I was wondering if there were and helpful threads/websites that I could check out in regards to making their own audio transformers (for a passive DI box).
I have a few spools of enamel coated wire laying around that I picked up at a garage sale years ago. I believe them to be around 38 or 40 awg. If I could use some of that, it would be great, if not, I'll get whatever I might need.
I'm curious what relationship (if any) physical attributes of the transformer (wire gauge, core size/shape, scattered winding vs. neatly wound, ect.) have on the sound/performance.
I know I could just buy a Jensen or cinemag and rest easy knowing that I have the best, but I'm more interested in the process of learning/making one myself. I would probably end up with something less than perfect, but that's ok.
I have experience & equipment in winding guitar & bass pickups, so I don't think I would have too much trouble doing something like this.
1. Depending on what parts (wire and core size) I end up using, is there a reference I can go off of to achieve ballpark primary & secondary impedances?
2. Is there anywhere I can purchase parts for DI type transformers (core laminations, bobbins, ect.)
Thanks in advance. 🙂
I have a few spools of enamel coated wire laying around that I picked up at a garage sale years ago. I believe them to be around 38 or 40 awg. If I could use some of that, it would be great, if not, I'll get whatever I might need.
I'm curious what relationship (if any) physical attributes of the transformer (wire gauge, core size/shape, scattered winding vs. neatly wound, ect.) have on the sound/performance.
I know I could just buy a Jensen or cinemag and rest easy knowing that I have the best, but I'm more interested in the process of learning/making one myself. I would probably end up with something less than perfect, but that's ok.
I have experience & equipment in winding guitar & bass pickups, so I don't think I would have too much trouble doing something like this.
1. Depending on what parts (wire and core size) I end up using, is there a reference I can go off of to achieve ballpark primary & secondary impedances?
2. Is there anywhere I can purchase parts for DI type transformers (core laminations, bobbins, ect.)
Thanks in advance. 🙂
This is a link to an older thread, but there are a lot of links in it. Maybe some of them still work.
Winding an audio transformer
Winding an audio transformer
I opened a thread on designing a line level transformer for the input stage of a classD amp. There might well be a lot of commonality between that and your application : Designing a classD amp input transformer - step by step guide
Many years before I used to wind my transformers.
Calculate turns per volt..
N = 100000000/(4.44*F*B*A) where
N=number of turns per volt,
F= frequency, minimum required 20Hz or 30 Hz as your case may be.
B=Flux density in lines per Sq cm (approx. 10000-12000 for power transformers, but depends on core material)
A = area of cross section of core.
Calculate the useful bobbin area, that goes in between the EI core.
(remember to allocate 2 or 3 mm thickness for the insulation paper and deduct)
About half will be used for the primary and other for secondary.
Find number of turns for required primary voltage.
Divide the primary bobbin area by the number of turns.
This will give the maximum diameter of the wire possible.
Choose one size smaller.
Similarly calculate for the secondary wire.
For close coupling, you can choose multiple primary and secondary windings that can be connected in series or parallel. Wind one primary coil, followed by one secondary coil, second primary coil second secondary coil etc.
You can also wind both primary and secondary coils together if the voltages are not more than 50 - 60 volts.
For complete isolation you can use split bobbins where one half will be used for primary and the other for secondary.
For screening, I used copper foil around the winding, the foil must not short to the foil beginning and foil end. Use only one wire to ground the screen.
Have in mind..
The impedance is limited by the turns ratio and the load on any one side.
Lower minimum frequency = larger size transformer.
Bigger the transformer, good low frequency response.
Many guitar amplifier output transformers are designed for 70-80 Hz operation.
Hope this is of some help to you.
Happy adventure in to your DI transformer.
Regards,
Mandu.
Calculate turns per volt..
N = 100000000/(4.44*F*B*A) where
N=number of turns per volt,
F= frequency, minimum required 20Hz or 30 Hz as your case may be.
B=Flux density in lines per Sq cm (approx. 10000-12000 for power transformers, but depends on core material)
A = area of cross section of core.
Calculate the useful bobbin area, that goes in between the EI core.
(remember to allocate 2 or 3 mm thickness for the insulation paper and deduct)
About half will be used for the primary and other for secondary.
Find number of turns for required primary voltage.
Divide the primary bobbin area by the number of turns.
This will give the maximum diameter of the wire possible.
Choose one size smaller.
Similarly calculate for the secondary wire.
For close coupling, you can choose multiple primary and secondary windings that can be connected in series or parallel. Wind one primary coil, followed by one secondary coil, second primary coil second secondary coil etc.
You can also wind both primary and secondary coils together if the voltages are not more than 50 - 60 volts.
For complete isolation you can use split bobbins where one half will be used for primary and the other for secondary.
For screening, I used copper foil around the winding, the foil must not short to the foil beginning and foil end. Use only one wire to ground the screen.
Have in mind..
The impedance is limited by the turns ratio and the load on any one side.
Lower minimum frequency = larger size transformer.
Bigger the transformer, good low frequency response.
Many guitar amplifier output transformers are designed for 70-80 Hz operation.
Hope this is of some help to you.
Happy adventure in to your DI transformer.
Regards,
Mandu.
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