TDA7293 Parallel kit from ebay (modular/slave style, no lossy emitter resistors) - Page 2 - diyAudio
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Old 7th March 2013, 08:21 AM   #11
AndrewT is online now AndrewT  Scotland
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Darp,
you have the transformer, measure it.
Connect mains and with secondaries open circuit measure the input voltage and the output voltage.
Now scale the output voltage up to the value it would be if the mains input voltage is at maximum supply tolerance.

I'll guess that the open circuit output voltage will be around 35Vac when mains is at maximum.
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Old 7th March 2013, 12:39 PM   #12
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Default Tractor versus sports car

Like a high torque tractor that doesn't falter under heavy load, this amp is a heavy current pusher especially for 4 ohm speakers where low loss is more important than a bit more output device noise, so there's not much advantage to use it with 8 ohm speakers.
Your transformer is over the practical maximum for use in a normal unregulated power supply with this chip. Datasheet maximums are for broadest figures maximizing the number of customers, so the maximums are for selling, not for using. Regulated power is possible; however, the labor and materials costs should probably be used for a different amplifier.

Alternative:
With those 30+30 vac transformers, I suggest to use the discrete Honey Badger project instead. Yes, it is a big project, but it handles your transformers, and the board from the diyaudio.com store turns complexity into something as easy as soldering practice. OStripper's test transformer has very similar voltage to yours, so you'd be easily in the voltage "sweet spot" for high quality results.
Here's the boards:
The diyAB "Honey Badger" Class AB Power Amp - 150W/Channel (2 Channels) - PCBs
Here's a build tutorial:
http://www.diyaudio.com/media/build-...guide-v1.0.pdf
Here's a schematic example for easily matching Mouser parts:
http://www.diyaudio.com/forums/attac...oneybadger.gif
Here's a link to Honey Badger build thread:
diyAB Amp The "Honey Badger" build thread
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Old 24th March 2013, 12:00 AM   #13
aerwyk is offline aerwyk  Panama
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Default Many Options

I checked the listings on EBAY....

There's a myriad of offerings with prices all over the place. If anyone ever wanted an inexpensive, quicky kit or completed AMP, this would be one place to start - especially if one prefers mosfets instead of bipolars for their output.

One or two sellers even offer a preamp - I'm not ready to say how good it my or not may be.

By starting this thread, you may have bitten off a pretty good chunk for us to chew.

May you never have a cold solder joint.
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Old 24th March 2013, 08:43 AM   #14
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For kits, I'd distrust anything that has the power supply on same board as the amp. The "included" power supplies are normally minimum "get by" designs that fit into the smallest space possible, which makes the board cost lowest possible, also at the cost of least possible audio quality. oops.

SO, I like the very tiny double-sided amp boards + DIY power supply board.
Those are clean.
From obviously the same designer as this compact parallel board, you can also find even smaller solo chip boards, and those can work well with 8 ohm speakers. I've seen both TDA7293 and TDA7294 kits available with a pair of the tiny double-sided boards.
The design is so elegant!
In my opinion, only the smallest of double-sided boards have thoroughly tamed the TDA7293, TDA7294, crazy pinout. So, it is the smallest boards that can give the clean performance, like a point to point, except easier to build.

The kits do all seem to come with bankrupt component values, either like the datasheet, or insignificantly better (and there's not much way to do worse), which is all a hot-running mid-fi of some sort. Sometimes the included caps are all very small for the only reason that tiny caps are less likely to be mashed in the mail. So, some of the designs have components selected for non-audio reasons.
However, some of the boards are good and you can plug in whatever components you'd like to use. I'm just glad that they finally invented nice little double-sided boards to support these chips!

P.S.
Compare: The kit boards that were available back in 2008 were approximately postcard size, per each chip, and were single sided with such a huge mess that it hindered audio quality. So, let's continue to avoid the big sloppy single side boards.
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Last edited by danielwritesbac; 24th March 2013 at 08:57 AM.
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Old 24th March 2013, 07:31 PM   #15
aerwyk is offline aerwyk  Panama
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Default Lots of Choices

In looking at the various offerings, It's easy to eliminate those you (Daniel) suggest rejecting. Actually, I'd reject any that come already soldered.

I have a dislike for power supplies and audio circuitry on the same chassis/board. There are some offered with separate power supplies and you must assemble and solder them yourself.

This seems like these are ready made for the DIY as you can easily change the value of those components you deem necessary. The big advantage is you now have a PCB that is ready to go. And, at some of the prices asked, it's not too unreasonable to buy more than one.

May you never suffer a cold solder joint
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Old 7th May 2013, 10:41 AM   #16
Tomom is offline Tomom  Australia
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I have bought two of those small boards with paralleled TDA7293. The suggested supply is 24 V. Can I use up to 40 V?
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Old 7th May 2013, 11:24 AM   #17
AndrewT is online now AndrewT  Scotland
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40Vdc, when?

When the Mains is at 220Vac, or @ 230Vac, or @ 240Vac, or @ 250Vac, or @ 254Vac?
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Old 9th May 2013, 11:57 AM   #18
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Quote:
Originally Posted by Tomom View Post
The suggested supply is 24 V.
That comment sort of makes sense in the case of a 24+24VAC transformer driving a split rail power board to about 35+35VDC.
See the TDA7293 Datasheet: http://www.st.com/st-web-ui/static/a...CD00001887.pdf
Quote:
Originally Posted by Tomom View Post
Can I use up to 40 V?
DC????
With 8 ohm speakers:
You can use a 28+28VAC transformer with a good split rail power board for DC power at almost 40+40VDC as suggested by the TDA7293 datasheet.

With 4 ohm speakers:
For 4 ohm speakers, I'd suggest a 25+25VAC transformer so that the split rail power board outputs about 36+36VDC.

With either 4 ohm or 8 ohm speakers:
A 25+25VAC transformer And a split rail power board, is pretty much standard for this amplifier.
Quote:
Originally Posted by Tomom View Post
Can I use up to 40 V?
AC????
Definitely not a 40+40VAC transformer. The amp would explode.
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Last edited by danielwritesbac; 9th May 2013 at 12:03 PM.
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Old 10th May 2013, 11:27 PM   #19
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Or, what not to do:
So, don't use 30+30vac transformer, don't use 32+32vac transformer, don't use 35+35vac transformer, don't use 40+40vac transformer, and don't use a higher voltage transformer.
The TDA7293 amp doesn't like those.
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Old 11th May 2013, 01:53 AM   #20
Tomom is offline Tomom  Australia
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lol...I laughed and you guys probably laughed too... sorry for my "murky" question, the suggested supply was +,- 24 V DC. So thank you for clearing it up, I'm glad I can use 25V AC that will give me 35 DC out. Also this particular board has "only" 100uF/100V caps, not 220uF or 330uF as Daniel suggested, so I will change that too. BTW can I use 63V cap instead 100V caps, as supply is only 35V DC? And if I bridge two amps, should that rating be lifted to 100V then? Thanks again...
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