Sonic Frontiers Line 1 Preamp from scratch

[Algar_emi]

I got the main PCB from an other diyaudio member at a good price. It a fully balanced design with sophisticated regulated power supply, almost completely DC coupled signal path (just one very good quality, low value capacitor) using a DC servo, high grade power transformer, very high quality 2oz copper PCB, three tubes per channel, input tube polarized with CCS current source, etc. For the price, I can never build such a sophisticated preamp, very nice indeed. To complete it, was only missing a delay timing circuit for the HV relays and a mute circuit that close when the already built-in DC error protection was detecting a DC offset at the output. This PCB was extensively moded with the best available, Vishay Bulk Metal foil, Caddock and Holco resistors. Multicap Thin-Foil fim capacitors, soft recovery diodes and instead of using the IC volume control, I use two external Noble potentiometers (much better, and no need for computer control). Here a picture of an original Line 1.

[Algar_emi]

Here my own version, top and back

[Algar_emi]

The original Line 1 has also an Headroom™ crossfeed headphone amplifier module. I built one too...