40w Amp with the NTE equivelant of the the TDA2030

[darwindeathcat]

Hi All,

I've been looking for an amp build that was: 1)easy, 2)in the 30-40 watt range, and 3)used a single rail power supply so that it was 4)cheap. After untold hours of searching, I seem to have found the solution in two schematics that use the TDA2030 in conjunction with two power transistors. The first schematic comes from a kit offered by quasar electronics (UK) (**broken link removed**) (schematic is a pdf listed at the bottom of the description, and the other is listed on elecfree.com (https://www.elecfree.com/circuit/power-amplifier/30w-amp-otl-by-tda2030-transistor/
Power Amplifier : Power Amplifier OTL 30W by IC TDA2030 +Transistor).
My questions for the list are as follows:
1) I would prefer to build from the schematic from the quasar kit because I know it is proven, and it puts out more power. However, they (of course) do not list any component values other than the IC and Transistor types, and the input voltages. I'm more of a "follow instructions guy" when it comes to amp building, so I have no idea how to calculate these values. Can I use similar values from the other schematic (the elecfree one)? That schematic is very similar except that it uses different transistors and has a lower input voltage (and is missing the equivalent of C2, R1, and R3 in the quasar schematic).
2) As the TDA2030 seems to be hard to find here in the states, I have looked up the NTE replacement for it, which is the NTE1380. Looking over the datasheet, it *seems* to be an exact duplicate. Is anyone aware of any deviations from the TDA2030 pinout?
3) As far as the transistor types: I was unable to find the exact types from the schematics. Can I uses some sort of generic equivalents? Any suggestions on which ones?
4) Any other suggestions about these schematics?

Any help would be greatly appreciated!!!

 

[Hero999]

Why are you building this?

Is it because you want to learn or because you really need it?

If you just want a cheap amplifier then buy some computer speakers.

If you want to learn something then build it yourself. I don't know how educational the kit is, for example if it doesn't contain a description of how the circuit works then you're really wasting your time.

 

[darwindeathcat]

Well,
I am building this amp because of several reasons. I am a blues harmonica player, and I have been frustrated with with expense of good boutique and commercial amps (effectively removing them from the realm of possibilities), and the crappyness and poor power of cheap commercial amps that are within my budget that I have tried. I am a strong and true believer in DIY, and I have brought that ethic with me as I have forayed into audio electronics. I have already built my own Mics, effects, preamps, and Cabs. I was able to learn how to build them and to get my sound the way I wanted for prices that I could afford. Right now I am playing through a very cheap used PA amplifier that only puts out 15 or so watts of power. My DIY cab can handle up to 45 watts, so the sound of that combination of amp and cab sounds pretty crappy. Also, I have yet to try building a power amp, and thought that I could solve this problem while also learning something new. Electronics has become another hobby for me, and I enjoy it very much. I like the sense of satisfaction you get from building something yourself and and then being able to use it for other things you enjoy doing. I DO want to learn things, but I am not an electrical engineer, and I'm not trying to learn all the things that go along with being one. I was hoping for some useful advice from people who know more than me.
By the way, I am NOT planning on buying or building the kit. I was planning on building something based the kit's schematics, tweaking it a little if it seemed right. THAT's what I'm asking for help with here...

 

[Analog]

**broken link removed**

 

[audioguru]

You found two very old crappy amplifier circuits.
The Quasar one says 40W. They say to use up to a 45V power supply.
But the absolute max allowed supply voltage for the TDA2030 IC is only 36V.
If it uses a 37.5V supply then the TDA2030 will be at its max allowed supply voltage and the power output at clipping into a 4 ohm speaker is only 30W.

The Elec-free circuit uses a 24V power supply. Then its output at clipping into a 4 ohm speaker is only 12.5W.
When you double the power then the sound is only slightly louder. You need 10 times the power for the sound to be twice as loud.

National Semiconductor has some amplifier ICs with as much real power as you want at very low distortion.

 

[darwindeathcat]

You found two very old crappy amplifier circuits.
The Quasar one says 40W. They say to use up to a 45V power supply.
But the absolute max allowed supply voltage for the TDA2030 IC is only 36V.
If it uses a 37.5V supply then the TDA2030 will be at its max allowed supply voltage and the power output at clipping into a 4 ohm speaker is only 30W.

The Elec-free circuit uses a 24V power supply. Then its output at clipping into a 4 ohm speaker is only 12.5W.
When you double the power then the sound is only slightly louder. You need 10 times the power for the sound to be twice as loud.

National Semiconductor has some amplifier ICs with as much real power as you want at very low distortion.

I wondered about this. The data sheet indicates that the TDA2030 will only ever put out around 14w at peak. But isn't it being used as a gain stage to drive the two power transistors? I imagined that the extra gain was being produced at the transistor stage in the circuit. I also thought that the extra input voltage was needed for that stage too. Is this a fallacy?
Also, which National Semiconductor IC's are you referring to? The lm3885?
As for the "El Cheapo" mentioned by the other poster: That one's also on my list, and the build instructions at that site are really great. I'm still trying to make a decision though! Thanks for all the help!

 

[audioguru]

40W into a 4 ohm speaker is a sine-wave of 12.7V RMS. It is a sine-wave with 36V peak-to-peak. An amplifier has a voltage loss when the top or bottom transistors conduct so the power supply voltage for a 40W amplifier into 4 ohms must be about 42V.

The LM3875 has an output of 56W into 8 ohms with a 70V supply.
The LM3886 has an output of 50W into 8 ohms with a 70V supply or 68W into 4 ohms with a 56V supply.
I have seen these amplifier ICs paralleled and bridged for much higher output power.

