Nina’s circuit is really quite unique, in that it uses a JFET & MOSFET cascode input section, followed by a CCS-loaded gain stage terminated with a direct-coupled cathode follower, using the 6922/6DJ8 or equivalent tubes.
We have gone down this hybrid road for a very good reason, an extremely low noise floor level on this preamp. Due to the high gain, we found that by going all tubes the risk of ending up with unacceptable levels of background noise is much higher.
Overall gain at 1KHz is around 50dB for both NAB and IEC equalizations.
A lot of time and care was taken in the design of the power supply, as any shortcomings here will show themselves in the resulting tone of this preamplifier. To that end, we chose a solid state power supply, a regulated B+ high voltage and a regulated DC filament supply, one for each channel. This results in an ultra quiet power supply that is extremely stable, with NO variations despite any variations there may be from your household 120VAC power outlet.
Two low-noise toroidal transformers are used. The toroid for the high voltage B+ supply is a medical equipment grade unit with an internal shield and the toroid for the DC filament supply is mounted on the outside of the rear panel housed in a shielded aluminum enslosure.
Nina can be wired for either 120VAC 60Hz or 220/240VAC 50Hz mains supply.
Only high quality components are used in the construction of Nina. Low-noise Vishay +/-1% variation metal film resistors are used throughout the signal circuit with high quality Panasonic metal oxide resistors in the power supply circuit. WIMA film and Nichicon electrolytic capacitors are used throughout. Coupling capacitors are Mundorf MCap EVO series.Tubes use shielded sockets.
The frequency shaping components, especially the film capacitors, are of ultra low +/- 3% variation.
For the balanced outputs, we use the excellent Lundahl LL1544A audio transformer. The balanced XLR outputs are an option for the cassette deck version of Nina.
The printed circuit boards are designed in house , manufactured to FR4-TG standards, and are double-layer with full ground planes on both sides to ensure complete screening of the circuits.
RCA and XLR sockets are gold plated. The selector switch is a fully sealed gold plated GRAYHILL unitfor the reel to reel version and a gold plated two position toggle switch for the cassette deck version.
Tubes are factory new - a pair of matched gold pin 6922's. Other tubes such as the E88CC or 6DJ8 can be supplied on request and may add to the cost.
These specs apply for both the reel to reel and cassette deck versions
Preamplifier gain - 50dB
Frequency response is 17Hz to 40KHz
Rack chassis : standard width, 2U height and 8" deep
Rack chassis weight : 11lb
Warranty: 2 years on the preamp, 6 months for the tubes