Does anyone know what the specified slew rate of the TDA2040 is supposed to be? I haven't found it in any datasheet, or anywhere else at the internet yet. The reason I wonder is because I just measured the slew rate of my old TDA2040 amp, and was just around 4 V/µs (!). No wonder it sounds worse compared to my other amps.
Could this really be right? 4 V/µs is a really low for a 25 W amp. I built the amp as suggested by the datasheet with a dual supply of +/-16V. One of my first projects as a teenager and thought it sounded ok then...
Could this really be right? 4 V/µs is a really low for a 25 W amp. I built the amp as suggested by the datasheet with a dual supply of +/-16V. One of my first projects as a teenager and thought it sounded ok then...
Yeah it is a power opamp, maybe it supose to work like this. But I never thought it would be such a bad "HiFi-amp". This has really change my perspective of chip-amps, are they all that bad? LM1875 etc...
2030 and 2050 are 8V/uS, expect the same for 2040.
Not mentioned in data sheet.
Same as 1875.....which is why I say putting fast op amps in the pre-amp section is a wasted effort, such as the practice of op amp rolling.
In any case the series is essentially the same chip family, with higher voltage ratings giving the higher output, compare the output / voltage diagrams...at the same points, the 2050 and 2030 give the same performance, the 2030 is of course lower rated. That tells me to expect 8V / uS, and the slow pre amp may need work, but 4558 is good enough.
4 implies a slow pre amp or input to me.
Not mentioned in data sheet.
Same as 1875.....which is why I say putting fast op amps in the pre-amp section is a wasted effort, such as the practice of op amp rolling.
In any case the series is essentially the same chip family, with higher voltage ratings giving the higher output, compare the output / voltage diagrams...at the same points, the 2050 and 2030 give the same performance, the 2030 is of course lower rated. That tells me to expect 8V / uS, and the slow pre amp may need work, but 4558 is good enough.
4 implies a slow pre amp or input to me.
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Don't know why I didn't check the LM1875 datasheet for comparison, thanks @WhiteDragon. I'd expect the TDA2040 to be have a little lower slew rate than LM1875, because of its lower power rating.
This is actually interesting, if the slew rate of TDA2040 is suppose to be 8V/µs (even the dataseheet doesn't say so for the TDA2040 for some reason). The amp I tested is only fronted with a passive attenuator, which shouldn't affect the slew rate I belive. And for signal I used my Wavetek 182 singal generator, 1 khz square wave. And drove a 4 ohm load, quite hard somewhere before clipping. Measured both "graphic" with my oscilloscope (which I believe gets the most accurate results) and by Douglas Self's method, using a rc link and oscilloscope. Both ways got me the same results.
This is actually interesting, if the slew rate of TDA2040 is suppose to be 8V/µs (even the dataseheet doesn't say so for the TDA2040 for some reason). The amp I tested is only fronted with a passive attenuator, which shouldn't affect the slew rate I belive. And for signal I used my Wavetek 182 singal generator, 1 khz square wave. And drove a 4 ohm load, quite hard somewhere before clipping. Measured both "graphic" with my oscilloscope (which I believe gets the most accurate results) and by Douglas Self's method, using a rc link and oscilloscope. Both ways got me the same results.
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Attempt to find a willing electrical engineer who might help you calculate slew rate from these data found in the datasheet:
... which is handy because the thing we call "slew rate" is a measurement of dV/dt
- Full power bandwidth = 100 kHz when driving 1 Watt (RMS) into 4 ohms.
... which is handy because the thing we call "slew rate" is a measurement of dV/dt
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I'm just an marine engineer myself, so I haven't managed to solve this equations yet. Instead I cheated and read Slone's book "High power amplifier construction manual" and there's a simplified formula for bandwidth and slew rate;
Sinusiodal slew rate = 6,28 * f * E(sine pk)
1W RMS into 4 ohm => U = sqrt (1 * 4) = 2V => E=2 * sqrt (2) = 2,82 V
Slew rate = 6,28 * 100 000 * 2,82 = 1 770 096 V/S = 1,8 V/µS
That's a dispointing result. Either the formula is wrong, or maybe the bandwidth specified in the datasheet is reffering to other limitations?
