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Old 16th May 2013, 07:20 AM   #471
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Thanks!
I can probably manage 10u||10n with the Parallel TDA7293 board or any of the little compact double-layer boards by same designer, or point to point, or really any excellent layout is also compatible with using a larger input cap. I already tried 5.5u with the TDA7293 Parallel board, and it was just fine.

Input load:
I'm curious about this. The valid range for input load seems to be 12k through 27k. Smaller figures do louder midrange and a few other things as well. There's no problem to use a 22k or 18k input load. Would that help?
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Last edited by danielwritesbac; 16th May 2013 at 07:23 AM.
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Old 16th May 2013, 03:29 PM   #472
tyger23 is offline tyger23  United States
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Quote:
Originally Posted by danielwritesbac View Post
There's no problem to use a 22k or 18k input load. Would that help?
Lower input loads would make the droop and phase issues worse.

FWIW - I would also recommend Nichicon KZ or FG caps for the inputs. Also, the Elna Silmic II caps are just as good if not better. There's no real need for a bi-polar cap on the input pin.
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Old 17th May 2013, 06:42 AM   #473
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Quote:
Originally Posted by tyger23 View Post
Lower input loads would make the droop and phase issues worse.

FWIW - I would also recommend Nichicon KZ or FG caps for the inputs. Also, the Elna Silmic II caps are just as good if not better. There's no real need for a bi-polar cap on the input pin.
Okay.
I'm willing to do larger size input caps, but only in case of good board layout which is the minority--the compact dual-layer boards listed in post#455, and also point to point (compact triple-layer). Perhaps these have the power caps located close enough to pins 7 and 8 that we have more freedom in fine tuning the amplifier. That's a guess, but I know for sure they're easier to work with for achieving an appreciable practical output. And, your big input caps will do just fine with those decent boards. . . which are the minority.

For the majority, 1u input cap is a safe bet to show on the schematic because the majority are the "inductive spaghetti" single layer boards that have the power caps too far away from the chip with annoying results that get worse if the input cap is made larger. Bad layout boards are the majority, which is what happens when sprawling single layer board design meets a chip with mad pinout. It is possible to make plug-in daughtercards for bypassing problem areas of bad boards; however, a thorough job of it bypasses every circuit and thus it would be so much easier to replace a bad board instead of fight with it.
Anyway, it is really a problem to show board specific values on any schematic that doesn't also show layout.
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Last edited by danielwritesbac; 17th May 2013 at 06:51 AM.
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Old 18th May 2013, 01:31 PM   #474
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I'm not repeating a whole post, since the original is here: TDA7293 Parallel Thread
But there was a pertinent photo that I'd like to share since I did first try it on Bob's TDA7294 board:
Click the image to open in full size.
On Bob's single layer TDA7294 board, a power circuit mod very similar to what is shown in the photos (same component values) did cut the need of compensation in half. Note: The TDA7293 Parallel amp board in the photo has V+ on the left side (your board might be different, so double-check). These parts and the 440u per rail are shown on this schematic. Powered like shown in the photo above, it will be much easier to fine tune the amp.

The feedback-shunt trimmer for adjustable gain goes a long way towards not needing added compensation at all. In addition to unimportantly setting the gain, it also varies the tone, mainly treble versus bass, which is expected because of changing the gain, so please use the trimmer to dial in a level response precisely. That's good but a midrange control was previously missing. To fix that, I've added adjustable input load to the schematic.
Functions:
Gain trimmer = Treble versus Bass (dial it in for level)
Input load trimmer = Midrange soft or loud
Notes:
You can replace the 100k input load trimmer with an equivalent resistor after you've completed your fine tuning; but, that is not true of the 100R gain trimmer--it needs to stay on the board. If your board has a fortunate layout for good behavior, then you'd be able to use an input cap larger than 1u, if desired.
Attached Images
File Type: gif TDA7294-Adjustable3.gif (33.6 KB, 491 views)
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Last edited by danielwritesbac; 18th May 2013 at 01:37 PM.
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Old 21st May 2013, 10:35 AM   #475
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in this case also this thread is of interest:
Why are there only disastrous PCB Versions for TDA7293/TDA7294/LM3886 etc. available?
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Old 21st May 2013, 12:57 PM   #476
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And, here is a shortlist of efficient dual-layer boards:
TDA7294 solo: TDA7294 Mono Amplifier Kit
TDA7293 solo: TDA7293 Mono Amplifier Kit
TDA7293 Parallel: Parallel TDA7293 Mono Amplifier Kit
TDA7293 Triple: Triple Parallel TDA7293 Mono Amplifier Kit

*See also this mods list with photos and assembly.


P.S. Honorable mention:
http://www.diyaudio.com/forums/class...han-lunch.html
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Last edited by danielwritesbac; 21st May 2013 at 12:59 PM.
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Old 24th May 2013, 05:47 PM   #477
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Quote:
Originally Posted by danielwritesbac View Post
I have just purchased a pair of TDA7294 finished boards for $11.4 and they arrived in under 2 weeks!
No stand offs, I guess the image is generic, but they came with mica and plastic insulators.
I think I can manage to cobble together a PS, I have several SS amps I will never use.
Amplifier PCB board TDA7294 Amplifier board(1+1) Dual channel 2*85W-in Printer Parts from Office & School Supplies on Aliexpress.com
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Old 25th May 2013, 05:16 PM   #478
redjr is offline redjr  United States
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Quote:
Originally Posted by radiosmuck View Post
I have just purchased a pair of TDA7294 finished boards for $11.4 and they arrived in under 2 weeks!
No stand offs, I guess the image is generic, but they came with mica and plastic insulators.
I think I can manage to cobble together a PS, I have several SS amps I will never use.
Amplifier PCB board TDA7294 Amplifier board(1+1) Dual channel 2*85W-in Printer Parts from Office & School Supplies on Aliexpress.com
Let us know when you get it hooked up. I'm getting too many TDA* based amps around here myself - with too little time to work on them. Plus a move to CT coming up this Summer. Might grab a couple of these for fun!
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Old 25th May 2013, 06:30 PM   #479
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Quote:
Originally Posted by radiosmuck View Post
I have just purchased a pair of TDA7294 finished boards for $11.4 and they arrived in under 2 weeks!
No stand offs, I guess the image is generic, but they came with mica and plastic insulators.
I think I can manage to cobble together a PS, I have several SS amps I will never use.
Amplifier PCB board TDA7294 Amplifier board(1+1) Dual channel 2*85W-in Printer Parts from Office & School Supplies on Aliexpress.com
Lucky, I ordered two of the 2 chip kits and got .... one 2 chip kit and one 3 chip kit!?!

Hopefully it'll resolve quickly so I can give Dan's circuits a try ...
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Old 25th May 2013, 06:49 PM   #480
Lo_Tse is offline Lo_Tse  Canada
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Originally Posted by danielwritesbac View Post
Daniel,

Thanks you the info! I came upon this thread by accident and your posts stoke my interest on these TDA792X chips. I was planning to try out the LM3886/3875 chips but these TDA seems to be much more economical to play with. I hope they sound "as good" as the LM chips.

I probably will build the amp as-is, and then mod it according to your and others suggestions, as a learmning process.

Regards,
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