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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 26th November 2014, 06:02 PM   #11
schdrag is offline schdrag  Switzerland
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Join Date: Nov 2014
Hi Buehgemeiste
Have you used a plastic enclosure?
How did you connect the 3 pin connector for the input? On ebay ther are special cables "2.0CH Audio Input Connector Cable" (i have bidden, but I don't want to pay EUR 5 for that cable, it's not even shielded). I have ordered the tda7498 today and I'm awaiting the delivery (I'm also waiting for the tda7297 board, which was € 3,23). Has anybody used the tda7498 with 12V? According to the data sheet, it would work and deliver about 12W, which would be sufficient to me with minimum distortions. I wonder weather or not the cooler is sufficient for 100W (passiv).
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Old 26th November 2014, 07:50 PM   #12
Buehgemeiste is offline Buehgemeiste
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Join Date: Oct 2013
omg, im really a noob, so i hope some of the more experienced guys will support us.

yes, i have tried both plastic and metal enclosures.
both work well for me.

the 3 pin connector is a special type of jst-connector.
jst + two letters, but i do not remind which atm.
for testing and fast switching between hardware i use dupont wire.
you can remove the connector carefully and wire the rca-connectors (or whatever you use) directly to the board.
inside one enclosure i gave to a friend i used a crimped connector like this one Housing Connector 2.54mm 3 Pins
but i had to cut away some of the plastic surrounding the pins on the amp, so the connector fits in.
if you are willing to modify the plastic you can use pretty much any connector for 2.54mm pitch.
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Old 26th November 2014, 09:08 PM   #13
Thor Ra is offline Thor Ra  Denmark
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Join Date: Nov 2012
Quote:
Originally Posted by schdrag View Post
I will use a metall case and I will use short cables to my subwoofer, because the cables and the speaker influence the characteristics of the class d amplifier (by the way I bought the US $12.86 tda7498 from aliexpress, tzt trading including free transport to Switzerland). I read that class d especially tripath cause high frequency emi, hopefully I needn't add an elektor HF Filter.
I have one of these on the way too (paid $12.67 during the 11.11 sale on Aliexpress) along with this PSU which I got for $18.65 including shipping. Will be fun to see what such cheap parts can do with my Q Acoustics 2050i speakers.
Btw. the impedance of the speakers is rated 6Ω nominal (4Ω minimum). Does that call for any mods?
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Old 27th November 2014, 09:33 AM   #14
schdrag is offline schdrag  Switzerland
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Join Date: Nov 2014
Quote:
Originally Posted by Buehgemeiste View Post
you can use pretty much any connector for 2.54mm pitch.
Thanks for the hint; st recommends a output low-pass filter, see page 23, figure 24 and 25, my speakers however have an impendance of 4 Ohm. Do I need this filter for the cheap tda7498 modules?
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Old 27th November 2014, 09:44 AM   #15
Buehgemeiste is offline Buehgemeiste
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Join Date: Oct 2013
Click the image to open in full size.

i disassembled the heatsink and one of the big white 5W resistors to see all the traces.
this is actually even more weird than i tought.
i used ltspice to draw a circuit diagram of the output filters i have on my board.
i'm waiting for this board to arrive:
Assembled TDA7498 (100W+100W) class A Power amplifier board-in Amplifier from Electronics on Aliexpress.com | Alibaba Group
i bought it on the 11.11.-sale.
it seems to use a lot of through hole components.
so my goal is to mod that with trevmar's suggestions from this thread:
http://www.diyaudio.com/forums/class...8-example.html
and compare it to the black board.

edit:
R1 and C1 are smd parts beneath the heatsink (long traces between the chip and the L's).
The 220n (blue) are 22K63 and look very cheap.
The 33n seems to be a film resistor.
R2 is a 5W rated cement resistor.

Last edited by Buehgemeiste; 27th November 2014 at 09:50 AM.
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Old 27th November 2014, 12:15 PM   #16
schdrag is offline schdrag  Switzerland
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sorry, I'm not knowledgeable in electronics (only the very basics). The shielding of the case doesn't seem to be that important, see diyaudio
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Old 27th November 2014, 03:43 PM   #17
schdrag is offline schdrag  Switzerland
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Join Date: Nov 2014
Quote:
Originally Posted by Thor Ra View Post
I have one of these on the way too (paid $12.67 during the 11.11 sale on Aliexpress)
Have you noticed any distortions? Have you tested another power supply (e.g. notebook power supply)?
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Old 27th November 2014, 06:35 PM   #18
tbj is offline tbj  United Kingdom
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Join Date: Oct 2012
Received the board tonight, so naturally I had to test it straight away

Pleasantly surprised. I'm not 100% on the sound yet (only tested it via Youtube on PC, need to find a CD player) but it sounds alright, with plenty of punch.

Building a case to put it in soon.
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Old 30th November 2014, 12:23 PM   #19
schdrag is offline schdrag  Switzerland
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what are the dimensions? What about the height including cooler excluding cooler? I want to build it into my subwoofer. The opening for the terminal box has the dimensions 75x98mmx21

(87 72) mm x ?

What about the CD player test?
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Old 18th December 2014, 05:48 AM   #20
Mobin is offline Mobin  United States
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Location: Wasatch mountians
How many amps are you supplying it? The only requirement i see for 100 watts is 36v supply
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