Specifications

Model 9762 – Dual Combo Owners Manual
5 Design Features
The 9762 has been designed and built with great attention to detail. In
particular, the input transformer and gain stepping network have been
painstakingly matched and optimized to present the proper load
impedance to the microphone at all gain settings. This refinement
combined with a super high quality input transformer gives the 9762 a
more detailed sound when compared to vintage units.
The enclosure and faceplate are made of heavy gauge steel for extra
strength and maximum shielding. All audio transformers and the AC line
power supply transformer are shielded internally with mu-metal housings
for maximum isolation and hum reduction. The power supply uses a
custom designed low noise audio grade toroidial type transformer.
5.1 Input Stages
The input transformers are optimized for 200-Ohm impedance
microphones or other devices having 200-Ohm source impedance. The
LO-Z impedance select switch configures the transformer input for either
50-Ohm (LO-Z) or 200-Ohm source impedance. Keep in mind that the
impedance select switching is accomplished by configuring the input
transformer primary wiring as either a series or parallel circuit, which
affects the transformer’s turns ratio. By nature, the impedance switching
affects the signal level by roughly 6 dB when switching impedances.
Miniature sealed gold contact relays are used for all audio switching
functions and increased reliability. The input stages include additional
muting logic for silent switching. Note that the mute logic circuitry uses a
special dual FET shunt type design for transparent mute operation
without degrading or coloring the audio signal path. The audio signal
does not actually pass through the FET devices, but instead, the FETs
act as shunt switches to mute the output signal during switching
operations.
A high impedance FET buffer stage is used in the instrument direct input
(DI) stage. The FET input buffer stage serves as a high impedance
conversion stage designed to prevent loading of the instrument pickups.
The DI switch allows manual selection of the DI or microphone input
source. Additionally the DI select switch may also serve as a channel
mute switch when the DI or microphone input is not in use.
5.2 Phantom Power
The phantom power switching circuitry uses a smooth power ramping
design to reduce pops and clicks during switching. The phantom voltage
ramps up gradually when enabled and gradually ramps down when
disabled. A high voltage regulator on the power supply circuit board
provides phantom power for both channels and is fully protected against
continuous shorting via each channel’s current limiting resistors.
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