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DI Box Transformer and cap question.

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diy didi

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Hi
I copied this circuit for the DI output section for another Fender amp.
The DI transformer is on the top right corner of the page of page 6.
My question is how do I determine the right capacitor value on the input prim of the transformer. In the attached schematic they used a 0,1uF.
When I connect the cap with my chosen transformer, an OEP A262A3E, I get a slight boost of the higher frequencies.
 

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MikeMl

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The cap is likely resonating with the primary inductance. Make it smaller, and the resonance will shift to higher frequency, likely above what you can hear...
 

Nigel Goodwin

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The cap is likely resonating with the primary inductance. Make it smaller, and the resonance will shift to higher frequency, likely above what you can hear...
Or, as it forms a low-pass filter with the 15K resistor, make it larger :D

I think it's probably a matter of trying different values until you get the sound you're looking for.
 

MikeMl

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Most Helpful Member
Or, as it forms a low-pass filter with the 15K resistor, make it larger :D...
Since he is complaining about a "boost", there is no way that a "low-pass filter" can do that... If you make the shunt cap lower, it is likely to move the resonance lower into the mid band.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Since he is complaining about a "boost", there is no way that a "low-pass filter" can do that...
The 'boost' is relative, it could just as easily be not attenuating the higher frequencies enough.

As I said, try different values (smaller and larger) to see which gives the sound he's looking for.
 
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