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Old 30th April 2013, 08:15 PM   #431
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Default Array power and prettier sound.

Packing my suitcase, rounding up the critters and heading to the farm today, Before I go, I thought I'd try bracing up the front end shield with a simplified array in order to dial back the compensation for a faster speed. Arrays are good in theory, but making them work usually involves active devices for series elements. This was astonishingly easy. . .

Cleaner
I changed the MBR schottky to ordinary old 6A05's from the radio shack. No need for the terminal block. These diodes plug right in to the V+ and V- pads of the amplifier board. V+ diode's stripe touches the board. V- diode points away from the board. DC cable connects to these. 0v is connected direct to the board's 0v pad normally. Now we can add more reservoir aboard for more clean power like this:
Stronger
Under the board, I soldered an additional set of 220uF capacitors. Now the power circuit has 220u||220u (low loss quick 440u) per each rail. That's your array power and it looks like: A set of 220u capacitors on top of the board AND again on the bottom of the board (high quality 440u per each rail). The diodes have allowed array power to work quickly, and likewise, regulators (optional) should work as well.
Faster
With the stronger shield providing better dampening (darn that single layer board!!), enough ringing has been removed, that now we can set the cruise control to higher speed--change the 82n lead lag cap to 47n (you can test drive 39n for treble difference). Wow, much less compensation needed.

Board issues
I cannot do more for the Jim's Audio TDA7294 single layer + mad pinout = disaster layout board, because the need of added compensation is board layout related. Please, please on new builds, choose the TDA7293 Parallel which has a better performing layout, greater linearity, twice the power and half the price. No wonder Klaus and Tom went all enthusiastic over power and layout. Yes, if you want a better amp, get a better board.

Okay. I'm off to the farm now.
Here's the corrected and stabilized schematic for the single layer Jim's Audio TDA7294 kit.
Attached Images
File Type: gif TDA7294-FidelityForce.gif (38.9 KB, 202 views)
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Last edited by danielwritesbac; 30th April 2013 at 08:25 PM.
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Old 30th April 2013, 09:24 PM   #432
redjr is offline redjr  United States
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Speaking of Klaus... what's the status of a the new board design/fabrication? Haven't read anything in months about it. Has it died an unenthusiastic support factor death?
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Old 30th April 2013, 09:49 PM   #433
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Geeze, are you sure you don't want to try different types of power supply caps while you're waiting for the car to warm-up?

... just go already!!!

Thanks for hammering it out before you left, I've ordered a pair of the parallels and I'll chime in after a few weeks.

Thanks Kean!
Any chance we could try for a lower gain version x20 or x10?

Enjoy your trip!

Thanks,
Jeff
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Old 1st May 2013, 12:48 AM   #434
redjr is offline redjr  United States
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Quote:
Originally Posted by AudioLapDance View Post
Geeze, are you sure you don't want to try different types of power supply caps while you're waiting for the car to warm-up?

... just go already!!!

Thanks for hammering it out before you left, I've ordered a pair of the parallels and I'll chime in after a few weeks.

Thanks Kean!
Any chance we could try for a lower gain version x20 or x10?

Enjoy your trip!

Thanks,
Jeff
Jeff - What particular parallel did you order. I'm about to pull the trigger on one too, but want to get the best one. But, then I expect Daniel to make it better.
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Old 1st May 2013, 01:06 AM   #435
bcmbob is offline bcmbob  United States
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Wow! I have to publicly thank Daniel not only for all the effort and time he has applied to this thread, but also my appreciation for keeping the thread itself alive and moving forward.

The parts I don't have will be in my next order and I'm anxious to hear the improvements.

You guys are great!

(I'll PM Klaus for info. He did say it was more of a long time project. I'm sure the interest is still there)
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Old 1st May 2013, 10:08 AM   #436
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Quote:
Originally Posted by redjr View Post
Jeff - What particular parallel did you order. I'm about to pull the trigger on one too, but want to get the best one. But, then I expect Daniel to make it better.
I hope that is this board. The behavior is really nice. And a link: TDA7293 170W | eBay
Click the image to open in full size.
That's the board that I'm fine tuning with intention to use it for refitting my Technics receiver.
Quote:
Originally Posted by bcmbob
The parts I don't have will be in my next order and I'm anxious to hear the improvements.
For the lead lag comp used to tame that single layer TDA7294v board, you might want a selection of 47n, 39n, 33n, 25n, 22n caps so you can fine tune the compensation. Different operating voltage, and different cap efficiencies affect the board differently, and so that would change the need of compensation as well. Smaller cap value = less compensation. Basically choose the cap value in that range for neither too little nor too much treble. Insufficient treble or uncomfortable weird ear pressure is unstable or ringing--cap is too small, but too much treble is cap too large.

