them; if they are only warm after an hour or two, you got lucky.

[docz]

It worked! - atleast first test worked out. I played music through the amp board with my makeshift power transformer. The wall warts did not get any hot. This was just all layed out on my work surface, I will do more test when I get this to the next stage.

What noticed was this: Treble control didn't have much effect, other than bring in RF interferance. Volume was not extremely high, but it had a lot of kick. I was also really amazed by the eight inch testing speaker I used. It cost me $10 so I was a bit scheptical but it delivered.

Next steps:

• Add mains fuse
• Add secondary fuse
• Bridge the two chips
• Build a chassis
• Build speaker / combo cabinet
• Add a preamp circuit
• More testing
• Figure out a way of measuring current while testing... I think I need to do some reading on this one.

If I find that I need more current, can I add more of these wall warts in paralell? Will two 12V 1A in paralell give me 12V 2A?

DocZ