TUBE-TECH LCA 2A
compressor and limiter
DESCRIPTION:
The TUBE-TECH LCA 2A is a two channel unit with an independent compressor and limiter per channel. The unit is all tubebased (except for
the power supply and sidechain circuit). Input gaincontrol is placed
before the input transformer. The VCA (1 dual triode) is placed between
the input transformer and the outputstage (2 dual triodes). The audio
signal is picked up after the VCA and fed to the sidechain circuit. The
control signal from the compressor and from the limiter is combined and
sent to the link switch and to the control amp, which feeds the VCA. The
bidirectional link busses are accessible at two 1/4" stereo jack sockets
on the rear panel. The channels can be linked together for stereo applications and also linked to other LCA 2A's via the two link busses and a
standard stereo jack/jack cord.
The compressor has six attack/release presets as well as manual control.
The limiter attack/release is fixed.
The LED display is fed from the control amp. The limiter LED is fed from
the limiter buffer.
The audio path is fully symmetrical from input to output.
Input and output have fully floating transformers.
All DC voltages are stabilized, except the anode voltage for the outputstage.
COMPRESSOR INTERCONNECTION:
The sidechain sockets for interconnection of several compressors is
located on the rear panel.
A switch (LINK 1, LINK 2) on the front selects which compressors are
interconnected, and on which bus they are connected. If you select LINK
1 on both channels, they will perform exact the same gainreduction.
Having several connected compressors in a rack, you can select which
compressors you will have working together.
By selecting e.g. compressor 1 ch. 1 on link 1, compressor 2 channel 2
on link 1 and compressor 3 ch 1 on link 1, they are now interconnected
and all three will perform the exact same compression.
The interconnection implies, that the unit which performs the most
compression is controlling the others.
To choose which one you want to control, select the attack/release time,
the threshold and the ratio on that unit, and turn the threshold fully
counterclockwise on the reminding compressors.
It is of course possible to have all the interconnected compressors
control each other simultaneously.
2
CONTROLS:
GAIN:
DISPLAY:
LINK SWITCH:
IN/BYPASS:
The
gain
loss which takes place when the unit is compressing. It is placed before the inputtransformer.
The
gain
-6 dB to +20 dB.
The green LED display shows the gainreduction for
both the compressor and for the limiter. A red LED
show if the limiter is active.
The display is from the factory supplied in dotmode.
This can be altered to a bar by placing a strap on
U6 (U106) from pin 3 to pin 9
Interconnects several compressors on linkbus 1 or
linkbus 2.
If the compressor is left in the off position, it
works entirely independently.
This switch switches the compressor in and out of
the signal path. In the bypass position the entire
unit is switch out.
control is used to "adjust" for the gain
-control is continuously variable from
COMPRESSOR:
RATIO:
THRESHOLD:
ATTACK:
RELEASE:
The
ratio
input signal is compressed.
If the ratio selected is to 2:1, and the input
signal increases 10 dB, the output signal is only
increased by 5 db.The
variable from 1,6:1 to 20:1.
The threshold is the point where the compressor
begins its action. It is defined as the point where
the gain is reduced by 1 dB.
The threshold is related to the output level and is
continuously variable from off to -10 dBm.
The
attack
pressor responds to an increase in the input signal.
The attack control is continuously variable from 0.3
to 10 milliseconds.
The
release
pressor responds to a decrease in the input signal.
The release control is continuously variable from
0,07 to 2 seconds.
control varies the ratio by which the
ratio
control chooses how fast/slow the com-
control chooses how fast/slow the com-
control is continuously
LYDKRAFT Aps
Ved Damhussøen 38, DK 2720 Vanløse
Denmark
ATTACK/RELEASE SELECT:
This switch selects how the compressor reacts to a
increase (
signal.
There are two settings of the switch:
1. Manual.
attack time: from 0.3 msec to 10 msec
release time: from 0.07 sec to 2 sec
2. Preset.
pos 1. 1,5 mS 0,25 S
pos 2. 1,5 mS 0,8 S
pos 3. 3 mS 2,2 S
pos 4. 6 mS 5,0 S
pos 5. 3 mS 0,5/4 S
pos 6. 1,5 mS 0,5/4/20 S
The release time in position 5 and 6 is program dependent, that is:
pos 5, 6 for short peaks: 0,5 S
pos 5, 6 for long peaks: 4 S
pos 6 for continuously high levels: 20 S
attack
) or decrease (
attack release
release
) of the input
LIMITER:
THRESHOLD:
We recommend that the balance adjustment of the VCA, is carried out
every 6 month.
The threshold is related to the output level and is
continuously variable from off to 0 dBm.
ratio: 20:1
attack: 0,6mS
release: 0,5 S
LYDKRAFT Aps
Ved Damhussøen 38, DK 2720 Vanløse
Denmark
4
ADJUSTMENT PROCEDURE:
CAUTION:
Before making any adjustment let the unit heat-up at least 30 min.
Always check the DC voltages at the power supply.
When the VCA tube has been replaced, adjustment of:
BASIC GAIN
GAIN REDUCTION
BALANCE
shall be carried out
The adjustment procedure refers to channel 1. The trimpots in
brackets is for channel 2.
At the sidechain jacksockets at the rear of the unit, the tip is
link 1 and the ring is link 2.
ADJUSTMENT OF BASIC GAIN:
1) Turn the
fully counter-clockwise.
