IGSL

[wallker]

Thanks for your reply Bernd.
Regards Marko.

[detecto]

Last night i look a little in IGSL lowpass and highpass filters, and get some unexpected answers. This is just for one chanel for second is the same. I used this RC filter calculator http://www.ekswai.com/en_lowpass.htm
Opinion? Answer? Conclusion?
Regards
Detecto

[simonbaker]

Last night i look a little in IGSL lowpass and highpass filters, and get some unexpected answers. This is just for one chanel for second is the same. I used this RC filter calculator http://www.ekswai.com/en_lowpass.htm
Opinion? Answer? Conclusion?
Regards
Detecto

Tell us what you are thinking -- what is your intuition?

I cannot easily think of those filters separately, but you have to think of the switch as a diode partly. When the switch is closed, all the filters combine; when opened, then just the combined filter on the left side is working.

Don't pay any attention to R29 - it goes to high impedance input and is essentially infinite. When the switch is open, the capacitor holds its charge steady.

Regards,

-SB

[wallker]

Hi guys,I looked at datasheets for LM833 and LF351 (U12) and noticed some differences, so i think that is better to use one more LM833 instead LF351. Of course pins have to be connected properly, take a look on a picture below. I planing to do this tomorrow so i would like the hear some opinions about this.
Marko.

[simonbaker]

Hi guys,I looked at datasheets for LM833 and LF351 (U12) and noticed some differences, so i think that is better to use one more LM833 instead LF351. Of course pins have to be connected properly, take a look on a picture below. I planing to do this tomorrow so i would like the hear some opinions about this.
Marko.

Would you tell us what the differences are between the LM833 and the LF351 that you think are important?

Regards,

-SB

(attached picture easier for me to see)

[simonbaker]

pot circuit question

Is there any important difference between the two pot configurations shown?

-SB

[wallker]

Would you tell us what the differences are between the LM833 and the LF351 that you think are important?

Regards,

-SB

(attached picture easier for me to see)

Take a look on both datasheets : http://www.ti.com/lit/ds/snosbh2/snosbh2.pdf http://www.ti.com/lit/ds/symlink/lm833-n.pdf
Also i did notice slightly different sensitivity of ferrous channel (more sensitivity on non-ferrous channel) which I think is caused with LF351 (other parts are the same for both channels).
Marko.

[wallker]

Is there any important difference between the two pot configurations shown?

-SB

There is difference, look on picture. If you want to make sure yourself measure resistance with ohm meter.
Also you will get different output steps on middle pin of pot (I have had experience with this in practice).

[Comp]

Is there any important difference between the two pot configurations shown?

-SB

Theoretically, there is a difference,.. total resistance will drop to (approx) 9 Kohms,.......
I find it hard to believe it will have any practical difference, {unless the wiper/slider connection was having to supply any appreciable level of current, which would be limited by the higher resistance of the track to wiper section,.....) As most feeds of this type are to high impedance FET or OPAMP inputs, I doubt if, in practice, you will notice any problems,........ but,maybe, buy a 10K pot???? Cheap enough from Silverdog!!


Cheers, Fred

[simonbaker]

Theoretically, there is a difference,.. total resistance will drop to (approx) 9 Kohms,.......
I find it hard to believe it will have any practical difference, {unless the wiper/slider connection was having to supply any appreciable level of current, which would be limited by the higher resistance of the track to wiper section,.....) As most feeds of this type are to high impedance FET or OPAMP inputs, I doubt if, in practice, you will notice any problems,........ but,maybe, buy a 10K pot???? Cheap enough from Silverdog!!


Cheers, Fred

Yes, I was thinking why not just use a 10K pot in the IGSL circuits. (Main reason would be if you only have 100K pots handy I guess!) I like to get rid of any unnecessary parts on the board if possible.

-SB

[simonbaker]

There is difference, look on picture. If you want to make sure yourself measure resistance with ohm meter.
Also you will get different output steps on middle pin of pot (I have had experience with this in practice).

As Fred says, as long as there is no load on the wiper, the voltage should vary same as a 9.1K pot. Should be same linearity, etc. I think a 10K pot would do fine in the IGSL circuit.

Regards,

-SB

[wallker]

As Fred says, as long as there is no load on the wiper, the voltage should vary same as a 9.1K pot. Should be same linearity, etc. I think a 10K pot would do fine in the IGSL circuit.

Regards,

-SB

You are right about everything, except about linearity.

[wallker]

Improvement

I just replaced LF351 with LM833 as i mentioned before, and i got improvement on sensitivity on Fe channel.
Also Disc. on this channel works better and both channels now have same amplification, which was my intension at first.
Picture in attachment shows connected LM833 without changing anything on PCB.
Regards Marko.

[simonbaker]

You are right about everything, except about linearity.

Why not linearity (assuming no significant current goes out the wiper)?

Can you explain?

-SB

[porkluvr]

Whether to use 10k pot, or parallel 10k fixed res with 100k pot? There is a very slight difference in overall response - oh about 2 degrees at the CW end but either way
looks like very good linearity.

You might say my simulation is invalid because as you can see I added a 3pF capacitor in the circuit. I don't think that having the inherent instability that is otherwise encountered
is a good idea. I think that using 3pF adds about one~two degrees of range at the CW end. In my experience, the disc ZCD waveform can be very erratic without that capacitor.

What I did is to use a linear potentiometer model and step the wiper position in eleven 10% increments, from 0% to 100%. These sims ran at ~15kHz.