Trident series 65 - adding a micpre transformer.

What happens to this 4 transistor micpre (see schematic) if I add a 600/3K input transformer in place of the two coupling caps? (C7, C3)

That would work. You can then also snip the upstream caps as well. But you will need to adjust the resistors on the bases to accommodate the impedance change and you might need a zobel across the secondary. Technically you should try to figure out the optimal source impedance of the transistors and make sure it's not too much of a mismatch. But I don't think it would make too much of a difference. The higher Z could easily be a better match actually. It will bump up the gain by ~6db though so you might want to increase R5 slightly or the gain labels won't reflect reality or there's a slight possibility that you could get some instability at the max gain setting.

Looking at that circuit, would a simple NE5534 or any other decent op amp be better and easier to sub in?

It probably wouldn't make much of a difference because virtually all of the gain is in the transistors. It's a nice circuit. I wouldn't mess with it too much.

mkiijam said:

What happens to this 4 transistor micpre (see schematic) if I add a 600/3K input transformer in place of the two coupling caps? (C7, C3)

Click to expand...

Take care! (C7 & C3) is really (C2 & C3) C2 instead of C7, the diagram is confused... 1478 Sowter Transformer or original zutt 012 will be ok ! Do not need anymore resistors changes, only take off C2&C3

I had a tech in Atlanta that did a transformer input to two of my 65 pres. Didn’t hear much difference.

But I would love to hear if you were a success. Did it add some nice character?

I know some techs here in Atlanta. Anyone I know?