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Spin Doctor and H-Box.

The prototype valve Spin Doctor and H-Box have completed their development. Tests and demonstrations have been positive. Suggestions and ideas have been taken into account in finalising the designs. Both are '2U' format, suitable for rack mounting, placing on another instrument or table top use etc.
Spin Doctor's heart is a rotary non-electronic mechanism, using a monophonic input signal to provide full stereo outputs. Adding stereo vibrato, stereo tremolo, vibrato chorus, plus the 'Spatial' effect, using a principle similar to Doppler shift. Panel & pedal controls allow speed to be switched between fast, slow, stop and variable. Changing from fast to slow (or vice versa) takes a few seconds, due to the motor's momentum.

The tonal beauty of many instruments is enhanced, even in stop position. The result has been likened to that of a top end Aural Exciter. For an instrument with a strong timbral response to playing velocity, such as a Rhodes, dynamic range is emphasised. A Clavinet's guitar like qualities are emphasised.

Valve electronics facilitate connecting to musical instruments and amplification etc. Originally conceived for Hammond organs & Rhodes pianos, guitars have also proved ideal. The three current mode pre-amps are linear up to full output, compressing beyond this point. If distortion for guitar is required, a suitable added effect device should be used.

Two transformer coupled, 'push-pull' class A, output amplifiers provide 100 Ohm balanced line signals. To drive 2 Hammond PR-40 tone cabinets or similar amplifiers, they are clean up to over 10 Volts (+22.3 dBu), more than enough for PR-40s. Due to their design, if they are over-driven, the result will be even and odd harmonic distortion. More musically pleasing, if distortion is required, than odd harmonics only, common to many push-pull circuits.

Two unbalanced jack outputs provide 400 milli-Volts (-5.7 dBu) suitable for most stage amplifiers, mixing desks or monitors etc. An earth lift switch, for the Spin Doctor chassis, retains power supply chassis earthing. This should only be used to defeat a problem hum loop, eliminating any need for the dangerous practice of disconnecting mains earth leads.

Ron Lebar. XHTML Edited: 30-8-12. Loaded:
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