Change to a larger power supply main capacitor, say from 2200 to 3300 uF, see if the sound improves.
Line level and speakers are also an important part of the listening experience.
Low levels and poor speakers will spoil the performance quality.
Line level and speakers are also an important part of the listening experience.
Low levels and poor speakers will spoil the performance quality.
Here's my 10kSq into 4 ohms.
Peak to peak is 10V.
Rise time = 1.6us (10-90%).
You may want to post your schematic.
It'll be easier to diagnose the issues.
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Thanks for sharing your results. The numbers are actually not very far from mine, 8/1,6=5 V/µS.
I built the amp as suggested in the datasheet. And powered it with about +/-15 volts from an unregulated power supply. Not sure that it is any issue with the amp. Maybe it is working as it should. Your results also tells me that the slew rate should be somewere about 8V/µS (as for LM1875, so a bit lower maybe).
I built the amp as suggested in the datasheet. And powered it with about +/-15 volts from an unregulated power supply. Not sure that it is any issue with the amp. Maybe it is working as it should. Your results also tells me that the slew rate should be somewere about 8V/µS (as for LM1875, so a bit lower maybe).
Try using a larger main PSU reservoir capacitor.
Also, if you have a dual channel scope, try seeing the response to triangular and sine wave inputs, one channel at in and out, you can see both wave forms.
And a drum solo, like a drum roll from a Sheila E performance (just an example).
Or a 2050, the 2040 was short lived in production at ST compared to the 2030 and 2050, or even a 1875, if you are finicky about the performance.
However, if you run it at about 2W, like most of us, do not expect a dramatic change.
Also, if you have a dual channel scope, try seeing the response to triangular and sine wave inputs, one channel at in and out, you can see both wave forms.
And a drum solo, like a drum roll from a Sheila E performance (just an example).
Or a 2050, the 2040 was short lived in production at ST compared to the 2030 and 2050, or even a 1875, if you are finicky about the performance.
However, if you run it at about 2W, like most of us, do not expect a dramatic change.
For resorvaoir caps I used 4700 uF per rail. Think that will be enough. Also tried a little different input signal, and haven't found anything really weird yet. As I said before, I think this is how the amp is suppose to work, just that the datasheet isn't really clear about it.
However, I measured the distortion today. At 1 W into 4 ohms load it was around 0,066% THD. Not the best equipment to measure with was used, my signal generator gives me 0,0015 % THD at the moment. But it's mostly 2nd order, the measurement shows mostly 3rd order so it's properly the amp.
The datasheet says 0,5 THD at 25W into 4 ohm. But as you say we usaully listen to the amp at 2 w (or less, small bookshelf speakers). I was pretty convinced then i compared the amp to anohter amp, and thought the TDA2040 sounded worse. And the numbers tells me the same thing.
However, I measured the distortion today. At 1 W into 4 ohms load it was around 0,066% THD. Not the best equipment to measure with was used, my signal generator gives me 0,0015 % THD at the moment. But it's mostly 2nd order, the measurement shows mostly 3rd order so it's properly the amp.
The datasheet says 0,5 THD at 25W into 4 ohm. But as you say we usaully listen to the amp at 2 w (or less, small bookshelf speakers). I was pretty convinced then i compared the amp to anohter amp, and thought the TDA2040 sounded worse. And the numbers tells me the same thing.
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Even at the full 30W 4ohm a 20kHz waveform has only 1.95V/us slew rate, so 4V/us is plenty for audio bandwidth for the TDA2040 - only when you exceed the max slew rate of the amp does the signal start to distort (think of this as current clipping internally in the chip). You can use 50% of the available slew rate without worrying, just like you can drive the output voltage halfway to the rail without worry.