I finally got a chance to trace one of these units. The drive section is a complimentary feedback pair, which appears to be a signature of Roger Mayer units. "DRIVE" control eliminates ac negative feedback as it is rotated CW, so it is an active gain control. This drives a passive tone network with high pass and low pass limbs. The two limbs feed each side of the tone pot, and the wiper feeds the germanium transistor stage, which is a simple 4 resistor type common emitter amplifier with series feedback, emitter resistor is not bypassed. There is plenty of supply line decoupling, another element of the Roger Mayer signature. The silicon section clips hard, fast, and asymmetrically before the germanium stage clips.
Notes from testing:
At Q2 collector (drive output), top of wave clips hard at 6V first, then bottom clips at 2.5V.
1Vp-p output before clipping.
Most of the circuit board designators give the value of the resistors except for 2 resistors in the germanium pnp transistor circuit. These are both from that stage's V+ (+9V in series with 19k and a 220µF filter cap) to the transistors base and emitter. These are just labelled "RB" and "RE" respectively. I am presuming that these are selected in final assembly to bias the germanium transistor correctly.
From Roger's website (with added breaks for easier reading):
The Concorde+ Treble Booster is housed in the new Vision Series enclosure design and uses both silicon and germanium transistors in a unique configuration to obtain the best tone qualities from the marriage.
When I first started designing pedals in 1961 I produced a Treble Booster that was tried and used by my friends including Jimmy Page who then played in local bands. The circuit configuration I used was a standard textbook example but required careful attention to biasing and selection of transistors to obtain the best from this simple circuit. There were many subsequent commercial versions produced in the 1960's of this type of circuit that followed after the time I first designed mine and now I have designed and produced a much more flexible and enhanced version of my early design.
The modern clones produced today of the ultra simple 1960 type treble boosters lack in flexibility and in my opinion are of very limited use. The Concorde + however departs from the clones and uses a unique approach of combining a low noise class A silicon drive circuit with passive tone shaping to drive a fully optimised germanium treble booster. This results in giving the simple circuit new life and explores its sonic boundaries to the maximum. It is now possible to add drive and distortion with EQ before the treble booster section.
It is also possible to set the silicon drive section to drive the treble booster section (germanium) much harder than any guitar pickup could ever do without any added distortion but with the added feature or having EQ prior to the treble booster. So if you want the qualities of soft germanium type distortion overload characteristics that this circuit will produce or you want to explore the more radical germanium distortion possibilities the Concorde+ will oblige. The front panels controls of Drive, Tone and Output control the many tone variations and brings the humble treble booster forward to the future.
The Concorde+ comes in a brand new enclosure design with many added extras to help the modern musician. Many players demand a package that is more modern, flexible and pedal board friendly and will welcome the additional features.