Point 2 Point (no PCB) for TDA7293, TDA7294, TDA7295, TDA7296. - Page 11 - diyAudio
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Chip Amps Amplifiers based on integrated circuits

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Old 18th April 2013, 06:43 PM   #101
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Default Got the new little CRC power supply done!

It has 2200u first caps, and the tank/reservoir section is 6x2200u per rail. The CRC resistor value is 0.3R and diode bypassed to prevent sag. The dual bridge rectifier is Fairchild Stealth. It has 2.2K drainers at first caps locale. It has orange LED indicators for each rail, near the output side. That board is 2-5/8" x 8" size.
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Old 22nd April 2013, 06:41 PM   #102
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Hi there Mr Daniel. this past days a friend came with a 8¨+tweeter active speaker;
it was a discrete amp about 50W, it was so burnt with a big hole thru the board.
So with the same psu as original, put in a 3886GC this i had it almost finished ( less
PS) so just try it! Maybe not sogood design its almost the same at M Feuerbacher
site.Tried it and sounded good,think it needs tweaking, but my friend just loved it and as he needed for playing, just took it like that.
Now reading thru your postings, i´m aware now that maybe the 7293 bridged conf. that i was considering, now i see what your answer was; the ps xformer is the limiting factor,
so i´ll try with a single chip, and go for your first post schem.
my xfrmr is center tapped, good quality , dual bridges cannot be used? trying to find out.
Well enough, have some duties before solder time.Parallel chips dont increase output
cause its an 8 ohm spkr. right? maybe just to make it more reliable? what would you suggest?
Anyway i think i´ll settle with 68k-2k7-220u for the feedback circuit i has a preamp and equalizer integrated at the input board.
Ok thanks for all your attention and time to answer our postings.
Martin Martinnez
Uruapan Michoacan
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Old 22nd April 2013, 08:22 PM   #103
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Sorry i meant to ask if dual rectifiers can be used wcenter tap
xfrmer! maybe i wasn´t clear.
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Old 23rd April 2013, 04:04 PM   #104
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Single chip is fine for 8 ohm speaker.
More research is going on here: Optimizing TDA7294 Output
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Old 23rd April 2013, 04:06 PM   #105
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Quote:
Originally Posted by martin martinez View Post
Sorry i meant to ask if dual rectifiers can be used wcenter tap xfrmer! maybe i wasn´t clear.
No, but center tap transformers can be modified, at some risk of slightly unlevel rails. I wouldn't do that modification for single chip to one 8 ohm speaker. The center tap should work well enough for a monobloc.
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Old 27th April 2013, 02:14 PM   #106
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Quote:
Originally Posted by martin martinez View Post
Parallel chips dont increase output cause its an 8 ohm spkr. right?
No, this is not a discrete amplifier.
The theory is correct, except for chip amplifier limiter engagement point of about 45 watts, whereupon the LM3886 will begin screeching an internal hard clipper or TDA7294 will omit the bass via internal soft limiter and in either case, it becomes more difficult to hear bass when you turn it up past about 45 watts or so. The limiter influence is either mild or inactive until you turn it up and wonder why it isn't as good as a discrete amp.

With your transformer, a PARALLEL chip amp and an 8 ohm speaker, the on-chip limiter (45W+45W=90W) can't interfere with your 70W application. Each chip sees half of 70W, 35W apiece and then on-chip limiters never switch on.

So, I have to report that the Parallel TDA7294S/TDA7293 Master/Slave configuration is ready to use and fits your application. This is the easiest parallel chip amp possible. I will be using it to upgrade my receiver as soon as the LM3886's are removed.

Notes:
At this time, I am currently working on "energetic efficiency" for the solo chip. I may have different news to report upon completion of that task. It is far more difficult with just 1 chip. And thus, the 1-chip application does not yet have the chair flipping power of the parallel amp.

It is possible to put the feedback resistor and feedback-shunt resistor(s) trackside, on bottom of the boards, in which case they sound almost identical to a point to point effort (no board related tone).
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Old 27th April 2013, 05:24 PM   #107
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thanks!
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Old 27th April 2013, 05:59 PM   #108
Art M is offline Art M  United States
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It is such a shame to waste intelligent resources
on these Nasty little integrated chips designed for WalMart applications.

Limiters don't have any specific affinity for program material in the
ordinary case. Tweets can trigger circuit protection as well as Woofs.
All amplifiers sound sickly once the output hits the rails.

Trying to apply magic components to these dogs will not render any
substantial performance improvements. These chips are great for
trying to make a silk purse out of a sow's ear.
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Old 28th April 2013, 07:20 PM   #109
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Or a much smaller silk purse, without the sow's ear problem.

An ordinary design of discrete amplifier offers one practical thing the chip doesn't offer, and that's output transistor linearity at higher power. For example. . .

A chip amplifier's built in output transistors are a bit smaller.
With the solo TDA7294/5/6, your options are:
(listed worst option first)
#1. Push for both bass and treble, causing unpleasant midrange instead
#2. Push for pretty treble and accept a bit less bass as the cost
#3. Push for bass power and install treble boost as a compensation
#4. Use Nested/Composite/Howland for linearity tracker/servo
#5. Under volt it to make the smaller more linear amplifier
Using the TDA7293 adds this option:
#6. Parallel output devices to make the larger more linear amplifier.

Clearly, this is an output transistor size versus linearity issue.
There is why the chips demonstrate strong affinity for good power circuits and the topic of energetic efficiency / dynamic power / peak power / music power / back-emf synchronization, which is a variety of language all used to describe Not riding the brakes on brief transient signal. Little output device can still deliver whopping big transient surges for clarity and bass too. But they never make suitable toasters, aka constant current reliance cripples them.

So, let's try the parameter matching.
Martin Martinez asked about a chip amplifier to use for one 8 ohm speaker and he has a 25+25vac transformer of 125VA. On the list above, there are three linear amplifier options, #4 is overly complex, #5 doesn't work with his transformer voltage, so #6, parallel output devices is the logical choice.
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Old 29th April 2013, 05:37 PM   #110
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thanks again
i dont mind sewing ears
i´ve been using chipamps because that´s what many amps use (instrument amps, power mixers, home systems etc) and also to replace very old amp sections.
They usually sound nicer and louder, and more abuse withstanding.
so its gonna be parallel 7293,p2p, and still deciding the feedback string
Let me thank you again.
time ius very valuable 4 me, so i apreciate much your attention.
martin martinez
uruapan michoacan
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