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Old 1st January 2013, 10:59 PM   #81
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Quote:
Originally Posted by bcmbob View Post
Also. when using the LED resistor calculator it appears a pot/rheostat is needed to get "actual values". Is that correct.
Near match resistor values: If the LED calculator says 9.4928371K, you don't need a variable resistor to dial that in exactly because an inexpensive 10K will do fine. Just use its "nearest" resistor estimator.
When in doubt, use less current, less milliamps.
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Originally Posted by bcmbob View Post
Before I build a bomb, where to connect the drain resistors at C1 & C2?
You can drain a capacitor by putting a resistor in parallel with the capacitor. See attached photo.
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File Type: jpg Drainer.jpg (46.9 KB, 457 views)
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Old 1st January 2013, 11:21 PM   #82
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For the power supply building, here's a few examples made for dual secondaries transformer.

Basic power supply
First example is the basic power supply with good performance.

Ordinary CRC power supply
Second example is the CRC power supply with noise filtering added at the cost of increased rail sag. This ordinary CRC power supply works for monobloc chip amplifier.

High Power CRC power supply
Third example is a CRC power supply with added diode that limit the filter sag. The diodes turn on and "brace up" the rails when the total amplifier power passes 50w. This high power CRC power supply is nice for Stereo chip amplifier.
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File Type: gif tank.gif (49.7 KB, 444 views)
File Type: gif tankandsmoothing.gif (71.4 KB, 429 views)
File Type: gif TankAndSmoothingNosag.gif (71.8 KB, 415 views)
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Last edited by danielwritesbac; 1st January 2013 at 11:31 PM.
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Old 2nd January 2013, 11:41 AM   #83
KSTR is offline KSTR  Germany
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Hi,

does anybody actually realize that ilimzn has shared the most complete and incredibly competent discussion about the TDA7293/94, mentioning all its issues and the remedies for it? His two posts really deserve to be split from the thread and become a sticky topic "getting the max out of TDA7294".

It's the best summary on the chip and how to use it that you will ever find, period. There is effectively nothing I could add to it, other than saying I can back up any sentence he wrote, notably the supply issues. If you precisely follow the design hints he is giving then you'll be rewarded with an amp that sounds as good as it measures...
...that is, you also need to take great care about the layout which mostly means indentify and seperate all the different current loops and make their enclosed area and hence mutual electromagnetic coupling as small as possible, as well as making any I*R drops irrelevant by referencing "GND" to the correct points. Then take care about higher impedance nodes and make their exposed surface area small to avoid electrostatic pickup.
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Old 2nd January 2013, 12:23 PM   #84
bcmbob is offline bcmbob  United States
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KSTR,

That would bring up the obvious question - are there members and resources available and/or willing to do what is necessary to develop a board that incorporates those ideas? Perhaps if a base PCB could be posted here, or on something like Google Docs, that development process could begin.

Anyone with good chops on a layout program willing to get the ball rolling ??? There may be the plausibility of sectioning off segments if it is unrealistic for just one person to do the complete base design.
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Old 2nd January 2013, 02:30 PM   #85
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Jay also posted an interesting feedback network at post#53
Quote:
Originally Posted by KSTR View Post
Hi,does anybody actually realize that ilimzn has shared the most complete and incredibly competent discussion about the TDA7293/94, mentioning all its issues and the remedies for it?
Yes, we saw it earlier. That thread is here: Tda7293v
And like Bob, I have a similar question. Where is the double-layer board for it? Due to the mad pinout of the chip in combination with the added complexity, it probably takes an expert PCB layout.

Do you see an easily doable solution for working with the boards that we already have? Adapter? Daughtercards?
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Old 2nd January 2013, 03:06 PM   #86
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I am not in a position to judge the validity of any suggestions related to this chip; I think KSTR meant that it might be better to change the path being taken at the moment (by following some advices made by some members he suggested) in order to truly get the best out of this chip. As Bob noted already, this requires a PCB to be designed. I believe this is one thing Bob has been trying to avoid since the beginning of this thread.

I do hope that future enlightening suggestions will come from members who can offer something that offers a single-sided PCB design, schematic simplicity, and components availability, yet flush the best out of this chip, why not? It is not always necessary that a complicated design will yield better results than a simple one.

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Old 2nd January 2013, 04:15 PM   #87
bcmbob is offline bcmbob  United States
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Let me try to clarify. I thought, and still do, that the sound from a simple $30 kit was pretty amazing. What was lacking in the quality of the top end sounded like it could be improved upon by primarily a few component changes. Though I'm still lagging a bit in implementing some of those suggestions, I plan to go through that process soon. I thought this thread might attract other builders of the same or similar minimalistic design (several eBay vendors offer it) and some comparative results and suggestions would be posted. Still think that's a good idea.

It quickly became apparent many advanced DIYers had recognized the potential of the TDA7294 and proposed a much more sophisticated implementation. That was far beyond my expectations and quite encouraging. Someone earlier stated the development of a new board would require a lot of time, commitment and money to pull it off.

What I think I see now is a dual track, one being the collection of work done by many into a concentrated effort to actually create a new high-grade PCB, the other being the original tweaking. I'm just one member with no design experience (though I am trying to learn some layout programs) but am fully aware a new board would require a lot from more than one source/person. I may have missed it, but I didn't see an actual/published board on the thread Daniel linked to this morning.

I experienced the collective effort that took place in the multi-year development on the MyRef amps, feeling it was enjoyable and productive for all involved. I looks like a lot of the theory work has already been done for this chip. Whether that is a track that proves useful here will be determined by the continuing discussions.
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Old 2nd January 2013, 05:06 PM   #88
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this depends on collaboration level among members and how many members are willing to go for the advanced schematic and high-grade PCB.
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Old 2nd January 2013, 05:46 PM   #89
KSTR is offline KSTR  Germany
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I'll happily volunteer for circuit design and PCB layout of some varieties of TDA7294 amplifiers, trying to cover all the important aspects.

Of course a clean implementation of the typical "datasheet page 1 circuit" already gives, say, 80% of the possible perfomance. If we stick to that basic**) implementation a good circuit and layout is not that hard a task but will take time and thought (give me 1..2 weeks or so). A simple trick for easy chip amp layout is either to use an aluminum L-bracket or mount the chip to the heatsink edge, in order to extend the PCB around the chip's pins to any length/area needed.

**) noninverting config. Personally I'd always go for inverting unless one wants to use a passive pre (volume pot >10k) ahead of it or anything exotic which cannot handle a load in the 1k...10k region. Also I'd omit any protection circuitry and I'd DC-couple the whole thing. Except for "gross user fault" this tends to be safe IME.

Eventually I'm heading to at least a 3 month's sabbatical (starting in March) so I'll finally find the time to delve more deeply into DIY projects where I can give full and sustained support (note that I'm planning to publish a composite chip amp if the thingy works out as expected).
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Old 2nd January 2013, 05:59 PM   #90
redjr is offline redjr  United States
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Bob - What you describe is what is known as scope creep in the project world. What started out as a few simple mods to a $30 PCB based amp, now has the potential to involve a complete redesign of not only the amplifier PCB, but the PSU PCB too! If we go down that path, then our minimalist $30 amp, now becomes, in all likely, several times over the original cost. As I mentioned in my earlier post, while this may be seen as a challenge for some, the additional investment in time, effort and money, may not justify the very subjective incremental improvements to the sound characteristics of the original amp for some. For others, it's like waving a red flag - implying - bring it on!

At least in the DIY community, people can decide for themselves the degree (and extent) to which they implement mods. I know the proper design of a PCB is no trivial matter. It takes a certain degree of knowledge and understanding of electrical characteristics to be done properly. Way outside my level of expertise. Perhaps there are such members that would be up to the challenge. As has been stated, both Daniel and ilimzn have provided a wealth of information relative to improving the 7294 design. And now, KSTR has volunteered his time to redesign the 7294 PCB. So, maybe there will be new 7294 amp in the near future.

Rick
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