Leestereo
Super Member
Here are some pictures from my circa 1990s NAD 106 preamp project. As can be seen, the 106's very plain looking fascia belies its designation in NAD's 1992 product line up as their "top of the line analogue preamp".
But there are some hints of its ambitions to be seen on the outside: the nearly ubiquitous "loudness" control is no where to be found and around the back, there are gold plated dual RCA outputs as well as XLR connectors.
Inside, there is a very clean layout on a single glass epoxy pcb. Immediately noticeable, is the sealed ALPS "Blue Velvet" volume control, the use of 1% metal film resistors and numerous encapsulated polystyrene capacitors. The topology appears quite nice with two regulated power supplies, and the line and phono stages are fully discrete transistor designs.
In stock condition, the preamp sounds very good, but I think that the potential of the design is let down by the use of TEAPO branded electrolytic capacitors. Accordingly, in this restoration/upgrade project, all of the non-signal path electrolytic capacitors will be replaced with low ESR, 105°C types and the signal path electrolytics will be replaced with "Audio Grade" electrolytics (e.g., Nichicon MUSE) or film caps (whenever possible).
Restore/Upgrade (Part 1):
In the main regulated power supply, the replacement capacitors used were all Nichicon PW types. There was no opportunity to increase the capacitance values due to space constraints on the pcb (the replacement capacitors are essentially the same size as the original ones). Nevertheless, the power supply is quite robust for a preamp with over 6300µF of filtering capacitance. I added heatsinks to the TO-126 regulator transistors since these run quite hot and the top cover is not ventilated.
Part 2 of the project will cover the phono stage.
But there are some hints of its ambitions to be seen on the outside: the nearly ubiquitous "loudness" control is no where to be found and around the back, there are gold plated dual RCA outputs as well as XLR connectors.
Inside, there is a very clean layout on a single glass epoxy pcb. Immediately noticeable, is the sealed ALPS "Blue Velvet" volume control, the use of 1% metal film resistors and numerous encapsulated polystyrene capacitors. The topology appears quite nice with two regulated power supplies, and the line and phono stages are fully discrete transistor designs.
In stock condition, the preamp sounds very good, but I think that the potential of the design is let down by the use of TEAPO branded electrolytic capacitors. Accordingly, in this restoration/upgrade project, all of the non-signal path electrolytic capacitors will be replaced with low ESR, 105°C types and the signal path electrolytics will be replaced with "Audio Grade" electrolytics (e.g., Nichicon MUSE) or film caps (whenever possible).
Restore/Upgrade (Part 1):
In the main regulated power supply, the replacement capacitors used were all Nichicon PW types. There was no opportunity to increase the capacitance values due to space constraints on the pcb (the replacement capacitors are essentially the same size as the original ones). Nevertheless, the power supply is quite robust for a preamp with over 6300µF of filtering capacitance. I added heatsinks to the TO-126 regulator transistors since these run quite hot and the top cover is not ventilated.
Part 2 of the project will cover the phono stage.
Last edited: