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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 24th March 2019, 05:13 PM   #711
pompebled is offline pompebled  Netherlands
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Join Date: May 2011
Location: Sneek
Marginally better.

6,8K is louder, but not nearly the 'power' I had without the Voltage divider.
With the 6K8 in place I can turn the volume up to the 12 o'clock position without hurting my ears.
Source is the TV with the volume bar at 50%.


Regards, Jan
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Old 24th March 2019, 06:43 PM   #712
chermann is offline chermann  Austria
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Join Date: Jan 2017
Location: Vienna
so you have reserves for 3 o´clock
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Old 24th March 2019, 11:24 PM   #713
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by pompebled View Post
Marginally better.

6,8K is louder, but not nearly the 'power' I had without the Voltage divider.
With the 6K8 in place I can turn the volume up to the 12 o'clock position without hurting my ears.
Source is the TV with the volume bar at 50%.

Regards, Jan
@pompebled, @Chris,

Sorry for the late reply. I had to go with the dog, else she (the dog) takes me for a walk . Then dinner was ready, Internet problems………..

As Chris explained well, there are output levels from any kind of music sources and they are rarely the same. Further, the output from the power amplifier depends on the output impedance of the source and the input impedance of the amplifier. For TDA7498, the input impedance should be 60KOhm. Old CD players used to operate with 47K-100K amplifier input impedance. I assumed some 25K would be OK.

The potential output power of the amplifier remains constant whether you use that potential or not. Even if the sound level with the reduction element inserted is not as loud as before, the amplifier can potentially deliver as much power as before. Most people never use the full potential of their amplifier. You say that above 12 o’clock it starts hurting your ears (and bring your wife back into chock). Then you still have the possibility to go all the way to 5 o’clock, damage your hearing and start a dispute with the neighbors. You still want more? Increase the 6.8K resistors.

I use such reduction elements myself because the gain in the signal chain is rarely as it should be.
The impedance of the reduction element (for yours, 22K+6.8K) should be rather low in order to keep noise down. But, the impedance must not be so low that the source cannot pull the reduction element. I assumed your CD player could handle down to 25K. I adjust my reduction elements such that I have “11 o’clock” at normal listening level. Perhaps I do not reach the full amplifier potential at 5 o’clock – so what? I bought a too powerful amplifier. The important fact is you have the sound level you like and not that you get out all the Watts you have paid for.
I understand that you have no more hiss and harsh sound – that is important.

Thanks to Chris for kindly referring to me as “expert”. I proudly show this to my wife who immediately tells me to be “expert” in cleaning up my electronics mess. Wifes have no respect for titles.

May the waters in Sneek not raise above safe levels,
FF

Last edited by FauxFrench; 24th March 2019 at 11:33 PM.
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Old 24th March 2019, 11:32 PM   #714
FauxFrench is offline FauxFrench  France
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Originally Posted by zeroFILL View Post
@FauxFrench: Is it Voltage Divider that you suggested to @pompebled?
Voltage Divider Calculator

Yep.
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Old 25th March 2019, 06:22 AM   #715
chermann is offline chermann  Austria
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Join Date: Jan 2017
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I proudly show this to my wife who immediately tells me to be “expert” in cleaning up my electronics mess. Wifes have no respect for titles.

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Old 25th March 2019, 08:46 AM   #716
pompebled is offline pompebled  Netherlands
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Join Date: May 2011
Location: Sneek
Hi guys,

I've been playing with the values in the Voltage divider yesterday and indeed found that increasing the 6K8 reduces the amount of Voltage reduction.
I'll experiment with larger values.

I used the amp to power my main speakers, to determen which of the two TDA7498 boards sounds the best for those main speakers. My goal is to use the most powerful and 'less pleasing' sounding amp on the subwoofer(s) with an electronic cross over at 80Hz.

It looks like that choice has been made already, now I have to get the black board TDA to deliver the maximum output without harshness (which I don't expect to be an issue when I have no signal on that amp over 80-100Hz upwards).

I'll keep you posted.

I know the 'clean up your shed routine' from my wife, testing the amps in the living is on the edge...


Sneeks lies below sea level, but we have sufficient pump capacity to keep our feet dry.
When the wind direction is not favourable for letting off the excess at low tide, the biggest steam powered pumping station in Europe is fired up to assist. This attracts lots of people to Lemmer, as it is open to the public and seeing it under steam is much better than to visit it when it's stationary.


Regards, Jan.

Last edited by pompebled; 25th March 2019 at 08:52 AM.
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Old 30th March 2019, 03:42 AM   #717
iowajosh is offline iowajosh  United States
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Join Date: Jan 2016
I had two boards die this week. I leave them plugged in with the volume turned to zero. Is that wrecking them? The one lasted for a long time but this second one for a day. Recommendations of one to try?
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Old 30th March 2019, 05:23 AM   #718
zeroFILL is offline zeroFILL
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Join Date: Oct 2018
Quote:
Originally Posted by iowajosh View Post
I had two boards die this week. I leave them plugged in with the volume turned to zero. Is that wrecking them? The one lasted for a long time but this second one for a day. Recommendations of one to try?
There are many variations of TDA7498 board out there, which one is yours? Also the power supply and speakers?
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Old 30th March 2019, 07:56 AM   #719
jimk04 is offline jimk04  United Kingdom
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Join Date: Jul 2018
Location: North Notts
I left a 7498 board powered up for months...no issue.
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Old 30th March 2019, 08:10 AM   #720
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by iowajosh View Post
I had two boards die this week. I leave them plugged in with the volume turned to zero. Is that wrecking them? The one lasted for a long time but this second one for a day. Recommendations of one to try?

I hope you had loads (speakers) on the boards all the time they were powered. No load on a class D amplifier when it is powered up may destroy the amplifier. Even for short moments.
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