Hi, can i use 1.5ohm resistor instead of 1ohm for lm1875 amplifier? I know that the value of this resistor isn't critical but still... has anyone had any experience in this regard? I've some good 1.5ohm 1watt flameproof resistors, so i want to use them. For zobel capacitor i'm going to use 0.22uf 100v wima.
........no problems with that.
a standard zobel is 10 ohm + 100nF what i often used in my chip amps (or 10 ohm + 68nF or ..........)
a standard zobel is 10 ohm + 100nF what i often used in my chip amps (or 10 ohm + 68nF or ..........)
I use 100 nF, 2.7 Ω with the LM3886. The cap can be a polycarbonate type or C0G ceramic. I go with a metal oxide resistor.
Tom
Tom
Low inductance is best, even a big carbon comp if you have one, of several watts rating.
Avoid high power, high frequency testing or you may burn it.
Carbon compositions are extremely rare nowadays, very expensive also. I think metal oxide would be better choice here. Less inductive, tight tolerance, high pulse power capacity etc. Anyway thnks to everyone 🙂
As you know lm1875 isn't good for low impedance load, don't you think as zobel resistor 1ohm is quite low compared to conventional values? 
https://www.edn.com/ic-audio-power-amplifiers-and-zobel-networks-one-size-does-not-fit-all/
https://www.edn.com/ic-audio-power-amplifiers-and-zobel-networks-one-size-does-not-fit-all/
I have read a lot about this subject but i failed to understand why TI engineers suggests 1R as lm1875 zobel resistor. With 1R and 0.22uf cut off frequency is very high; about 700khz compared to 160khz with 10R and 0.1uf. I can't think why they would set the frequency so high, whats the reason behind this? Don't you think 1R is too low for RF?? Even Mr.Rod Elliot, D.Self all use 10R and 0.1uf in that position. The value is really very strange and as far as i know the resistor approximates to the expected load impedance, and is usually between 2.7 and 10R. Because this RC network will be in parallel with loudspeaker it will also reduce the expected load impedance to somewhat lower value, lower than 2 Ohm! 
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I don't know a reason for such a low value. I'm almost sure it will work ok with 4R or 10 R resistors too.
I can only note that the impedance of 1 R resistor and 0.22 uF cap is lower than the impedance of 4-10 R resistor and 0.1 uF. For example, 2.2R and 0.1 uF has the same f3 frequency (as 1R 0.22uF) but the higher impedance of each element. Possibly that is a reason?
I can only note that the impedance of 1 R resistor and 0.22 uF cap is lower than the impedance of 4-10 R resistor and 0.1 uF. For example, 2.2R and 0.1 uF has the same f3 frequency (as 1R 0.22uF) but the higher impedance of each element. Possibly that is a reason?
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Of cause, I agree. But how much less inductive they are?
I measured the inductance of common type 1-2 W through hole low Ohm resistors - metal film, oxide, and carbon type (0.1R..10R). And it is very similar. The difference was not more than 1.5-2.0 times between the different types (not more than 1.5 times usually), and quite low. I expected much more different values but it is not.
I measured even wired 0.15 Ohm 5W (or 3W?) soviet resistor and it has almost the same inductance as a metal firm, oxide, or other through hole ones.
(My RLC meter is Mastech MS5308).
So, basically, any type will work fine. In newer designs, I use SMD 2510 size resistors (or 1210), and the problem with choosing the 'right' type is gone (any 2510 size type is fine)
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God knows! I'm sure the value you suggested will also work fine but i'm curious to know why they chose 1R as zobel resistor instead of more conventional values. 😕
True, i also have reached the same conclusion. Even engineer like D.self advocates for wirewound as zobel resistor. But their is a good reason for choosing metal oxide for zobel, which is they fail open instead of closed.