How can i remove standby and mute from TDA 7294 ? - diyAudio
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Old 25th April 2011, 03:55 AM   #1
sunny is offline sunny  India
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Default How can i remove standby and mute from TDA 7294 ?

How can i permanantly remove those standby and mute from TDA 7294 Bridge Amp circuit ? I read somewhere in this forum to connect pins 3 and 9 directly to positive supply and in other post it is mentioned to leave pins 3 and 9 as open (NC ). So which method is correct ?

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Old 27th April 2011, 06:41 PM   #2
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Cable pin9 from amp1 to amp2
Cable pin10 from amp1 to amp2

On one amp, power up the mute, pin 10, with a 10k resistor.

On one amp, power up the standby, pin 9 with a 20k resistor--To avoid a loud noise at power-up, cause that 20k resistor to charge up a 22uF cap for a delay on feature.

See also:
http://www.svet-el.si/download/Brutu...0W-S%20ang.pdf <--- bridge amp for 8 ohm and 16 ohm speakers
and
http://www.st.com/stonline/books/pdf/docs/1057.pdf <--- CHIP MANUFACTURER'S DATASHEET

As ST explains, the standby and mute pins (9 and 10) need voltage but Not too much current. Therefore, the minimum investment to operate mute and standby is a resistor.
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Old 27th April 2011, 06:53 PM   #3
AndrewT is offline AndrewT  Scotland
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wire the standby and mute pin to be permanently inactive. This prevents the standby function operating and prevents the mute function operating.
You are being short sighted, you will find why these two functions were included by the manufacturer after you have deactivated them
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Old 28th April 2011, 01:36 AM   #4
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Concur. You don't want to deactivate the standby function.

Even an amplifier as tiny as this (pictured below), has the standby function employed to slightly delay power up.
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File Type: jpg TDA7294-Mini.jpg (63.1 KB, 289 views)
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Old 28th April 2011, 09:04 AM   #5
sunny is offline sunny  India
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I just finished building this bridge amplifier.I connected like this:

Cable pin9 from amp1 to amp2 and connected directly to +ve supply without any resistor.
Cable pin10 from amp1 to amp2 and connected directly to +ve supply without any resistor.

Now is there any harm to speaker and Chip Amp by using this connection?

Sunny
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Old 28th April 2011, 09:15 AM   #6
AndrewT is offline AndrewT  Scotland
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what does the datasheet say about the connections you have made?
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Old 28th April 2011, 10:00 AM   #7
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Quote:
Originally Posted by sunny View Post
I just finished building this bridge amplifier.I connected like this:

Cable pin9 from amp1 to amp2 and connected directly to +ve supply without any resistor.
Cable pin10 from amp1 to amp2 and connected directly to +ve supply without any resistor.

Now is there any harm to speaker and Chip Amp by using this connection?

Sunny
Yes, that's harmful--too much current! ONE event of load protect will draw all current and break loose inside. Click here and read ---> http://www.st.com/stonline/books/pdf/docs/1057.pdf

Why do it wrong on purpose?

Doing it right takes only 3 more parts.
20k resistor and 20uF cap for standby (pin or cable)
10k resistor for mute (pin or cable)

P.S.
If you don't want mute and standby inside your chip then buy a different chip!
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Old 28th April 2011, 10:01 AM   #8
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The datasheet spec is to use 10k and 20k pull-up resistors (connected to PS+) as posted earlier.
The chip might get damaged because of no current limiting under some conditions...maybe...dunno.
By the sound of comments made already, the mute and standby/delayed start up are there for good reason....to avoid thumps and screams out of your speakers during power up/power down.
Datasheets are published for good reason....start reading them.

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Old 28th April 2011, 11:44 AM   #9
sunny is offline sunny  India
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ok,now i've connected standby pins 9 of both chips with 22k resistor and 22uf capacitor to +ve supply.
Mute pins 10 of both chips are connected to +ve supply through 10k resistor. Is this ok ?

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Old 28th April 2011, 12:22 PM   #10
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http://www.st.com/stonline/books/pdf/docs/1057.pdf
Figure 17: Single Signal ST-BY/MUTE Control Circuit......PAGE 17.

Eric.
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