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-   -   TDA7293 Parallel kit from ebay (modular/slave style, no lossy emitter resistors) (http://www.diyaudio.com/forums/chip-amps/211746-tda7293-parallel-kit-ebay-modular-slave-style-no-lossy-emitter-resistors.html)

danielwritesbac 29th April 2012 04:56 AM

TDA7293 Parallel kit from ebay (modular/slave style, no lossy emitter resistors)
 
2 Attachment(s)
The easy little kit

This chip has Fet output built in, so it doesn't need lossy resistors at the output for paralleling.
http://www.diyaudio.com/forums/attac...arallelkit.jpg
Making two chips as easy as one.
This is documented in the TDA7293 datasheet as a modular approach.

Notes-------------------------------------
Ebay link:
(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

Power circuit:
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).

Voltage:
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.


Cap values:
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.


Resistor values:
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.
The above is new text and new schematic. Previously, there had been some problem getting sufficient gain; however, a just-right gain divider setting with resistors direct (not inserted to pcb), and a power circuit update was the combination that got this little amp up to high fidelity.
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.
(5x3300u caps per rail and a pair of prefab bridge rectifiers is similar but easier.)

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.

CharlieLaub 29th April 2012 05:18 AM

Daniel - a link to the Ebay auction or seller please?

These look great. Very interested.

-Charlie

danielwritesbac 29th April 2012 05:22 AM

Quote:

Originally Posted by CharlieLaub (Post 3005000)
Daniel - a link to the Ebay auction or seller please?
These look great. Very interested.
-Charlie

Sure. There are several vendors. Here is one. Parallel TDA7293 You can find others just by comparing with the photograph in post1.

P.S.
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.

danielwritesbac 29th April 2012 07:44 PM

Gain, bridging, preamp and modern sources
 
1 Attachment(s)
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.

Modern sources:
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.

Bridging:
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:

danielwritesbac 7th May 2012 01:11 AM

Power circuit looks like:
Transformer >
Rectifier >
Smoothing caps (big ordinary standard power caps)
cable >
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.

noddy55 30th October 2012 07:52 PM

Mr.daniel,

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?

Thanks.

danielwritesbac 2nd November 2012 04:14 AM

Quote:

Originally Posted by noddy55 (Post 3221440)
Mr.daniel,
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?
Thanks.

Those are both competent amplifiers, therefore nearly identical sound and high resolution for both. Comparisons between the two, look like any attempt to compare small amp versus big amp. I've tried to answer the question of which I like best, but cannot do so. You'd have to choose depending on how much output power you'd need.

Einric 3rd November 2012 03:35 PM

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?

danielwritesbac 4th November 2012 12:20 AM

Quote:

Originally Posted by Einric (Post 3226489)
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?

I like this amp board for the easy way to drive difficult speakers at high power. I like the convenience that any fine tuning is done to only the "master" chip--not having to do everything twice. I like the layout of the board that is pretty despite 30 pins. And, I like that parallel chip amplifiers can sound effortless when used at less than max. It takes 2 amp boards for stereo.

It is most likely that any little preamp will do fine.
.

DarpMalone 6th March 2013 09:46 PM

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.

Thx


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