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Optimizing TDA7294 Output
Optimizing TDA7294 Output
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Old 9th July 2019, 06:06 PM   #901
tnvijay is offline tnvijay  India
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Can't go through the entire thread. But I thought I should share this .Moderators kindly remove the post of the schema is already discussed. There are a couple of Russian designers who has done extensive work on tda 7294 series chips. Unfortunately,they are all in Russian and a regular Google search like tda 7294 doess not yield those pages..
1.Search for TDA 7294 LINCOR MF1 .The Russian pages can be translated and read in English. The schema is a mixed voltage and current feedback ,and uses a F shaped feedback loop. The. Author ,whose pen name is LINCOR, gives explanation and explains how he tried to achieve near flat response across frequently spectrum without resonance peak boom. There is a printable PDF layout and the construction is very easy ,even for novice.Now, most importantly,how does it sound..? Having used this amplifier for about one year, I can vouch for its sonic quality. Subjectively, the music is very fluid and easy to listen. No listener fatigue , A special word on the deep, yet controlled bass. One has to build and listen to believe... Considering the cost and simplicity to build,this could make one fine amplifier...
2. Search for tda 7294 audiokiller. Another Russian, with the pen name audio killer,has a entire page dedicated to tda 7294 . He also proposes mixed feedback topology and gives software for calculating feedback resistor for tweaking.. Really a different dimension for these chip amps..I will try to copy the link tomorrow.
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Old 9th July 2019, 08:27 PM   #903
Astaro is offline Astaro  Russian Federation
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The best Board design of the amplifier based on TDA7293. One channel - Share Project - PCBWay
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Old 15th July 2019, 12:52 AM   #904
santitrucco is offline santitrucco  Argentina
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Hi all people..!!

Can a Chip amp , like TDA7293, TDA7294, LM3886 , obtain a sound quality like a discrete amplifier ( Bipolar , Mosfet , Darlington ) ?

Santiago
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Old 15th July 2019, 01:04 AM   #905
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by santitrucco View Post
Hi all people..!!

Can a Chip amp , like TDA7293, TDA7294, LM3886 , obtain a sound quality like a discrete amplifier ( Bipolar , Mosfet , Darlington ) ?

