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Old 12th July 2013, 07:49 AM   #51
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Thanks! That's a good idea! Well, the SMD is a good idea.

However, I'm not doing board design at this time because some of the accessories (and I love accessories) are TBD (not yet built). In any case, if you wanted it streamlined and inexpensive, then you probably want the boards listed in post#1 of this thread.

A more minimal mod version is possible, for a much easier assembly of something that was already easy. And, the performance is almost as good (very similar). Is that of any interest?
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Old 12th July 2013, 03:23 PM   #52
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Quote:
Originally Posted by danielwritesbac View Post
Thanks! That's a good idea! Well, the SMD is a good idea.

However, I'm not doing board design at this time because some of the accessories (and I love accessories) are TBD (not yet built). In any case, if you wanted it streamlined and inexpensive, then you probably want the boards listed in post#1 of this thread.

A more minimal mod version is possible, for a much easier assembly of something that was already easy. And, the performance is almost as good (very similar). Is that of any interest?
Hi,

I don't really mind paying for an optimized PCB since I like a clean look, even though it will be hidden in a chassis. If someone has the skills and is interested in doing a PCB layout using part SMD and through hole it would be great!

Thanks
Do
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Old 16th July 2013, 04:54 AM   #53
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Quote:
Originally Posted by danielwritesbac View Post
If what is shown in the photos is too much work, simple 220u and MBR1635 (or MBR1645) per rail works great, is low loss, and still performs on stereo separation.
Optionally, MUR diode can be used. Or MURS diodes with the nicely insulated tab may be even better.
Quote:
Originally Posted by pinnocchio
I don't really mind paying for an optimized PCB since I like a clean look, even though it will be hidden in a chassis. If someone has the skills and is interested in doing a PCB layout using part SMD and through hole it would be great!
Clean look? Okay. See photo. It is an illustration. But it shows a simplified means to get nearly the same performance, and that clean look too.
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File Type: jpg TDA7293-easier.jpg (240.7 KB, 432 views)
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Old 5th August 2013, 12:53 AM   #54
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Default Class G, actually Manual Class G and a gain switch too.

Power
The easy way for Class G is to arrange a sturdy DPDT switch to change the transformer to half voltage. This is done by switching the dual primaries toroid transformer to series or parallel for voltage change. For example, my 28+28vac transformer changes to a 14+14 transformer. In this case, the switch changes the amplifier to either 70W for high power fun or 14W for energy saving normal use.

I'm currently looking for an "Off, On, On" switch that could, if the center position is low power, perform a rudimentary soft start, since it always goes to low before it goes to high.

Gain
This also gives the possibility to use a small DPST for reducing the gain on the amplifier boards for whenever they're set to low voltage. Yes, these TDA7293's can run lower gain and image well, when used as 14W amplifiers. So, this additional switch is also low-high. High would be a gain of 38X, but low could simply engage additional negative feedback. There's a few different options to explore, but they are switchable. The amp likes lower gain when run lower voltage, and it likes higher gain when run higher voltage. So, two different settings are probably necessary.

Results
Given these two switches (one for power, another for gain), you can have option of a pretty little 14W amp with the switches set on low or flip both switches to high for a highly palatable tone at high power.

4 ohms
With 4 ohm speakers, the power output is about 25 watts per channel on low or 90 watts per channel on high.
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Old 5th August 2013, 07:59 AM   #55
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would the chipamp compensation need to be changed when the gain is changed?
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Old 6th August 2013, 07:14 AM   #56
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would the chipamp compensation need to be changed when the gain is changed?
Cutting the power voltage in half causes the need of compensation readjustment that may could be done by setting lower gain. But I really wonder. . . How do you recommend doing the cabling for switchable gain?
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Old 18th August 2013, 07:38 PM   #57
routhun is offline routhun  United States
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Default Here is mine

Hi Folks,

Here is mine. I bought PCB, power supply PCB and case from eBay. Case came with power, speaker and RCA connectors. Built according to schematics except Rf, Ri changed to 47k, 1,5k - Feedback capacitor changed from 22uf to 220uf and the bootstrap to 150uf.

