Correct. Found the first post hard to read.
OP seems to miss the point that the preamp itself might have a DC offset voltage at its inputs. MM cartridges are not BFF with DC.
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These are all tone control boards. Once I understand them. The final plan is to build a RIAA compliant phono stage also.
I'm stuck progress on that because as the RIAA standard they already are doing drastic cuts at low freq. So why have a rumble filter and a RIAA stage.
I have just installed Tinia-Ti, Micro Cap. We normally use Proteus.
So I have to now worry about input impedance also. How do I pick that number ?. My inputs right now are blue tooth module, 3.5mm audio jack from phone / mp3 player, CD player and finally a Phono stage will also be added. For the phono stage I know I will probably use a 47K resistor to ground. Followed by a regular RIAA circuit of some sort.
I have a pile of various boards. None of which seem to work as promised. My logic is first figure out how to fix these boards then take on building your own from what you learned along the way.
I'm stuck progress on that because as the RIAA standard they already are doing drastic cuts at low freq. So why have a rumble filter and a RIAA stage.
I have just installed Tinia-Ti, Micro Cap. We normally use Proteus.
So I have to now worry about input impedance also. How do I pick that number ?. My inputs right now are blue tooth module, 3.5mm audio jack from phone / mp3 player, CD player and finally a Phono stage will also be added. For the phono stage I know I will probably use a 47K resistor to ground. Followed by a regular RIAA circuit of some sort.
I have a pile of various boards. None of which seem to work as promised. My logic is first figure out how to fix these boards then take on building your own from what you learned along the way.
Line inputs should be high impedance greater than 100k and less than 1Meg. Noise isn't an issue with high impedance because the source impedance shunts the input once you connect it to something.
Phono inputs are typically 47k for a moving magnet type cartridge plus any recommended parallel capacitance. Don't be under any illusions about transferring a circuit on paper into a silent and hum free real build.
Well, if you want to get picky, µ is alt code 0181, Ω is alt code 234, and π is alt code 227, and Kilo should be upper case K.
But as long as you don't mix up micro, milli, and mega, I don't care. Entering alt codes can be a pain if you are in a hurry, and on some web sites alt sends the browser into convulsions, so you have to create the alt codes in notepad etc. and copy them into the post. I don't bother unless there is a real danger of misinterpretation.
About the OP, 16Hz is typical in tube amps (100nF & 100KΩ )and 1.6Hz is OK but less than that invites transient issues like when you switch to a source that has a bit of DC. And larger caps are probably polar, which is not ideal where there is no DC, and/or it could be backwards.
Sorry but no.
The "word" kilo may be written in upper case in casual writing, or at the start of a phrase or paragraph, following grammatical conventions, but the Unit uses lower case k
https://www.stouchlighting.com/blog/electricity-and-energy-terms-in-led-lighting-j-kw-kwh-lm/w
You remember wrong. It is flat from DC to 50.05Hz, then 6dB/octave LPF to 500.5Hz, then 'flat' to 2122Hz, then 6dB/octave LPF forever. See the graph above.
You may be thinking of the obsolete IEC amendment.
Ok so sorry yes maybe I mixed it up.
So its obvious that I need a low pass filter. (I see my old posts where I kept calling it a high pass filter.) Its not its actually a low pass filter.
So basically I need to find a section which does both i.e. cuts low freq below 20hz. And cuts high freq i.e. above 25Khz.
So far I have not comes across such a circuit. They are either using a low pass filter or a high pass. Never both.
If you know of any such schematic or circuit pls share.
So its obvious that I need a low pass filter. (I see my old posts where I kept calling it a high pass filter.) Its not its actually a low pass filter.
So basically I need to find a section which does both i.e. cuts low freq below 20hz. And cuts high freq i.e. above 25Khz.
So far I have not comes across such a circuit. They are either using a low pass filter or a high pass. Never both.
If you know of any such schematic or circuit pls share.
Normally i aim for 3Hz & below. As input cap i like Wima film caps because they're cheap & good enough for me.
If you're talking about rumble you need a highpass filter. You don't need to worry about > 25kHz as a low pass filter is already in place from 2122Hz, so you are already < -20dB at 25kHz. Unclear what you're really asking here.
So I need a rumble filter if I plan to use Phono. at any point. With a matching RIAA filter.
Then I need one filter to make sure that Freq below 20 Hz do not enter my system.
Then I need one filter to make sure that Freq above 25Khz does not enter the signal.
I don't understand your comment that low pass filter is already in place from 2122Hz.
Im looking at all the boards I have plus those I want to design and none of them seem to cover all the bases I need covered.
I repeat. The RIAA curve is already a low pass filter from 2122Hz upwards, so by definition it is already at least 20dB lower at 25kHz than it was at 2122Hz, which is already nearly -3dB from what it was at 1kHz. See the graph above. Why isn't this enough? Why do you think you need to filter again from 25kHz? What is your requirement?
Ok understood your point. Its the way my mind works. Im planing the project in blocks as in first build the opamp preamp then add tone. Then at a latter date add on RIAA or a RIAA section . I try to break down projects into blocks and attack them one at a time. That is how my Akai AMp is designed i.e. phono only kicks in when you use Phono input. Without it its just your tone control. Sorry about the confusion.