Suggestions on how to implement transformer coupled output to EROS

[Tubejack]

I would like to add a transformer coupled output to my EROS, with two objectives - to reduce output Z (200-500 ohms) and facilitate XLR outputs.  I'm assuming a parallel feed transformer coupled connection, but not quite sure how to determine cap value and transformer needed.  Suggestions?

[Paul Joppa]

You might want to read the Jensen AN-003 application note. It includes several options, only one of which is a transformer at the output.

We have used the Altec 15095 (15K to 600CT) in the Repro Amp. Two options:

In the Repro Amp we added a gain stage with the 15095 as output transformer; this is a line driver stage and gets the signal up to studio type 0-dBu nominal level. It would be an adventure to design and build such a thing, though.

You can hang the 15095 off the Eros as is - the 1uF output capacitor is about right in our experience, and the 15K load is about the minimum for proper operation of Eros or Seduction. You will lose some 14dB of signal level, so the following preamp will need extra gain. Easiest would be to put the transformers in a separate box with short unbalanced interconnects to the Eros, and XLR connectors for the balanced lines out.  Jensen does not normally make RCA to balanced iso-max boxes, presumably because the signal will be attenuated so much, but they might make up a custom one for you.

[Paul Birkeland]

I would like to add a transformer coupled output to my EROS, with two objectives - to reduce output Z (200-500 ohms) and facilitate XLR outputs.  I'm assuming a parallel feed transformer coupled connection, but not quite sure how to determine cap value and transformer needed.  Suggestions?

I am guessing you are driving TVC's or some type of pro audio preamp?

If I had do to this, and I couldn't buy a Repro or a Tube Phono, I would build an active buffer in a separate enclosure.  Run short single ended cables from the Eros to the buffer, do a 6CG7 voltage amplifier into some 15k:600 output transformers, then run your balanced lines from there.  You could even put a pair of 100k trim pots at the input to get the balance really dialed in. 

If I had to guess, you could probably grab a Seduction kit and build the buffer on that chassis, enlarging the output holes for XLR jacks and maybe.  You could use one 6CG7 or 12AU7 in one 9 pin hole, and an 0A2 with some creativity as a gas shunt reg tube in the 2nd available 9 pin hole.  (A small adapter would need to be fabricated)

-Paul