2) Apply a signal of 1 kHz, 0,0 dBm to the input of the compressor.
3) Turn the
4) Adjust the preset
an output-reading of +20,0 dBm.
ADJUSTMENT OF GAINREDUCTION
1) Turn the
fully counter-clockwise.
2) Apply a signal of 0,0 dBm, 1 kHz to the input of the compressor.
3) Adjust the
4) Apply a DC-voltage of +5,000 V into the sidechain jacksocket
(tip).
THRESHOLD
GAIN-
THRESHOLD
GAIN
-control for the compressor and limiter
control fully clockwise (+20).
GAIN
-control for the compressor and limiter
-control to an output-reading of 0,0 dBm.
P3 (P103) (located on amp/psu PCB) to
:
5) Set the
has dropped to -20,0 dBm.
6) If this is not the case, adjust the level with P 7 (P107) at
the sidechain PCB, to obtain a drop of exactly -20,0 dB.
-switch at LINK 1 and observe that the outputlevel
LINK
LYDKRAFT Aps
Ved Damhussøen 38, DK 2720 Vanløse
Denmark
ADJUSTMENT OF DISPLAY
:
1) Turn the
fully counter-clockwise.
4) Apply a DC-voltage of +5,000 V into the sidechain jacksocket
(tip).
5) Set the
just turns off and the -20 LED is on
6) If this is not the case, adjust P 8 (P108) at the sidechain
PCB.
ADJUSTMENT OF BALANCE IN THE VCA TUBE (V1, V101):
1) Turn the
the
GAIN
2) Switch the
3) Apply a sine wave of 1 kHz, +15 dBm via a 1KΩ resistor into
the sidechain jacksocket (ring).
The +15 dBm shall be measured before the 1KΩ resistor. *
4) Adjust trimpot P2 (P102) (located on amp/psu PCB) to a minimum
reading at the output.
THRESHOLD
-switch at LINK 1 and observe that the -13 LED
LINK
THRESHOLD
-control, fully counter-clockwise.
LINK
-control for the compressor and limiter
-control for the compressor and limiter, and
-switch to LINK 2.
5) Reduce the level of the sine wave to -5 dBm.
6) Adjust trimpot P1 (P101) (located on amp/psu PCB) to a minimum
reading at the output.
7) Repeat step 3 - 6.
8) When both adjustments are at minimum, the level at the output
in step 4, shall be lower than -20 dBm. If this can not be
obtained, the VCA tube shall be rejected and replaced with new
one.
* If the sine wave from the oscillator is observed on oscillo-
scope after the 1KΩ resistor, the negative part of the sine
wave have been clamped to ground and will therefore be missing.
The balance adjustment of the VCA, should be carried out every
6 month.
LYDKRAFT Aps
Ved Damhussøen 38, DK 2720 Vanløse
Denmark
6
LCA 2A
SPECIFICATIONS:
Gain:
Input impedance:
Output impedance:
Distortion
(THD+n @ 40 Hz):
-6dB - +20dB
> 2kΩ
< 60Ω
0 dBm: < 0,15 %
10 dBm: < 0,15 %
max output (1% THD+n): > +26 dBm
Noise
(Rg=200Ω):
Gain: 0 dB 20 dB:
22Hz-22kHz: < -85 dBm < -85 dBm
CCIR-468-3: < -78 dBm < -78 dBm
Frequency response
Crosstalk
CMRR
(@ 10kHz): < -60dB
(20Hz-22kHz): < -75dB
(-3dB): 5 Hz - 50 kHz
LED display for gain reduction: 0dB to 20dB
Compressor:
Ratio: 1,6:1 to 20:1
Threshold: off to -10dBm
Attack (manual): 0,2 to 10 mS
Release (manual): 0,1 to 2 S
Preset attack/release:
attack release
pos 1. 1,5 mS 0,25 S
pos 2. 1,5 mS 0,8 S
pos 3. 3 mS 2,2 S
pos 4. 6 mS 5,0 S
pos 5. 3 mS 0,5/4 S
pos 6. 1,5 mS 0,5/4/20 S
The release time in position 5 and 6 is program depen-
dent, that is:
pos 5, 6 for short peaks: 0,5 S
pos 5, 6 for long peaks: 4 S
pos 6 for continuously high levels: 20 S
Limiter:
Threshold: off to 0dBm
attack: 0,6mS
release: 0,5 S
ratio: 20:1
LED indicating limiting
Tubes:
Dimensions:
Weight:
4xECC82, 2xECC83
H: 2 units, W: 19", D: 165 mm
6.5kg
Power requirements:
(115V/230V, 50-60Hz): 65W
All specifications at RL=600Ω
Lydkraft reserves the right to alter specifications without prior notice
LYDKRAFT Aps
Ved Damhussøen 38, DK 2720 Vanløse
Denmark
7
SERVICE HINTS
SYMPTOM CAUSE REMEDY
Noise Noisy VCA tube (V1,V101) Replace and adjust
Noise Unbalance in VCA tube Adjust balance
Noise Control amp IC 4 (IC 104) Replace. Check gain
Hum +12V, +110V ,+15V PSU Repair
Overshoot when
compressing Unbalance in VCA tube Adjust balance
Oscillations with no signal and
max ratio and low threshold Unbalance in VCA tube Adjust balance
:
reduction and readjust
(replace tube)
LYDKRAFT Aps
Ved Damhussøen 38, DK 2720 Vanløse
Denmark
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