Ebay cheap TDA7498 boards

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broadways

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Joined 2016
I have a basic doubt - how is the power consumption of class d boards?

I have this tda7498 amp. Its stock 2200uf35v cap has been replaced with 2200uf62v cap. The 5w resistors have been shorted.

and I'm powering this amp with a 36v 5.5amp smps = that's about 198 watts max without heatsink or external cooling

I'm using two Aiwa 50w 6ohm 3 way speakers

I keep the volume knob on my tda7498 at about 15% average. 20% is the bearable limit. Beyond 20%, it becomes difficult to stay in the same room.

I don't have a watts meter. I want to know in theory, how much power is it consuming assuming volume knob is at 20%. Is it related to volume knob or something else?
 
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broadways

Member
Joined 2016
I have a basic doubt - how is the power consumption of class d boards?

I have this tda7498 amp. It's stock 2200uf35v cap has been replaced with 2200uf62v cap. The 5w resistors have been shorted.

and I'm powering this amp with a 36v 5.5amp smps = that's about 198 watts max without heatsink or external cooling

I'm using two Aiwa 50w 6ohm 3 way speakers

I keep the volume knob on my tda7498 at about 15% average. 20% is the bearable limit. Beyond 20%, it becomes difficult to stay in the same room.

I don't have a watts meter. I want to know in theory, how much power is it consuming assuming volume knob is at 20%. Is it related to volume knob or something else?
 
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thommio

Member
Joined 2014
broadways said:
I have a basic doubt - how is the power consumption of class d boards?

I have this tda7498 amp. Its stock 2200uf35v cap has been replaced with 2200uf62v cap. The 5w resistors have been shorted.

and I'm powering this amp with a 36v 5.5amp smps = that's about 198 watts max without heatsink or external cooling

I'm using two Aiwa 50w 6ohm 3 way speakers

I keep the volume knob on my tda7498 at about 15% average. 20% is the bearable limit. Beyond 20%, it becomes difficult to stay in the same room.

I don't have a watts meter. I want to know in theory, how much power is it consuming assuming volume knob is at 20%. Is it related to volume knob or something else?
Click to expand...

Watts is not related to the percentage of the volume knob. It depends on the efficiency of your speakers, the amplifier gain and the input signal.
Could be your amplifier is maxing out at 20% volume.

If you have a multimeter you can put it in series between the amplifier and your SMPS. Then measure the Amps. The amplifiers power consumption will be the "measured amps x SMPS voltage".
 
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chermann

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Joined 2017
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thommio

Member
Joined 2014
ravels said:
If you are planning to use a 36V supply, the first thing you should replace is the 2200uF 35V power supply filter capacitor.

Replacing the input caps on that board is a pain unless you are familiar with reworking SMD components.
Click to expand...

Will do that, I have tons of capacitors. Also will bypass the white resistors since I'm planning to use 6ohm speakers.

I think replacing the input Caps wil go fine. I'm quite good at soldering. But will it be worth it?
 
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ravels

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I think .47uF may be a bit too low and rolls of some of the bass frequencies. I replaced the .47uF SMD caps with 1uF Elna bipolar caps. With that combo, low pass filter isn't attenuating bass frequencies too much any more. The caps you have should work too, but they are quite big and may not be easy to attach to the pads for the original .47uF SMD caps. You may not want to have too much unshielded wiring going on with your audio input signal.
 
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thommio

Member
Joined 2014
So I was wondering this;

Since I have 6 Ohm speakers, but there is a 2 Ohm resistor in series in the output filter. Does this mean the output filter sees my speakers as 8 Ohm?

The datasheet says it will need an 470nF cap parallel with these setting. But there s a 330nF installed from the factory. Would it benefit the sound to replace it with a good quality cap from my parts-bin?

And what would be the best cap rating when I bypass/remove the white 2Ohm resistor?
 
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rackabajsarn

Member
Joined 2016
A lot of people here use SMPS to power their boards. Do you filter the DC at all? I've just finished building my active speaker and there is some noise (even without anything connected), so I'm considering trying to clean up the DC. It is not really that prominent, so if it's too hard to filter it, I'll just let it be. Any tips?
 
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Buehgemeiste

Member
Joined 2013
thommio said:
So I was wondering this;

Since I have 6 Ohm speakers, but there is a 2 Ohm resistor in series in the output filter. Does this mean the output filter sees my speakers as 8 Ohm?

The datasheet says it will need an 470nF cap parallel with these setting. But there s a 330nF installed from the factory. Would it benefit the sound to replace it with a good quality cap from my parts-bin?

And what would be the best cap rating when I bypass/remove the white 2Ohm resistor?
Click to expand...

Matching the output filter to your speakers is maybe the best improvement you can do.
That makes most sense if you design a zobel filter for your speaker first and then match the output filter to the flattened impedance.
The values of the parts depend on your speakers.
 
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thommio

Member
Joined 2014
So my order for from China with the black TDA7498 is taking very long. Probably lost in transit.
So I looked for other TDA7498 chip I found this one SANWU DC 8-32V TDA7498 | eBay and ordered it.

Looks like the output filter is exactly like the reference design from Texas Instruments. What do u guys think? Good deal?

Heatsink is a bit small but thats an easy fix.

$_57.JPG

$_57.JPG
 
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Globulator

Globulator

Member
Joined 2004
cutestudio.net
rackabajsarn said:
A lot of people here use SMPS to power their boards. Do you filter the DC at all? I've just finished building my active speaker and there is some noise (even without anything connected), so I'm considering trying to clean up the DC. It is not really that prominent, so if it's too hard to filter it, I'll just let it be. Any tips?
Click to expand...

I found the noise of the SMPS was a lucky dip, if you bought a noisy one it was virtually impossible to filter (RF travels in mysterious ways) and it was easier and cheaper to throw it out and buy another one.

I've had cheap good ones too, it just depends on the actual switching noise generated - once it's out it seems that's it. I've had more luck with ones in metal cages BTW.

Hook up a 100MHz scope probe and have a look, my SMPS noise ended up on the speaker outputs and nothing I did got rid of it until I changed the PSU out.
 
Globulator

Globulator

Member
Joined 2004
cutestudio.net
thommio said:
Any particular guides that can help me with this proces?
Click to expand...

Zobel's rely on you researching, measuring and drawing an impedance vs frequency curve (resistor, scope + App for generating the tones + graph paper).
The result is well worth it as class D really only has a flat FR into a stable impedance.

I had your 2ohm 7498 design myself. I modded it - removed all caps, coils and the resistors and replaced the coils with 4 air cores of 10uH and 4 220nF capacitors.

Note you can also raise the frequency although it was a bit fiddly and reduce the huge gain. It may be easier to buy a new one - the one you show in your last post looked good to me too. Switchable gain is good - far easier than solder SMD for me.

As also noted improve the supply caps. With my new filter it had a nice sound but like all class-D it's quite speaker dependant although my simulations suggested to me that my filter values (10uH into 220nF) gave the best compromise with a 4,8,16 ohm range.

Your mileage may vary.
 
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