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Sunday, December 16, 2012

The Modular Preamplifier, Part 14: DHT Gain Stage - Finished Signal Chassis


A quick update on the progress of the DHT gain stage. The circuit and completion of the power supplies have been covered in previous posts. This post shows the completion of the signal chassis.

The signal chassis is constructed in a similar style as the power supplies. Most parts are mounted on plates which form a sub assembly that is inserted into the wooden frame:

Tubes and capacitors are mounted on the top plate. Most of the signal wiring is done directly under the plate. Still lots of connections necessary between the parts in the chassis and the top plate before the chassis can be closed:

The finished gain stage with it's power supplies, ready for testing:

The back sides with the umbilicals attached:

The combo fired up:

Initial tests look good. The B+ voltage divides about equally across the 801 and 841.

The frequency response looks good. The bandwidth is mainly determined by the LL1660 line out transformer. Voltage gain is about 53x with unloaded output which equates to about 34dB.

Stay tuned for the listening report and how it performs in the phono section.

Best regards



  1. Congratulations, Thomas!

    Unbelievably beautiful housings....but pleeeease: change the green LEDs into red or ornage ones ;-)


  2. Hi Peter,

    thanks! Also unbelievably heavy ;-)

    Nope, LEDs have to be green IMHO and no other color, no red no yellow and especially no blue. In real life they don't glow as bright as on the photos. It is a nice and comfortable green.

    Best regards


  3. YEEEES, Thomas... that's why you're my electronic hero:-)))
    NO blue LEDs, never... and green is TRULY appropriate and a beauty...
    Like for traffic lights... Red is stopping... with Green... you goooooooooooooooooo:-)))!