Graaf WFB One and WFB Two, two legendary preamplifiers from the Modena school. Among the most interesting products ever to come out of the design school of Giovanni Mariani, founder of Graaf, the WFB One and WFB Two preamplifiers hold a special place. Born in an era when Graaf was synonymous with research, unconventional solutions, and no-compromise construction, these two preamps represent two different phases of the same philosophy: getting the most from music through simple, refined circuits focused on real listening quality.
Over the years I have had the opportunity to service several units, both WFB One and WFB Two, and this direct experience is what led me to describe them together in a single article. The two units are in fact very similar in concept, layout, and function, but deeply different in the solution adopted for the phono stage, which is the real turning point between the two versions.
From a reliability standpoint, both have proven to be extremely robust. In the vast majority of cases, service work is limited to checking or replacing the line tubes, a few tired electrolytic capacitors, and, more rarely, a resistor that has become noisy after many years of service.
Graaf WFB One
The fully tube-based preamplifier with no compromises. The WFB One was the first to appear and is probably the most fascinating from a conceptual point of view. Mariani designed it with a clear goal: to create a fully tube-based preamplifier, including the phono stage, with no use of semiconductors.
From a circuit standpoint, the WFB One is a project of great elegance. The line stage uses 6922 (E88CC) dual triodes, while the phono stage employs a sophisticated configuration with cascoded and SRPP PC900 (4HA5) tubes, followed by a passive RIAA network and a low-impedance buffer. The result is a phono stage capable of working with both MM and MC cartridges without step-up transformers, thanks to three gain levels and three selectable impedances: 100, 500, and 47000 ohm.
On paper and in listening, the WFB One is a very high-level phono stage: quiet, dynamic, with a wide soundstage and a naturalness that few circuits can match. The problem has never been the design itself, but rather the choice of the PC900 tubes.
The PC900 are small UHF triodes originally developed for TV tuners, with electrical characteristics that are ideal for a low-noise, high-gain phono stage. Unfortunately, in practice many PC900 tubes are microphonic, unstable, or prone to ringing and feedback. This forced Mariani to carry out extremely strict selection. I have personally seen batches of hundreds of PC900 from which only a small number were chosen as truly suitable for use in the WFB One.
This is a fundamental point for anyone who owns this preamplifier: the PC900 in the WFB One must never be replaced casually. Rolling PC900 tubes is the best way to turn a great preamp into a noisy, unstable, or unbalanced machine. These tubes should be changed only if instrumental measurements show that they are faulty or worn out, which is actually very rare. In the WFB One the PC900 operate at very gentle conditions and they are all NOS, so they can easily last decades, often 30 or 40 years.
From a maintenance point of view, in the WFB One units I have serviced over the years, the typical interventions have been:
- Replacement of the 6922 line tubes when worn.
- Replacement of a few electrolytic capacitors.
- In only one case, the replacement of two noisy resistors.
Other than that, these are machines that age very well.
Graaf WFB Two
The mature and rational version, with a hybrid phono stage. The operational difficulties related to the PC900 tubes led Mariani to a pragmatic choice: designing an evolved version of the preamp, the WFB Two. Externally and in its general concept, the WFB Two is very similar to the One, with the same sober styling, the same control layout, the same 6922 tube line stage, and the same attention to component quality and low noise.
The real difference lies in the phono stage, which in the WFB Two becomes hybrid. The input and first gain are handled by transistors and JFETs, while the line and output stages remain tube-based. This eliminates at the root the problems of microphonics, selection, and instability typical of the PC900, while preserving the refined tonal character of the rest of the circuit.
From a practical standpoint, the WFB Two is much easier to manage, more stable, and less sensitive to aging of the active devices in the phono stage. Not by chance, many units I have serviced over the years were virtually perfect in terms of operation, requiring only:
- Checking the 6922 tubes.
- Replacing a few electrolytic capacitors.
- Verifying the phono stage trimmers and microswitches.
The internal construction of the WFB Two is of very high level, with neat wiring, selected components, well-filtered power supplies, and a background silence that is still remarkable today for a tube preamplifier.
In listening it retains all the typical qualities of the Graaf school: tonal balance, wide soundstage, extremely natural voices, absence of listening fatigue, and the ability to sound excellent with both digital sources and, especially, vinyl.
Two paths, one philosophy
The WFB One and the WFB Two are not competitors, but two different answers to the same question: how to build a truly musical, quiet preamplifier capable of handling MC cartridges without compromise. The WFB One is Mariani’s purest and most radical vision, fully tube-based, but it requires respect, expertise, and above all not touching the PC900 unless strictly necessary. The WFB Two is the more rational version, preserving the sonic quality while eliminating operational fragility. In both cases, these are machines designed to last, and even decades later they continue to prove that good analog engineering never grows old.