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Simple Cheap Compact IC-based High Performance Amp 
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I've been suffering a pair of cheap chinese computer speakers as my only sound system for 1.5 years. It's time to upgrade... I asked Andy if he'd like to layout a simple board for me and he seemed enthusiastic, so here we are!

Goals:

  • Uses TDA7293 integrated amp IC
  • Single board per chip/channel as small as reasonable with 2 layers without compromising noise performance
  • Simple interface to power and IO signals
  • Combine three together sharing a toroidal and main power filter caps for stereo bookshelfs + optional sub

Method:

  • Use reference schematics and layout as guides in order to minimise time to completion and effort required
  • Linkwitz Riley 24db/octave two way + merge electronic crossover to handle splitting signal for sub and bookshelfs
  • Internal star grounding scheme
  • Add some sophistication and quality by force to the circuit
  • Incorporate ground lift circuit to ensure ground-loop free operation
  • Utilise clip detection feature to drive LED on front panel per channel (20mA, make it obvious)

Components:

  • 3x TDA7293V
  • 3x PCBs (yet to be designed)
  • 3x other required components on board
  • 1-3x solid heatsink(s) with lowest thermal resistance possible for space
  • 2Nx big filter caps (2 or 4 or 6 or 8, whatever makes sense costwise/physically
  • 1x large bridge rectifier
  • 1x 250VA 30V toroidal transformer
  • 1x Reused mains X cap (to kill line noise)
  • 1x Reused old 70s/80s cassette deck housing including RCA jacks

Pics and more discussion to go, will unlock and bump when done.

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Sat Nov 24, 2012 4:35 pm
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The schematic is the first step and should be based on this modified version of the one supplied in the datasheet:

Image




The above should be modified to include the single control line sub-circuit shown below:

Image




In addition to that, I want to include an RC Zobel network on the output, and possibly a low resistance series inductor too:

Image




Finally we need to provide an LED drive, as the datasheet specifies 10k pullups to 5V (not currently available, but perhaps required) which isn't strong enough to brightly light a red LED. A simple zener supply should be OK. Rail voltage will be 45V peak or so. 2.4k with 5.1V zener will make 18mA available and dissipate 1W continuously. Perhaps a linear part would be better, or a 20k resistor just to allow the IC to provide a signal, but then what to drive the LED? Ideas welcome :-)

Values recommended for a single module are as follows:

Image




And my annotated version is here, showing what I plan to mess with for various reasons:

Image




After the schematics are complete and agreed upon we can move on to layout, and something similar to their design, possibly enhanced/redesigned for two layers, will be good:

Image




This is my tweaked variant of the chip pin out diagram:

Image




I still need to figure out the input circuit values, and Zobel values and decide on an output inductor, or not. I also need to pick up the parts to use, so the footprints can be obtained from them. Especially the 1000uF+ decouple caps.

Comments welcome :-)

Fred.

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Sat Nov 24, 2012 7:27 pm
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This is what I'm currently suffering:

Image

Pity the fool.

Fred.

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Sat Nov 24, 2012 7:56 pm
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Updates:

Here's a design with bulk caps, and two channels and some protection on just 140x80mm http://www.ebay.com/itm/TDA7294-TDA7293 ... 0486292885

And another (with terrible English) with huge connectors on just 58x60mm http://xtronic.org/circuit/amplifier/po ... 7293-dmos/

Looking at those, it MAY be possible to go seeed 50x50 for this depending upon how big the components I pick up are. However, going over that into 50x100 or 100x100 territory isn't a big deal, really. ($10 >> $25) + shipping.

Note on layout: Only three of the connections are high-current noise generators: V+ V- and Out, so they need to have well thought out routes from connection points to IC pins (via the decoupling electros). Currently I'm thinking that those three should connect near the heatsink edge and the others on or near the opposite edge. Input and ground matter, however stby/mute and clip do not. That's just 7 connection points in total and I don't need connectors, just well-placed solder points.

About the maybes in the component chart: They're all yeses. The low frequency roll off is way too high with those values, so they need to be increased. Some German drew a chart here:

Image

Fred.

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Sun Nov 25, 2012 11:25 am
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Updated the base schematic for clarity.

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Sun Nov 25, 2012 12:00 pm
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Zobel/Inductor diagram updated!

I have a shopping list mostly assembled now. Will likely pick up most of the bits this week some time. Still don't have a good source for a heatsink and still haven't figured out the input/feedback resistor values, but the rest is DONE!

Next steps:

  1. Find suitable heatsink
  2. Figure out input resistors
  3. Wait for/work on schematics
  4. Obtain dimensions for components (including buying suitable hookup wire and sizing the solder holes for it)
  5. Wait for/work on layout
  6. Order boards
  7. Assemble boards
  8. Integrate all parts into the enclosure
  9. Find or build some speakers
  10. Enjoy the smell of magic smoke :-p

Fred.

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Sat Dec 01, 2012 4:12 pm
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I have dimensions for my inductors!

Image

Note that although the wire is 1.5mm, I've tinned it, so the holes will need to be 1.6-1.8mm inside diameter.

I've only made one, but it came out so nice that I'm happy to try to match it twice more and roll with the size they are.

:nopics:

Pics coming soon!

Fred.

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Mon Dec 03, 2012 11:33 pm
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Mon Dec 03, 2012 11:56 pm
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All done! :-)

Image

Image

Image

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Tue Dec 04, 2012 11:42 pm
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Love this maori shit, keep up.


Tue Dec 04, 2012 11:51 pm
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