TDA7294 sub-amplifier

Danko · 7th April 2006, 11:05 PM

Hello!

I would like to build an amplifier to my subwoofer, with TDA7294. Can I make a low-pass filter with the TDA7294, if I connect paralell with R3 a capacitor?
I have to calculate that capacitor with the C=1/(2*pi*f*R3) equation, am I?

I attached the schematic, where you can see R3.

Thanks in advance!

Bazukaz · 8th April 2006, 01:48 AM

Hi,
For a sub-woofer , you need a 12 db/octave filter at least(i would prefer using 18-24db).
If you connect a cap in paralell to R3 , you will not get more than 6db/octave.

Also , the phase of subwoofer and main speakers must be matched , or there will be frequency response nonlinearities at crossover point.
You can find some examples of active filters here :
http://sound.westhost.com/projects-3.htm

Also , there are lots of programs , like LSPCad , which allow you to calculate any order active filters easily.

Regards,
Lukas.

Danko · 8th April 2006, 06:53 AM

Oh, I just wanted to avoid +1 circuit :-)

I have biuld a few of this:
http://sziget.mine.nu/~danko/aramkor...filter-sch.png

I'm going to build another one.

Thanks, Bazukaz, for explaining why required an active filter!

Original Burnedfingers · 20th June 2006, 10:15 PM

Just curious to see if anyone has used this one for a full range "CHIP AMP" and if so how it performed.

ilimzn · 21st June 2006, 09:14 AM

Yes - there is an old thread about it. To my ears it performs surprisingly well, but then I did use a separate well filtered and regulated supply for the input part of the chip. This requires some precautions to be taken in order to produce correct power supply sequencing (what voltages come at which time at power up), which mostly can be satisfied with two diodes. Chosing proper (higher) voltages for the input power supply also gets you rid of the bootstrap capacitor.
With good attention to wiring and layout, this amp is dead quiet - no hum, no noise. The suond is detailed but has some of that MOSFET 'slightly withdrawn mids' character - which is heared whenever you listen to a recording that was overly mangled in the studio. It also clips far more gracefully than the bipolar LMxxxx amps, which gives it a much better sound on transients.
Still, keep in mind this is for an amp that has a special power supply arrangement designed to halp all this.

8th April 2006, 06:53 AM	#3
Danko diyAudio Member Join Date: Apr 2004 Location: Hungary	Oh, I just wanted to avoid +1 circuit :-) I have biuld a few of this: http://sziget.mine.nu/~danko/aramkor...filter-sch.png I'm going to build another one. Thanks, Bazukaz, for explaining why required an active filter! __________________ Best regards, Danko

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8th April 2006, 01:48 AM	#2
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	Hi, For a sub-woofer , you need a 12 db/octave filter at least(i would prefer using 18-24db). If you connect a cap in paralell to R3 , you will not get more than 6db/octave. Also , the phase of subwoofer and main speakers must be matched , or there will be frequency response nonlinearities at crossover point. You can find some examples of active filters here : http://sound.westhost.com/projects-3.htm Also , there are lots of programs , like LSPCad , which allow you to calculate any order active filters easily. Regards, Lukas.

20th June 2006, 10:15 PM	#4
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Just curious to see if anyone has used this one for a full range "CHIP AMP" and if so how it performed.

21st June 2006, 09:14 AM	#5
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	Yes - there is an old thread about it. To my ears it performs surprisingly well, but then I did use a separate well filtered and regulated supply for the input part of the chip. This requires some precautions to be taken in order to produce correct power supply sequencing (what voltages come at which time at power up), which mostly can be satisfied with two diodes. Chosing proper (higher) voltages for the input power supply also gets you rid of the bootstrap capacitor. With good attention to wiring and layout, this amp is dead quiet - no hum, no noise. The suond is detailed but has some of that MOSFET 'slightly withdrawn mids' character - which is heared whenever you listen to a recording that was overly mangled in the studio. It also clips far more gracefully than the bipolar LMxxxx amps, which gives it a much better sound on transients. Still, keep in mind this is for an amp that has a special power supply arrangement designed to halp all this.

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