Lowest noise and distortion Chip

[Anders_denmark]

Hi,

I need a chip with the lowest possible distortion and noise for an amplifier for measurements. I figured this would be the place to ask... Any suggestions?

It must be capable of delivering at least 10 watt into a load of 8 ohms.
The gain should be easily configured in the range from 20 to 30 dB.

Best regards
- Anders

[DJ Exprice]

LM3886 is nice but I don't know what other people say...but it would probably for really well for you.

[jackinnj]

if you only need 10W the LM3886 is a very good choice in the inverting mode --- the LM4780 is a pair of LM3886 dies in one package and here's what it can do:

[DJ Exprice]

Non-inverting works too. If you're using the amp for very Hi-Fi sound, isn't the non-inverting amp better?

[sangram]

Actually the 3875 has the lowest THD, noise and IMD among the entire range of National's chips (or is it the 1875?).

Also National specifies that inverting configuration may result in better THD+N.

However the input impedance drops in inverting mode so a preamp or buffer is needed, or a capable source.

Gain configuration is simple if the feedback loop consists of a fixed resistor + a variable resistor, with the variable providing a 10dB adjustment. Most of these chips should be able to handle this gain range just fine.

Or if you have a buffer you can set up the buffer for a 0-10dB gain and the chipamp for a fixed 20dB gain.

[Zero One]

I think it is the 1875 that has the lowest figures, but it is a close contest from memory of looking at all the stats with the 2886 chip, I have a pair but I haven't done anything with them.

They will all produce 10 watts easily enough. Bridged chips and NAT Semi have a few including 3 channel versions (though they are not stellar performers) will give the lowest figures but they will not change crossover distortion fugures, but I guess for your implementation this is not an issue anyway.

[Bazukaz]

Originally posted by sangram
Actually the 3875 has the lowest THD, noise and IMD among the entire range of National's chips (or is it the 1875?).

Here are some comparisons of THD+N from national's site. However , if you think about measuring loadspeaker's THD and other parameters , i don't think that amplifier will have much influence.While distortion of these amps is less than 0.1% , THD of loadspeakers may be a few percent.

Regards,
Lukas.

[MikeB]

Originally posted by Bazukaz
While distortion of these amps is less than 0.1% , THD of loadspeakers may be a few percent.

I think that's a fairy tale... I did measurings with my speakers (not highend,but diy,visaton,2 x w170s8,1 x g20sc) see attachment.
The spikes are caused by room acoustics, blue is 2nd harmonic and red is 3rd harmonic. Crossover is at 2.5khz, the tweeter has <0.1% 3rd harmonic. Microphones are also distorting, so you see the product of soundcard/amplifier/speaker/microphone/soundcard.
Also, speakers are unlikely to create high order distortions if not defect.
The 3rd harmonics stop at 8khz in this measuring because of limited samplerate of soundcard.

I don't know where this myth originated that speakers have several % of thd...

Mike

[Anders_denmark]

Thanks for the suggestions.

From looking at the figures achieved by jackinnj it looks as if the LM5780 is outperforming the other chips you suggest - that is the LM1875 and the LM3875.

In the 1875-datasheet it is said that:
"THD levels at 20 kHz with 10W output to an 8Ù load should be less than 0.05%, and less than 0.02% at 1 kHz."

Comparing with jackinnj curves at 1 kHz the THD+Noise for the finished amp is below 0.003%. Almost a factor 10 better. At 20 kHz the THD+Noise is below 0.02% - thats 2,5 times better for the LM4780.

Any comment on this? Can it be due to the inverting design?

[Bazukaz]

Originally posted by MikeB


I think that's a fairy tale... I did measurings with my speakers (not highend,but diy,visaton,2 x w170s8,1 x g20sc) see attachment.
The spikes are caused by room acoustics, blue is 2nd harmonic and red is 3rd harmonic. Crossover is at 2.5khz, the tweeter has <0.1% 3rd harmonic. Microphones are also distorting, so you see the product of soundcard/amplifier/speaker/microphone/soundcard.
Also, speakers are unlikely to create high order distortions if not defect.
The 3rd harmonics stop at 8khz in this measuring because of limited samplerate of soundcard.

I don't know where this myth originated that speakers have several % of thd...

Mike

Hi,
At what output power did you measure THD ? Did you measure IMD ?

Regards,
Lukas.