Point 2 Point (no PCB) for TDA7293, TDA7294, TDA7295, TDA7296. - diyAudio
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Old 9th November 2012, 08:34 AM   #1
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Default Point 2 Point (no PCB) for TDA7293, TDA7294, TDA7295, TDA7296.

I received a request for a build thread with TDA7294 point to point.
Please feel free to add comments, questions and suggestions.
DMOS = Lateral Fet = Power MosFET, and are inside these chips.

Here it is step by step, with photos. . .
Click the image to open in full size.
The above photo shows TDA7294/5/6 pinout.

Click the image to open in full size.
The above photo shows the schematic. It is especially suited to under-volting applications.
Here is a new full power schematic that doesn't require a preamp <click link
Note that TDA7294S and TDA7293 have advanced features at pins 5, 11, and 12. We shouldn't ground those. I've no idea if my TDA7294 chip has those features, so I'm going to remove those pins by wiggling them; with the benefit of more room for soldering.

Click the image to open in full size.
Now, the pins marked N.C. (5, 11, 12) are definitely not connected, and 12 pins is easier than 15. At this time, I'd like to mention that if you favor parts swapping for fine tuning and quality control, then you may rather use PCB boards for the first build. Here are some compatible kit boards. <--link

Click the image to open in full size.
The above photo shows: Bending the V+ pins (8, 15) almost to the chip face, bending the V- pins (7, 13) up a bit and then bending the ground pins (1, 4) to midway. This is for rails horizontally across the chip. I've also bent the small signal, down away from the power pins, and spread them very slightly.

Click the image to open in full size.
The above photo shows V+ and V- rails with ground at center. I used Gel Flux for assuring good connections done easier.
Those are low-ESR 220u caps. Optionally, you can use parallel pairs of ordinary 100u caps (makes low loss 200u).

Click the image to open in full size.
The above photo shows nanofared caps added to V+ and V- for HF bypass duties.
Also shown is 2u polyester at rail to rail (one cap from V+ to V-) for quality control.

Click the image to open in full size.
From boostrap pin (6), the 47u boostrap capacitor goes to output pin (14).
The above photo also shows 60k feedback resistor from output pin (14) to inverting input pin (2). That feedback resistor pictured is a parallel pair of 120k, for quality control, and fortunately doubly sturdy with minimized inductance.
Feel free to sleeve anything with heat shrink tubing if you want to (even in that case, please do have some air space in-between).
EASIER BUILD?: If you're going to do any fine tuning or want an easier build, then consider allowing the pins to hang down below the heatsink and put the feedback resistor on back so that you can change values easily and there is much more room to build small signal area. Tone changes by both operating voltage and gain setting, and you will want to fine tune that to your own preferences.
LACKING A PREAMP?: Click Here for alternate higher gain schematic.

Click the image to open in full size.
The above photo shows:
Standby (9) to V+ via 22k
Standby (9) to ground via 10u.
Mute (10) to V+ via 10k

Click the image to open in full size.
The above photo (bottom side) shows:
220u NFB cap at ground pin (1)
2.7k (carbon) feedback-shunt resistor from NFB cap to to inverting input pin (2)
10k (metal film) input load from ground rail to non-inverting input pin (3)
Notes:
The 220u NFB cap is for authentic chip, but if cull/fake use 100u or smaller NFB cap.
Cable for input and cable for speaker can be added before attaching chip to heatsink.
RF filtering of speaker output RC (6.8R and nanofareds cap) can be added at speaker jack.
RF filtering of input can be added with 1M||220p from + to - at the small signal input cable
Suggested input cap size is 1u (or smaller) and may be at the output of volume pot.
If volume pot is omitted, the input cap size of 1u (or smaller) can be at the RCA jack.

Click the image to open in full size.
And there it is, TDA729X point to point.

Voltage and current note:
Authentic chips are capable of the specs listed in their datasheets; however, please check ST's Authorized Reseller list to see if you bought or can buy from a reliable source. If you have any reason to suspect that your chip may be either fake or cull or misbehave, please use 4400u (or more) worth of "output cap" (capacitance in series to speaker blocks DC accidents) as a speaker protector, and use 8 ohm speakers. A parallel pair of 2200u creates a low loss 4400u cap suitable for output cap (parallel pair of 3300u creates a low loss 6600u output cap for larger speakers); however, it may be less expensive to purchase authentic chips. Of course mains fuse and speaker jack fuses are good too. Authentic ST chips (from authorized reseller) can drive both 8 ohm and 4 ohm speakers at high power.

First startup:
Use "output cap" to protect your test speaker and use safety bulb test to protect amplifier.

Transformer for TDA729x chips:
TDA7293, 24+24vac toroid or 48vct (24,0,24vac) 5a
TDA7294, 22+22vac toroid or 44vct (22,0,22vac) 5a
TDA7295, 20+20vac toroid or 40vct (20,0,20vac) 4a
TDA7296, 18+18vac toroid or 36vct (18,0,18vac) 3a
Cull/Fake, 15+15vac toroid or 30vct (15,0,15vac) 2a

Power supply:
Click the image to open in full size.
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Last edited by danielwritesbac; 15th May 2013 at 07:07 PM. Reason: Added a "no-preamp" option.
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Old 9th November 2012, 04:30 PM   #2
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this is lovely, congratulations.
Prehaps this should.. have its own place, where people looking for something verry easy and cool to make. People who are looking for a first build maybe?
Adding a similar "tutorial" on the powersupply part of things, and a basic pre-amp with minimal functions could make this sorthof "ultimate" resource for beginners.