Adjustable gain, is really helpful when trying to sync compensation. It replaces the 510R+220R Feedback-Shunt resistor seen on the schematic. Instead of the fixed value, we make the Feedback-Shunt resistor adjustable (within a practical range). To install that, you just put 1 outboard pin of a 100R multi-turn trimmer right on the NFB-shunt cap "+", and then glue the trimmer down to the board, and then the other two pins (center pin plus opposite outboard pin of the trimmer) connect to a 680R, which then goes in a straight line, right over to pin2 of the chip. This is really easy. It is the same for both boards. A 200R trimmer can be used, if your amp is under-volted.
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Last edited by danielwritesbac; 1st May 2013 at 10:22 AM.
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Old 1st May 2013, 10:47 AM   #437
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I just searched ebay for "TDA7293 Parallel" ($20) but I did find a slightly cheaper one ($15):

TDA7293 x2pcs 170W Mono amplifier board Kit -29

TDA7293 x2pcs 170W Mono Amplifier Board Kit 29 | eBay



If you really wanna commit, here's a super-cheap 5 pack (home theatre!)

5 PCx Assembled Finished 170w TDA7293*2 Dual Parallel Mono power amplifier board

5 PCX Assembled Finished 170W TDA7293 2 Dual Parallel Mono Power Amplifier Board | eBay
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Old 1st May 2013, 03:42 PM   #438
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Lightbulb TDA7294

Quote:
Originally Posted by danielwritesbac View Post
I hope that is this board. The behavior is really nice. And a link: TDA7293 170W | eBay
Click the image to open in full size.
That's the board that I'm fine tuning with intention to use it for refitting my Technics receiver.

For the lead lag comp used to tame that single layer TDA7294v board, you might want a selection of 47n, 39n, 33n, 25n, 22n caps so you can fine tune the compensation. Different operating voltage, and different cap efficiencies affect the board differently, and so that would change the need of compensation as well. Smaller cap value = less compensation. Basically choose the cap value in that range for neither too little nor too much treble. Insufficient treble or uncomfortable weird ear pressure is unstable or ringing--cap is too small, but too much treble is cap too large.

Adjustable gain, is really helpful when trying to sync compensation. It replaces the 510R+220R Feedback-Shunt resistor seen on the schematic. Instead of the fixed value, we make the Feedback-Shunt resistor adjustable (within a practical range). To install that, you just put 1 outboard pin of a 100R multi-turn trimmer right on the NFB-shunt cap "+", and then glue the trimmer down to the board, and then the other two pins (center pin plus opposite outboard pin of the trimmer) connect to a 680R, which then goes in a straight line, right over to pin2 of the chip. This is really easy. It is the same for both boards. A 200R trimmer can be used, if your amp is under-volted.
[SIZE="<font><font>4</font></font>"]PCB 240W Stereo Amplifier TDA7294 Yiroshi. Design and Redesign YIROSHI mnicolau[/SIZE]

TDA 7294 STEREO AMPLIFIER 240W

regards.
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Old 1st May 2013, 05:16 PM   #439
redjr is offline redjr  United States
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This is the one I ended up ordering.
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Old 2nd May 2013, 05:46 AM   #440
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Quote:
Originally Posted by redjr View Post
This is the one I ended up ordering.
Good!
Kean and I have that board too. I guess Zoe re-stocked pretty fast.
Quote:
Originally Posted by AudioLapDance
Any chance we could try for a lower gain version x20 or x10?
Yes! This well illustrates the need of installing adjustable gain. Of course, low gain will sound as dreadful as the datasheet sample design. However, the trimmer dial would let you install the desire for low gain and still be able to dial in appropriate quality anyway (at higher gain, of course). In addition to so easily resolving that conflict, you can use the dial to precisely synchronize compensations. And, ideal gain varies by both rail voltage and load too. So, I think that adjustable gain should be mandatory.

TDA7294 can use a gain range of 38X~40X in non-inverting mode, or it can use somewhat lower gain in inverting mode, which also needs a transistor buffer added. TDA7294S/TDA7293 has an optional 1X gain mode, which is where the onboard front end is disabled and you add a replacement front end externally, from tubes or transistors or op-amp.

Except for the 1X option, low gain means first ruin the quality and then apply greater negative feedback to recoup some but not all of the quality. Basically, it is a voltage amp, and asking it not to amplify voltage is asking it not to work. That has a few caveats. Low gain can also be done by severely under-volting the amp, but that has the caveat of a lot less output power, which is yet another way to do a lot less amplifier.

Once again, the Honey Badger discrete amplifier has a gain of 41X, and so our gain of 38X is three times less voltage amplification. Given a 1v source, such as a computer, and not running the source all the way to faltering/clipping then means that we need gain in the upper 30's for the power amp to reach the rails. In the most common applications, our 38X is only slightly too much. Even so, I think that adjustable gain is quite important so that you can determine these factors for yourself.

Adding the trimmer is a lot more powerful for audio quality than any amount of audiophile parts. A multi-turn trimmer at feedback-shunt for adjustable gain can let you dial in appropriate standard gain comp to support your specific operating voltage and speaker load. Adjustable gain used for system symmetry will get optimal performance from the TDA729X family. Conversely, arbitrary fixed settings will not result in optimal performance. SO, it seems that we shall need that dial.
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Last edited by danielwritesbac; 2nd May 2013 at 05:58 AM.
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