Hi, lo pass filter

[john & Jake the dog]

Hi,
After scouring the net all night I found this, a calculator for my proposed high/low pass filter.

In my application, between cd player and two amps, one bass, one mid/top, do I need both filters or just one.

http://www.muzique.com/schem/filter.htm
I have entered 10 ohm for the resistor an 22 uf for the cap and it comes up with a frequency that seems a good starting point when compared to the frequency response of the B200.

Are lytic caps ok, polarised or not?

[Will]

This will help http://lalena.com/Audio/

[Nick]

You need two, one hi pass, one low pass.

Don't worry about small values, its not at the speakers anymore, thats one of the advantages of doing it this way.

10k 0.022u will give the same freq as 10 ohm and 22uf.

Sorry, but unless I have missed something, its all in the answers in the last thread. You don't need to understand the maths, just plugging the values in the formula will give the same answers as that web page. Give it a try, it will help you understand whats going on to create those numbers.

R in Ohm
C in farard, so 1uF = 0.000001F
F in Herts
Pi as 3.14145
2 as 2

[john & Jake the dog]

hi Nick, thanks for the clarification.
Formulas and me haven't understood each each other since 1963 when I was introduced to the strange concept of putting letters in place of numbers:
if x = y times pi how many men does it take to dig a hole?

I'll have a go at putting some caps and resistors together ( hopefully in the right places ) and see what comes out.

[john & Jake the dog]

Hi Will,
many thanks for surfing, I did find that in the early hours and put it in my favourites to use if I decided I had to build a new crossover.
I'ts the clearest explanation I've seen.
I've found this calculator now and Nicks idea of building a low/high pass filter before the amps has finally sunk in, so I'll give it a whirl.

[Nick]

Formulas and me haven't understood each each other since 1963 when I was introduced to the strange concept of putting letters in place of numbers:
if x = y times pi how many men does it take to dig a hole?

Ok, I guess its ok to expect something that doesn't make sense, to not make sense.

Come on, how hard can it be?

F = 1 / ( 2 * Pi * R * C )

R = 10k
C = .022uf

F = 1 / ( 2 * 3.414 * 10000 * 0.000000022 )

You can even do it by pasting it into google

http://www.google.com/search?q=1+%2F+%2 ... 8&oe=utf-8

[Cressy Snr]

Hi John

Like you I hated algebra at school and just didn't get it.
I was only when I went to uni in the early 90s to retrain as a teacher after being made redundant from BT that it fell into place.

This is how one lecturer put it and it has stayed with me since.

The way to think of an equation is not in terms of changing numbers to letters.
The way to think of an equation is to think of the letters as terms that are meant to stand for something.
An equation is nothing more than generalisation. Since you cannot express a generalisation in absolute terms, which is what digits are. (2 is 2 and thats all there is to it.) That is the reason letters are used.

What an equation is saying is simply "If you do this, then this will be the result" No matter how complicated or "mad scientist" the route , that it what it all boils down to.

So if you plug a number or numbers into the "if you do this part" of the equation then what comes out of the other end, the "result" end is predictable, every time.

Nick's example is a perfect illustration of this principle at work.
If the teachers at my secondary school had explained algebra like that lecturer then I would not have had to have 3 months of crash learning just to gain a grade 6 GCE O level (a bare pass).

Steve

[Nick]

What Steve says is a good description, but I do have to slightly add to what he said (the pedant in me comes to the fore)

An equation is nothing more than generalisation. Since you cannot express a generalisation in absolute terms, which is what digits are. (2 is 2 and thats all there is to it.) That is the reason letters are used.

I can't entirly agree with that, as in a sense it make s the version with number in "more real" that the expression, I would suggest its the other way around, a expression defines the relationship between those terms, in one sense, the expresion is the real thing, what you get when you plug numbers in is just a static instance of the expression.

[Cressy Snr]

What Steve says is a good description, but I do have to slightly add to what he said (the pedant in me comes to the fore)



I can't entirly agree with that, as in a sense it make s the version with number in "more real" that the expression, I would suggest its the other way around, a expression defines the relationship between those terms, in one sense, the expresion is the real thing, what you get when you plug numbers in is just a static instance of the expression.

That's what I meant to say Nick, but despite being reasonably OK at algebra these days I'm still am amateur at explaining the minutae

Steve

[john & Jake the dog]

Hi guys,
I'm sorry but turning numbers into letters just doesn't do it for me, give me a calculator any day and don't get me started on log tables
Maths was the worst lesson for me and my mates at school, saved only by the fact that it was an all boys technical secondary school where the teachers and pupils were quite relaxed about teaching as long as the work was done.
People say their happiest days were at school, well mine certainly were, great fun having banter with the teacher whilst dodging the blackboard rubber, all in great fun.

[andrew Ivimey]

Interestingly I nearly cut a finger right off in a maths lesson, not quite out of sheer boredom. It seems that I haven't learned very much about sharp knives or aslgebra since.

But I am okay with Ohms Law! And there is something neat about algebra; its just that I often get it wrong. How my dearly beloved laughs at me.

And, after an almost Road to Damascus happening I not only understand statistics, I like them.

Mathematicians say Stats isn't Maths.

Who am I to disagree?

Maths really does help understanding valves though. Indeed with what is actually quite simple maths, valve amplifiers are pretty simple too.

[Scottmoose]

deleted

[john & Jake the dog]

Hi all,
yes, but can I use electrolytic caps, polarised or otherwise

[al newall]

One area in which i have come unstuck in the past.
Knowing exactly which units to use when substituting values into an equation or more usually formula.
Millilitres or litres, cm or metres etc.
A good explanation should include this info .IMHO.
Of course i'm a bit wiser now but mistakes have been made.

[Nick]

yes, but can I use electrolytic caps, polarised or otherwise

Yes, you can use whatever you want, but look at my answer, why do you need to use a 22uf cap, when 0.022u would work just as well.

But go on, give it a go, try putting those numbers into a calculator, see what happens, then try changing the cap value, and see what the number does.

If you can't do that, then you are only able to follow instructions other give.