Looks good, Jan.
The datasheet I use: https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiC16PCjZjhAhWw34UKHV0SAb0QFjAAegQIBBAC&url=https%3A%2F%2Fwww.st.com%2Fresource%2Fen%2Fdatasheet%2Fcd00244535.pdf&usg=AOvVaw3iLNT0I6eMGAOlMNEpQMpJ
TDA7498 is different from TDA7498E.
I know the problem with SMD size - I have to use reading glasses (+2.0/+2.5) when I work with SMD. I buy them for around 1EUR at Action.
You most likely have to remove the heatsink but for that model it is only fastened with screws, not glued. Check before doing the modification that pins 30 and 31 are actually connected to VDDS (3.3V) and not grounded already.
Luckily the hiss seems not to origin from the TDA7498 board itself. The damping element I described (22K/2.2K) may do the job on its own.
The datasheet I use: https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiC16PCjZjhAhWw34UKHV0SAb0QFjAAegQIBBAC&url=https%3A%2F%2Fwww.st.com%2Fresource%2Fen%2Fdatasheet%2Fcd00244535.pdf&usg=AOvVaw3iLNT0I6eMGAOlMNEpQMpJ
TDA7498 is different from TDA7498E.
I know the problem with SMD size - I have to use reading glasses (+2.0/+2.5) when I work with SMD. I buy them for around 1EUR at Action.
You most likely have to remove the heatsink but for that model it is only fastened with screws, not glued. Check before doing the modification that pins 30 and 31 are actually connected to VDDS (3.3V) and not grounded already.
Luckily the hiss seems not to origin from the TDA7498 board itself. The damping element I described (22K/2.2K) may do the job on its own.
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Hi JAN
you are in goo hands with FF...he is an expert.
just my 2 cents to avoid: you wrote that you push from the sound card the max volume level....do you know what voltage RMS that card will do? maybe this is too much for the input of the TDA7498 board..
chris
Hi Chris,
The output from the soundcard is amplified with this amp (volume at 10 o'clock):
Kebidumei 3D Speler 100 W Digitale Mini Versterker High Power A960 HIFI Muziek Geluid Systeem Mini Stereo Audio Versterkers EU plug in Kebidumei 3D Speler 100 W Digitale Mini Versterker High Power A960 HIFI Muziek Geluid Systeem Mini Stereo Audio Versterkers EU plug van Stereoversterkers op AliExpress.com | Alibaba Groep
The cable has a split to direct the fullrange signal to a subwoofer filter and a mono amp (IRS 200W D-class) powering a bandpass sub which lives under my desk.
Both amps are fine with the output from the soundcard at full throttle.
But, I sometimes lower the volume of the soundcard if I listen to music (or Youtube) which has been recorded/compressed to a level I don't enjoy listening to for very long....
Regarding the matter at hand; the 'other' TDA7498 with the 24V DC Switching power supply has been playing since this afternoon in my livingroom, powering the same two MTM speakers, amplifying the TV audio, same as I did yesterday with the black board 32V DC version.
The difference is remarkable, not a trace of the harshness and treble emphasis I experience with the 32V powered version.
It is not as loud (volume at 12 o'clock, signal reduced with the remote), but that was to be expected due to the lower Voltage and the fact I left the gain adjustment at the setting the switches came on, 21,6dB.
Before I take the heatsink off the 32V version, I'll use the 24V switching power supply to see if the higher Voltage affects the sound quality of the amp.
If that is the case, I guess a lower Voltage is in order for this Amp, as close to 35V DC induces distortion.
I'll also solder the reduction circuit in the input and see what that does, while using the 32V Power supply.
That's for tomorrow though, time to tuck in.
Regards, Jan.
Today I soldered the reduction circuit in place and kept the 35V DC powersource.
No more hiss and distortion, so that's a good thing.
A substantual reduction in output at the speakers, that's not so good.
I'm going to reduce the values of the resistors ane emperically work out at which point the hiss and harsh treble rears it's ugly head again.
Is there a calculator available so it's less emperical?
What I found sofar requires data I don't have/don't know anything about...
Regards, Jan.
No more hiss and distortion, so that's a good thing.
A substantual reduction in output at the speakers, that's not so good.
I'm going to reduce the values of the resistors ane emperically work out at which point the hiss and harsh treble rears it's ugly head again.
Is there a calculator available so it's less emperical?
What I found sofar requires data I don't have/don't know anything about...
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
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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.
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.
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There are many variations of TDA7498 board out there, which one is yours? Also the power supply and speakers?
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.
Which is which?
I've hooked this board: TDA7498 2*100W Digital Power Amplifier Board Class D Dual Audio Stereo H 613707304588 | eBay up to a 24V-5A switching powersupply:
AC85 265V Om DC24V DC12V Schakelende Voeding Board AC DC Power Module 24 V 4 6A 6 8A 100 W in AC85-265V Om DC24V DC12V Schakelende Voeding Board AC-DC Power Module 24 V 4-6A 6-8A 100 W van Stroomvoorziening op AliExpress.com | Alibaba Groep
It performs nicely, but isn't as loud as the 35V powered board we discussed earlier (I'm currently at 9K, slowly getting there).
The board mentioned in the link has two switches with four gain settings; am I correct in assuming the lowest setting (21,6dB) is the highest gain?
Next question: as it has the same TDA7498 on board, it should also work on 32-35V, right?
But, the onboard capacitors are 220uF 35V...
I have a bunch Nippon-Chemicon, 220uF-50 volt, which I could wriggle onto the board creatively, as the stock 35V are Ø8 mm and the 50V are Ø10 mm, meaning every second capacitor would be either under the board instead of on to, due to space issues, or 'on stilts' partly on top of the first, third and fifth capacitor.
Having them alternate on top and under the board would be my preference, what do you say?
Regards, Jan.
I've hooked this board: TDA7498 2*100W Digital Power Amplifier Board Class D Dual Audio Stereo H 613707304588 | eBay up to a 24V-5A switching powersupply:
AC85 265V Om DC24V DC12V Schakelende Voeding Board AC DC Power Module 24 V 4 6A 6 8A 100 W in AC85-265V Om DC24V DC12V Schakelende Voeding Board AC-DC Power Module 24 V 4-6A 6-8A 100 W van Stroomvoorziening op AliExpress.com | Alibaba Groep
It performs nicely, but isn't as loud as the 35V powered board we discussed earlier (I'm currently at 9K, slowly getting there).
The board mentioned in the link has two switches with four gain settings; am I correct in assuming the lowest setting (21,6dB) is the highest gain?
Next question: as it has the same TDA7498 on board, it should also work on 32-35V, right?
But, the onboard capacitors are 220uF 35V...
I have a bunch Nippon-Chemicon, 220uF-50 volt, which I could wriggle onto the board creatively, as the stock 35V are Ø8 mm and the 50V are Ø10 mm, meaning every second capacitor would be either under the board instead of on to, due to space issues, or 'on stilts' partly on top of the first, third and fifth capacitor.
Having them alternate on top and under the board would be my preference, what do you say?
Regards, Jan.
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