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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 25th September 2017, 04:49 PM   #371
df audio is offline df audio  Canada
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Has anyone tried switching these boards on and off using the "standby" pins as opposed to switching the actual DC input? The standby power consumption of the 7498 is pretty low, and the only thing I'm worried about is whether the speakers will pop if I don't utilize the "mute" pin as well. I plan to simply place a small switch across the standby pins, and keep the original DC barrel jack to connect to a laptop power supply.

The datasheet reports that one should pull up the standby pin and then pull up the mute pin to minimize popping on startup, then do the opposite on shutdown.

(BTW my board hasn't arrived yet, and probably won't be for quite a while)

Last edited by df audio; 25th September 2017 at 04:53 PM.
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Old 25th September 2017, 05:02 PM   #372
DreadPirate is offline DreadPirate  United States
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I have a switch to break the (+) in the DC in on the way to a 10K uF tank cap and I do not get any popping.
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Old 4th October 2017, 03:41 AM   #373
df audio is offline df audio  Canada
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So my Sanwu board (deluxe version with the rca jacks) arrived today. Turns out they actually forgot to solder one of the capacitor legs onto the pcb; I had to do that myself. I'm running this on a 24V 3A supply.

Simply switching the standby pin (as I asked about in my previous post) to turn the amp on and off does work without popping.
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Old 7th October 2017, 12:02 PM   #374
JonesySA is offline JonesySA  Australia
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I just perused all pages. What is the best sounding board and is there an on/off pop? I'm not sure if I should build a tda or another tpa.
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Old 7th October 2017, 12:13 PM   #375
Ingborgbo is offline Ingborgbo  Sweden
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I'm waiting for that 2.1 YJ board to arrive. Meanwhile I'm toying with the blue heatsink veraion and I love it. No on/off pop and it's performing very well with my 8ohm apeakers. I haven't tried the praised Sanwu board but the blue heatsink one I do recommend. Well worth the 12-13 dollars
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Old 7th October 2017, 12:32 PM   #376
Yatsushiro is offline Yatsushiro  France
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Quote:
Originally Posted by JonesySA View Post
I just perused all pages. What is the best sounding board and is there an on/off pop? I'm not sure if I should build a tda or another tpa.
I have 3 7498/7498E boards, this is my favourite (driven by RPi running PcP, Allo Piano DAC, into Q Acoustics 2050i speakers). Adjustable gain, can be switched into mute/standby modes, low current 12v out for LED, smooth volume pot, no pops - a very quiet amp.

TDA7498E 160WX2 digital stereo amplifier board PBTL 220W mono channel 24v-36v | eBay
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Old 8th October 2017, 01:32 AM   #377
JonesySA is offline JonesySA  Australia
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Quote:
Originally Posted by Yatsushiro View Post
I have 3 7498/7498E boards, this is my favourite (driven by RPi running PcP, Allo Piano DAC, into Q Acoustics 2050i speakers). Adjustable gain, can be switched into mute/standby modes, low current 12v out for LED, smooth volume pot, no pops - a very quiet amp.

TDA7498E 160WX2 digital stereo amplifier board PBTL 220W mono channel 24v-36v | eBay
Have you compared it with the Sanwu boards?
Having read the whole thread most of the pictures do not work. Is this the best Sanwu board everyone refers to:
Sanwu Amplifier TDA7498
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Old 8th October 2017, 12:52 PM   #378
Yatsushiro is offline Yatsushiro  France
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Quote:
Originally Posted by JonesySA View Post
Have you compared it with the Sanwu boards?
Having read the whole thread most of the pictures do not work. Is this the best Sanwu board everyone refers to:
Sanwu Amplifier TDA7498
These are the other 7498 boards I have (I actually run a 4th, a mono driving a sub):

TDA7498 100W + High-power Digital Amplifier Board AMP Board with Radiator 100W | eBay

TDA7498 dual-channel digital Audio Stereo amplifier board 100W+100W 12V 24V car | eBay
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Old 28th October 2017, 12:24 PM   #379
MALATO is offline MALATO  Australia
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Originally Posted by DreadPirate View Post
I have removed and measured these 1000uF/35V Sanyo WG caps and found them all to be .02-.03 mΩ, so they measure okay, but these are known counterfeit capacitors. The "bulging" was probably just a quality control issue on these caps, true bulging caps would reflect a poor ESR measurement and these did not. But I did replace them with ZLH capacitors, 470uF/35V anyway. This is the only mod I have done thus far.

I have tried both 32V and 24V switching power supplies on this unit and, for now, I am believing his board to be just "OK." It is not among the best Class D I have heard, but it does exhibit good detail and plenty of bass. But I find the sound "busy" and "congested" and somehow not satisfying musically.

I plan on changing the input caps to 2.2uF MKT 1822. Also, note the output filter is different than the datasheet. The board has 22uH inductors with 470nF differential caps with 10Ω resistors, other caps value unknown. I may try to modify this to be closer to the datasheet, but working with these SMD devices is not something I'm looking forward to.

The board is generally quiet with no hiss or hum and I believe the gain (which is adjustable via jumpers) is at the default 26.
Hi DreadPirate,
Can I ask why you would replace the 35V/1000uF capacitors with a smaller value of 35V/470uF? Generally i thought an upgrade entailed increasing the capacitance and not to decrease?

Cheers,
Malato
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Old 28th October 2017, 07:09 PM   #380
DreadPirate is offline DreadPirate  United States
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Quote:
Originally Posted by MALATO View Post
Hi DreadPirate,
Can I ask why you would replace the 35V/1000uF capacitors with a smaller value of 35V/470uF? Generally i thought an upgrade entailed increasing the capacitance and not to decrease?

Cheers,
Malato
The TDA7498 datasheet has a single 2200uF on the power rail, so 4x470uF (1880uF) for both channels is actually pretty close to the datasheet.

For reference, see that Class D amp datasheets rarely have a great deal of capacitance at this location, here is a list of several amps I have and their datasheet capacitance per channel on the power rail:

TA2020: 180uF
TA2024: 180uF
YDA138: 1uF
TDA7297: 470uF
TPA3110: 100uF
TPA3116: 220uF

And in almost all cases, these are bypassed by one or more smaller capacitors:

TDA7498: .1uF and 1uF
TA2020: .1uF
TA2024: .1uF
YDA138: --
TDA7297: .1uF
TPA3110: .1uF and 1nF
TPA3116: .1uF and 1nF

I also put a large capacitor, 10000uF or so (whatever I have on hand) at the incoming power jack. Why? Because I have a bunch of capacitors that need a home .

Typically, the Chinese boards put a lot more capacitance on the board at this location than is called for by the datasheet. I figure the chip manufacturer is in a better position to determine what is best for the chip.

I cannot say one way or another whether the caps I replaced are responsible for this board sounding so good now (I changed them right off the bat when I got the amp and also put MKT1822 2.2uF on the inputs), but on a YDA138, they made a drastic difference in sound quality, I would not underestimate the importance of having a good quality capacitor here, it can make a large improvement in sound.
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