TDA7498 too loud

misfits73

Member
2012-09-26 6:08 pm
I bought this toy the other day, replaced the 10xcaps with 470uF/35V,added a 3300uF at the input terminals and feed it with my laptop's 19V supply.

It pumps strong bass, much better than the 3116 i used to have and it's more lively than the lepai 2020a+ that i still have.

The problem is that it's too loud even at the lowest gain setting, is there a way to fix that?

I also read that shorting the input diode. adding a higher capacitor value at the input and using a 24V supply will make it sound better, is that the case?
 

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multisync

Member
2008-01-31 10:34 pm
Carp
according to the data sheet there are 2 pins on the chip that can change the gain. you will have to remove the heat sink to locate the pins to see how the pins are configured.

https://www.st.com/resource/en/datasheet/tda7498.pdf

the data sheet shows the performance of the chip, distortion, output power etc at 36VDC for the chip. You installed 35 volt caps so do not exceed that rating.
 

misfits73

Member
2012-09-26 6:08 pm
according to the data sheet there are 2 pins on the chip that can change the gain. you will have to remove the heat sink to locate the pins to see how the pins are configured.

https://www.st.com/resource/en/datasheet/tda7498.pdf

the data sheet shows the performance of the chip, distortion, output power etc at 36VDC for the chip. You installed 35 volt caps so do not exceed that rating.

This board has dip switches for the gain (see photo) and they are set to the lowest setting.
I'll go with a 24V supply but i don't know if there is gonna be any improvent from 19V
 

bullittstang

Member
Paid Member
2013-05-09 2:14 pm
Detroit, MI
This board has dip switches for the gain (see photo) and they are set to the lowest setting.
I'll go with a 24V supply but i don't know if there is gonna be any improvent from 19V

The data sheet shows 14V to 39V supply. I think he is telling you not to go any higher than 35V, since your caps won't handle it.

24V PSU versus 19V will make it even louder. More voltage=more wattage.

You could try lower PSU, possibly 14-15V, but shouldn't make a noticeable change from 19V IMO.

You will need to change the fundamental gain, even before the DIP switches, which is why he mentioned removing the heatsink and altering the resistors at those chip pins - according to the datasheet that is linked to.
 
I bought this toy the other day, replaced the 10xcaps with 470uF/35V,added a 3300uF at the input terminals and feed it with my laptop's 19V supply.
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I also read that shorting the input diode. adding a higher capacitor value at the input and using a 24V supply will make it sound better, is that the case?
With the capacitors you have already changed and added, I doubt that more can be heard as long as you use an SMPS/power adapter. 24V supply instead of 19V will give a higher output power but hardly change the sound.
 

Tube Radio

Member
2012-02-24 6:29 pm
My suggestion is to go with 30Vdc B+ as that will produce more output power than 19 and 24 volts.

To reduce the input level, use a series resistor then use a trimmer resistor after the series resistor and tie it to ground.

That way you can tweak the level to exactly what you need it at.
 
My suggestion is to go with 30Vdc B+ as that will produce more output power than 19 and 24 volts.

To reduce the input level, use a series resistor then use a trimmer resistor after the series resistor and tie it to ground.

That way you can tweak the level to exactly what you need it at.

That will do with 8 Ohm speakers but not with 4 Ohm because of current limitation.