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TDA 7293 ---- done right ?
TDA 7293 ---- done right ?
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Old 30th September 2021, 05:01 PM   #111
MalleMike is offline MalleMike  Spain
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Join Date: Dec 2018
Location: Mallorca
Got them from China but I know how to measure them to know if they are the real thing , tested them already. They cannot fake laser-engraving and more important they cannot fake several resistance-measurements between pins of the original ones !


At a 1.50 each if they were fakes I can still use them for other means and experiments

Last edited by MalleMike; 30th September 2021 at 05:04 PM.
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Old 30th September 2021, 05:14 PM   #112
WLA is offline WLA  United States
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Thanks!
I had problems in the past with fake TDA7294. The IC chip looked as the original one, but could not stand more than ±35V.
Could you please explain what kind of measurements are those?
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Old 30th September 2021, 05:44 PM   #113
joensd is offline joensd  Germany
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Of the tda7293 there are several versions which has been discussed here. I believe they are V6 and v7 mainly. Can't remember which is which but one can take a higher voltage.
That said, if you want an amp that works with both, 4 and 8 ohms I wouldn't even go up to +-35v.
I tested mine with 4 ohms and 2x22vac and the temperature protection kicked in before 1minute passed. That was with full swing and sinewaves though. You will need a good thermal coupling to a big heatsink if you want to use +-35v with 4ohms. I personally would go with the values from the lm3886's datasheet and stick with +-28v or so for 4 ohms (~18vac).
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Old 1st October 2021, 05:35 AM   #114
MalleMike is offline MalleMike  Spain
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There is a thread on the subject of fakes already and I recommend you read it .



How to spot fake TDA7293
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Old 1st October 2021, 06:41 AM   #115
Dibya is offline Dibya
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Join Date: Apr 2018
Location: Inside your preamplifier
Quote:
Originally Posted by WLA View Post
A few years ago I built a similar inverting TDA7293 with separate ±VSS and ±PWVSS as +VSS = +PWVSS +10V and -VSS=-PWVSS -10V. In this way you don't need bootstrap cap. BTL configuration (slew rate around 20V/us) worked nice.
I don't think that any circuit would increase the slew rate except BTL configuration.
On the other hand, applying too much corrections in the feedback might diminish further the slew rate in a composite circuit, which would be really bad.
Can you show me the circuit?
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Old 1st October 2021, 06:50 AM   #116
Dibya is offline Dibya
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Join Date: Apr 2018
Location: Inside your preamplifier
Quote:
Originally Posted by joensd View Post
Of the tda7293 there are several versions which has been discussed here. I believe they are V6 and v7 mainly. Can't remember which is which but one can take a higher voltage.
That said, if you want an amp that works with both, 4 and 8 ohms I wouldn't even go up to +-35v.
I tested mine with 4 ohms and 2x22vac and the temperature protection kicked in before 1minute passed. That was with full swing and sinewaves though. You will need a good thermal coupling to a big heatsink if you want to use +-35v with 4ohms. I personally would go with the values from the lm3886's datasheet and stick with +-28v or so for 4 ohms (~18vac).
TDA7293 on V6 can handle up to 40v rail , V7 can take 50V rail.

Provide Big heatsink and 35V rail , everything will be fine.
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Old 1st October 2021, 08:59 AM   #117
MalleMike is offline MalleMike  Spain
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I am still working on my circuit and do not know what WLA was working on , but anyway here goes . Just take a good op-amp input-stage using LM 49720 for example , followed by a long tail pair of BC560 with an emitter-degeneration and a current-mirror , about 220 ohm-resistors , to transfer the op-amps output to the negative railvoltage , then follow that with a complementary VAS-stage using any good pair of complementary transistors with 100V max , a gain of 50 or higher , like BF469/BF470 see datasheet , where the upper transistor is configured as a constant current source set to about 10...15mA , and inject the output into the pin 11 of a slave-configured TDA7293. Experiment along these lines , you can , if you want , take the vas of a well known and well performing discreete amp and copy it . Feedback from output of TDA to inverting input of the opamp . The closed loop gain can be unit provided the vas is compensated for high frequency so you atre not limited by the gain of the TDA , normally 20x minimum. this is aprox what I am working on.


What I am trying out now is a second feedback from the output of the vas to the long-tailed pair to linearize these two stages to the max. Then the over-all feedback , due to the extremely high open loop gain of the op-amp, should get me vanishingly low distortion as long as the TDA´s output-buffer functions correctly with rising frequency so it will help me to find out what the frequency-bandwith of this buffer without the rest of the TDA is , because both the op-amp and the vas will not be the limiting factor .

Last edited by MalleMike; 1st October 2021 at 09:25 AM.
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Old Today, 07:09 AM   #118
bebo65 is offline bebo65  Germany
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Join Date: Jun 2021
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Hello Mike,

do you have news for us? Do your circuit work as expected?


Otherwise here is some news from me, another circuit topology that does fine in simulation and needs a prototype to see if this works also in reality. This time i had an eye especially on the risetime of the ICs envolved. (Again this are only ICs that are similar in characteristic to the ones to get used in the real circuit!)
Attached Images
File Type: png composite simu risetime.png (42.9 KB, 21 views)
Attached Files
File Type: asc composite-amp_variante-double feedback_10_21.asc (3.4 KB, 1 views)
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