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manual abstract
Due to the speaker technology of the time (and having been played for many years by Brian) it has a relatively mellow sound when compared to today’s hi-tech, hi-fidelity speaker systems. As it happens, said mellowness is actually quite complementary when the original Deacy is used in conjunction with Brian’s homemade guitar and Treble Booster. Due to the very low input impedance (12kOhms) of the amp John Deacon salvaged from a pile of rubbish (remember, in all probability it was originally designed for use in a car radio), it is actually not very useable when a guitar is plugged directly into it. This is because guitar pickups need to see a much higher impedance in order to do their job properly. Hence the use of Brian’s homemade Booster pedal was vitally important, not only in terms of tone but also in terms of the overall compatibility of the signal path. As also already stated, all the components used in the original Deacy, including speakers and the batteries used, are no longer in production. It is also worth reiterating two other facts: i) The original Deacy had no controls what-so-ever. & ii) It was always used in conjunction with Brian’s homemade Treble Booster — which, to be accurate, actually boosted the upper mid-range frequencies. © Richard Gray 2) The new Brian May Special To recap on DETAILS, after many meetings with Brian it was decided that this model would satisfy the following three criteria: i) It would sound and feel exactly like his homemade “Deacy system” which comprises of his Treble Booster and the original Deacy amp built by John Deacon. ii) It would also offer more power, features and tonal flexibility. & iii) It would be as affordable as possible. Brian May Special Signal Path Flowchart GAIN 9V BATTERY SIMULATOR GAIN SWITCH SPEAKER SYSTEM EMULATION 10 Watt POWER AMP OUTPUT TRANSFORMER SIMULATION VOLUME HEADPHONE AND RECORDING OUTPUT EXTERNAL LOUDSPEAKER OUTPUT TONE BOOSTER ONLY OUTPUT JACK INTERNALLOUDSPEAKER(FULL RANGE RESPONSE) 9V BATTERY SIMULATOR PUSH-PULL OUTPUT STAGE PREAMP & DRIVER STAGE BOOSTER TREBLE S T S R T S R T S T With reference to the above flowchart: i) The TREBLE BOOSTER stage is a direct copy of Brian’s homemade Treble Booster pedal. The only things different are: a) Our circuit is connected to the gain switching circuit to reduce the pedal booster gain in the LOW Gain switch position. This is required to clean up the operation of the pedal circuit b) The output is fed through the GAIN control. The original pedal does not have this. With the GAIN control turned up full (i.e. on “10”) and the GAIN switch on HIGH, this is equivalent to the original pedal. The GAIN control allows for different sounds to be produced. ii) The BOOSTER OUTPUT jack allows the Booster to be fed into another amp (AC30 Normal channel for instance) for Brian’s on-stage sound. Use of this jack makes the rest of the Brian May Special inoperative. This has been done for the reason that, due to circuit constraints, the output from the booster pedal section is different depending on whether or not it is plugged into the “Deacy” circuit, or into another amp that has a much higher input impedance. iii) PREAMP & DRIVER STAGE. This follows the original as much as possible, but: a) Silicon PNP transistors are used in place of the original obsolete Germanium types, but they have been chosen for similar operation, and also have extra circuitry to help them “believe” they are Germanium. b) The inter-stage driver transformer has been replaced by an electronic transformer simulation. This was required to try and emulate the performance of the original obsolete transformer. c) The addition of the gain switching circuit. iv) PUSH-PULL OUTPUT STAGE. Again the original format was studied and for the reasons outlined above has been changed to accommodate available technology: a) Germanium PNP changed to Silicon PNP. b) The output transformer has been changed to an electronic simulation. v) The TONE circuit was not on the original Deacy amp. This has been added to give more flexibility to the amp. It is placed after the distortion developing original circuitry, and can be used to colour the sound from mellow “-” to quite aggressive “+.” Its effect is inactive in the central, “off” position “0.” vi) SPEAKER SYSTEM EMULATION. This circuit emulates the “miced” tonal response of the original speaker system. The output of this is sent to both the RECORDING/HEADPHONE OUTPUT jack, for direct connection into a recording or PA system, and into the onboard 10-Watt POWER AMP system. vii) VOLUME controls the output volume of the POWER AMP. viii) 10 WATT POWER AMP. This is a flat response amplifier and speaker system, recreating the same signal that is sent to the recording/PA system. ix) EXTERNAL LOUDSPEAKER JACK. This allows the monitor amp output to be sent to an external speaker system (NOTE: using this mutes the internal speaker). This can either be a full range monitor system or, if desired, a guitar type cabinet. Bot...