proper design of pi-filter for Aleph 30

[h_a]

Hi folks!

When dimensioning the inductor vor this CLC-filter, how is it done properly? Here is a nice schematic, however it is for 180 000uF which is more than I want.

I'm more interested in 3x 22 000uF caps, so the inductor would go between the first 2 caps I think.

But how to calculate the proper inductor value?

3.9mH won't fit I think.

Any ideas?

Have fun! Hannes

 

[Nelson Pass]

Any value will improve the noise, so just do the largest you
can.

 

[Zen Mod]

again............

http://www.duncanamps.com/psud2/index.html

download it and play with

read help to know more

 

[jeapel]

in my aleph 3 68000uF+1.2mH +68000uF

with good result supply ripple = 25mv ac

standard value are 2mH to 4mH

but inductor has resistance

air core = no saturation but maybe more resistance and heat

and magnetic induction in your aleph

i test my 1.2mH iron core for no saturation @ 10A

wire=no 16 resistance=0,15 ohm

 

[h_a]

Thanks for all replies!

Well. so is there no optimum value? Since capacitors cause a phase shift, I thought there's an optimum inductor value that shifts the phase of the remaining ripple perfectly back to 0° - which I guess should be the best.

What makes me wonder is if it's only positive to use a CLC, why wasn't it used in the original Aleph30 or Pearl?

When it's so nice, I'll add one also to the pearl of course, or is this just of academic value, because the fets contribute far more noise?

Interesting subject!

Thanks guys!

Any input appreciated! Have fun! Hannes

 

[jeapel]

"thought there's an optimum inductor"

in my book maybe yes?

if you look CLC like C +LC

for LC fc=1/(6.28 x squareroot( LC) )

for power 50hz ripple=100hz
for power 60hz ripple=120hz

fc with factor 5 to 10 of ripple hz is good

optimum:

1-too low L = no effect
2-optimum is factor 5 to 10
3-too big L = difficult to find with low R and R= voltage drop and heat

 

[h_a]

Ok, I see what's the problem, you'll never get the inductors you would need.

So for a 3.9mH choke you would need just 26 Farads capacitance...

Or for 66000 uF only 1.55 Henry inductance...

So with what I could get, I'm just a factor 50 off what would be ideal.

I see. So better get a 6.8mH inductor then.

Have fun! Hannes

PS: but why are inductors so rarely used then? Too expensive or less efficient than adding capacitance for the same money?

 

[jeapel]

?????????

if
L=3.9mH
C=66000uF

fc=9.92hz very good factor 10 and a little more

if my calculator hp is rigth or me

 

[h_a]

Ah ok I misunderstood you!

You mean fc times 5-10 to get the 100/120Hz ripple would be ideal!

I see, thanks a lot for clarification!

Why 5-10 times?

Thanks a lot! Hannes

 

[jeapel]

why factor 10

thumb law for me factor 10 reduction of ripple is already very good

to give a good step down on speaker hum

factor 20 or 30 is better if and only if :

1-big inductor with big wire for low R

2-no magnetic saturation @ 10A (also thumb law)

3-maybe the money talk also

in my aleph 3 the factor is 6,8 with good 25mv ac ripple

bye

 

[jeapel]

the right expression is "rule of thumb" not "thumb law"

french speaking Jean

 

[harryeng]

Why doesn't everybody use Inductors?

I am building an Aleph X, with CLCRC.

When I calculate with my 10mH inductor (100 mOhm), I will end up with a ripple of 17 mV
When I calculate with a resistor with the same resistance (100m), I would get 21 mV

That means for an extra 170 dollars, I only got an extra 4 mV improvement. Not everybody thinks that is good value for money. (I got mine second-hand, so my ratio is better...)

By the way, splitting things up with smaller values and introducing another resistor only brings an improvement of 1mV (CRCRCRC)

Greetings, Harry

 

[Zen Mod]

Why doesn't everybody use Inductors?

I am building an Aleph X, with CLCRC.

When I calculate with my 10mH inductor (100 mOhm), I will end up with a ripple of 17 mV
When I calculate with a resistor with the same resistance (100m), I would get 21 mV

That means for an extra 170 dollars, I only got an extra 4 mV improvement. Not everybody thinks that is good value for money. (I got mine second-hand, so my ratio is better...)

By the way, splitting things up with smaller values and introducing another resistor only brings an improvement of 1mV (CRCRCRC)

Greetings, Harry

you probably use PSUd for calculating?

so- you know for 100 (120) Hz ripple .........what is with upper freqs and with "supply modulation"............there you'll see difference between R and L

 

[harryeng]

Hi Zen Mod,

You are right of course!

There are several goals one has to achieve when designing power supplies. One of the reasons I like chokes, is that it filters a lot of the HF I have on my powerline. When I installed chokes in my Aleph 5, and my DAC everything was kind of less stressing to listen to.

You should check the Bob Cordell interview on Power Supplies thread in Solid State amplifiers. There people argue that the rise time from the PSU should be slower than the lowest frequency the amp is designed for.

I try to incorporate a CL before the CRCc in a way that I always have enough capacity after the L not to have to bother with the influence of L on my power supply for the amplifier. In my Aleph 5 design I calculated the minimun capacity, and went on from there. I was very dissapointed with the result, so now I just over-design.

To be honest, for the Aleph X I am building now (70W RMS on 4 Ohm) my criteria were: more than 100 mF per rail (after choke), and a ripple smaller than 10mV. These numbers are not substantiated by hearing tests, just best guesses. Now I am building with 3 60mF capacitors, a 10mH choke (70A), 50MOhm resistors and a small 8uF capacitors to top it off. With my 700W tranny this also means I have to use a softstart, which I made with power resistors (70Ohm) and some relays.

Greetings, Harry

 

[Zen Mod]

Hi Zen Mod,

You are right of course!

There are several goals one has to achieve when designing power supplies. One of the reasons I like chokes, is that it filters a lot of the HF I have on my powerline. When I installed chokes in my Aleph 5, and my DAC everything was kind of less stressing to listen to.

You should check the Bob Cordell interview on Power Supplies thread in Solid State amplifiers. There people argue that the rise time from the PSU should be slower than the lowest frequency the amp is designed for.

I try to incorporate a CL before the CRCc in a way that I always have enough capacity after the L not to have to bother with the influence of L on my power supply for the amplifier. In my Aleph 5 design I calculated the minimun capacity, and went on from there. I was very dissapointed with the result, so now I just over-design.

To be honest, for the Aleph X I am building now (70W RMS on 4 Ohm) my criteria were: more than 100 mF per rail (after choke), and a ripple smaller than 10mV. These numbers are not substantiated by hearing tests, just best guesses. Now I am building with 3 60mF capacitors, a 10mH choke (70A), 50MOhm resistors and a small 8uF capacitors to top it off. With my 700W tranny this also means I have to use a softstart, which I made with power resistors (70Ohm) and some relays.

Greetings, Harry

just for teasin' ya..........what you'll change if you make X for 16 ohms lload ...........
anyway-I don't think that you need at all that R part in your filter.....
but-if you'll be happier , just go for it
btw , my babelfish CLC is 10 x 10mF - 9mH(0,2 ohms) - 10 x 10mF.....all that for stereo 4A Iq