Minimus is a small amplifier capable of delivering up to 9.4W + 9.4W to a pair of 4Ohm speakers and up to 5.2W + 5.2W to a pair of 8Ohm speakers. This amplifier has controls for volume, balance, bass and treble, and a switch for loudness compensation. Unlike some of my other amplifier related projects, it doesn't rely on external supply rectification and filtering. As so, Minimus has its own rectifier and a generous filter capacitor for that purpose. Minimus only requires a simple external AC step-down transformer as power supply. If you are using 4Ohm speakers, you should use a 60VA transformer. However, if you are using a pair of 8Ohm speaker with this amplifier, you can use a smaller 30VA transformer with no problem.

This project uses a TDA2009 as output stage. Although this power amplifier is not very efficient, it was chosen for its simplicity and reliability. It requires very few components. Like Quattuor, Minimus also uses an LM1036 for audio control. However, in this particular project, the IC is supplied via the LM7810 voltage regulator. Not only the regulator will protect the audio control IC from excessive voltage, but it will eliminate completely the humming caused by supply voltage ripple. Plus, added the reliability of the TDA2009, it makes Minimus a hard beast to kill, since it can withstand reasonable voltage transients present in poor quality transformers.

List of components:
C1 – 15mF electrolytic capacitor (35V);
C2/5/19/27 – 100nF polyester capacitor (63V);
C3/14/22 – 10nF polyester capacitor (63V);
C4 – 100µF electrolytic capacitor (35V);
C6-9 – 220nF polyester capacitor (63V);
C10 – 47µF electrolytic capacitor (16V);
C11 – 22µF electrolytic capacitor (35V);
C12/20 – 10µF electrolytic capacitor (16V);
C13/21 – 330nF polyester capacitor (63V);
C15/23 – 470nF polyester capacitor (63V);
C16/24 – 2.2µF electrolytic capacitor (6.3V);
C17/25 – 220µF electrolytic capacitor (35V);
C18/26 – 2.2mF electrolytic capacitor (35V);
D1-4 – 1N5400 rectifier diode;
D5 – Red LED (GaAsP/GaP)
HS1 – 33°C/W passive heatsink (for TO-220);
HS2 – 2,4°C/W passive heatsink;
IC1 – LM7810 voltage regulator (with HS1 heatsink);
IC2 – LM1036 audio control;
IC3 – TDA2009A audio power amplifier (with HS2 heatsink);
J1 – 5.5mm x 2.1mm DC socket;
J2 – 3.5mm TRS socket (stereo phone socket);
JW – 26AWG stranded wire;
R1 – 1,5KR carbon resistor (5% tol., 1W);
R2/4/6/8 – 47K potenciometer (10% tol., 1/8W);
R3/5/7/9 – 47K carbon resistor (5% tol., 1/8W);
R10/16 – 1K carbon resistor (5% tol., 1/8W);
R11/17 – 560Ohm carbon resistor (5% tol., 1/8W);
R12/18 – 2.7K carbon resistor (5% tol., 1/8W);
R13/19 – 1K carbon resistor (5% tol., 1W);
R14/20 – 39Ohm carbon resistor (5% tol., 1/8W);
R15/21 – 1Ohm carbon resistor (5% tol., 1/8W);
S1 – SPST switch;
S2 – SPDT switch.

Electrical parameters:
- Va min = 9.62V RMS
- Va max = 20.64V RMS
- Ia (Va = 15V RMS, Z = 4Ohm) = 3.424A RMS
- Ia (Va = 15V RMS, Z = 8Ohm) = 1.907A RMS
- P (Va = 15V RMS, Z = 4Ohm) = 51.35W
- P (Va = 15V RMS, Z = 8Ohm) = 28.60W

Amplification characteristics (each channel):
- Input impedance: 967.7Ohm
- Input sensitivity: 316mV RMS
- Gain (pot R4 centered): 26.87dB (22.06V/V)
- Gain (pot R4 all to left or all to right): 28.45dB (23.48V/V)
- Frequency response (-3dB, Z = 4Ohm): 44-80000Hz
- Frequency response (-3dB, Z = 8Ohm): 22-80000Hz
- Output power (Z = 4Ohm): 9.4W
- Output power (Z = 8Ohm): 5.2W

Translations:
- Agudos - Treble;
- Alimentação 15V~ 50Hz - 15V~ 50Hz supply;
- Balanço - Balance;
- Canal direito - Right channel;
- Canal esquerdo - Left channel;
- Entrada de áudio estéreo - Stereo audio input;
- Graves - Bass;
- Compensação de sonoridade - Loudness compensation;
- Secção - Section;
- Volume - Volume (no translation here).