Santiago
I have designed chip amps and class ab and d amps and cant tell the difference between them.
The only one that sounded a touch better was a hybrid TDA7294/12AU7 valve amp.
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Old 15th July 2019, 08:17 AM   #906
stupidboy is offline stupidboy
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Finally hybrid FB. Finally real output optimization.
tnvijay, thank you!
However, i have even simpler plan. First, i didn't discover anything new. I am convinced such design exist for long time, but is not discussed publicly.
I do not like inverting amplifiers, that is why i go this way.
So:
Pick whatever kit you can/wish, with non inverting amp. Any chip, or even discrete, depending on your knowledge. Get it working as is. Optionally replace input and FB shunt caps to get better low end response. In my case with TDA7293 i throw 4.7u at input and 220u at FB shunt. Don't bother with other parts in FB.
When it works stable, pick some low value resistor and put it between speaker and ground. My speakers happen to be 6-7 ohm effective, so i paralleled 2x0.47ohm/2w. Idea is to achieve just a little bigger current FB amplification (calculated) compared to existing voltage FB. Say, +1, +2 more. For real 8ohm speakers this resistor should be something like 2x0.47 in parallel, with one more 0.47 in series to them. Some experimenting is needed, because no one knows real impedance of the speakers.
Pick a cap, say, equal to voltage shunt FB cap and place it between speaker/resistor junction and - input of your amplifier.
That is all! Magic is here! You have non-inverting hybrid FB.
If you wish, you can calculate and further optimize this design. I will not put calculations here because they are pretty complex and will not give a lot to mass users.
How it sound? Different! I like it. No, to be more correct: because of this hybrid now i hate my multi-thousand euro sound system, built and optimized over the years. For me it sounds better even compared to valve amps.
How it measures? Most likely very bad! O-scope 'audiophiles' definitely will not like it. But i use my ears for listening and scope for other things.
With this simple addition almost any amp can be 'fixed', virtually for free.
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Old 15th July 2019, 07:20 PM   #907
tnvijay is offline tnvijay  India
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Quote:
Originally Posted by stupidboy View Post
Finally hybrid FB. Finally real output optimization.
tnvijay, thank you!
However, i have even simpler plan. First, i didn't discover anything new. I am convinced such design exist for long time, but is not discussed publicly.
I do not like inverting amplifiers, that is why i go this way.
So:
Pick whatever kit you can/wish, with non inverting amp. Any chip, or even discrete, depending on your knowledge. Get it working as is. Optionally replace input and FB shunt caps to get better low end response. In my case with TDA7293 i throw 4.7u at input and 220u at FB shunt. Don't bother with other parts in FB.
When it works stable, pick some low value resistor and put it between speaker and ground. My speakers happen to be 6-7 ohm effective, so i paralleled 2x0.47ohm/2w. Idea is to achieve just a little bigger current FB amplification (calculated) compared to existing voltage FB. Say, +1, +2 more. For real 8ohm speakers this resistor should be something like 2x0.47 in parallel, with one more 0.47 in series to them. Some experimenting is needed, because no one knows real impedance of the speakers.
Pick a cap, say, equal to voltage shunt FB cap and place it between speaker/resistor junction and - input of your amplifier.
That is all! Magic is here! You have non-inverting hybrid FB.
If you wish, you can calculate and further optimize this design. I will not put calculations here because they are pretty complex and will not give a lot to mass users.
How it sound? Different! I like it. No, to be more correct: because of this hybrid now i hate my multi-thousand euro sound system, built and optimized over the years. For me it sounds better even compared to valve amps.
How it measures? Most likely very bad! O-scope 'audiophiles' definitely will not like it. But i use my ears for listening and scope for other things.
With this simple addition almost any amp can be 'fixed', virtually for free.
Thanks . I am a self taught electronic hobbyist.To Understand your design principle,can you post a schematic, for ex with a TDA2050 ?
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Old 16th July 2019, 10:54 AM   #908
stupidboy is offline stupidboy
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Here is schematic with generic amp. Things in red represent what is added. Math is near approximation, giving satisfactory result and starting point for fine tuning.
Starting image was pick from random internet site.
Attached Images
File Type: png generic_amp.png (9.3 KB, 119 views)
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Old 12th August 2019, 09:52 AM   #909
Hushang is offline Hushang  Iran
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Quote:
Originally Posted by danielwritesbac View Post
Thanks! And, then we have these (attached).

We're not likely to see any "in the wild" because this is DIY and they're likely to get modded (no matter how nice they are if not modded). Therefore, the normal usage for these is the solid place to start that was not provided by the datasheet.

The under-volted 45W example will image better (used along with 20-0-20 and 22+22 transformers). At the expected voltage (printed on the schematic) and with the assumption of excellent compact (I mean tiny!) layout and route the gain divider's resistors most directly (rather than most decoratively), then the cermet trimmer is set to 780R but can be fiddled to support different applications, including different voltages and other modding. Of the two schematics presented below, the lower voltage example has higher resolution. Sounds like a hi-fi.

However, the #1 most popular mod for amplifiers is a push for power build. So, I generated a second schematic showing the higher rails and different gain setting involved (used along with 25-0-25 and 28+28 transformers). Note the cheap little 680R film resistor has not performed optimally as a base stopper; however, if you replace that with a cermet trimmer, you can dial it to 730R. Also, the series elements are high efficiency MBR1645 schottkies, which have smallest voltage drop but still work just barely well enough to secure the excellent power decoupling necessary for clear audio.
Some of the imaging/3d/realism quality of the undervolted 45W example isn't accomplished by the higher power 65W example, and that's the cost of 20 more watts, which won't boost the speaker output by so much as 1.5db--certainly not worth the compromise, except for people who equate watts with quality. That is actually popular. The higher power version (with higher voltage rails), has a pretty tone and will certainly work well enough to rock the house for a party and for woofer amplifiers as well. Sounds like a party amp.
Hi Daniel
first of all, thanks for sharing, I want to build this amp. my transformer is double 24volt. want to make a 3 way system, wonder that can I use two of these in bridge mode for woofer? do you recommend this topology for your schematic? or should I change it?
thank you
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