FiveFish Studios SC-1mk2 User manual

SC-1mk2 Mic Preamp Kit
Solid State, DC-Servo, Balanced Mic Preamplifier
with Input Transformer Option
Simplicity Counts, Detail Matters.
No part of this document may be reproduced, either mechanically or electronically, posted online on the Internet, in whole or in
part, without the expressed, written permission of FiveFish Studios. This document is solely provided
to the kit builder of the SC-1mk2 Mic Preamp Kit.
Copyright 2008 FiveFish Studios
www.fivefishstudios.com
Last Revision: November 14, 2008

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Copyright 2008 FiveFish Studios
www.fivefishstudios.com
SC-1mk2 Microphone Preamp Kit
SC-1mk2 Mic Preamp
Solid State, DC-Servo, Balanced Mic Preamplifier
with Input Transformer Option
Congratulations and thank you for your purchase of the SC-1mk2 Mic Preamp Kit.
This is the 2nd generation design of our popular SC-1 Mic Preamp Kit.
Hundreds of hours have been spent in the design, manufacturing and packaging of this kit to deliver to you a great preamp, with
the same features and performance found on some high-end boutique preamps. All at a very affordable price!
There are no special, expensive tools or techniques required to assemble this kit. All you need is the ability to follow
instructions, use common sense, and the confidence in knowing that YOU can do this.
PLEASE READ THIS DOCUMENT COMPLETELY BEFORE YOU ASSEMBLE YOUR PREAMP KIT.
I know people sometimes don’t want to read manuals. But unlike software, there is NO UNDO for this project. READ THIS
ASSEMBLY GUIDE COMPLETELY FIRST. Take your time, and ask questions if you are unsure of something. Work methodically
and carefully. I promise you, you’ll be rewarded with a great preamp when you’re finished. And you’ll have pride and joy when
you tell others that “Yes, I built this!”
Features, Advantages and Benefits of the SC-1mk2 Mic Preamp
-NEW: Option to use input transformer for added sound “flavor”
-NEW: Gain range from +12 to +72dB, in 6dB increments from +12db to +42dB; 4dB increments from 46dB to 72dB.
-NEW: Onboard Power Supply Regulation, adjustable +/- voltage rails
-Low-Noise, High-Quality Mic Preamp
-All solid-state design, using chipsets from THAT Corp and Burr-Brown
-Soft-start, slow ramp-on +48V phantom power
-Crystal clear Red LED indicator for phantom power
-Electronically balanced input and output stages (option to use input transformer for transformer balancing)
-12-position Grayhill gain selector switch

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SC-1mk2 Microphone Preamp Kit
-Input RFI protection
-Input clamping protection
-Output surge protection circuit
-Output RFI protection
-Reduced clicking and popping when changing gains
-High quality Bourns, sealed, conductive plastic potentiometer for volume control
-High quality PCB Mounted DPDT Switch
-Gold-plated, machined, low-profile IC sockets
-Use of high quality 1% Metal Film resistors, and high-quality ceramic and electrolytic capacitors
-Solder pads for optional INSERT jacks
-On-board jumper terminals
-Easy to assemble, easy to troubleshoot design
-Each component carefully labeled, protected and packed in separate zip bags
-Thick PCB board with 2oz. copper
-Very affordable!!! No, this is not “cheap junk” but a high quality product that is reasonably affordable! (i.e. because
there is no middlemen, and we don’t do expensive glossy magazine advertising! )
Basic Tools Required
A few basic tools are required to build this kit.
1. Soldering iron – adjustable temperature recommended, but not necessary. Your soldering iron must have a sharp
conical tip. I do not recommend a “flat-head, screwdriver-type” soldering iron. DO NOT USE A SOLDERING GUN. They
are usually rated at 100Watts and are overkill for this project.
2. Mini Pliers Cutter – to cut component leads, wires, strip insulation off wires (if you don’t have a wire-stripper tool).
3. Mini Long Nose Pliers – to bend component leads, use as a heatsink, hold components, tighten bolts.
4. Manual Solder sucker pump or desoldering gun– sucks up solder when you made a mistake soldering components on
the PCB. Pictured below is a Hakko model.