It sounds wonderful, in the pictures it is sitting on top of VSSA. Main differences between these two are - VSSA is bit more transparent you can perceive the layers of sound. TDA7293 amp has bit more punch in the bass region. We can find the difference between these amps when we do A/B testing. Otherwise we can equally enjoy the sound of both these amps and you forget the differences.

Finally, I would like to Chinese sellers on eBay, without them I couldn't build this high quality amp with such a low price. I do remember how hard to get the PCBs, only way is to order in bulk. Forget about the chassis, there was no place to buy a good chassis at reasonable prices.
Attached Images
File Type: jpg TDA7293 Amp Front.jpg (274.0 KB, 302 views)
File Type: jpg TDA7293 Amp Inside good.jpg (528.3 KB, 305 views)
File Type: jpg TDA7293 Amp Back.jpg (315.3 KB, 295 views)
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Old 19th August 2013, 03:24 PM   #58
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That is a beautiful job on the build!
However, I do have some comments on the electronics.

I see a center tap configuration, which has an opportunity.
Transformer reacting with your bridge rectifier makes noise that can cause masking. But we could hinder the problem. One variable RC made with a 2.2uF polyester cap series to a 50 ohm variable resistor can be hooked up from ~ to ~ (across the transformer) to dampen that area so that the high pitched racket doesn't put masking into the amplifier power circuit. This RC doesn't attach to ground. Turn the dial for best treble imaging clarity.
After that. . .
Quote:
Originally Posted by routhun View Post
. . . it is sitting on top of VSSA. Main differences between these two are - VSSA is bit more transparent you can perceive the layers of sound. TDA7293 amp has bit more punch in the bass region. We can find the difference between these amps when we do A/B testing. Otherwise we can equally enjoy the sound of both these amps and you forget the differences.
This is for the layers of sound, aka open sound.
It may be important to note that, with a chip amp, the entire amplifier board is the small signal area.
Click the image to open in full size.
This photo matches up with the schematic at Post#1.
The photo shows amplifier board power decoupling forced to work, which is the most certain way to guarantee that it does work. The diodes also provide virtual dual mono stereo separation since each amplifier board has a little bit of somewhat "private" power.
All of the above is good for clarity and imaging.
These diodes are runing on only DC (you Do still use a power supply board). Suitable diodes include standard silicon diodes like 6a05 (at the radio shack) 6a01, 6a02, 10a05, 10a01, 10a02 and similar. This small voltage drop doesn't decrease usable audio output power at all, but it will do less constant power, more peak power, which is more useful, more dynamic and more lifelike.


Also,
This is a gain compensated amplifier and it needs to be set precisely; so, I would suggest to use a multi-turn variable resistor at feedback-shunt resistor. In your example with 1.5k, you can use 1k multi-turn trimmer series to 510 ohm resistor. The ideal location is very close to and directly between the nfb-shunt cap and pin2 of the master chip (which are conveniently close to each other). My schematic has this adjustable gain dial because the ideal compensation (and therefore ideal gain) depends on the power supply voltage used. The sweet spot is very narrow and nearly impossible to get with fixed resistor values. Consider it an audio quality dial.

P.S.
Just like a discrete amp, the chip amp can benefit from cleaner power and precision compensation.
After completing the work, then it could then be more interesting to do the A-B comparisons.
I hope this information helps.
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Last edited by danielwritesbac; 19th August 2013 at 03:27 PM.
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Old 19th August 2013, 05:51 PM   #59
routhun is offline routhun  United States
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Hi Daniel,

Thank you for detailed feedback and suggestions for improvement. I'll go through them and implement them at my free time and surely post my findings in this thread. I can tell you this seems so simple but it is a serious amplifier that can easily compete with other high end ones.

Thanks
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Old 20th August 2013, 12:29 AM   #60
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Indeed a low price for so many concert tickets. It doesn't sound fake--it sounds like the concert, with all the energy and lifelike excitement. That's why I like it.
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