Tube Tech Lca 2b Service Manual

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TUBE-TECH LCA 2B
compressor and limiter
DESCRIPTION:
The TUBE-TECH LCA 2B 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). Output gaincontrol is placed between the VCA and output stage.
The VCA (1 dual triode) is placed between the input transformer and the output
stage (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 bi-directional 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 2B'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 and equipped with an on/off switch.
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 stabilised, except the anode voltage for the output stage, which
is only filtered.
COMPRESSOR INTERCONNECTION:
The sidechain sockets for interconnection of several compressors are 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. LCA 2B no 1, ch. 1 on link 1, LCA 2B no 2, ch. 2 on link 1 and LCA
2B no 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 counter clockwise on
the reminding compressors.
It is of course possible to have all the interconnected compressors control each
other simultaneously.
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
1
CONTROLS:
GAIN:
The gain control is used to "adjust" for the gain loss, which takes
place when the unit is compressing. It is placed between VCA and
output stage. The gain-control is continuously variable from -6 dB
to +10 dB.
DISPLAY:
The green LED display shows the gainreduction for both the
compressor and for the limiter. A red LED shows if the limiter is
active.
The display is from the factory supplied in dot mode. This can
be altered to a bar by placing a strap on U6 (U106) from
pin 3 to pin 9
LINK SWITCH:
Interconnects several compressors on link 1 or link 2.
If the compressor is left in the off position, it works entirely
independently.
IN/BYPASS:
This switch switches the compressor in and out of the signal
path. In the bypass position the entire unit is switch out.
COMPRESSOR:
RATIO:
The ratio control varies the ratio by which the 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 ratio
control is continuously variable from 1,6:1 to 20:1.
THRESHOLD:
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 dBU.
NOTE:
If both the RATIO control and the THRESHOLD control are
at their extreme (> 15:1 and < -5 dB), overreaction can be
expected.
ATTACK:
The attack control chooses how fast/slow the compressor
responds to an increase in the input signal.
The attack control is continuously variable from 0.3 to 70
milliseconds.
RELEASE:
The release control chooses how fast/slow the compressor
responds to a decrease in the input signal.
The release control is continuously variable from 0,07 to 2
seconds.
(940530)
2
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
ATTACK/RELEASE SELECT:
This switch selects how the compressor reacts to an increase
(attack) or decrease (release) of the input signal.
There are two settings of the switch:
1.
Manual.
Attack time: from 0.3 mS to 10 mS
Release time: from 0.07 sec to 2 sec
2.
Preset.
Attack
1,5 mS
1,5 mS
3 mS
6 mS
3 mS
1,5 mS
pos 1.
pos 2.
pos 3.
pos 4.
pos 5.
pos 6.
Release
0,25 S
0,8 S
2,2 S
5,0 S
0,5/4 S
0,5/4/20 S
The release time in position 5 and 6 is program dependent, that is:
pos 5, 6
pos 5, 6
pos 6
for short peaks:
for long peaks:
for continuously high levels:
0,5 S
4S
20 S
LIMITER:
ON/OFF
This switch defeats the limiter when in the off position
THRESHOLD:
The threshold is related to the output level and is continuously
variable from off to 0 dBU.
Ratio:
Attack:
Release:
20:1
0,6 mS
0,5 S
We recommend that the balance adjustment of the VCA, is carried out every 6
month.
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
3
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 trim pots in brackets are for
channel 2.
At the sidechain jack sockets at the rear of the unit, the tip is link 1 and the
ring is link 2.
ADJUSTMENT OF BASIC GAIN:
1)
Turn the THRESHOLD-control for the compressor and limiter fully
counter-clockwise.
2)
Apply a signal of 1 kHz, 0,0 dBU to the input of the compressor.
3)
Turn the GAIN-control fully clockwise (+10).
4)
Adjust the preset GAIN P3 (P103) (located on amp/psu PCB) to an output-reading of +10,0 dBU.
ADJUSTMENT OF GAINREDUCTION:
1)
Turn the THRESHOLD-control for the compressor and limiter fully
counter-clockwise.
2)
Apply a signal of 0,0 dBU, 1 kHz to the input of the compressor.
3)
Adjust the GAIN-control to an output-reading of 0,0 dBU.
4)
Apply a DC-voltage of +5,000 V into the sidechain jack socket (tip).
5)
Set the LINK-switch at LINK 1 and observe that the output level has dropped
to -20,0 dBU. If this is not the case, adjust the level with P7 (P107) at the
sidechain PCB, to obtain a drop of -20,0 dB.
The level might increase a little (+0.5 to +1 dB) from the instantaneously value
(940530)
(within 5-10 sec.). This is quite normal.
4
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
ADJUSTMENT OF DISPLAY:
1)
Turn the THRESHOLD-control for the compressor and limiter fully
counter-clockwise.
2)
Apply a DC-voltage of +5,000 V into the sidechain jack socket (tip).
3)
Set the LINK-switch at LINK 1 and observe that the -15 LED just turns off and
the -20 LED is on.
4)
If this is not the case, adjust P8 (P108) at the sidechain PCB.
TEST OF TRACKING:
1)
Turn the THRESHOLD-control for the compressor and limiter fully
counter-clockwise.
2)
Apply a signal of 0,0 dBU, 1 kHz to the input of the compressor.
3)
Adjust the GAIN-control to an output-reading of 0,0 dBU.
4)
Apply a DC-voltage of +1.750 V into the sidechain jack socket (tip).
5)
Set the LINK-switch at LINK 1 and observe that the output level has dropped
to within -7,0 dBU and -9,0 dBU. If this is not the case, the VCA tube shall be
rejected and replaced with a new one.
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
5
ADJUSTMENT OF BALANCE IN THE VCA TUBE (V1, V101):
As a quick check of the balance of the VCA tube, adjust the output to a level
of 0 dBU and turn the LIMITER THRESHOLD slow CW until the LIM led turns
slightly on.
If the led turn on abruptly or starts oscillating, the balance should be readjusted.
1)
Turn the THRESHOLD-control for the compressor and limiter fully counter
clockwise, and the GAIN-control fully clockwise.
2)
Switch the LINK-switch to LINK 2.
3)
Apply a sine wave of 1 kHz, +15 dBU via a 1K
resistor into the sidechain
jack socket (ring).
(The +15 dBU shall be measured before the 1K resistor.) *
4)
Adjust trim pot P2 (P102) (located on amp/psu PCB) to a minimum reading at
the output.
5)
Reduce the level of the sine wave to -5 dBU.
6)
Adjust trim pot 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 shall be:
+15 dBU less than -13 dBU
+5 dBU less than -14 dBU
-5 dBU less than -21 dBU
If this cannot be obtained, the VCA tube shall be rejected and replaced with
new one.
*
If the sine wave from the oscillator is observed on oscilloscope after the
1K
r