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SC-1mk2 Microphone Preamp Kit
5. Multitester – A simple meter/tester to measure resistance, and voltages. A digital read-out is a big help.
6. Soldering Lead – 60/40 lead or lead-free solder
7. Magnifying glass – to see what you’re doing! Especially when soldering IC pins and the Grayhill selector switch.
8. Clean and well-lighted work area – Lots of good lighting, clean work area. You want to be able to leave your work-in-
progress without packing everything away.
Extra Tools (Nice to have, but not required)
1. Vacuum desoldering pump – if you make a mistake, you need to pull out the component from the PCB
2. Component lead bender – bend component leads like resistors uniformly and evenly
3. PanaVise – to hold PCB while you’re working on it
4. Tweezers – to pick tiny things
5. Masking tape – to hold components on the PCB while working
6. Wire-stripper – for cutting wires and stripping its insulation

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SC-1mk2 Microphone Preamp Kit
SC-1mk2 Parts Identification and Assembly Notes
For the newbies, this is not meant to be a full tutorial about electronics. But I want you to be able to identify components,
recognize them and know what their basic functionality is.
In these sections, you’d also find instructions on how to use the INSERT jacks, and other geeky stuff. You’d also learn why I
chose certain parts for this kit, even though they may be 3x more expensive than another equivalent part.
Resistors
All resistors used in the SC-1mk2 Kit are 1/4 watt resistors. Most, if not all, of them are 1% tolerance, Metal-Film type resistors.
These are high quality resistors, way way much better than carbon composition type resistors
(usually 10-20% tolerance).
Resistors provide resistance, and are measured in OHMS, the unit of resistance.
1,000 OHMS = 1 KOhms (pronounced KiloOhms, where kilo = 1,000)
If you see a resistor value marked “1K”, it means 1 KiloOhm. Sometimes, you would see values
written as 6K8, or 3K3.
6K8 is also the same as writing 6.8 Kohm. The decimal point position is implied by the “K”
letter.
3K3 is also the same as 3.3 KOhm, or 3,300 Ohms.
I don’t need to teach you how to read resistor color codes since all the SC-1MK2 parts are already labeled for you. But if you’re
curious on what those bands of wonderful technicolors mean, you can go here.
http://www.samengstrom.com/nxl/10116/5_band_resistor_color_code_page.en.html
Capacitors
There are many types of capacitors used in the SC-1mk2 Mic Preamp project. Some are big, some small, some are polarized,
some are non-polarized. We’ll discuss the different types here.
Ceramic Capacitors
Ceramic capacitors look like the picture on the left. On the SC-1mk2 kit, these are colored “yellow” and
“blue” and are very small in size. Ceramic capacitors are non-polarized, and therefore it does not matter
what orientation they go in. They can go in either way.
They are rated in microfarads
(abbreviated as “uf”). They also have
a voltage rating (abbreviated as “V”).
In a design, the voltage rating must not be exceeded.
Otherwise, you’ll ruin the capacitor. Either short it out, or
blow it open.
Capacitor parts are therefore rated with their capacitance
(in microfarads, uf) and voltage… specified like this:
0.1uf 100V
Capacitance values may be expressed in microfarads (uf),
nanofarad (nf) or picofarads (pf). The conversion between
these units are shown on the table above.
Electrolytic Capacitors
Electrolytic capacitors are cylindrical in construction. They look like the picture on the
right. Unlike ceramic capacitors, electrolytic capacitors USUALLY/MOSTLY have polarity.
One side is marked with the (-) sign, also called the Cathode, or negative side. The
unmarked side is the (+) or Anode.
Just like ceramic capacitors, they are also measured in microfarads (uf). have a maximum
voltage rating.
WARNING: It is VERY IMPORTANT not to insert Electrolytic capacitors backwards, or in the
wrong polarity orientation. Doing so may/will cause the capacitor to explode. Yes, you
read that right… EXPLODE. Do not the let the small size of an electrolytic capacitor fool
you. Even a tiny electrolytic capacitor can explode with a lot of force.

