Gain, Preamp, Efficient Driver

pra3718

Member
2009-01-13 7:29 am
Excuse me, if it is discussed before.

My current project is tda7265 with Gain=33 (3.3K/100R) Power by 22 (+/-) sounding good but not much louder. Assume, my source is poor or my speaker is not that much efficient, which I can not change because, already I have purchased it. I have only two options.

Option 1 : Increase the gain between 39 to 47 ( Simple for me. )

Option 2 : Adding simple preamp gain between 1 to 2

Which option is good.

Thanks & Best Regards.
 
Does it not go any louder, because the gain is too low? Then both options will work. 25 W into 8 Ohm corresponds to ~14,1 V. With a gain of 33 you need 428 mV for max output power. Modern CD players tend to have more than 2 V which requires no further action. Normal line level should be around 360 mV, so a gain of 39 would be okay. Other devices like MP3 players can have less, e.g. 150 mV. For such a source you would need a preamp with a gain of 3. Check what your source delivers and choose accordingly.

Or does it not go any louder, because you have reached the amplifier's power limit? You will notice, when the amplifier starts to sound distorted. Then neither option will help you.
 

pra3718

Member
2009-01-13 7:29 am
measure the maximum output of your source.

AndrewT, you are right I should measure the maximum output of my source. If it less than it should be then only I need preamp. But I don't know how to measure it.:sad:

My source is DVD Player. It has various features...

Channel : Stereo / 5.1 = If I switch stereo to 5.1 loudness drops.
Speaker : Big / Small = If I switch Big to Small loudness drops.
Subwoofer : On/Off
Prologic II : On/Off/Auto = To change this loudness varies.
It has preset equalizer = If I change NONE to ROCK,LIVE,POP,TECHNO loudness varies.
It has 3D surround effects = To change this loudness varies.

If I keep all features silent and listen only on stereo mode then only it sounds louder.

Now what is your comment.
 
Hi,
connect an interconnect to the main outputs of the player.
Temporarily solder a 10k resistor across the far end of the interconnect.

Play the loudest music source you have and measure the maximum AC voltage across the 10k resistor.
Compare that voltage to the specification given in the users Manual.

I wonder if there is a standard way to generate test tones to put onto the audio tracks of a video DVD to allow checking of maximum output levels?
Any links anyone?
 
Test CDs with defined signal levels, e. g. 0 dB or -10 dB are available. Google turns up several sites where you can download test tones or test signals which can then be copied to a CD/DVD. Software for loudspeaker design and testing often comes with built-in tone generators.

Before you measure the output level with a normal multimeter, check the frequency range in which it works best. If no specs are given, use a tone in the range below 200 Hz. Some meters (at least older ones) don't work well at higher frequencies, because they usually are meant for 50 Hz to 60 Hz only.
 

pra3718

Member
2009-01-13 7:29 am
Assume I need Preamp. What is your advice for attached picture.

Is 100R optional ?
 

Attachments

  • myPreamp.GIF
    myPreamp.GIF
    2.4 KB · Views: 264

Sangram

Moderator
Paid Member
2002-09-25 11:01 am
India
prashant, I'm responding to your email. The problem is insufficient acoustic output from a speaker you cannot measure (and thus have no idea how much power you need).

I'm not keen to do the math on the thread, but it seems to me that you need a lot more power than you have currently, and that will mean a bigger amplifier and more rail voltage along with increased gain. I think you should crunch a few numbers.

Adding a preamp will increase the input voltage going to the power amplifier, but the output is limited by the physical ability of the chip and the power supply voltage and current capabilities.

I don't know how loud you like it and how big your room is/how far you sit from the speakers, but it would seem that you may only be satisfied with PA levels, which means you have to get a very high efficiency driver and a lot more juice.

I have been able to scare neighbors a block away with 10 watts of power and some 106dB+ efficient Alnico FR speakers when I was 19. That was 20 years ago, my requirements for loudness have progressively decreased but it's an idea you can use.

The preamp circuit you've drawn is extremely wrong, the entire input section is doomed to terrible peaking in the highs and too low of an input impedance. ESP has some good circuits, like PB has stated.

Good Luck.
 

pra3718

Member
2009-01-13 7:29 am
Thank you sangram & pacificblue, Please continue...

Somewhere I must be wrong.

but it would seem that you may only be satisfied with PA levels,

I would be happy if my system produce loudness & sound quality similar to 22" CTV. (videocon tda7265)

but the output is limited by the physical ability of the chip and the power supply voltage and current capabilities.

tda7265 25+25Watts in which condition what is the MINIMUM input voltage, gain, speaker efficiency, power supply voltage and current capabilities.

Anyway, I build audio systems for my hobby. I am not an electronics man.

Please find updated attached file again. I am looking for preamp schematic having treble boost and not bottom cut.
 

Attachments

  • myPreamp.GIF
    myPreamp.GIF
    7.7 KB · Views: 131
I build audio systems for my hobby. I am not an electronics man.
Have you reached the stage where you need to invest some time in your hobby, to help you understand what you want and/or need?

I can see you looking for +-18Vdc from a 16-0-16Vac transformer.
Do you know when the regulators will drop out as the mains voltage drops?
 
Last edited: