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Class D Switching Power Amplifiers and Power D/A conversion

Ebay cheap TDA7498 boards
Ebay cheap TDA7498 boards
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Old 12th February 2018, 04:41 PM   #561
taita is offline taita  Netherlands
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Quote:
Originally Posted by FauxFrench View Post
Yes, 10000uF is fine. Connect in parallel to the "+" and "-" supply terminals. Just short the polarity protection diode (between the filter chokes) first and be careful with the polarity in the future. The 10000uF will work for both channels.
I connected the capacitor without shorting the polarity diode. Why do I need to short this?

Quote:
Originally Posted by FauxFrench View Post
Air coils is something I relate to passive speaker filters (low impedances and no saturation) where the frequencies are up to 20KHz such that radiation is less a of a problem. And, from old radio receivers where ferrite handling HF frequencies well was difficult to find.

Looking at the cheap amplifier modules, in particular I buy, they cost from 1 EUR to 20 EUR (I recently bought a TDA3255 board at 42 EUR as an exception). You can imagine what can be produced in your country for max. 20 EUR? The amplifier modules we buy (origin probably always from far east) are terribly cheap (we cannot compete with such prices). But, to sell at such prices, also out there (east) they need to save on anything they can.
Then, we put this max. 20 EUR amplifier on our speakers that cost several hundreds of Euro. Not necessarily a balanced spending on the system components. Therefore, only spend very good chokes on amplifiers where the other amplifier components deserve really good chokes. Buy cheap amplifiers for experiments and gain of knowledge and eventually put better chokes in temporarily - if the amplifier is destroyed during the experiments, OK it was cheap and the best components are recovered for the next project.
I agree with your observations of the balance between expensive speakers and cheap amplifier. At the other hand I think most of these amplifiers are not balanced as well as the quality of the chip in many cases is better than the rest of the board.

Buying these cheap boards is somehow addictive the more I know of it, although I have some failing ones you are aware of.

The 7498E board with fan you discussed in your former post has good chokes, but the capacitors to me seem very small. Are these folie capacitors? The pp capacitors I use for crossover filters are larger.
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Old 12th February 2018, 08:53 PM   #562
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by luxury54 View Post
thanks for clarifying, one friend bought a supposedly TDA7498E board like this in your link but together with an aluminium enclosure; the chip fried after some experiments and after taking out the heatsink he found out that the chinese supplier sold him a plain TDA7498 without "E"; after this he ordered a genuine "e" chip from mouser and now he is happy with it; did you had the curiosity to look under that heat sink?
also, do you happen to know what value are those chokes on the output? are they in the 10-15 uH range to be suitable for 4 ohm loads or would I have to buy other ones?
I found these 2 options on ebay, maybe you can take a look

Coilcraft DO5010H-123ML 12uH inductor Irms=5.2A, Isat=8.5A, 28milliohms | eBay

5pcs 10uH 7.5A Small Toroidal Inductor Magnet inductance Coil Anti-Interference | eBay
To cheat and mount a TDA7498 instead of a TDA7498E is a lousy thing to do if it was sold as a TDA7498E. Replacement requires a steady hand. I had the curiosity when I shorted the polarity protection diodes and mine is a real TDA7498E.

The chokes on Chinese boards are often a guess. The chokes on this red board use red cores which is the better. Exact value?
NXP (formerly Philips) suggests 10uH/1.5uF for 4 Ohm loads, 15uH/1uF for 6 Ohm loads and 22uH/680nF for 8 Ohm loads. NXP is generally a very competent company. But, the values need not be exact and 15uH/1uF can be used in case of doubt for 4-8 Ohm. I would try the initial ones for a start without replacement.

Chinese chokes: I know three types - red core (the better with lower permeability but higher current before saturation and probably less abrupt saturation), black core
5pcs/KS065060 17MM Iron silicon aluminum 15UH 1.2 Line 10A Magnetic ring inductors Annular inductance-in Inductors from Home Improvement on Aliexpress.com | Alibaba Group
3pcs/23MM 22UH 1.3 Line Iron silicon aluminum Magnetic ring inductors Annular inductance 90 125A 15A-in Inductors from Home Improvement on Aliexpress.com | Alibaba Group
(which I have used with success) and blue/green/yellow-ish (which I cannot recommend as they seem to have very high core losses - I have tried them).
Toroidal cores are color coded according to characteristics but unfortunately every manufacturer uses his own codes and we do not know the manufacturer:-((

The first ("Coilcraft") choke you suggest is a semi open SMD type. The semi open may leave quite some stray-fields (noise) and I have only seen such used for low power amplifiers. I have no experience myself.
The second type you suggest is a toroidal choke on a blue/green/yellow-ish core, hence, with important core losses according to my experience.

I have tried the two black-core types shown above with good results.
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Old 12th February 2018, 09:39 PM   #563
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by taita View Post
I connected the capacitor without shorting the polarity diode. Why do I need to short this?
You "need" not do it but I did it. The reason is that if I want my external decoupling capacitors to assist the onboard capacitors the best, I do not want a voltage drop from the diodes in-between. I want the supply voltage charge to be available with as little impedance as possible.