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SC-1mk2 Microphone Preamp Kit
All of the electrolytic capacitors used in the SC-1mk2 preamp have polarity, except the (2) blue electrolytic
capacitors. 10uf 50V NP, shown on the picture on the right. These (2) electrolytic capacitors, labeled C12 and
C13, are Non-Polarized, so it does not matter how you insert them. But the rest of the capacitors in the SC-1mk2
kit should be inserted in the proper polarity.
Diodes
Diodes are semiconductor devices that permit current flow only in one direction. Think of it as a one-way valve.
The SC-1mk2 preamp kit uses 3 different kinds of diodes.
1. The first type of diode we’re using is the ZENER DIODE. These zener diodes are used as input protection to the mic
preamp circuitry. You can find the zener diodes in the locations shown on the photo to your right. [insert photo
here…]
PLEASE NOTE: Even though the SC-1mk2 preamp uses input protection, please turn OFF phantom power, and wait a few
seconds (5-10 seconds) before unplugging your microphone. Also, do not plug a mic while phantom power is ON. If you’re
using the SC-1mk2 with TRS jacks connected to a patch bay or another gear, do not turn ON phantom power… NEVER, EVER
plug a jack into a patchbay with Phantom Power turned ON. You risk of damaging any gear connected at the other end of
the patch bay and may even possibly damage your preamp. In short, turn OFF phantom power before
connecting/disconnecting the microphone and/or jack. It takes only a few seconds to do this. Don’t risk damaging your
gear.
2. The second type of diode we’re using is the SIGNAL DIODE. They look almost exactly like the Zener diodes. Nothing to
worry about, I packed the Signal Diode in a separate Zip bag for easy identification.

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SC-1mk2 Microphone Preamp Kit
3. The third type of diode we use is the General Purpose, Rectifier Diode. They are black, with a white/silver band.
NOTE: Diodes have polarities just like electrolytic capacitors. One side is denoted as the
ANODE (or positive side) and the other side is the CATHODE (or negative side). If you
soldered these diodes in the wrong position, your phantom power or preamp may not work.
Follow the band markings on the PCB silkscreen layout.
Inductors
The SC-1mk2 Preamp kit also uses inductors for RFI protection in the output stage. Inductors have no polarities, and just like
resistors can be inserted in either orientation. The inductors we use look just like resistors. For your convenience, they are
packed in a separate zip bag and labeled.

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SC-1mk2 Microphone Preamp Kit
Transistor
We’re using a transistor as a switching device in the SC-1mk2 Mic Preamp Kit. The transistor has (3) legs, the Collector, Base and
Emitter terminals. Looking from the top, the transistor has a half-circle shape, like a half-moon.
Take note when inserting transistors that you do not insert them backwards. Otherwise, phantom power will not work, and
possibly even ruin the transistor. The flat side should be facing to the right.
Grayhill Selector Switch
The SC-1mk2 uses a sealed, high-performance, high-quality,
12-position, Grayhill selector switch. This is one of the most
expensive items in this kit.
Some boutique preamp manufacturers also use Grayhill selector
switches for their preamps. They are durable, reliable, have a
nice solid feel to it, and provide good resistance to RF
Interference. This switch will be the most commonly
used/abused mechanical device on the SC-1mk2 preamp. I want
this part to withstand being turned and turned and turned.
DPDT Switch (Dual Pole, Dual Throw.)
The SC-1mk2 also use a high quality, PCB mounted DPDT switch.
This is another one of the expensive items in the kit. Again, since
this is a mechanical device, I want it to withstand repeated use of
toggling on and off.
You need to toggle the switch to the leftmost position (pointing
to the LED) to turn on phantom power. If you mount the SC-
1mk2 PCB vertically, the switch will be turned ON pointing
upwards. If you mount the SC-1mk2 PCB horizontally, the switch
will be turned ON pointing left, towards the LED.
Bourns Sealed Potentiometer
This is another high-priced item in this kit because it is another
mechanical component and I want this part to withstand the use
and abuse of being rotated constantly. I want it to provide a
smooth feel, and not wore out easily, and become “scratchy” like
a cheap, carbon potentiometer. I want it to have a longer life
than plain “guitar potentiometers.” This is also sealed from the
elements so dirt, grime, oil, and impurities will not contaminate
the resistive element and produce a “scratchy” volume control.
The resistive element inside is made of conductive plastic. Unlike
carbon potentiometers, these will last a very long time even after
repeated rotations.