 

Is the max power so low because your home has walls made of rice-paper?

I made an amplifier similar to yours about 35 years ago for the beach. It had a sub-woofer (4" speaker) with 6W and two satellite speakers (3" speakers) with 3W each. It was powered from a Nicad battery. I didn't use tone controls because the speakers had a good frequency response.

 

Is the max power so low because your home has walls made of rice-paper?

No, fortunately my walls are made of bricks. If you read the datasheet you will see that the TDA2009 is somewhat inefficient. I could power it using a 16VAC supply so as to give out more power, but that would result in a far greater risk of burning the IC, since the worst case scenario would result in a possible max voltage with repeated peaks of about 28.7V, accounting that the sinusoidal wave can have peaks 1.06 times above the nominal voltage and that an unloaded high power transformer can have an increased voltage 1.2 greater than loaded. Fortunately, you can subtract the rectifier bridge dropout voltage to that, but it is still risky. I though about using two bridged amplifiers, but a bridged TDA2009 will have 1% to 2% of distortion, considering that a bridged amplifier will have typically 10 times more distortion when bridged.

However, the TDA2009 is a good amp, since its frequency response is extended to 80KHz, and although we can't hear frequencies above 20KHz, they are important to music since they bring out some instruments and add brilliance. Plus, it has only 0.1% to 0.2% distortion and it is short circuit proof, unlike other amps that would die at the smallest transient.

The solution for a low power amplifier that is meant to be small and "portable", considering you want to ear music really loud, is to use decent speakers with 90dB (1W/1m) sensitivity or above.

I made an amplifier similar to yours about 35 years ago for the beach. It had a sub-woofer (4" speaker) with 6W and two satellite speakers (3" speakers) with 3W each. It was powered from a Nicad battery. I didn't use tone controls because the speakers had a good frequency response.

Sorry, but I can't imagine a 4'' sub-woofer. I have a pair of 5'' speakers that are considered to be bass-midrange. Plus, you would you power a 12W amp with a nicad battery?

 

My 4" speaker had a resonance at 90Hz when sealed and I added a tuned port at 40Hz. With a little bass boost then it produced 40Hz through the port just fine. 30Hz was low level but still audible.
My pc speakers are only 3" but they have a low resonant frequency, a long throw and huge magnets. They produce frequencies down to about 80Hz.

My 35 years old beach sound system used bridged and bootstrapped amplifier ICs driving 4 ohm speakers so the Ni-Cad battery was only 7.2V (six C cells).

A bridged amplifier has double the max output current of an amplifier that is not bridged. So the distortion is slightly more than doubled, certainly not 10 times more unless the amplifier simply cannot produce that much current.

 

A bridged amplifier has double the max output current of an amplifier that is not bridged. So the distortion is slightly more than doubled, certainly not 10 times more unless the amplifier simply cannot produce that much current.

The TDA2009A datasheet states clearly that the bridged amplifier will have 1% distortion.

My 4" speaker had a resonance at 90Hz when sealed and I added a tuned port at 40Hz. With a little bass boost then it produced 40Hz through the port just fine. 30Hz was low level but still audible.
My pc speakers are only 3" but they have a low resonant frequency, a long throw and huge magnets. They produce frequencies down to about 80Hz.

Well, I was just criticizing the fact that you called your "tiny" 4'' speaker a sub-woofer, as oposed to your comment on the Quattuor project, that uses 4" full-range speakers:

Will the stickers help the tiny speakers produce some bass sounds??

You are always making bad impressions and bad reviews about my projects. You once said that my "Quattuor" amplifier would not reproduce more louder than headphones sitting on a chair. Really, so 92.70dB can be produced by headphones sitting on a chair at a distance of one meter? If you don't believe that 4W can be loud, check my videos on YouTube (and I was not even using full volume). You always point defects that we can't cope with and I never saw a constructive critic from you. Let me tell you something: I could tune Quattuor to reproduce bass lower to 40Hz, but sure it wouldn't have a flat frequency response and I would end with a major bump in the bass section. Is that how you say that you are a audiophile, by calling others stupid? I'm sorry, but I don't see an audiophile using an enclosure greater than the one that should be used, or calculating a port different, unless you want to end with a bass boost noticeable up to at least 150Hz.

