Two interesting circuit diagrams

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?

*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?

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.

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.

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

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.

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

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.

You can use LM3914.