Aurora Jupiter Guitar Preamp Build Log: Part V: The final frontier!

This one took a little longer than I wanted but hey life gets in the way!

A very small final step in the completion of the Jupiter preamp. The DI (dry) guitar output.

Essentially what is happening is the input of the DI board is tapped directly from the input jack as can be seen in the photo below then it goes through a buffer with the option to reverse the phase before hitting the transformer and finally off to the DI output.

This transformer is one of the key parts as it provides isolation for both the ground and signal path. This is crucial to avoid large signal level losses and ground loops.

The buffers purpose is to drive the isolation transformer. If the transformer was used alone it can only handle a frequency range of 200hz-15khz. Obviously this is no good for a guitar signal as you would be losing a lot of the lower range and have a thin ratty signal.

With the buffer this drives the transformer better which expands the frequency range right down to about 30hz (im yet to measure this to be certain)

However there are still some losses using this method. Specifically in signal volume the output of the transformer will be 1-3dB quieter but this can easily be compensated by adding a small volume boost in your DAW.

DI out 1
In this top down view you can see the guitar signal coming in on the left of the board and the opamp buffer and phase toggle which feeds into the transformer and out the other side to a fully isolated Jack

Another noteworthy thing is the Phase toggle switch. This is handy if you are continuing an old recording session where the phase on existing DI tracks doesn’t match or if you are feeding this signal into another amp for dual amp tones and the amps are out of phase with eachother.

And finally here is a clip normalised. The first part is the guitar direct into my Tascam US 4×4 interface and the second is the same audio reamped into the preamp then the DI output recorded.

Direct & DI Output comparison clip. Dry guitar only and the tracks have been normalised to highlight the lack of loss.

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