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SC-1mk2 Microphone Preamp Kit
LED or Light Emitting Diode
The LED chosen is small in size, small in power consumption, crystal clear when OFF, but bright red when
turned ON. Lower power consumption means less heat, and less current draw from the power supply. High
efficiency means the LED lamp is bright even without using a lot of current. This is a little more expensive
than your normal, old-style LED lamp that consumes about 20mA of power. This LED uses only 4.9mA.
Just like a diode, there is a required correct polarity orientation for it to work properly.
Jumper Terminals
To facilitate easy setup, jumper terminals are used in the SC-1mk2 Mic Preamp. There is (1) jumper terminal on the board
labeled JP2. (JP1 has been removed from the SC-1mk2 model.) In normal use, the header terminals must be shorted and
“jumpered.”
Solder the short ends of the HEADER to the PCB as shown on the photo on the right.
INSERT Solder Pads and JP2 jumper
You’ll notice (3) solder pads on the PCB, behind the blue potentiometer. These are the INSERT Solder Pads.
Pin 1 = very bottom hole = GND = Ground Terminal
Pin 2 = middle hole = SEND
Pin 3 = top hole = RETURN
In normal operation, JP2 shorts the SEND solder pad to the RETURN solder pad.
TROUBLESHOOTING NOTE: If you forget to put in jumper JP2, you will NOT hear any sound from your preamp. So if you’re not
getting any output, check that JP2 is connected and shorted with a jumper jack.
So what’s the INSERT Solder Pads for? You can wire the preamp to optionally use an INSERT TRS Jack.
These 3 pads connect to a switching TRS jack. You must then wire the TRS jacks properly so that without any external jack
plugged in, the SEND and RETURN makes an automatic connection. If you plug in an INSERT CABLE, the internal connection is
broken and the signal is routed to the external signal processing device, and brought back to the preamp using the RTN pad.
Therefore…. If you’ll be wiring an optional INSERT JACK with your SC-1mk2 preamp, remove jumper JP2. Otherwise, leave jumper
JP2 in place. See page 16.

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SC-1mk2 Microphone Preamp Kit
Integrated Circuit (IC) Chips
IC1
IC1 is a THAT1510 Preamp IC. It has low noise characteristics,
and an even lower noise at low gains, wider bandwidth, higher
slew rate, lower distortion, and lower supply current.
You can substitute a THAT1512 chip for IC1, bringing down the
gain selection from +6dB to +66dB. The 1512 chip was also
tested and found to work the SC-1mk2 preamp.
It is also pin-compatible for use with
SSM2019/SSM2017/INA217/INA163. However, performance and
functionality was not tested with these older SSM/INA chipsets.
IC2, IC3
IC2 is a Burr-Brown OPA2134 chip. This is another ultra-low
distortion, low noise chip designed for audio applications. This
FET-input chip has high output drive capability, excellent DC
performance and wide output swing, capable to within +/- 1V of
the power supply voltage, which allows increased headroom. IC2
is used as a DC Servo in the SC-1mk2 Mic Preamp Design.
IC3 is also an OPA2134 chip. But this chip is used as a buffer
before the TRIM potentiometer and after the potentiometer. This
also serves as a buffer before/after the SEND/RETURN insert
pads.
IC4
IC4 is a THAT1646 Balanced Line Driver output. Using OutSmarts technology, this chip is stable driving long cables and
capacitive loads and is also capable of high output (18Vrms into 600 ohms according to manufacturer). Just like the Mic preamp
chip, and the DC servo chip, this chip has low noise, low distortion, high slew rate and wide output swing.

