TDA20XX AMP power supply question/s.

[jogina111]

Hi, I'm planning on making another practice amp and this time, using a TDA2030/40/50. So I checked what components I'm missing. The only problem I saw is these amp chips  USES SPLIT POWER SUPPLIES YET WHAT I have left is a 21v laptop power supply.. I'm also planning on powering the preamp from the same power supply since it got a lot of power. Any tips on how I can get this to work?
Also, i have some lm317 I think I'm gonna use to limit the voltage to the preamp.. So which chip is best to use with the 21v power supply?

[armdnrdy]

How much current draw are you looking at for the whole thing?

[jogina111]

10 to 35 watts maybe. I think it would depend on which  chip can take the power supplies voltage without the regulator chip but if 12 to 21 volts, 1 ampere would be enough to run both preamp and power amp at a good wattage and plenty of headroom, then even  a 10 watter would be great....

[armdnrdy]

Do some research on the MC34063A DC to DC converter IC to design a bipolar power supply using your 21 volt power supply.

The MC34063A can accept up to 40 volts and can output in excess of 1.5 amps.

There are online calculators for the external components.

[jogina111]

Do I really need a bipolar supply? i saw some schematic using a single rail power supply.. And I wanna know what disadvantages it has...But if the MC34063A is a necessity, then, I hope i can find one on stores on my town...If I'm to use a MC34063A, is 1.5A enough to get the most of the tDA2050?

[armdnrdy]

Hi, I'm planning on making another practice amp and this time, using a TDA2030/40/50. So I checked what components I'm missing. The only problem I saw is these amp chips  USES SPLIT POWER SUPPLIES

I based my suggestion from your statement.

I would imagine that if you are planning to build an amp using a TDA2030/40/50 and the design calls for a bipolar power supply then unless you want to redesign the whole thing....then yes a bipolar supply.

Looking at the data sheet, it looks like the TDA2030/40/50 can run on a single supply as well.....so look around for a design with a single supply.

[jogina111]

Yeah, but I would like to know if using bipolar design will yield better results compared to the single rail. And if I can still GET FULL POWER FROM THE 2050 USING SINGLE RAIL..

[Jdansti]

Have you looked at the TDA2025?

http://www.bsselektronika.hu/pdf/ic_etc/tda2025.pdf

No bipolar supply needed. A 20V PS gets you over 20W.

[jogina111]

ooops..cant find a 2025 john,  I'd be using that one if I found something like that from shops here... Since only 2030,40 are the only ones available, I gotta find a way to work this out. I've already  got a schematic using a single ended PSU and it should put out 15w I think..yet, I doubt the 2030 could endure 21volts...
I'm gonna post this just to verify if the 2030 could really handle 24volts which I believe is beyond the chip's maximum operating voltage..http://www.eleccircuit.com/wp-content/uploads/2009/11/circuit-tda2030-amp-otl-15w.jpg
help please...

[Jdansti]

The data sheet for the TDA2030 says max Vs is +/- 18V (36), and it says, "Typically it provides 14W output power (d = 0.5%) at 14V/4Ω; at ± 14V or 28V, the guaranteed output power is 12W on a 4Ω load and 8W on a 8Ω (DIN45500)."   I don't know enough to be able to vouch for the safety of using the monopolar 24V supply as shown on the schematic you referenced, but maybe someone more knowledgable can help out.

[jogina111]

would  an 18v 1A psu be enough to get 10 or 14 watts from the tda2030?

[Jdansti]

^The data sheet specifies that the peak output current is 3.5A, so I assume that the capacity of the power supply has to be at least that. However, that might be for the maximum voltage which is 36V. If you we're to use an18V supply, would the current draw be half (1.75A)?  I'm not sure, but it seems that 1A might be low. Perhaps a person with a few more brain cells than I have can confirm this.

[PRR]

> Do I really need a bipolar supply? i saw some schematic using a single rail power supply..

No you do NOT need a bipolar supply. And you do not want a voltage converter, a significant complication.

21V DC with a perfect amplifier will make 7.4Vrms, which is almost 8 watts in 8 ohms or 16 Watts in 4 ohms. Somewhat less with any real-world amplifier.

Use the hook-up on the first page of the TDA2030 datasheet. There's a PCB layout on page 6. For guitar you can go 1,000uFd for the output cap. With 21V supply all caps may be 25V rating.

> I think..yet, I doubt the 2030 could endure 21volts...

Read the datasheet.

---------------------

> data sheet specifies that the peak output current is 3.5A, so I assume that the capacity of the power supply has to be at least that.

No. Imagine low supply voltage and high load impedance. The chip would shut-down at 3.5 Amps, *but* with 21V in 8 ohms the peak current is at-most 10.5V/8r= 1.3 Amps (and less because you can't really get 10.5V peak with a 2*10.5V supply).

