LaChapell Audio 503, 500 User Manual
500 Series
User Guide
PRODUCT SUMMARY (583E, 583S): The LaChapell Audio 583 series modules feature single-ended vacuum tube
preamplifiers designed for use in the “500 series” format. The microphone input configuration is based on the 992EG
and consists of an input transformer with a turns ratio of 1:10 and one ECC83/12AX7 vacuum tube. The instrument
input stage 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. The model 583E features an ultra-clean transformer-less three-band EQ section
with fully sweeping frequency controls and cut/boost settings of +/- 8dB... the EQ can run as an integrated EQ
(serving the preamplifier) or separate as its own autonomous module apart from the preamplifier.
PRODUCT SUMMARY (503): The LaChapell Audio 503 is a 3-band transformer-less EQ based on the EQ section of
the 583E pre/EQ. The 503 feature additional cut/boost range of +/12dB, 2-position high-pass and 2-position low-pass
filters along with a gain trim stage of +/- 6dB.
Stated below are a few areas that you must take the time to read before you install and use your 583. You as the
owner/user are responsible for completely understanding how to operate this device safely and properly.
UNPACKING: Inspect thoroughly. Although we take extreme care at final assembly and packing, things can
happen during transit. It is very important that you 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 as long as it is made within 7 days of receipt. Included in every package should be: (1) preliminary operating manual, (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.
• SERVICE/REPAIR: 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 583 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 supply off and remove 583 from the chassis, wait five minutes to allow
the vacuum tube to cool before attempting to remove it. 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. When a replacement tube is installed double check that you’ve inserted the correct tubes
into the 583’s tube socket BEFORE powering up.
NOTE: The 583’s standard tube is the EH 12AX7. However, there are many different ECC83/12AX7
variants that are virtually identical and can be used in either 583 module. 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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583E Controls:
Input Gain Control
Phantom Power
20dB Input Pad
Output Gain Control
High Frequency EQ Band
Polarity Reverse
Mic/Hi-Z Input Select
Hi-Z Input
Input Gain Control: Provides variable control
over how much input source signal is driven onto
the vacuum tube. Specifically, this control is positioned after the Jensen input transformer and just
before the 12AX7 tube. Think of this control as
your “throttle” for tube coloration/harmonics
(distortion).
Phantom Power (48v): This toggle provides a 48
volt supply of DC current for all condenser microphones. Each 983S is calibrated to exactly 48V
during final assembly.
20dB Input Pad (-20): When engaged, microphone input source signal is reduced by 20dB.
Specifically, this action occurs before the Jensen
input transformer. CREATIVE TIP: For near
transformer-less sound, consider engaging this
pad function and compensate for the loss of gain
by increasing the input gain control. This approach effectively minimizes the gain coming
from the Jensen input transformer while drastically increasing the character of the vacuum tube
(this is only possible with the microphone path).
Polarity Reverse: Reverses the polarity of the
output line level signal.
Input Select: Alternates between rear panel microphone XLR input or front panel ¼ Hi-Z input.
Each position defeats the other.
Hi-Z Input: The Hi-Z input stage is transformerless and operates with an input impendence of
100Kohm. It cannot make use of the -20dB pad.
Mid Frequency EQ Band
Low Frequency EQ Band
EQ Assignment Select (Auto Patching)
Output Gain Control: Provides variable control over line level signal strength. Think of this
control as your source for clean gain. Typically,
this control is used to establish the desired line
level after the input gain has been set.
High Frequency Band: Fully variable sweep
range; 2.5kHz to 20kHz. Q value of 1 at +8dB
Mid. Frequency Band: Fully variable sweep
range; 325Hz to 5kHz. Q value of 1 at +8dB
Low Frequency Band: Fully variable sweep
range; 30Hz to 400Hz
EQ Assignment Select: Auto-patches the EQ
to run independent or as part of the preamp
output path.
Pre + EQ: In this mode, the EQ section is
internally routed to serve the preamp’s output signal;
effected signal is sent out the left bay output jack.
Independent EQ: In this mode, the EQ section
is available as a completely independent module. The
corresponding rear/right side XLR connectors are
now active allowing you to use the EQ on any external souse while the preamp remains available on the
left bay. In this mode, think of the 583E as two modules.
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