Hi everyone,
As part of my ongoing project (making a DAC) I have finally got to the output stage. Not only the output stage but the filtering of the output stage!!
Anyway, enough celebrations. I need a ~30mH inductor for use in my filter. I know it seems big, but that is due to its location, which is right at the end of the output stage, right before the final buffer.
Question is:
1) Where can I buy such an inductor?
2) How can I make an high value inductor like that?
I know that Solen make a nice 30mH inductor which is expensive $35US! and very big...because it is aircored. I've also found some sites that contain information allowing the design of aircore inductors. Has anyone here made their own? What is a practical way to do it? How long does it take? Would it be OK to use a metal cored inductor here? Circuit is posted below for information:
As part of my ongoing project (making a DAC) I have finally got to the output stage. Not only the output stage but the filtering of the output stage!!
Anyway, enough celebrations. I need a ~30mH inductor for use in my filter. I know it seems big, but that is due to its location, which is right at the end of the output stage, right before the final buffer.
Question is:
1) Where can I buy such an inductor?
2) How can I make an high value inductor like that?
I know that Solen make a nice 30mH inductor which is expensive $35US! and very big...because it is aircored. I've also found some sites that contain information allowing the design of aircore inductors. Has anyone here made their own? What is a practical way to do it? How long does it take? Would it be OK to use a metal cored inductor here? Circuit is posted below for information:
Attachments
The key questions are, how much capacitance can you tolerate in it, any DC current, AC level, frequency range...
Tim
Tim
The program
Hi Zodiac,
I found the program I used. Its a DOS program and is called filtry10.zip
You can find it on the web. Try it out , it's easy. If you have any difficulty finding it , I can email it to you. Its very small.
I've made coils using the program at Calsod's web site. It's free. Very easy and accurate. IMHO don't use any metal cores. Use very thin wire - 0.1mm or thereabouts. The coil will be small enough to make easily. I think you should get a dc R or less than 100 ohms. Coil core diameter of 5mm and width of 10 mm. I can't remember the thickness of the full coil ( or number of layers).
Cheers.
Hi Zodiac,
I found the program I used. Its a DOS program and is called filtry10.zip
You can find it on the web. Try it out , it's easy. If you have any difficulty finding it , I can email it to you. Its very small.
I've made coils using the program at Calsod's web site. It's free. Very easy and accurate. IMHO don't use any metal cores. Use very thin wire - 0.1mm or thereabouts. The coil will be small enough to make easily. I think you should get a dc R or less than 100 ohms. Coil core diameter of 5mm and width of 10 mm. I can't remember the thickness of the full coil ( or number of layers).
Cheers.
Some real coil values.
Coil with 0.08mm dia wire
3037 turns dc R = 253 ohms L= 31mH
Coil with 0.1 mm dia wire
2776 turns dc R = 170 ohms L= 31mH
Coil with 0.12 mm dia wire
2555 turns dc R = 124 ohms L=31mH
Core (air) diameter 5mm
Coil width 10mm
Coil layers ( height ) depends on wire used.
The 170 ohm coil causes about 0.25 db loss in your peak. You may need to tweak some more to get 3db or use a thicker wire for the coil. remember that the bigger the coil , the harder it might be to protect it from stray hum fields. I am not sure if that is a real problem. I will try to attach the inductor program to this post. It is free and does not require any sort of registration etc.
Cheers.
Coil with 0.08mm dia wire
3037 turns dc R = 253 ohms L= 31mH
Coil with 0.1 mm dia wire
2776 turns dc R = 170 ohms L= 31mH
Coil with 0.12 mm dia wire
2555 turns dc R = 124 ohms L=31mH
Core (air) diameter 5mm
Coil width 10mm
Coil layers ( height ) depends on wire used.
The 170 ohm coil causes about 0.25 db loss in your peak. You may need to tweak some more to get 3db or use a thicker wire for the coil. remember that the bigger the coil , the harder it might be to protect it from stray hum fields. I am not sure if that is a real problem. I will try to attach the inductor program to this post. It is free and does not require any sort of registration etc.
Cheers.
Jackinnj,
The peak is there on purpose to counteract sin(X)/x rolloff when a nonos dac is used. This results in around -3db at 20kHz, that is why there is a peak there.
Cheers
The peak is there on purpose to counteract sin(X)/x rolloff when a nonos dac is used. This results in around -3db at 20kHz, that is why there is a peak there.
Cheers
Try Panasonic power supply LINE FILTERS. Available at digikey.
For around 33mh, It's a dual inductor which shares the same core. I think the listed inductance is the 2 inductors wired series.
medium high current = 1.4 amp, about 7$
medium current = 1 amp, about 4$
lower current = 0.4 amp, under 2$
peewee current = .1 amp, about 4$ The smallest 1, probably best for line-level sound.
If these inductors are 33mh each, then just get a 15mh-18mh unit and wire the 2 in series to create a single 33mh inductor. Using just 1/2 of the line filter may just add noise. Or, using the 2 for a balanced XLR output design may be benificial.
For around 33mh, It's a dual inductor which shares the same core. I think the listed inductance is the 2 inductors wired series.
medium high current = 1.4 amp, about 7$
medium current = 1 amp, about 4$
lower current = 0.4 amp, under 2$
peewee current = .1 amp, about 4$ The smallest 1, probably best for line-level sound.
If these inductors are 33mh each, then just get a 15mh-18mh unit and wire the 2 in series to create a single 33mh inductor. Using just 1/2 of the line filter may just add noise. Or, using the 2 for a balanced XLR output design may be benificial.
Sorry to resurrect this nearly 20 year old thread.
I think this a common mode choke and that inductance is specified only with the flux from the two coils cancelling each other out.
I think if you connect these in series you will get something like the leakage inductance specified in the data sheet.
But I’m not sure.
I think this a common mode choke and that inductance is specified only with the flux from the two coils cancelling each other out.
I think if you connect these in series you will get something like the leakage inductance specified in the data sheet.
But I’m not sure.