 

[darwindeathcat]

That certainly clears things up a bit. I must admit that I was not entirely sure of how input voltage and output wattage were related. Many of the "gain clone" amp designs I have been sorting through on the internet use the LM3886 (I mistakenly wrote LM3885 before). I was specifically looking at this one http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=58&Itemid=26
As it was intended for instrument (guitar) amplification instead of as a HiFi amp. One of my main questions (to which I have had difficulty finding an answer) when it comes to IC amps is why they need +/- split voltage rails? The low power IC and transistor preamps I've built all ran on single positive voltage rails, allowing easy use of battery and wall wart power supplies. I was temped by the two TDA2030 designs because it seemed that that particular IC was capable of running on either a single positive supply or a dual positive negative supply. I could help keep build costs low by eliminating the need for an expensive center-tapped transformer, and instead use one of the of the more nicely filtered DC wall supplies I've collected from goodwill (all transformers, regardless of quality can be had at goodwill for $1)... I know this sounds a little chincey on my part, but I am a starving student, and I have to stick to my paltry budget!
I suppose I another way to use these transformers would be to use a voltage regulating IC to get me the +/- supply rails I need, but I wasn't too sure about that. If I am adamant about using a single DC supply, do you think it is a better idea to go with an LM3886-based circuit (like the one I link to above) with such a voltage regulator IC, or to try to make a discreet amp design like the El Cheapo?

 

[audioguru]

You won't find an 42VDC/2A/80W wall adapter. They are usually 9VDC/500mA/4.5W or less. It can power four LM386 amplifiers each with an output of 0.6W into 8 ohms.

A power amplifier with a single power supply voltage needs more parts such as the huge output capacitor that reduces bass frequencies.
An amplifier with a single supply voltage usually makes a loud POP when it is turned on and again when it is turned off.

 

[darwindeathcat]

To all who helped me, I think I have found my optimal solution. According to this (**broken link removed**) very informative and helpful website, one can use a computer power supply very successfully with a simple lm3875 gainclone amplifier. I have discovered many helpful guides on how to use an ATX power supply, of which I happen to have a couple in my parts bin already. Not only will I get +/-12v at a couple of amps for the power amp, but I can easily get multiple +9v supplies for multiple integral preamps and/or effects as well. I should be able to easily make a really nice, customized combo amp out of it, operating at a decent 30ish watts into 4ohms. I will most likely order the components from this site (**broken link removed**, so I can get a nice PCB as well, but I believe I can get all the necessary components from Digikey for around $25, and I could wire up the amp point to point. Overall, I believe that with the ATX power supply, and my hommade cab, the amp project should come in under $40 total. Which I believe is a fantastic budget.
By the way, at the goodwill, you can buy wall power supplies that were meant to go with specific appliances and electronics, rather than the generic 9v/500ma types you find at radioshack, target, etc. I have goodwill wall supplies that are rated (and measured with my multimeter) at, for example: 32v/2.5a, 47v/3a, 25v/2a, and several others... These all come with standard dc plugs, and could be easily used as power supplies for various electronics projects. They are quite large, and I believe there is plenty of room for there to be quality filtering caps in the housings... I have not opened any up, so I don't know for sure.

 

[audioguru]

Look at the datasheet for the LM3875.
With only plus and minus 12V for a supply, yhe power at clipping is only 5W with an 8 ohms load and only 8W with a 4 ohms load.

The -12V from the ATX power supply will be delivering its max 1A when two amplifiers deliver only 6W each. A little louder than a little clock radio.

My little computer speakers are 3W each but use 4 ohm speakers so they are powered from a 12V/1A wall-wart.

 

[darwindeathcat]

To all who helped me, I think I have found my optimal solution. According to this (**broken link removed**) very informative and helpful website, one can use a computer power supply very successfully with a simple lm3875 gainclone amplifier. I have discovered many helpful guides on how to use an ATX power supply, of which I happen to have a couple in my parts bin already. Not only will I get +/-12v at a couple of amps for the power amp, but I can easily get multiple +9v supplies for multiple integral preamps and/or effects as well. I should be able to easily make a really nice, customized combo amp out of it, operating at a decent 30ish watts into 4ohms. I will most likely order the components from this site (**broken link removed**, so I can get a nice PCB as well, but I believe I can get all the necessary components from Digikey for around $25, and I could wire up the amp point to point. Overall, I believe that with the ATX power supply, and my hommade cab, the amp project should come in under $40 total. Which I believe is a fantastic budget.
By the way, at the goodwill, you can buy wall power supplies that were meant to go with specific appliances and electronics, rather than the generic 9v/500ma types you find at radioshack, target, etc. I have goodwill wall supplies that are rated (and measured with my multimeter) at, for example: 32v/2.5a, 47v/3a, 25v/2a, and several others... These all come with standard dc plugs, and could be easily used as power supplies for various electronics projects. They are quite large, and I believe there is plenty of room for there to be quality filtering caps in the housings... I have not opened any up, so I don't know for sure.

 

[audioguru]

Look again at the datasheet for the LM3875.
With a power supply as low as plus and minus 12V, the power at clipping into a 4 ohm speaker is only 8W.
A power supply with plus and minus 22V will let the power be 35W.

The guy who wrote the article had four ATX power supplies with their +12V/6A outputs disconnected from ground and two were used as plus 24V and two were used as minus 24V. Then he got 43W into 4 ohms.