TDA7293 Parallel kit from ebay (modular/slave style, no lossy emitter resistors)
The easy little kit
This chip has Fet output built in, so it doesn't need lossy resistors at the output for paralleling.
Making two chips as easy as one.
This is documented in the TDA7293 datasheet as a modular approach.
(link 1) Two board *stereo* kit TDA7293 Parallel from HappyShop
(link 2) Two board *stereo* kit TDA7293 Parallel from Min9988
(link 3) One board mono TDA7293 Parallel from Happyshop
(link 4) One board mono TDA7293 Parallel from Fly-XY
Fortunately, the kit came with 220uF power caps for the amp board, which is perfect for clear sound and cool running of TDA7293. This setup with 220uF (or 330uF) power caps assumes that there will be larger power supply capacitance (a real power supply board).
If you push for quality, the Antek AN-3222 transformer is low priced, drops only 2v @13a and has ideal specs for use with TDA7293. If you push for power instead, AN-4228 is about max. However, 25+25vac dual secondaries transformer is typical and that's what I'm using.
I'm changing the 47uF bootstrap cap to 100uF to assist low bass (valid range 68uF to 100uF).
I will omit the 10uF Mute cap (location is right side of the board, near speaker jack) for zero delay.
A highly effective power circuit upgrade is shown at post#30.
Instead of the 22uF NFB-shunt cap (which is far too small), I'm using a 680uF 16v cap paralleled with a 0.47uF electrolytic cap for good treble. I'm also using a 1n4007 antiparallel pair as safety clipper to restrict this big cap's discharge to 0.65v. Photo is at post#29
The 105, 1uF box cap is your input cap, but there's other fun options to use, such as 4.7uF (or smaller) Elna Cerafine paralleled with a tiny polyester (to DIY your own low cost blackgate), etc. . . Try some variety and choose which you like.
The leftmost 22K resistor is Input Load. Valid range is from 15k to 28k. A difference in value can alter the midrange loudness. If you don't need the adjustable feature shown in the schematic with 100kVR||39k, then just use a simple 22k or 25k resistor for input load.
The gain divider is the factory standard 22K/680R and although this will work, I disagree with bad performance that generic values cause. Instead, I would like to use 27K/730R for great quality. If you want quality results, the feedback resistor and the feedback-shunt resistor(s), MUST be placed underneath the board, close to the NFB-Shunt cap. The feedback resistor is installed from pin14 to pin2. The feedback shunt resistor(s) are installed from pin2 to NFB-shunt cap. It fits easily and shown at post#24.
See assembly photos starting at post#24
It does use a power board:
Due to the power circuit mods for power filtering at the amp board (in the photo attachments at Post#30) we didn't need a CRC type power board, so here's a simpler edition.
See also Bob's power supply
Yes, new content that uses the schematic (above) starts at post#24--previous discussion might not be applicable to the new schematic, so you will probably want to skip ahead to post 24.
Daniel - a link to the Ebay auction or seller please?
These look great. Very interested.
These boards are monophonic--it takes 2 for stereo. These will drive 4 ohm speakers easily.
If bridged (stereo takes 4 kits and 2x op275), they'll drive high power 8 ohm speakers abundantly.
Gain, bridging, preamp and modern sources
Quantity: This amp runs out of capacity for gain prior to reaching max output if driven by a dac, chip player or other modern sources. . . and if you set the amp gain too high, quality is lost. Quality: There could be higher quality by setting lower gain, like 62K/2.7K at the power amp.
The conflict between quality versus quantity is resolved with a preamp, such as the very adjustable class A Moosefet IRF510 or the NE5534 class A preamp at Decibel Dungeon.
The concept is that a bigger higher voltage transformer in your power amp didn't make your computer bigger, didn't make your computer more powerful.
For more information, download and use free RightMark Audio Analyzer.
With a high power amp: The source works harder (noise) -or- The amp is about maxed for gain (noise) -or- You use a nice preamp.
A preamp allows you to run a gain stage on nice clean regulated/capmulti power, thus that portion of your gain is clean.
A bridge adapter, such as homemade version with op275, provides an additional, yet upside down, copy of the source signal. Even if built for unity, 1x, this device is effectively unity doubled (two copies), or 2x. It uses regulated/capmulti power and approximately the same parts as any good preamp. At end result, the output gets twice as big without increasing the demand from the source device.
See Rod Elliot bridge adapter circuit and you can read the good explanations there. And, see the very similar schematic attached below:
Power circuit looks like:
Smoothing caps (big ordinary standard power caps)
Tank caps (speaker return, star ground, big low esr caps)
very short cable >
Amplifier bypass caps (low esr 220uF caps upon the amp board/chips)
The one spot to use the standard power cap (like Mallory or Nippon Chemicon) is where you want to destroy signal and this need is present at the rectifier (power noise signal must be flattened) where you want smoothing, 0hz, no signal, DC. I use six 2,200uF per each rail. The group makes a low inductance assembly. So, the tone is good, but that thing still works to smooth DC.
However, all of the other caps are signal caps and can be low-esr type. The low esr types are great for bypass ("pass the buck") and decoupling since they transit the signal intact. That would be terrible at a rectifier but fantastic everywhere else. ;)
That was an overly complex way to say that you can have some large capacitance ("tank caps") near the amp board (to help the speaker) without having to put the rectifier section ("smoothing caps") near the amp board.
The result looks like a CRC with cable instead of "R" for low loss results and yet still work.
Did you find the sound quality of TDA7293 kit parallel build more lavishing or is it that the LM1875 parallel build outperforms this on 8ohms load? Which one you like the most among both?
So I take it you like this Ebay amp then?
I have a 20db gain preamp that I really enjoy.
Would that be sufficient to drive this amp to full capacity?
It is most likely that any little preamp will do fine.
Hi Daniel. Since you're paralleling these chips what's the max safe voltage you can run into 8 Ohms? I just found 2 nice 30-0-30 450VA transformers that I can hopefully use here.
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