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Old 4th January 2014, 05:55 PM   #521
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Quote:
Originally Posted by danielwritesbac View Post
Guesstimation table for new production chips:
V7 TDA7293 = Real higher cost TDA7293
V6 TDA7293 = Real low cost TDA7294H (max 25+25vac transformer)
TDA7294 = TDA7295 or dirt cheap cull (terrible audio quality)
TDA7295 = TDA7295 or dirt cheap cull (terrible audio quality)
TDA7296 = Real TDA7296 OR a cheap substitute

This also affects authorized vendors. The ST chips that I have purchased from Mouser and Digikey have been identical to those in the eBay kits.

You really can buy an old-production quality TDA7294; but, it won't have "TDA7294" printed on the casing, AND all 15 pins will work.

Attempting to purchase TDA7296's sometimes works, and I guess that is because old stock of the less popular chip hasn't run out yet.
The use of the HCA topology by an integrated (monolithic) amplifier like an outline of a TDA7293V must actually be a good idea.
ckeck out this threads:
Chip Amp based on the topologies from Yamaha MX-10000 and Quad 405
Yamaha's Hyperbolic Conversion Amplification (HCA) Circuit
Marriage from "ZEN" - and ordinary class AB topology about HCA - why not realized ??
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Old 4th January 2014, 07:10 PM   #522
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Default Some curiosities.

First of all, the TDA7294S Datasheet (all 15 pins work, like TDA7293): http://www.startfetch.com/fidelityfo...t/tda7294s.pdf

And next, in the the attachment, that TDA729X "Hi Fi" schematic that has been floating around the internet for some years. That thing was prone to explode so I have edited it to replace the BY diodes with more efficient MBR diodes to decrease explosions.
I didn't design this one!
It looks somewhat impractical and may produce speaker burning offset. Also 50x is beyond the 43x maximum, so the gain divider is serving up a catch function rather than helping resolution. That doesn't look appropriate, but it may produce interesting tone effects.
Now the good part:
The power circuit is worth a closer look . . . in the attachment. This MBR schottky diode bypass can allow playing with separate rails, without cracking the chip's substrate.
Attached Images
File Type: gif TDA7293-hi-fi.gif (21.7 KB, 420 views)
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Last edited by danielwritesbac; 4th January 2014 at 07:22 PM.
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Old 12th January 2014, 02:31 PM   #523
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Hi guys,

I've made this layout for a stereo TDA7294 board. What do you think of the routing and the placement of the components? Any suggestions are welcome

Click the image to open in full size.
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Old 14th January 2014, 02:06 PM   #524
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Old 26th January 2014, 08:38 PM   #525
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any trick to spot fake 93 and 94 ?

there are some cheap ones on reichelt.de
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Old 27th January 2014, 01:38 AM   #526
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Quote:
Originally Posted by marconi118 View Post
any trick to spot fake 93 and 94 ?
here are some cheap ones on reichelt.de
Yes.

For the 93, just make sure all the pins work. It includes a TDA7293-specific bootstrap cap hookup, a built in clipping indicator pin, and it has a preamp output pin (the output of the built in small signal voltage amp). Version 7 is the higher tolerances power chip with a higher price. Version 6 has the voltage tolerances of TDA7294, a very low price, and functions nicely. A real version 6 routinely sells for $2 and is Exactly the same part, with the same markings, with the same audio performance as the $7 part at Mouser.
With V6, you can use a 24+24vac or 25+25vac transformer.
With V7, you can use a 28+28vac or 30+30vac transformer.


For the 94, here's how to tell:
If it sounds nice like a TDA7293, that's Old production TDA7294.
If it sounds dreadful but doesn't explode, it is a New TDA7294.
If it explodes, it is a lower voltage amp in a big TDA7294 casing.

*Some of the new plonkers and fakes can be redeployed as a decent ~12W amplifier by setting lower gain and using a 14+14vac transformer (max).