Quote:
Originally Posted by taita View Post
I agree with your observations of the balance between expensive speakers and cheap amplifier. At the other hand I think most of these amplifiers are not balanced as well as the quality of the chip in many cases is better than the rest of the board.

Buying these cheap boards is somehow addictive the more I know of it, although I have some failing ones you are aware of.
The amplifier chip sets the limits of the complete amplifier and the external components should be selected to match the chip quality. But, class D chips are often very cheap and many buy because they see "TDA7498" at an attractive price without considering if the amplifier implementation is well made.
I bought a Bluetooth+TPA3110 board (it worked) but realized that the quality of the TPA3110 is above that of the Bluetooth chip. It is one board so I cannot change that implementation. Next time I bought an external
HIFI Class Bluetooth 4.2 Audio Receiver Amplifier Car Stereo Modify Support APTX Low Delay-in Wireless Adapter from Consumer Electronics on Aliexpress.com | Alibaba Group
to use with a separate amplifier and the combined result was much better. Should the amplifier fail, I still have the Bluetooth receiver.

Quote:
Originally Posted by taita View Post
The 7498E board with fan you discussed in your former post has good chokes, but the capacitors to me seem very small. Are these folie capacitors? The pp capacitors I use for crossover filters are larger.
These are polypropylene foil capacitors if I am not mistaken. Standard quality but OK. Can be found even better (lower ESR) but is it worth spending perhaps another 6 EUR on a 16 EUR amplifier for a more marginal improvement?
Why are cross-over capacitors larger? (oh, it is decades ago I build my own speakers). I looked at various cross-over filters for loudspeakers and found that they typically use 5uF-50uF bipolar capacitors. Thus, a first reason is the difference in value. Next, the class D output filter capacitors do not carry the current in the speaker units (many of the cross-over capacitors do) as they only carry the ripple current from the PWM modulated signal (300KHz-400KHz). The cross-over capacitors carry a much higher ripple current and accordingly need lower ESR. A second reason for the difference in physical size.

Last edited by FauxFrench; 12th February 2018 at 09:50 PM.
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Old 13th February 2018, 05:30 PM   #564
taita is offline taita  Netherlands
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Quote:
Originally Posted by FauxFrench View Post
You "need" not do it but I did it. The reason is that if I want my external decoupling capacitors to assist the onboard capacitors the best, I do not want a voltage drop from the diodes in-between. I want the supply voltage charge to be available with as little impedance as possible.
Ok, I understand but why not connecting the additional capacitor to the capacitors on the board? Then its not needed to short the protection.

Another question: I am thinking of combining different amplifiers for active loudspeakers for instance 7598E for woofer and 7498 for tweeter. Does this give any complications?
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Old 13th February 2018, 05:43 PM   #565
r_kalar_2 is offline r_kalar_2  Bangladesh
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Originally Posted by Uzver View Post
Could you please advise me which TDA7498 board i should buy ?
8 Ohm speakers
I can vouch for my sanwu blue board for 8 ohm. You don't have to modify anything at all. In my opinion the board has better build and better components. Price difference isn't that big also. For cheap SMPS use a capacitor at power input as FauxFrench suggested or can build a capacitance multiplier as I have done. Totally worth it.
Aiyima TDA7498 Amplifiers Digital Stereo Power Audio Amplifier Board 2X100W Amplificador Dual Channel Speaker Impedance 8 ohms-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
Price has gone up since I have bought it.
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Old 13th February 2018, 05:53 PM   #566
zek is offline zek
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Quote:
Originally Posted by FauxFrench View Post
You "need" not do it but I did it. The reason is that if I want my external decoupling capacitors to assist the onboard capacitors the best, I do not want a voltage drop from the diodes in-between. I want the supply voltage charge to be available with as little impedance as possible.
.
Are these two diodes you're talking about?
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Old 13th February 2018, 06:19 PM   #567
luxury54 is offline luxury54  Romania
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I see that you took off the aluminium radiator, is your chip variant also with "E"? is that fan on top always blowing air for cooling or it kicks in just on high power demand? I might buy one of these boards
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Old 13th February 2018, 07:24 PM   #568
chermann is offline chermann  Austria
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@ zek
yes...these are the diodes
go back to
Ebay cheap TDA7498 boards

go back to page 44 i did some measuremnts and Fauxfrench help...as usal
the fan is starting about 41 C and blowing quite silent to the point i measure 37 C and then it stops.

chris
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Old 13th February 2018, 07:51 PM   #569
zek is offline zek
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Originally Posted by chermann View Post
@ zek
yes...these are the diodes
go back to
Ebay cheap TDA7498 boards
chris
Thank you for reminding me, I'm a little older, so I forgot.
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Old 13th February 2018, 08:07 PM   #570
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by taita View Post
Ok, I understand but why not connecting the additional capacitor to the capacitors on the board? Then its not needed to short the protection.

Another question: I am thinking of combining different amplifiers for active loudspeakers for instance 7598E for woofer and 7498 for tweeter. Does this give any complications?
You are right, if you can put the additional capacitors on the board itself, you need not short the diodes. Perhaps you can arrange them on the rear side.

You probably mean (TDA)7498E and, with an electronic cross-over, you can combine the 7498E with a 7498. You can even use a class AB amplifier for mid-range and treble, if you like. The bass demands the most power.
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