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SC-1mk2 Microphone Preamp Kit
Here’s a photo showing the locations of IC1, IC2, IC3 and IC4. Note the proper orientation of the chips.
The green dot marks the location of PIN 1 of the IC chip. There is also a notch on the IC body to show the proper orientation of
the IC chips. See photo below for closeup.

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SC-1mk2 Microphone Preamp Kit
Voltage Regulators
The SC-1mk2 uses additional on-board voltage regulation. This improves performance when you have (4) or more preamps
powered from a single Power Supply Circuit. It also provides a second level of voltage regulation, effectively reducing/removing
any ripple present.
Please note that the voltage regulators (labeled IC5 and IC6) look the same but are DIFFERENT. The positive
voltage regulator is an LM317, and the negative voltage regulator is an LM337. DO NOT INTERCHANGE the two
regulators or you may damage the chips. Read the marking on the body!

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SC-1mk2 Microphone Preamp Kit
Trimmers
Besides each voltage regulator is a blue trimmer, with a top adjustment screw terminal. Use these trimmers to
adjust the voltage on the preamp board to +/-18Volts.
Looking at the board, the top regulator and trimmer is the (+) positive voltage regulator.
The bottom regulator and trimmer is the (-) negative voltage regulator.
TP+ is a test point when measuring/adjusting +18Volts.
TP- is a test point when measuring/adjusting –18Volts.
More information about voltage adjustments can be found later in this document. (See Pre-Flight Check
Adjustments).

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SC-1mk2 Microphone Preamp Kit
SC-1mk2 Parts Kit
I’ve taken the time to individually package and label every component used in the kit. Just read the part # printed on the zip
bag.
Some bags will contain 2, 3 or 5 different components. Other bags will contain just one part#. I want you to be able to build
this kit, without sorting through hundreds of parts and not know what to do. This will save you a lot of time, and headaches!
Some of you may not even have a multitester (buy one, okay?) so I’m assuming even if you don’t have one, or don’t know how to
use one, you’d still be able to figure out which is the 680-ohm resistor from the 6K8 resistor. It’s all labeled!
Assembly and Soldering Tips
Use a clean soldering iron tip. Heat the component lead and PCB pad, then apply the solder to the component lead while heating
both with your iron. Do not apply the solder only to the iron.
Do not remove all the parts from the zip bags until you are ready to solder them. I’ve taken the time to sort them out; do not
make a big unsorted pile out of them.
The holes on the PCB are plated through. This is also a double-sided PCB. Solder needs to make good contact inside the holes
and on both sides of the PCB. Check that some solder flowed on the other side of the PCB, or that the holes are completely filled.
Be careful that you do not solder resistors in the wrong locations. For example: Resistors R9 to R20 form the gain staging
resistors. It is important not to swap the locations of any of these resistors. Otherwise, your gain steps will be out of order
depending on which resistors you swapped locations with each other… For Example: 6dB, 12dB, 24dB, 18dB, 30dB The
resistors for the 18dB and 24dB were swapped with each other in this example.
Note the orientation of diodes, and electrolytic capacitors. There is only one correct way to mount them. There are (2) non-
polarized electrolytic capacitor nearest IC4. The orientation of these (2) capacitors does not matter. But the rest of the
electrolytic capacitors need to be mounted in the correct orientation. Do NOT mount electrolytic capacitors backwards.
When soldering multiple-pin devices (like IC sockets, jumper pins, Grayhill switches, DPDT, Pots) solder one leg/pin first. Then
check if the device is still flushed to the board, straight and not crooked. If crooked, re-heat the leg and straighten with your
fingers while the solder is still soft/melted. (DO NOT STRAIGHTEN THE PINS AFTER THE SOLDER BECOMES HARD. You’d risk
ruining the PCB or breaking the part.)
I sometimes use masking tape to hold the component in place on the board, while I solder the leads on the other side. This is
very useful when soldering resistors, inductors, jumper connectors, IC sockets, small parts, etc…
Use a magnifying glass when soldering. This prevents you from using too much solder and let’s you see what you’re doing. Also,
the Grayhill switch has very fine pin spacing. You need good eyesight to solder all pins properly without shorting them together.