**The physical location of the terrible performance on New production TDA7294 is observable due to the bootstrap arrangement; therefore, I would like to guess that Post#54 will let you turn a bad 70W amp into a good 40W amp. Basically, the voltage amp power needs connected to the output buffer power via schottky diodes, so that the voltage amp's power supply voltage cannot go smaller (there is a fragile parasitic diode internal to the chip's negative rail, in the core, and we bypass this with a more efficient and more sturdy schottky diode to prevent exploded chip). And, then you run the voltage amp about 8v higher so you can remove the bootstrap cap. This is also your opportunity for "Front End On Regs" quality enhancement. With the output buffer run at 8v lower, you get 40W@8R, 60W@6R, 80W@4R, Music Power which is the point of clipping; HOWEVER, the built in limiter disallows bass beyond 45W RMS power. Therefore I think that ilimzn's (post #54) dual rails, no bootstrap, plan for a higher quality 40W amp doesn't reduce usable output power except for 5W worth of noise is gone and you won't miss that. Remember to install the schottky before you play with quad rails. You can then figure out how to waste 8v on the way to the output buffer OR boost 8v on the way to the internal small signal voltage amp. That makes the bootstrap cap removable and thereby removes the audio problem of the new production TDA7294.
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Last edited by danielwritesbac; 27th January 2014 at 01:45 AM.
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Old 1st February 2014, 06:52 AM   #527
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That was too wordy! Sorry. 2nd try:
The easy way to spot a Fake TDA7294 is when it says TDA7294 on it; AND, the easy way to spot a Fake TDA7293 is when less than 15 pins work.
Obviously, place your bets on the TDA7293 when buying new.
And, as with all of audio, price does not indicate performance.

Was that better?
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Old 1st March 2014, 10:43 PM   #528
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Old 2nd March 2014, 09:13 AM   #529
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Quote:
Originally Posted by danielwritesbac View Post
Yes.

For the 93, just make sure all the pins work. It includes a TDA7293-specific bootstrap cap hookup, a built in clipping indicator pin, and it has a preamp output pin (the output of the built in small signal voltage amp). Version 7 is the higher tolerances power chip with a higher price. Version 6 has the voltage tolerances of TDA7294, a very low price, and functions nicely. A real version 6 routinely sells for $2 and is Exactly the same part, with the same markings, with the same audio performance as the $7 part at Mouser.
With V6, you can use a 24+24vac or 25+25vac transformer.
With V7, you can use a 28+28vac or 30+30vac transformer.


For the 94, here's how to tell:
If it sounds nice like a TDA7293, that's Old production TDA7294.
If it sounds dreadful but doesn't explode, it is a New TDA7294.
If it explodes, it is a lower voltage amp in a big TDA7294 casing.

*Some of the new plonkers and fakes can be redeployed as a decent ~12W amplifier by setting lower gain and using a 14+14vac transformer (max).

**The physical location of the terrible performance on New production TDA7294 is observable due to the bootstrap arrangement; therefore, I would like to guess that Post#54 will let you turn a bad 70W amp into a good 40W amp. Basically, the voltage amp power needs connected to the output buffer power via schottky diodes, so that the voltage amp's power supply voltage cannot go smaller (there is a fragile parasitic diode internal to the chip's negative rail, in the core, and we bypass this with a more efficient and more sturdy schottky diode to prevent exploded chip). And, then you run the voltage amp about 8v higher so you can remove the bootstrap cap. This is also your opportunity for "Front End On Regs" quality enhancement. With the output buffer run at 8v lower, you get 40W@8R, 60W@6R, 80W@4R, Music Power which is the point of clipping; HOWEVER, the built in limiter disallows bass beyond 45W RMS power. Therefore I think that ilimzn's (post #54) dual rails, no bootstrap, plan for a higher quality 40W amp doesn't reduce usable output power except for 5W worth of noise is gone and you won't miss that. Remember to install the schottky before you play with quad rails. You can then figure out how to waste 8v on the way to the output buffer OR boost 8v on the way to the internal small signal voltage amp. That makes the bootstrap cap removable and thereby removes the audio problem of the new production TDA7294.
interesting to know and completly new for me. Jeff Rowland, Linn and some other manufacturers use this ICs and often the LM4766 just because by BjT power devices are many fakes resp. counterfeits on the market - go to
how to identify fake transistors
So use the avoid of transistors nothing more.
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Old 2nd March 2014, 12:33 PM   #530
jayadev is offline jayadev  India
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Quote:
If it sounds dreadful but doesn't explode, it is a New TDA7294.
Hi Daniel,

Please help me understand the meaning of 'sounds dreadful'.

How bad it sounds,does it sound like as if improper bias, coarse, grainy or is it very subtle audible to discerning ears?

I have made 7294 amp 7 years ago to my friends and they still plays very well.
Seeing this I have purchased a few more lately. One of them I have used for a sub-woofer amp,I felt nothing to be concerned.

Regards
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