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08-29-2021, 06:40 PM
Hi John
Using the Jensen transformer to drive the PA deferentially only works if the winding has a centre-tap OR if you create a faux-CT using resistors. If the transformer has only the one secondary, then you cannot use it for a line out at the same time.
On S-PRE, you can create a "balanced" out by slashing the plate connection for the CF(V2B) and inserting 47k5 in the break, then use a 470n-400V to couple the signal to the PA. Add 475k to ground off the output end of the cap. This turns the CF into a concertina, which has two outputs in opposite phase. The gain and frequency response of the outputs are different but this will help to offset the low-fidelity of the class-D amp - it is NOT "digital". In this wiring, you can still add a transformer from the S-PRE main output but the level is dependent on how hard the PA is driven.
Have fun
Using the Jensen transformer to drive the PA deferentially only works if the winding has a centre-tap OR if you create a faux-CT using resistors. If the transformer has only the one secondary, then you cannot use it for a line out at the same time.
On S-PRE, you can create a "balanced" out by slashing the plate connection for the CF(V2B) and inserting 47k5 in the break, then use a 470n-400V to couple the signal to the PA. Add 475k to ground off the output end of the cap. This turns the CF into a concertina, which has two outputs in opposite phase. The gain and frequency response of the outputs are different but this will help to offset the low-fidelity of the class-D amp - it is NOT "digital". In this wiring, you can still add a transformer from the S-PRE main output but the level is dependent on how hard the PA is driven.
Have fun
