26 Line/Preamp

This preamp is based on Ale Moglia’s  design that can be found at http://www.bartola.co.uk/valves/dht-pre-amplifier/26-dht-pre-amplifier-gen3/. Thank you Ale.

My approach:

  • PSU and amp in a compact design (same enclosure). This comes with a noise level compromise.
  • low and high gain options. Using LL2745 in Alt Q (2.8:1) and Alt R (5.6:1) I have option for 3-4dB (low gain) or 9-10dB (high gain). Again this comes with a compromise: low gain has low Zout (about 300 Ohms), high gain has higher Zout ( about 1k)
  • power transformers and chokes are home-made using Edcor laminations(EI87x1.4″). The power transformer, in addition to the end bells has a 5 mil copper screen connected to earth ground

Here are the schematics ( sorry if they are hard to read):
IMG_1610 IMG_1609

Some pictures during building:

IMG_1614 IMG_1613 IMG_1612 IMG_1611 IMG_1594 IMG_1592 IMG_1588 IMG_1586 IMG_1585 IMG_1584 IMG_1583 IMG_1581 IMG_1580 IMG_1579

More about sound and measurements to follow…

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