low pass filter for DSD

[merlin el mago]

Very well explained, thank you.

 

[merlin el mago]

Due to the great result using tx, what about to use an OPT with gain to match 2Vrms as CD players? 600Ω : 10K 1:16 ratio? custom wich parameters?

 

[merlin el mago]

@abraxalito
Mine friend Jordi from Tarragona sent me today a couple of tx 15K : 300Ω that I want to try in place of 1:1 tx

I have several doubts about reflected primary impedance can affect your 50Ω characteristic impedance filter to match de Amanero 50Ω output impedance.

Mine maths helped with other forum members are:

-Impedance ratio 50:1 (15000:300)
-Impedance ratio square root 50 = 7 aprox. = 7:1 turns ratio
-15K secondary tx in parallel with 100K load (26 preamp or 5687 headphone amp) = 13K043 secondary load
-13K043 secondary load / 50 impedance ratio = 260.86R reflected primary impedance instead 300R

¿Loading opt tx x2 or x3 times so 50Ω x2 or x3 times = 100 or 150 Ohms and here is x5.72 times this can affect the Amanero's output impedance of 50Ω & your filter?

 

[abraxalito]

I'm only a beginner with impedance specs of trafos but those impedance figures represent the load impedances not the characteristic impedance(s) of the windings themselves.

The impedance factor of 50:1 means 100k from your preamp becomes 2k at the output of the filter, this is about 2.5% reduction of 50ohm not really a problem, you could increase the 50ohm load resistor to 51ohm but I doubt its worth the effort.

 

[merlin el mago]

How do you get 2.5%?

The load impedance doesn't affect the characteristic impedance of filter?

 

[abraxalito]

The 2.5% comes from just approximating in mental arithmetic. 2k is 40X 50ohm, 1/40 is 2.5% so I figure the 2k will reduce the impedance (originally 50ohm) by 2.5%. I haven't run the numbers in my calculator though.

 

[merlin el mago]

Brilliant.

So decreasing the 50ohm of filter, next to originally 50ohm?

 

[abraxalito]

Doing the parallel calculation, with a 51ohm resistor in parallel with 2k we get 49.7ohm, certainly it is close enough (better than 1%).

 

[merlin el mago]

I will left first try the 50R.

 

[merlin el mago]

Will be necessary the 470uF cap before the OPT?

 

[abraxalito]

Because you're now using a step-up transformer, the primary shunt inductance is going to be lower. So the cap before the trafo should be bigger - I think try 3300uF.

 

[merlin el mago]

I don't have on han 3300uF but can parallel several 1000uF to get 3000 or 4000uF, wich one better?

How do you calculate the shunt inductance?

 

[abraxalito]

I'd go for 3 * 1000uF. Shunt inductance is measured rather than calculated.

 

[merlin el mago]

Thank you.

 

[powerpz]

Did somebody else tried low pass LCLC ? I did, but there is a lot of noise, more than signal.. I tried also first schematic R-C --> 3.3k , 1nF again the same ?!

 

[powerpz]

I am wondering if I need to reprogram firmware on Amanero 384 pcb with "DSD only firmware", to use direct connection to pin 3,5 - DSD1 and DSD2, because they are multiplexing with I2S data and clock
Think that merlin el mago can say

 

[merlin el mago]

I don't remember exactly the firmware of Amanero but isn't the latest beta. I can tell you because the computer laptop was gone.

 

[powerpz]

I don't remember exactly the firmware of Amanero but isn't the latest beta. I can tell you because the computer laptop was gone.

you mean that you didn't change the firmware and use as is?
Unfortunately Ive got chinese clone, and it is dead now, amanero flashing utility cannot recognize PID and DID and refuse to program it after erasing
And I didn't expect that I am buying the clone

 

[merlin el mago]

No. I changed the firmware only for DSD, I'm using Daphile as player so Linux based.

Try this one:

firmware 2005be & Cpld_for_1081

If doesn't works for you, try this other:

firmware_1099c & cpld_for_1080

If your board is a chinese clon start with firmware 1099c

 

[merlin el mago]

@ abraxalito
I want to use the 1:1 OPT for a gain of 6dB (attached pic), could still use your filter without modification?