Hi,
I'm looking to build a filter for an off-the-shelf 12 V DC linear supply from Tripp Lite. The supply is really 13.8V at 5 amps. At $60 it's relatively cheap.
It's going to a DAC/headphone unit which requires 12 at 2A but will be closer to 3-4 Amps when headphones are connected.
Based on ancient and dusty knowledge, ill gotten, I planned to use 100uF, 0.4mH/0.2 Ohm, and 100uF as a good starting point. This is somewhat convenient as I have lots of left-over coils from crossovers, and hopefully still have lots of leftover Panasonic FM caps.
I was thinking of trying to drop about half to a volt across the inductor at maximum current.
What do you think of the overall plan?
Best,
Erik
I'm looking to build a filter for an off-the-shelf 12 V DC linear supply from Tripp Lite. The supply is really 13.8V at 5 amps. At $60 it's relatively cheap.
It's going to a DAC/headphone unit which requires 12 at 2A but will be closer to 3-4 Amps when headphones are connected.
Based on ancient and dusty knowledge, ill gotten, I planned to use 100uF, 0.4mH/0.2 Ohm, and 100uF as a good starting point. This is somewhat convenient as I have lots of left-over coils from crossovers, and hopefully still have lots of leftover Panasonic FM caps.
I was thinking of trying to drop about half to a volt across the inductor at maximum current.
What do you think of the overall plan?
Best,
Erik
Hi,
Model it in Tina-Ti. I can't see how headphones would
add around 10VA to 20VA to the power supply load.
rgds, sreten.
Model it in Tina-Ti. I can't see how headphones would
add around 10VA to 20VA to the power supply load.
rgds, sreten.
Is your linear supply already regulated? What headphones do you have which take 1 - 2A of current?
im just going by the recommended and maximum current from the maker and being overly careful. I suspect the real current draw will be arond 3 Amps total.
Best
Erik
Best
Erik
You need around 1ohm resistor in series with that inductor or it may even sound worse. You can use just a CRC, but C(LR)C works better if you can target frequencies that are likely to be present (noise in the diode noise range, I suggest to target). That's actually fairly high inductance in this application.
Consider the SRF of the inductor needs to be higher than the target range.
Consider the SRF of the inductor needs to be higher than the target range.
Headphones are typically 95dB to 105dB per milli-watt.
If you assume an insanely too loud transient of 120dB that equates to an input power to the 100dB headphones of 0.1W
No where near your estimate of
Imax = sqrt( Pmax/impedance)
for a 30ohms headphone at a Pmax of 0.1W you will find that 58mA is the maximum AC current that passes into the far too loud heaphone.
for a 300ohms headphone at a Pmax of 0.1W you will find 18mA and if the 120dB is a peak transient value, then that 18mA is a peak value
If you assume an insanely too loud transient of 120dB that equates to an input power to the 100dB headphones of 0.1W
No where near your estimate of
Imax = sqrt( Pmax/impedance)
for a 30ohms headphone at a Pmax of 0.1W you will find that 58mA is the maximum AC current that passes into the far too loud heaphone.
for a 300ohms headphone at a Pmax of 0.1W you will find 18mA and if the 120dB is a peak transient value, then that 18mA is a peak value
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Andrew,
Please keep in mind that was the estimate for the entire DAC/preamp/headphone amplifier.
Lots of amp designers like to go overboard with class A amps and high voltage railes, stuff like that so I was adding headroom.
The unit's maker stipulates 2 Amps as required.
Best,
Erik
Please keep in mind that was the estimate for the entire DAC/preamp/headphone amplifier.
Lots of amp designers like to go overboard with class A amps and high voltage railes, stuff like that so I was adding headroom.
The unit's maker stipulates 2 Amps as required.
Best,
Erik
Based on all of this I think I'll probably wait to get the power supply and look on the scope to see what's going on before picking any parts.
Best,
Erik
Best,
Erik
That's great. Don't go adding another 1A to 2A for the headphones.
2A as specified by the manufacturer is plenty.
The second capacitor could have been much bigger, (for example 10000 uF) this way you can avoid resonance and provide a low source impedance, that is important for highly varying load.
yes, most important point is to avoid resonance a fc (cut frequency of the 2nd order filter LC). A small resistor in series with the second cap is another way to damp the filter (another is yours, a R in // of L). See following AN from TI :
https://www.ti.com/lit/an/snva538/snva538.pdf
Don't be afraid by math. Just understand the schematics and some explanations then use TINA-TI software for simulation and find correct values.
https://www.ti.com/lit/an/snva538/snva538.pdf
Don't be afraid by math. Just understand the schematics and some explanations then use TINA-TI software for simulation and find correct values.