Sound Skulptor MP73 User manual

www.soundskulptor.com
Document revision 1.2 – Last modification : 27/06/11
M 73 Setup guide
Follow the testing procedure in the shown order. If one test fails, find out the problem, correct it then resume.
Always unplug power between steps because it is very easy to create a shortcut when moving a DMM probe. And most
of the time, shortcuts are fatal to the circuits.
Step Description
1. Short circuit check Do a basic short circuit check with your digital multimeter (DMM) set to Ohms between
Test point T 4 (GND) and T 3 (V+).
You should get a value greater than a kilo-Ohm. If it is not the case, find out and fix the
short before applying power.
2. Test setup At this point, you need an assembled and wired SKM case.
Install your M 73 in a free slot. Connect a ribbon to the M 73 board (look at the “SKM
assembly guide”).
Disconnect all other mic pre's by removing their ribbon cable.
Connect the power supply leaving the mains plug disconnected.
Turn trimmer 7 anti-clockwise all the way down (25 turns).
Turn trimmer 6 clockwise all the way up (25 turns).
Warning : Be very careful when pre-positioning 6 and 7. Doing it the wrong way round
will surely smoke several components !
3. General power check lug in power and check that the 3 LEDs on the SL1 or SL2 are lighting normally. If one
LED is staying off or is lighting too low or too bright, immediately plug off power and
start checking your board.
lug off power.
4. Voltage setup Set your DMM to DC Volts on a 30 V scale and connect it between T 4 (GND) and T 3
(V+). Use test hooks and be careful not to create shortcuts.
lug in power. Check that you get a positive voltage and that it changes when you turn
7. Adjust to 24V. lug off power.
Warning : Do not confuse 6 (Bias) and 7 (V+ adjust).
5. Bias adjust With 6, we are going to adjust the
biasing of Q10 in order to flow a 70mA
direct current in the output transformer
primary. To do this, we are going to
measure the voltage between the +24V
point and the collector of Q10.
Set your DMM to DC volts.
lace the (+) probe of your DMM on the
test pin T 3 (V+). lace the (-) probe of
your DMM on the collector of Q10, that is
the metal plate at the back of the
transistor case. You will have to reach it
underneath the heatsink which is insulated.
Adjust 6 until you read 1.80 Volts on the DMM.
Warning : Do not confuse 6 (Bias) and 7 (V+ adjust).
Warning : If you do not see any voltage change when turning 6, stop adjusting and check
your board. You probably have a wiring error.
Copyright ©2007 SoundSkulptor

www.soundskulptor.com
Document revision 1.2 – Last modification : 27/06/11
Step Description
Warning : Turning 6 anti-clockwise increases the current in Q10. If you turn it too far,
the current will reach a value that WILL smoke R65 !
6. Sound check Connect the input and output XLR wires to the board terminals.
lug in a dynamic microphone to the input XLR.
Connect the output to your monitoring system. It can be a headphone amplifier or it can
go through one of your ADC inputs if you run a software studio.
Set Gain switch to “Mid”, “Level In” knob to minimum, 48V to Off and “Level Out” to
maximum.
lug in power.
Slowly turning up “Level In” knob, check that your micpre is working. Check the 3
positions of the gain switch, the hase switches and the “Level Out” pot.
Make the same test with a static microphone, with the 48V switch set to On.
lug off power.
Set the 48V switch to Off.
7. DI check If using SKM version 1, plug the board's ribbon cable to connector CN1 or CN2 on the
DI02 board.
Insert an instrument jack into the corresponding front panel jack socket.
lug in power.
You should hear your instrument when playing.
lug off power.
8. Clip LED setup For this setting you will need to use the knobs and front panel marking so finish
assembling the board as detailed in the “SKM Assembly Guide”.
Connect a 0.5VAC, 1KHz sine source to the input.
You can use your multitrack software loop playing a sine tone like the one that is
downloadable from the “Downloads & Useful links” section on our website. Route the
signal to a DAC and connect your DMM to the DAC output. Your DMM should be set to
AC Volts. Adjust the software output level in order to get around 0.5VAC. Connect this
output your micpre input.
Set the “Level In” knob to minimum, Gain switch to “Low” and “Level out” to maximum .
the micpre output is still connected to your monitoring system.
The important point here is that we are going to bring the micpre to clipping but we don't
want to clip in the monitoring chain. Check with your Vu meters. If the micpre output
signal is too hot for your monitoring input, you will have to build a pad, look at the next
step.
There are 3 trimmer potentiometers to adjust , corresponding to the 3 amplifier stages.
Start by turning 3, 4 and 5 anti-clockwise all the way down (25 turns).
lug in power.
Stage 3
Set the “Level In” knob to minimum, Gain switch to “Low” and “Level out” to maximum .
Slowly increase the “Level In” knob and listen to the sine tone until you just hear the
clipping coming in. It is quite easy to hear when the new harmonics break into the sound.
Back off slightly until you hear no clipping at all.
Lower by 3dB the DAC signal in the software. You can choose a different value like 4.5 or
6dB if you prefer a greater margin.
Adjust trimmer 5 to the point where the red LED just starts lighting up while turning
Copyright ©2007 SoundSkulptor

www.soundskulptor.com
Document revision 1.2 – Last modification : 27/06/11
Step Description
clockwise.
Stage 2
Set the “Level out” knob to 1 O'clock. Gain switch to “Mid”.
Slowly increase the “Level In” knob and listen to the sine tone until you just hear the
clipping coming in. Back off slightly until you hear no clipping at all.
Lower by 3dB the DAC signal in the software.
Adjust trimmer 4 to the point where the red LED just starts lighting up while turning
clockwise.
Stage 1
Keep “Level out” knob to 1 O'clock and set “Level in” to 9 O'clock. Set the DAC output
level to about 50mVAC by adjusting the level in the software . Set the gain switch to “Hi
gain”.
Slowly increase the level in the software and listen to the sine tone until you just hear the
clipping coming in. Back off slightly until you hear no clipping at all.
Lower again by 3dB the level in the software.
Adjust trimmer 3 to the point where the red LED just starts lighting up while turning
clockwise.
lug off power.
9. Output pad This is needed if your monitoring
chain clips before the micpre.
Use one female and one male XLR
plugs and wire 2 resistors as shown.
Insert the pad between the micpre
output and your monitoring system.
Go back to step 8.
10. Congratulations You did it !
Copyright ©2007 SoundSkulptor
female XLR male XLR
2K2
220
3
2
1
3
2
1