VT-25 DHT Preamp Update

Well, it was just a question of time to make an update to the VT-25 DHT preamp. I wanted to try the BSH111BK as lower FET as shown below:

The result is visible on the frequency response. It does have an improved FR and the bandwidth gets up to 800kHz on same testing conditions. If you increase the HT to 280-300V you can increase the anode current to 30mA which should be good as well. 

I love the sound of this stage driving the 4P1L PSE output stage. It has a deep bass as well as clear treble. Dynamics on the system are fantastic. 

The bass on my system is fantastic now. Stronger than with previous setup. That is what you get when you marry low ra (4P1L pair) with a high-quality OPT.

I have a pair of pre-soldered BSH111BK boards (which are painful to solder) so I will give them away on a first come first serve basis

Weather is really nice today in London, so I’m going out right now…

6 Replies to “VT-25 DHT Preamp Update”

  1. Dear Ale,

    Iam inetrested in the pair of pre-soldered boards. pls send me your offer.
    Enjoy sunny London with your family . We have a blue sky in Gdansk as well.

  2. Happy to see you’re still working on that preamp. That BSH111BK seems the way to go for higher currents than BF862. I started to check what are the “realistic” operating points using filament bias (meaning reliable set up) in that case.

  3. Ale – great update. I always enjoy reading about your adventures. I wanted to ask whether or not the BSH111BK needs the protect zeners that you show in the schematic. According to the BSH111BK datasheet, it already has ESD protect diodes built in. So are you being extra careful or are the diodes just a holdover from previous builds using devices like the BF862 which don’t have internal protection diodes?

    1. Thank you for your feedback! The diodes in the schematic which aren’t numbered are built-in on the FET, with exception of the VDS zener of course

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