Help with power supply for a TDA2030 amp

[luckett]

I'm planning to build a TDA2030 amp with a single power supply based on the datasheet schematic driving an 8 ohm speaker.  I was initially going to power it with a split power supply from the GGG schematic, but I came upon an old printer power supply that I want to use if will work ok. I have a few questions about the feasibility of using that PS. This is just an amp to use while breadboarding, so I don't need to extract all the performance the chip is capable of.  I just need enough clean headroom to prototype stuff.

The 2030 is rated for +/-18V or +36V, 3.5A peak output current.

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000128.pdf

http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf


1)  The printer PS is rated at 13.5V/1A, but measures about 17V without a
load.  Why is it measuring that high?  Will the output voltage drop when the
PS has a load on it?


2)  The 2030 datasheet says the wattage output is about 4W with 17V, but is 1A
enough current?   


3)  The single supply schematic has a 2000uf cap on the output to the speaker,
but there is no cap on the split supply schematic.  What does this cap do?


4)  What about building a circuit to give me a split supply from the printer
PS so I can build the amp with a split supply.  That will give me the option
to swap out the PS for another PS like the GGG +/-PS if I'm not getting enough
power out of it.  Good idea?  Bad idea?  Any schematics you could point me to
for this?


5) Any suggestions for what I should be looking for in a transformer if I do
build the GGG PS for +/-18V?

[J M Fahey]

1)  The printer PS is rated at 13.5V/1A, but measures about 17V without a
load.  Why is it measuring that high?  Will the output voltage drop when the
PS has a load on it?

Normal on cheap unregulated PSUs.

2)  The 2030 datasheet says the wattage output is about 4W with 17V, but is 1A
enough current?

Somewhat tight but for experimenting will do.

3)  The single supply schematic has a 2000uf cap on the output to the speaker,
but there is no cap on the split supply schematic.  What does this cap do?

In the Single Supply mode, you have 1/2 the PSU voltage there. The capacitor allows audio through but blocks DC.

4)  What about building a circuit to give me a split supply from the printer
PS so I can build the amp with a split supply.  That will give me the option
to swap out the PS for another PS like the GGG +/-PS if I'm not getting enough
power out of it.  Good idea?  Bad idea?  Any schematics you could point me to for this?

Use it as single supply.

5) Any suggestions for what I should be looking for in a transformer if I do
build the GGG PS for +/-18V?

12+12V AC , 25/35 V.A.

[luckett]

Thanks!  I'll give it a try with the single PS and see how it goes. 

I suppose I should put a regulator in the circuit.  The 78xx datasheet says "The input voltage must remain typically 2.0V above the output voltage even during the low point on the input
ripple voltage."

Does this mean that I need to use a 7815 as a fixed output regulator that will drop the voltage to 15V from the 17V coming out of the PS ?

http://www.fairchildsemi.com/ds/LM/LM7815.pdf

That will drop my output wattage down to about 2W.  Do you think that will give me enough clean volume?

[Enzo]

Why do you want a regulator?  I don't see the need.

I haven't looked at the data sheet. Was that 4w at 17v for a 17v split supply?  (+8.5v and -8.5v)?   Or did they mean +17 and -17?


Oh, I guess rough calculations show the former.

[joecool85]

Looks like the bare minimum is +/- 8v which would give you 3w @ 8ohms or 5w @ 4ohms.  So your PSU will just barely make it work, but should suffice for a low power amp.  You could always upgrade the power supply later for more wattage.  No need for a regulator.  You will need to set it up for bipolar power though.

[luckett]

Why do you want a regulator?  I don't see the need.

I haven't looked at the data sheet. Was that 4w at 17v for a 17v split supply?  (+8.5v and -8.5v)?   Or did they mean +17 and -17?

I neglected to mention that I was planning to put a TL072 buffer in front of the amp.  The TL072 is rated to 18V and JM Fahey implied that the PS is unregulated so I want to be sure I don't fry the TL072.  I guess I could use a 25V max jfet like a 2N5458 instead and avoid having to use a regulator.

~4W for 17V single supply or +/-8.5V

You could always upgrade the power supply later for more wattage.  No need for a regulator.  You will need to set it up for bipolar power though.

Why would I need to set it up for bipolar?  Are you saying I should build it for +/-8.5V now (instead of +17V single supply) so I can upgrade it to a bigger split PS in the future?

[joecool85]

You could always upgrade the power supply later for more wattage.  No need for a regulator.  You will need to set it up for bipolar power though.

Why would I need to set it up for bipolar?  Are you saying I should build it for +/-8.5V now (instead of +17V single supply) so I can upgrade it to a bigger split PS in the future?

I think the TDA2030 requires bipolar voltage supply, if someone knows otherwise, please correct me.

**edit**
According to the datasheet you can do bipolar or single supply.  So no worries there.  Also, technically +/-6v (12v total) is the bare minimum to operate, it just isn't on the graphs so it's hard to say how much output you'd have at that level.

[luckett]

If I did want to split the 17V to +/-8.5V, how would I go about doing this?   I found some examples of splitting the PS using a MAX1044, but it's only rated up to 10V on the input.  Is there a chip with a higher voltage rating that I can use for this?

[Loudthud]

You could use another TDA2030A to split the supply, but why? Most chips you find can't handle the current needed to drive a speaker. Unless your power supply has a center tap, a split supply is more trouble than it is worth. Just use the single supply circuit. The bonus is that you don't have to insulate the TDA2030 from the heatsink. The tab is grounded.

[luckett]

You could use another TDA2030A to split the supply, but why? Most chips you find can't handle the current needed to drive a speaker. Unless your power supply has a center tap, a split supply is more trouble than it is worth.

I don't plan to do it.  I was just curious how it would be implemented.  That explains why I couldn't find any examples of it being done.

[Enzo]

I think you will find the TL072 is rated to 18v on each rail - +18 and -18.  SO that is 36v across the IC.  Your 18v supply will not stress the 072 at all.

[luckett]

I think you will find the TL072 is rated to 18v on each rail - +18 and -18.  SO that is 36v across the IC.  Your 18v supply will not stress the 072 at all.

Thanks for pointing that out.


Is the 2200uf cap on the output acting as an RC highpass filter with the speaker?  The corner would be at 18Hz coupled with a 4 ohm speaker.  With an 8 ohm speaker, can I use a 1000uf cap (20Hz corner) here instead?

[Enzo]

No, it is blocking DC, preventing it from hitting the speaker.

Well I guess that makes it a highpass blocking 0Hz.  I am sure it does act as you suggest, but that is not its primary function.  And I don't think that in a guitar amp 20Hz or 18Hz matters much

Remember, with a single supply, the output will be sitting at half the supply voltage, so if you run the amp from 18v, then there will be 9v on the IC output pin.  That cap lets the signal voltage pass, but not the 9vDC.

[luckett]

I know that it's there to block the DC, but is the 1000uf big enough to to serve that function.  If the 1000uf works, I can use that with my 8 ohm speaker and keep the freq rolloff adequately low.

[J M Fahey]

Yes you can.
In fact 1000uF is a popular choice.