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Old 7th December 2012, 01:28 AM   #11
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Having no bias isn't the end of the world.
You tend to hear crossover distortion at lower levels.
At medium to higher power outputs you wont notice it.
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Old 7th December 2012, 05:29 AM   #12
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Quote:
Originally Posted by nigelwright7557 View Post
......You tend to hear crossover distortion at lower levels.
At medium to higher power outputs you wont notice it.
Well, that's somewhat true when we use serious amplifiers at pro. entertainment levels but with newb home audio and imaginary power that won't often be used above low levels, they won't sustain medium to high levels for long at all. Speakers to handle the high power are going to be more expensive than the amplifier.

They'll typically just sit in the garage or bedroom playing into domestic speakers and sounding like fingernails on a chalkboard.
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Old 7th December 2012, 08:56 AM   #13
djk is offline djk
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The 'music power' rating of the TDA is 100W at 10% distortion, 70W at 0.5% distortion.

The extra outputs will allow it to drive a lower impedance, so you might get 150W/4Ω with a stiff 40V supply.

An 8Ω resistor should be hooked from the output of the TDA to the speaker out.
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Old 7th December 2012, 08:58 AM   #14
AndrewT is offline AndrewT  Scotland
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Originally Posted by jaycee View Post
I'd say around 90W into 8 ohms..........
I am going to say that is an over estimate.

If the supply droops by 3V and the losses through the amplifier account for a further 3V then the maximum peak voltage into the load is 40-[3*2] = 34Vpk.
The maximum output power would be 34^2/16 = 72W into 8r0.
If the two losses are 4v each, then max Power would be 64W into 8r0.
If the two losses are 5v each, then max Power would be 56W into 8r0.

These are the kind of assessments that readers of data should be doing, rather than accepting wild claims that cannot possibly be anything other than downright lies.

"Back of a fag packet" assessments do not need to be accurate, they are fast and every Member who is interested in building amplifiers should be capable of learning how to do this. It is DIY after all.
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Old 11th December 2012, 12:16 PM   #15
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Quote:
Originally Posted by AndrewT View Post
I am going to say that is an over estimate.

If the supply droops by 3V and the losses through the amplifier account for a further 3V then the maximum peak voltage into the load is 40-[3*2] = 34Vpk.
The maximum output power would be 34^2/16 = 72W into 8r0.
If the two losses are 4v each, then max Power would be 64W into 8r0.
If the two losses are 5v each, then max Power would be 56W into 8r0.

These are the kind of assessments that readers of data should be doing, rather than accepting wild claims that cannot possibly be anything other than downright lies.

"Back of a fag packet" assessments do not need to be accurate, they are fast and every Member who is interested in building amplifiers should be capable of learning how to do this. It is DIY after all.
comvencioanl best to use the TDA7294 in bridge mode. It's much better.
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Last edited by SERGIODS; 11th December 2012 at 12:20 PM.
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Old 11th December 2012, 01:02 PM   #16
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its a simple fact that both of the original circuits are rubbish from any possible aspect IE sound quality , stability, and rated power .

The only interesting here is to try to understand why ( this should be the benefit of this thread and only )

In theory and given as a fact low losses and perfect power supply the circuit might work and even might produce original specs taking also as a fact that we talk about classic tests which is 1KHZ sine wave at resistive load .

In a speaker inductive load security/safety mechanisms inside the tda will not allow the same performance

By the same logic the resistor of 8 ohms from TDA to actual load might lift the TDA away from the problems and increase performance by a bit .

Also let us not forget that he basis of all these circuits is the original application of the TDA 2030 but on a single rail and coupled with a capacitor in the output of course...

Now for those who don't remember the specific geriatric circuit featured lower distortion eventhough not so much power , extremely musical , and very tolerant to weird/low loads long cables and so on and on ....

Kind regards
sakis
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Old 11th December 2012, 10:23 PM   #17
AJT is offline AJT  Philippines
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Quote:
Originally Posted by nigelwright7557 View Post
Having no bias isn't the end of the world.
You tend to hear crossover distortion at lower levels.
At medium to higher power outputs you wont notice it.
yes...and for PA duties no big deal really....
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Old 11th December 2012, 11:42 PM   #18
wahab is offline wahab  Algeria
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Originally Posted by djk View Post
T

An 8Ω resistor should be hooked from the output of the TDA to the speaker out.
That s the solution to keep on working on AB class at low power
but the actual most efficient value is about 1R.
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Old 12th December 2012, 12:09 AM   #19
JMFahey is offline JMFahey  Argentina
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To make a long story short:
1) dear sergiods: don't build that amp.
2) Yes, *maybe* the designer tried to extrapolate the old "boosted TDA2030", why not?
But he missed biasing and a couple extra details.
Of more importance is that the TDA7294 is not a good choice here.
a) it does not swing close to the rails , wasting necessary voltage (while a discrete drive stage or a dedicated driver chip is meant to do that) and
b) its power dissipation and current capability is wasted .
Plus its inherent rail voltage limit is way below what the the output transistors can handle.
To drive power transistors run from +/- 40V, you really don't need much more than what a couple TIP31/32C can offer.
But, hey!!, we all began one way or another !!!
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