LaChapell Audio 983s User Manual

LACHAPELL AUDIO
Model 983S Two Channel Vacuum Tube Preamplifier for
Microphones and Instruments

Operating

Manual

PRODUCT SUMMARY: The LaChapell Audio 983S is a two channel microphone and instrument

preamplifier. Both the microphone and Hi-Z input configurations are based on our very popular
Model 583 500 series module. Each channel consists of an input transformer (Jensen JT-115k)
with a turns ratio of 1:10 and one ECC83/12AX7 vacuum tube. The instrument input stage (Hi-Z)
is transformer-less with the signal essentially going strait to the grid of the tube. The output stage
utilizes premium Burr-Brown and THAT Corporation line drivers along with an 80% nickel alloy core
transformer to generate a balanced line-level output signal with very low 8 ohm output impedance.
With this precision, double-balanced output stage, the 983S is capable of driving many hundred of
feet of cable without significant less of signal quality.

Before You Get Started:

Stated below are a few areas that you must take the time to read before you power up and use
your 983S. You as the owner/user are responsible for completely understanding how to
operate this device safely and properly.

Inspect thoroughly. Although we take extreme care at final assembly and
packing, things can happen during transit. It is very important to contact LaChapell Audio if
there is anything broken or damaged upon receipt of package. Shipping is always insured and
we will do our absolute best to satisfy any legitimate claim made within 7 days of receipt.
Included in every package should be: (1) preliminary operating manual, (1) Model 983S
preamplifier, (1) A/C power cable, (1) packet of mounting screws, (1) registration card. It is a
good idea for you to retain the packaging (box & foam case) in case there is a need to return
the unit for service or repair at a later date.

CONTACT INFO: [e-mail] 615-837-4598

With the exception of tube replacement (see below) the user should
NOT attempt to service this unit in any way, due to the risk of electrical shock and the presents
of lethal voltages inside the 983S while powered. Only LaChapell Audio personnel are to
perform maintenance and service activities. The user should also take note that excessive
‘swapping’ of tubes will Introduce undue wear on the tube socket. It is therefore recommended
that tube replacement be performed only when necessary and by technically competent
individuals.

Tube replacement: Turn power off, disconnect the power cable and wait five minutes
to allow the vacuum tube to cool before attempting to remove it. Waiting five minutes
also allows the power supply caps to discharge adequately if the tube is not pulling
current as it should. Using your fingers, apply a slight circular/rotating motion as you pull
it away from the socket. It is important to replace the tube with the same type of

tube.

NOTE: The 983’s standard tube is the Electro Harmonic 12AX7. However, there are

many different ECC83/12AX7 variants that are virtually identical and can be used in the
983S preamp. These include: ECC803, E83CC, CV4004, 6057, M8137, C492, 7025
and the 5751 (you will notice a slight drop in gain when using the 5751).

WARNING: Warrantee may be void if tubes other than those listed above have been used at any
time.

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