Probably builds documented whitin the same style should be collected, in case if its posted by well known and properly educated members of the forum.
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Old 10th November 2012, 07:08 AM   #3
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Thank you for the compliment!

In my opinion, 1st build beginners are best served with a solo LM1875 on a board, and a preamplifier unnecessary for it.
However, if one owns 4 ohm speakers, and/or other higher power needs, it may be better to consider the TDA729X or any parallel amplifier for the quality that "current headroom" offers.

I am considering your request for power supply build thread. Since TDA729X's needs are basic, it doesn't need regs and it doesn't need dual mono, but it would like a CRC, yet it needs stiff rails, I could do a "constrained CRC" power supply that will adaptively turn off the CRC feature when higher current is needed for good bass. Do you want a power board with that feature? If not, then there are plentiful basic power supplies already posted online.

My apologies that some weaker sources like onboard computer sound chip, phone, and digiplayer might need a preamp. The TDA729X can do lovely big open sound in high resolution if at standard/low gain; but, the perceived sound-field size shrinks if high gain is used, so I'd rather use a preamp instead of a mid-fi. Click Here to browse the preamplifiers section of diyaudio.com. Upgrade computer sound cards and CD players probably don't need a preamp.

Personally, I would like to have a shunt comp class A buffered preamp made from discrete parts, but run from chip regulators. However, the MooseFet IRF510 preamp from Classic Valve Design will do just fine. Decibel Dungeon also shows a chip preamp biased to class A with two transistors, which is approximately where performance and simplicity meet.


The following attachments are for display at post 1. Previously they were stored on a different server, but it display is more reliable when they are attachments to a thread.
Attached Images
File Type: gif pinout.gif (13.8 KB, 2778 views)
File Type: gif schematic.gif (12.4 KB, 201 views)
File Type: jpg pinremove.jpg (48.6 KB, 2770 views)
File Type: jpg pinbend.jpg (63.4 KB, 2760 views)
File Type: jpg feedbackbootstrap.jpg (58.4 KB, 2737 views)
File Type: jpg mutestandby.jpg (50.6 KB, 2740 views)
File Type: jpg rails.jpg (64.2 KB, 2762 views)
File Type: jpg railbypass.jpg (51.4 KB, 2747 views)
File Type: jpg input.jpg (59.4 KB, 2734 views)
File Type: jpg completed.jpg (68.7 KB, 3511 views)
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Old 10th November 2012, 08:39 AM   #4
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In- and in+ are inverted on the diagram.
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Old 10th November 2012, 09:05 AM   #5
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Thank you for spotting that!

P.S.
The fixed schematic attached is linked to display at post 1.
Attached Images
File Type: gif schematic.gif (12.4 KB, 3496 views)
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Old 19th January 2013, 10:32 AM   #6
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Hi Daniel, is the schematic recommended by you.You suggested in the past some 2200 mf near the power supply and some others.Now you have 220uf, and 47 uf in bootstp,60 k in feedback resistor.You also have 2uf between +,_ power supply, you also recommended to short input no 2 to gnd through just 680ohms without caps.is that the latest tweak?

Last edited by simply14prem; 19th January 2013 at 10:50 AM.
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Old 19th January 2013, 06:20 PM   #7
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Quote:
Originally Posted by simply14prem View Post
. . .you also recommended to short input no 2 to gnd through just 680ohms without caps. . .
I can't find any 680R on the schematic. This isn't a 47 labs style gainclone. It could be done, but I didn't do it. See the schematic at post 1.
Quote:
Originally Posted by simply14prem View Post
Now you have 220uf, and 47 uf in bootstp, 60 k in feedback resistor. You also have 2uf between +,_ power supply, . . . is that the latest tweak?
Well, really almost any combination that a miller comp discrete amplifier could use, can also be used by the TDA7294. The schematic doesn't necessarily show the latest tweak, but rather it shows a place to start. This page shows low gain, and that puts the component-based audio influence all in one place--the nice clean feedback resistor, not the caps. So, everything is much easier, except that now you need a preamplifier.

If there was a latest tweak, it would be: Allow the pins to hang down below the heatsink so that there is much more room for building. I built all on one side; however, it would have been much easier to put the feedback resistor and other small signal on the back side.
Quote:
Originally Posted by simply14prem View Post
Hi Daniel, is the schematic recommended by you. You suggested in the past some 2200 mf near the power supply and some others.
Here are the 2200u caps:
Click the image to open in full size.
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Old 20th January 2013, 12:05 AM   #8
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Sorry I mean the shunt resistor ,mine is 680r ,,I just short it to ground,does is it make any difference,,what is the benefit in your case,you are having 220uf +2.2k. From input 3 ,to ground Im using 22k,,also for feedback 22k, yours is 10k and 60k.Power caps near the ic is 220uf +200nf.What is your 2u unpolarised doing there ?The stanby pin 9 is connected with 22uf.I have 220uf as bootstrap,,is it too large?

Last edited by simply14prem; 20th January 2013 at 12:23 AM.
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Old 20th January 2013, 12:42 AM   #9
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my tda 7294,,Sorry i just modified your pic,,I don't have any pc now ,,so just edited from my Android.
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Old 20th January 2013, 03:11 AM   #10
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That looks just like using TDA7294 for a gainclone. I've never tried that. Sorry, I wouldn't know anything about it.
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