Sorry for my aggression, but I'm fed up with you. Thanks to your bad reviews, my projects always end up being forgotten!

 

The datasheet shows an 18W/1% distortion into 8 ohms bridged amplifier but its power supply voltage is not shown. Any amplifier can have its input too high and produce 1% clipping distortion. A single-ended amplifier is shown with 0.25% distortion at clipping with an 8 ohm and a 4 ohm load.

EDIT:
The power supply voltage for the TDA2009A power amplifiers is 19V, not 10V. So the output power is as rated here.

 

EDIT:
The power supply voltage for the TDA2009A power amplifiers is 19V, not 10V. So the output power is as rated here.

A voltage of 19V is supplied to the TDA2009, and a regulated voltage of 10V is supplied to the LM1036. The amplifier will have the rated max wattage as shown under 10% clipping distortion.

The datasheet shows an 18W/1% distortion into 8 ohms bridged amplifier but its power supply voltage is not shown. Any amplifier can have its input too high and produce 1% clipping distortion. A single-ended amplifier is shown with 0.25% distortion at clipping with an 8 ohm and a 4 ohm load.

You can assume that Vs is 24V, and the 1% distortion is due to THD + N distortion. The distortion when clipped in case of excessive input voltage can be far more than 10%. However, in terms of wattage, the output wattage will not increase significantly if it passes 10% distortion due to clipping.

Note: This amplifier (Minimus) will not clip if the voltage of the input signal is equal to or smaller than 316mV RMS.

 

The datasheet for the TDA2009A does not show graphs of output power and distortion when two ICs are bridged.
But since the current in each amplifier is exactly double when bridged then the graph for 4 ohms can be doubled when an 8 ohm speaker is driven from a bridged amplifier.
The single-ended graph for distortion when the supply is 24V and the speaker is 4 ohms and shows an output power of 12.5W but another graph shows clipping beginning at an output of 10.5W when the distortion is 0.25%.

So the bridged amplifier with a 24V supply and an 8 ohm speaker has an output of 21W at 0.5% distortion.

Why am I talking of 1% distortion and you are talking about an awful-sounding 10% distortion? Hi-fi is 0.05% distortion.
Why don't you make a real audio amplifier with LM3886 ICs? They cost the same as one litre of beer in a bar. The distortion is only 0.03% at 60W into 4 ohms without being bridged.

 

The datasheet for the TDA2009A does not show graphs of output power and distortion when two ICs are bridged.

The TDA2009A datasheet from ST specifies that the bridged configuration will have 1% distortion (quite noticeable) right above the corresponding schematic diagram. Refer to figure 16 in the datasheet.

Why am I talking of 1% distortion and you are talking about an awful-sounding 10% distortion?

The power graph for 10% distortion states the maximum power, that occurs when you have 10% distortion. It doesn't mean that the IC will always have 10% distortion. That is clipping distortion. The THD+N distortion for this IC is 0.2%, and that is the distortion that this IC will produce as long as you don't overdrive it.

The single-ended graph for distortion when the supply is 24V and the speaker is 4 ohms and shows an output power of 12.5W but another graph shows clipping beginning at an output of 10.5W when the distortion is 0.25%.

One graph shows power without clipping. So such power for this amp (Minimus) would be 4.5W at 8Ohm and 8W at 4Ohm. However, the rated power I'm referring to is the real max power (clipped, 10% distortion). It is useful to refer to the real max power when calculating values such as heatsink thermal resistance.

Why don't you make a real audio amplifier with LM3886 ICs? They cost the same as one litre of beer in a bar. The distortion is only 0.03% at 60W into 4 ohms without being bridged.

Already thought about it, but there is no point spending the extra $$$ when most noise is introduced by the LM1036. The LM1036 alone has a THD of 0.06%, but can be maxed to 0.3%. The TDA2009A is cheaper. Besides, the TDA3886 ideally requires a split power supply. That means it will operate better with a split power supply instead of a single one. In the future I'm planning to make a hi-end Hi-Fi amp using the TDA3886, but using discrete op-amps for filtering and equalization. However, this amp sounds pretty good!

 

Hello AAC!

Finally the PCB for this project is finally available for download. Just refer to the start of the thread.