Dizengoff? Audio D864 User manual

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Dizengoff!Audio!
D864!Owner’s!Manual!
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Thank you for purchasing the D864 varimu compressor. This manual is intended
to serve as an overview of functions and technical specifications.
Overview
The D864 is a modernized take on the Federal AM864 varimu compressor.
Varimu compression has a very unique sound and behavior when compared
with other varieties of compression. Its sound, to my ears, is thick, with a
sort of pillow-y quality to the compression dynamic. Its behavior can seem
deceivingly neutral, at least initially.
The D864 has been designed to have very low noise, and is rather tolerant of
settings and tube mismatch. By this I mean that it doesn’t seem to
‘swamp’as easily as other varimu compressors I’ve heard. It can pull
20dB of compression under certain circumstances and still sound good.
In spite of this, the D864 takes a little time and patience to really get to know
it. This manual is intended to walk the user through the feature set.
Chassis
The D864 uses an all aluminum 2U rack mount enclosure.
Power
The D864 is powered by either 120volt or 240 volt AC. It uses a unique R-core
power transformer for low noise operation. Power inlet is via a standard
three-prong IEC cable.

Signal Flow and Gain
The D864 has approximately 30dB of gain, which is about 15dB less than the
original AM864.
When using the D864 with a mic preamp, it’s important to utilize appropriate
gain staging. There is no need to set the mic preamp for the same amount of
gain used when the D864 is not in the signal chain. Doing so may cause
distortion.
Optimum input signal is about -10dBV to about +6dBU. If you feed it 0dBV to
+4dBU, and you want your output to be about the same level, set the input
knob between 4 and 5 (about 9 o'clock as it relates to a clock face). With no
compression (all knobs set to 0) there will be some signal gain. You can use
the meter in output mode (switch down) to measure the output level and
calibrate as necessary.
Switch Features
All switches are normally flipped up to turn features off and enable
compression.
Growl Switch
The Growl switch is a parallel germanium compressor. At low levels it will
act like a hard knee limiter and add a little bit of edge. At higher levels it will
saturate and add extra harmonic distortion. With a 0dBV input signal and
about 5-7dB of gain reduction, you'll see about 0.5% THD without the Growl
feature engaged. With the Growl engaged THD can get as high as 3-5%.
Glow Switch
The Glow switch shifts the output stage bias and transformer saturation point.
As it does this, it gives an apparent 'bump' to the 1-2kHz band. The signal
response is flat, but the distortion curve shifts. I find it's helpful in bringing

out a vocal or snare crack while compressing. There can be a slight pop
when switching between states.
Bypass/Link
To bypass compression or to link another D864 in stereo operation, flip the
Bypass/Link switch down.
Dim Switch
The "dim" switch is located at the bottom of the switch matrix next to the
meter. It cuts the maximum gain to 25dB, but does this by padding the output
signal down (kind of like the EMI RS124 does). It’s useful for reducing signal
level from hotter sources. Flip the switch down to engage it.
Meter Switch
The Meter Switch allows a user to switch between compression mode and
output level mode. In compression mode (switch up) the meter will show the
approximate amount of compression. In output mode (switch down) the
meter will show the approximate amount of output signal.
It’s worth noting that the meter circuit is an exact copy of the original--which
means it behaves exactly like and old school meter behaves. The original
AM864 compression meter circuit simply measures the amount of current
passing into the input stage tubes as it relates to the level detector. That
means certain changes to attack or ratio can affect the meter’s behavior.
Its behavior isn’t 100% accurate, but it’s close enough to do the job.
Compression Features and Behavior
The compression circuit is based around a half-wave rectifier (6SQ7 tube,just
like the Federal). It's not a very efficient circuit, which means the response
can be a little slow and unusual compared to modern designs. But it's part of
the Federal's unique soft-knee sound. It also means that the compression

control knobs will all interact with each other slightly. I find its lack of
accuracy on signal peaks means that you'll need to set compression settings
higher than you need and then back down. The harder you hit it, the less
"ratio" you'll need to use.
Input Section
The large input knob is a trim stage, used to trim the amount of input signal
that reaches the two 6SK7 pentodes responsible for compression. 0 is the
lowest setting, and trims the input signal down completely.
Attack
The attack knob is at its lowest setting when pointing to the ‘0’and is at its
highest setting when pointing to ‘10’. The attack ranges from 20ms at its
lowest to 200ms at its highest point.
Release
The release knob ranges from 5ms at ‘0’to 50ms at ‘10’.
Ratio
Ratio is approximately 1:1 at its lowest setting and 1:8 at its highest setting.
Threshold
Threshold is at its lowest setting at 0 and highest setting at 10. The threshold
knob uses a high-wattage wirewound potentiometer, and it has a somewhat
coarse feel to it when turned.
Tubes
The D864 uses four octal tubes. The two input tubes are 6SK7 pentodes. The
level detector and gain control amplifier are 6SQ7. The output tube is 6SN7.
It is worth noting that enclosure clearance is low, so when replacing tubes

it’s important to limit replacement to metal can or short bottle versions
(under 2.25 inches in height). Taller versions won’t fit inside the enclosure!
Power and Indicator Lamp
The D864 uses a vintage style power switch and large red jewel power
indicator. This lamp uses a standard 6.3-volt screw in type T3 pilot bulb.
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Input and Output
The D864 features XLR input and output jacks located on the rear of the unit.
It also features a TS link jack for stereo operation.
Copyright 2015, Dizengoff Audio. All rights reserved. The information contained in this manual may be updated at
any time without prior notice.
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