esi
stor, the negative part of the sine wave has been clamped to ground.
The balance adjustment of the VCA should be carried out every 6 month.
NOTE:
0 dBU = 0,775V
(941010)
6
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
SPECIFICATIONS FOR LCA 2B
-6 dB - +10 dB
> 2 k
< 60 
Gain:
Input impedance:
Output impedance:
Distortion (THD+n @ 40 Hz):
0 dBU:
10 dBU:
max output (1% THD+n):
(Rg=200
Noise
):
Gain:
0 dB
22 Hz-22 kHz:
< -85 dBU
CCIR-468-3:
< -75 dBU
(-3
dB):
Frequency response
Crosstalk (20 Hz-22 kHz):
CMRR (@ 10 kHz):
Tracking (0 to -20 dB gainreduction):
LED display for gain reduction:
< 0,15 %
< 0,15 %
> +26 dBU
10 dB:
< -80 dBU
< -70 dBU
5 Hz - 50 kHz
< -70 dB
< -60 dB
+/-1 dB
0 dB to 20 dB
Compressor:
Ratio:
Threshold:
Attack (manual):
Release (manual):
Preset attack/release:
1,6:1 to 20:1
off to -10 dBU
0,2 to 70 mS
0,1 to 2 S
pos 1.
pos 2.
pos 3.
pos 4.
pos 5.
pos 6.
attack
1,5 mS
1,5 mS
3 mS
6 mS
3 mS
1,5 mS
release
0,25 S
0,8 S
2,2 S
5,0 S
0,5/4 S
0,5/4/20 S
The release time in position 5 and 6 is program dependent, that is:
pos 5, 6
pos 5, 6
pos 6
for short peaks:
for long peaks:
for continuously high levels:
Limiter:
Threshold:
attack:
release:
ratio:
LED indicating limiting
0,5 S
4S
20 S
off to 0 dBU
0,6 mS
0,5 S
20:1
2xECC81, 2xECC82, 2xECC83
H: 2 units, W: 19", D: 205 mm
6.5 kg
Tubes:
Dimensions:
Weight:
Power requirements:
(115V/230 V, 50-60 Hz):
30-45 W
All specifications at RL=600
Lydkraft reserves the right to alter specifications without prior notice
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
(941010)
7
SERVICE HINTS:
(940530)
SYMPTOM
CAUSE
ACTION
Noise
Unbalance in VCA tube
Adjust balance
Noise
Noisy VCA tube (V1, V101)
Replace and adjust
Noise
Control amp IC 4 (IC 104)
Replace. Check gain reduction and readjust
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 (replace tube)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
8

User`s Manual TUBE-TECH LCA 2B compressor and limiter

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