Hi all, this thread is about a JFET & MOSFET preamp I am cooking for sometime now. Its two stage single ended Class A circuit.
It was developed on the bench involving much experimentation with topology and a range of active parts. Simulations came second.
Some speakers are insensitive, some amps also, or a source is relatively low output like a phono stage. So a line preamp with gain is good to have.
Its named DCG3 because it has DC servo and three MOSFETS. Its standard gain setting is also times three.
The main schematic is attached* Click for circuit description
Some THD plots when driving 1.5kOhm line input and various headphones are also attached.
*(12 Oct 2016 updated and build guide/bom pdf added)
erratum: C6,C7 should read 4x in the BOM. J3 in preamp's schematic is named Q5 on the actual board.
About J3/Q5 possible tolerances read post#452
Thanks for your reply, so I can leave it as it is.
I just ordered the chassis and a ladder volume control (a chinese one which will be pimped with reasonable resistors).
I had luck to get the same chassis as my dac, so the units will look familar.
Nominal resistance is one thing. That's what the source sees. But ask them for one with no more than 5K output resistance. Else the preamp will slow down its rise time to more than its meant to be.