Why are there only disastrous PCB Versions for TDA7293/TDA7294/LM3886 etc. available? - diyAudio
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Old 3rd November 2012, 02:30 PM   #1
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Default Why are there only disastrous PCB Versions for TDA7293/TDA7294/LM3886 etc. available?

Why are there only disastrous PCB Versions for TDA7293/TDA7294/LM3886 etc. available?

There are an extremly wide range of PCBs and Kits available for this and similar other monolitic audio amp ICs.
For me unfortunately the position of the copper conductor tracks are absolutely
disadvantageous by all examples, which are to find by Google image search - go to

audio amplifier tda7293 - Google Search
audio amplifier tda7294 - Google Search
lm3886 - Google-Suche

By this high resolution example - go to
F200# Audio Enthusiasts DIY AMP TDA7293 Amplifier Board for sale
you will see, that the positive voltage supply rail and the negative rail goes very close to the signal pads and inverted input pad for NFB. Additional there are only cheap caps for the power supply in use without screw terminals. Consequently a certain standart of sonic quality cannot be exceeded. By all showed images unfortunately this situation I note.
I am almost certain, that nothing of the showed versions from image-search sounds really good (at best like Linn's LK85 in genuine condition - i. e. with original part and wire equipment).

After performed tweacking of Linn's power amp model LK85 (equipped with TDA7294V) I observe an exceptionally enhancement by sound quality due to additional use of caps with screw terminals and change the routing of the wires for the main voltage rails.

According to my requirements four holes would be drilled in the PCB near by the pins 13 and 15 in case of TDA7293/TDA7294 (in opposite of the sensitive area). The cans of the caps must go downward (solder side/bottom side) and the screws for the caps must be screwed from the component/top side.

Then I avoid interchanges between the (very short) supply rails to the sensitive areas and I get the possibility to use top class capacitors in outlines like that from
http://www.audiocap.co.uk/ekmps/shop...0a153ke063.gif
or
http://s.eeweb.com/resized/images/re...76_455_332.png
instead low cost high CV versions in "snap in" outline.

Are such printed circuit boards really still not available ??
If yes, is this unbelievable. OTOH - there are too many copies of copies (clones of clones), particularly in far east.

Where is the excellent engineering from early days concerning proper PCB design ??
Attached Images
File Type: jpg Linn-LK85-inside-1.jpg (64.6 KB, 1661 views)
Attached Files
File Type: pdf Linn LK140 4xTDA7294V.pdf (139.8 KB, 445 views)

Last edited by tiefbassuebertr; 3rd November 2012 at 02:52 PM.
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Old 3rd November 2012, 03:01 PM   #2
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Why do you think so?
There are some...
4-layer board
Blog – S-AUDIO
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Old 3rd November 2012, 05:04 PM   #3
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As for XY LM3886 kits, I do not know if this PCB can be considered as desastrous or not though the sound is five stars as is, i.e. no mods.
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Old 4th November 2012, 09:20 AM   #4
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Quote:
Originally Posted by bobodioulasso View Post
As for XY LM3886 kits, I do not know if this PCB can be considered as desastrous or not though the sound is five stars as is, i.e. no mods.
As long supply rails to find close to the sensitive areas PCB design is for me clearly desastrous.
Here an other example in the right direction; Jeff Rowland's wiring diagram of Concentra/Concentra II and Model 10 looks interesting
Jeff Rowland LM3886 Amplifiers
hifi-advice.com
Attached Images
File Type: jpg Jeff Roland Design Group Concentra I - E00342 0060.jpg (124.8 KB, 1562 views)
File Type: jpg JRDG Concerto.jpg (196.9 KB, 1530 views)

Last edited by tiefbassuebertr; 4th November 2012 at 09:33 AM.
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Old 4th November 2012, 10:43 PM   #5
Minion is offline Minion  Canada
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I suppose it should only be considered "Disasterous" if the curcuit self-destructs or at the very least sounds like crap , but a lot of PCB"s don"t follow every rule of proper PCB design and work just fine and sound just fine .....
The PCB in the TDA7293 Datasheet isn"t a particularly well designed PCB (though is was odviously designed by an engineer) but the PCB works and sounds just fine ......
I suppose to some poeple it is more important that a PCB follow all proper conventions of PCB design than the actual performance of the PCB ......
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Old 5th November 2012, 11:35 AM   #6
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If making the PCBs, why not make 'em better?

Anyone else got a good chipamp pcb/schematics examples?

tiefbassuebertr, i'm laying-out some lm3886 right now, this one (latest published) -
http://s3t.it/data/uploads/lm3886v5.jpg
The trimpot is next to opamp right now.

http://s3t.it/data/uploads/lm3886_v4.pdf
LM3886 regulated u-Gainclone

This one is wrong too? (criticism is welcome)
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Old 5th November 2012, 11:55 AM   #7
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Quote:
I suppose to some poeple it is more important that a PCB follow all proper conventions of PCB design than the actual performance of the PCB ......
The whole point of doing a PCB is sothat the circuit works as designed, everything else is secondary, though if the PCB cannot be made then its a pointless exercise. The elctrical functionality always comes first if the board is being designed properly, and the main skill in PCB layout is component placement, get that right and all else follows.
For chipamps layout is not as critical as it is for SMPS's and Class D amps, now there you can see some disasterous layouts.
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Old 5th November 2012, 01:21 PM   #8
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How close is close? If the supply is well filtered and doesn't have a lot of noise on it, and if the capacitance and leakage between the traces is low, there shouldn't be any problem. Phase also matters. Can you define a rule for length and distance that divides acceptable and unacceptable?
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Old 5th November 2012, 01:25 PM   #9
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I don't know 'bout other ICs, but LM3886 has it's output/PS pins nicely aligned pretty far from it's input. That should be the least distance between high-current and low-current nodes.
Yet, keeping the PS rails close to ground/each other has more significance than extending the distance between high-current and low-current nodes.
/imho/
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Old 5th November 2012, 01:45 PM   #10
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For low level analogue a minimum of 3W where W the general track to track spacing, and the basic track width, this allows a guard track between the two signal traces.
The best way if forthe engineer to put this information onto (or better still built in) to the schematic.
When doing sensitive audio (or other analog designs) I use different trace codes for different signals, usually "mic" for low level, "line" for higher level signalsand so on, the engineer draws the schematic using the defined codes, then when you lay the board out you can see the different signals in pretty colours defining the different types of signals. So you dont route a mic trace near a line traceor use more space betweenthe different signals to avoid cross talk and other interference.
For digital the same basic rules apply, but for sensitive digitalsignals such as clocks, also on digital I have various EMC advisores and simulation toolsthat we can use to checkthe whole layout.
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