Trident series 65 - adding a micpre transformer.
« on: April 06, 2021, 11:33:37 AM »
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)


squarewave

Re: Trident series 65 - adding a micpre transformer.
« Reply #1 on: April 06, 2021, 12:07:17 PM »
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.

Re: Trident series 65 - adding a micpre transformer.
« Reply #2 on: April 06, 2021, 01:44:01 PM »
Looking at that circuit, would a simple NE5534 or any other decent op amp be better and easier to sub in?


squarewave

Re: Trident series 65 - adding a micpre transformer.
« Reply #3 on: April 06, 2021, 03:34:25 PM »
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.


 

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