30W Audio Amp Pre-Amp & Power Supply Circuit for Stereo Setup + Simple LED Battery Tester

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#1 21669850 20 Sep 2013 14:19

Johan De Beer Johan De Beer

Anonymous

Post #1
21669850 20 Sep 2013 14:19

1) Want to build the 30W audio amp, but there is no circuit of the pre-amp and power supply. Also want to know what to do if I want a stereo system for this amp.

2) Want to build a simple LED battery indicator for testing AA; AAA; 9V Batteries. What circuit can I use?
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#2 21669851 20 Sep 2013 14:38

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #2
21669851 20 Sep 2013 14:38

*Audio Amp*
The "standard" input signal for an audio power amp is 1 V RMS. This should be available from any modern audio source whether it is a PC, an MP3 player, or a CD play. So, no preamp is needed.

What voltages does your 30 W audio amp require? For a stereo system two mono amps can be used and this is what all high-end systems use.

*Battery Tester*
Your battery tester circuit design will be driven by the type of battery chemistry. Do you have a particular chemistry in mind, such as Alkaline?
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#3 21669852 20 Sep 2013 15:41

Johan De Beer Johan De Beer

Anonymous

Post #3
21669852 20 Sep 2013 15:41

Thanks for the reply David.

1) I want to use the op-amp because I need the Treble, bass and volume. Actually I want to use it for my TV Audio output and maybe later as a guitar amp. Can I use 1 single amp, and 2 pre-amps? I post the circuits for you, I did get it from you site about 5 months ago, they said in the pre-amp section: twin concentric-spindle dual gang for stereo, for the Potentiometers, If it is the case, can I use 1 single pre-amp for stereo, how do I connect it to the power amp, or is ther a change in the circuit? Sorry I am in the darkness.

2) The battery's is the ordinary Alkaline. All that I want for this circuit to do: Take a eg. AA battery, 1.5V, put it in the test socket, and then show me the voltages between 0-1.5V, also for the AAA battery (1.5V), and the 9V as well 0 - 9V. I don't want to use a meter, LED's will do; say ± 1-4 in a row, maybe more in a row for a 9V. A meter is too expensive.
#4 21669853 20 Sep 2013 16:15

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #4
21669853 20 Sep 2013 16:15

One amp with two preamps will give you mono audio, but that works. You can also drive the one amp with two audio sources through a resistive network that combines the signals and has two volume controls. I can post such a circuit here.

You can actually use the amp without a preamp. The preamp is there only to provide Bass and Treble control, volume and balance control. High end audio systems never have tone controls and I don't use them with my vacuum tube stereo. It is not uncommon for two separate volume controls to be used. That gets around the need for a volume control and a balance control and it also gets around the issue of two ganged potentiometers having to track closely.

About 20 years ago I built a battery indicator that used a National Semiconductor part and 10 LEDs. I can see if National still makes the part.
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#5 21669854 20 Sep 2013 18:02

Johan De Beer Johan De Beer

Anonymous

Post #5
21669854 20 Sep 2013 18:02

Ok Dave I understand. But I need a treble, bass and volume control. Sometimes I play music CD's or music video's on the DVD player, and then I need the controls. I don't have a Hi-Fi stereo that I can use so I have to make use of the TV and DVD player. Music through the TV without a surround sound or Hi-Fi don't sound so good. But please post the circuit for me that you have on the resistive network I will appreciate it.

The semiconductor part that you mention, is it a LM3914? If it is: a very nice IC, I do have a circuit that use this IC, but it is only to monitor a 12V car battery, but maybe I can use this circuit for the job that I want to do, with a few adjustments, I can post it to you if you want, I will need your help if there are adjustments. You see Dave I can build the project etc. but I can't do circuit designing, if there are adjustments to be done, I need help with the design...

Thanks alot for your help so far
Johan
#6 21669855 20 Sep 2013 18:53

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #6
21669855 20 Sep 2013 18:53

Yes the part is the LM3914 and I see that Digikey has it in stock for $2.15.

It requires a power supply of 3 volts or more and I would power it from a standard 9 volt battery. A momentary push switch can be used to apply power and to apply a load to the battery under test.

I can post a circuit suitable for testing an AA Alkaline cell.
#7 21669856 21 Sep 2013 00:38

Johan De Beer Johan De Beer

Anonymous

Post #7
21669856 21 Sep 2013 00:38

Hi Dave, thanks! Sorry I was sleeping. Please post the circuit for me? I do have the IC in stock, what do I own you for all your help? You can post it to my Email jdebeer56(_at_)gmail.com

Thanks again
Johan
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#8 21669857 21 Sep 2013 17:46

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #8
21669857 21 Sep 2013 17:46

http://www.ti.com/lit/ds/symlink/lm3914.pdf

The circuit on page 2 of the datasheet is configured for 1.5 volts full scale when R1=6.8k and R2=1.3k.

For 9 volts full scale R1= 1.1k and R2=6.8k.

Since you need Bass and Treble controls the passive audio input circuit won't be suitable.
#9 21669858 03 Oct 2013 23:41

Jibby Benjamen Jibby Benjamen

Anonymous

Post #9
21669858 03 Oct 2013 23:41

You can use LM3914.
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Topic summary

The discussion addresses building a 30W audio amplifier with pre-amplifier and power supply circuits for a stereo setup, alongside a simple LED battery tester for AA, AAA, and 9V alkaline batteries. For the audio amplifier, a standard 1 V RMS input signal from modern sources typically negates the need for a preamp; however, to achieve treble, bass, and volume control, an op-amp based preamp is recommended. Using two mono amplifiers is advised for stereo output, as commonly done in high-end systems. A resistive network with two volume controls can combine two audio sources into one amplifier, though this yields mono output. Tone controls require a dedicated preamp stage, as passive input circuits lack bass and treble adjustment.

Regarding the LED battery tester, the LM3914 LED bar graph driver IC is suitable for indicating battery voltage levels. The IC operates from a 3V or higher supply, commonly powered by a 9V battery, and can be configured for different voltage scales by adjusting resistor values (e.g., R1=6.8k and R2=1.3k for 1.5V full scale; R1=1.1k and R2=6.8k for 9V full scale). A momentary push switch can apply power and load during testing. The LM3914 circuit can be adapted from existing designs for car battery monitoring to test alkaline cells with multiple LEDs indicating voltage ranges without using a meter.
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30W Audio Amp Pre-Amp & Power Supply Circuit for Stereo Setup + Simple LED Battery Tester

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