[Jdansti]

^ Thanks, Paul. If he decides to use an 18V/1A supply, again using Ohm's Law, he would be looking at 9V/8r= 1.125A, and actually less than that, which would put the current draw around 1A. This is also the output rating of his PS, so it seems that the 18V/1A PS would be pushed to its limit. Correct?

[jogina111]

Thanks Paul and john, so that actually means that my power supply is actually low to get the full power from the 2030 right? And to get the most out of it, I actually need more voltage since the PSU I have is 4amps. Am I right?

[Jdansti]

>Thanks Paul and john, so that actually means that my power supply is actually low to get the full power from the 2030 right?

To get the "full power" of the amp, the max Vs is 36V, but I don't think they recommend actually running it that high.

Depending on the speaker impedance:
Vs= 18V, output is ~4-6W
Vs= 21V, output is ~6-10W
Vs=32V, output is ~14-24W




>And to get the most out of it, I actually need more voltage since the PSU I have is 4amps. Am I right?

I don't understand your question.  A current rating of 4A just tells you the limit of how fast the PSU can pump out electrons. It will only deliver what the circuit demands.

A few posts back, you asked if you could use an 18V/1A PSU. I think the current rating of 1A might be cutting it too close.

In the OP you said you have a 21V PSU. Is that one rated at 4A?

4A is plenty to run this at any "allowable" voltage. You don't need "more voltage" because of the 4A rating. The amperage rating of any PSU just let's you know if the PSU can pump out electrons fast enough to keep up with the current demand of the circuit you are powering. 

Using Ohm's Law (I = V/R), and assuming that R (the resistance of your load) is fixed, then I is directly proportional to V. The higher the voltage (how "hard" the PSU is pushing), the higher the current (the rate of electron flow).

As Paul pointed out, a 21V PSU would need to have a minimum current rating of ~1.3A: (21V/2)/8Ω

If we do the same calculation for a 32V PSU, it would need to have a current rating of 2A: (32/2)/8Ω

Does this answer your question?

[jogina111]

Yes it does. thanks.. and sorry for the misunderstood part. Its just an idea of using LM317 to lower the 21v PSU to 18v... thanks for the help.. next is the Preamp. 

[jogina111]

Ok, so for the preamp, I want it to be a jfet booster to a tonestack to a buffer stage circuit. Or the shaka HV from aron.Is it ok if I put a voltage regulator on the Vcc rail to give 18v to the preamp? Or would a voltage divider do?

[Jdansti]

It depends on the preamp you're looking at. You might have to adjust the JFET bias to get it work. For example, Tillman says that his preamp can be powered by 18V, but you won't see much headroom improvement:
http://www.till.com/articles/GuitarPreamp/

You would need to change the 6.8K drain resistor to something that would give you around 6V on the drain. You could do this with a trimmer or use a regular pot to find the right resistance that gives you the right bias voltage AND sound (fine tune the bias by ear).

[PRR]

> a 21V PSU would need to have a minimum current rating of ~1.3A: (21V/2)/8 ohms

That's the PEAK current.

For a square-wave, half the time we pull current from the + supply, half the time from the - supply (here that's also called ground).

So assuming a good-size capacitor (>1000uFd) across the rails, the power supply itself only feels the average of 1.3A half the time: 0.65A.

In audio it is traditional to assume Sine Waves. The 1.3A peak happens only for an instant and then fades to zero (then to 1.3A the other way for an instant). The magic number is 0.707. The average power supply current is 0.707*0.65A= 0.46A.

For other supply voltages: It is useful to picture this as a resistance. 21V/0.46A= 46 ohms.

In general, a single totem-pole (not bridge) power amp looks-like about 6 times the load impedance.

(The number on the calculator is 5.65*load. However we have ignored the losses of a real amplifier. In most amps the voltage losses dominate. A number "2V each side" was tossed into this or a nearby thread. Maybe 1V(!!), often 4V, sometimes more. When you include losses the number is usually higher, and "6" is a good approximation.)

So a 4 ohm load "acts like" 24 ohms to the supply. If supply is 12V, the maximum average supply current is 0.5A.

Now when you get into Bridge Mode amps (most car radios; also Tiny Giant) you have to count carefully. Say the speaker is 4 ohms. But there are two amplifier units (often in one chip). Each one sees half the load, 2 ohms. So each one is 2*6= 12 ohm load on supply. There's two of these. Total 6 ohm load on supply. At 12V it pulls 2 Amps. This is why a TG power supply only needs to be >2A. (However most laptops need much more, so 3A-6A supplies are readily available, and that's fine.)