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SC-1mk2 Microphone Preamp Kit
SC-1mk2 Assembly Guide
The general guideline in electronics assembly is to solder the smallest/shortest component first (resistors, diodes, inductors),
and solder the bigger/taller components last (ceramic capacitors, electrolytic capacitors, switches, etc).
The last step is inserting the IC chips into the board.
NOTE: The photos on this Assembly guide may not match exactly the PCB you received. But the instructions are still valid.
Follow this checklist during your construction.
STEP 1. Solder all 1/4-watt resistors to the PCB. The orientation does not matter.
Build Notes:
a. DO NOT SOLDER RESISTOR R31, R32. (These are marked as 2M2 resistors on the PCB. Leave blank.)
b. If you’re NOT using the Input Transformers, solder jumper wires for the transformer. See the dashed lines printed on the PCB
board. Solder 2K67 resistor for RLP. (located to the right of the transformer)
c. If you’re USING Input Transformers, leave RLP blank and solder 6K8 resistor for RLS (located to the left of the transformer)
d. DO NOT INTERCHANGE the 100R and 100K resistors. (100R is 100-ohms. While the 100K resistor is 100,000 ohms. )
R28 besides IC3 is a 100-ohm resistor.
R29 and R30 besides IC1 and IC2 respectively are 100K resistors.
STEP 2. Solder the (2) inductors to the PCB. The orientation does not matter.
STEP 3. Solder all diodes to the PCB (except LED diode, LED1). These include Z1 to Z4, and D1 to D9. Note the orientation of the
diodes. All diode bands should be pointing to the RIGHT, or pointing UPWARDS.
STEP 4: Solder all IC sockets to the PCB. Note the orientation of IC3 socket. Make sure to mount the IC3 socket in the correct
orientation. (This will serve as a reminder on how IC3 chip will be inserted.) TIP: Use masking tape to hold the IC sockets in
place while soldering. See photo on right.
STEP 5: Solder all ceramic capacitors to the PCB. These are the yellow and blue capacitors. The orientation does not matter.
Note. This capacitor is UNUSED. C25, 33uf/ 50V
STEP 6: Solder the jumper connectors, JP2. Make sure they are soldered straight up, and not crooked to the left or right. TIP:
Solder one leg first. Check if it is straight. Then continue soldering the other leg.
STEP 7: Solder the Transistor. Note orientation of the transistor. The flat side should be facing to the right. You will need to
bend the middle pin backwards to go through the hole.
STEP 8: Solder all electrolytic capacitors. Note the orientation of where the (-) leg should be inserted. The unmarked leg of the
capacitor is the (+) leg. All (+) legs are positioned either to the right, or up. Capacitors C12 and C13 are non-polarized so their
orientation does not matter.
Build Notes:
a. It may be more convenient to solder C18 and C27 last. These are the big, tall electrolytic capacitors located at the bottom of
the board, near the power supply pins.
STEP 9: Solder the Trimmers. Solder on leg first; check to make sure the trimmers are flushed to the board and straight. Then
solder the rest of the pins.
STEP 10: Solder the voltage regulators. It may be easier to attach the heatsinks to the TO-220 voltage regulators first before
soldering them to the board.
Build Notes:
CAUTION: The positive voltage regulator is labeled LM317. The negative voltage regulator is labeled LM337. DO NOT
INTERCHANGE THE TWO PARTS!!!
STEP 11: Solder the DPDT switch. This switch has 6 legs. You may need to adjust the legs and move them slightly left and right
for them to insert properly into the PCB. All (6) legs must be properly aligned for the switch to go into the PCB. Solder one leg
first; check that the switch is still flushed to the PCB. If everything is flushed, solder the remaining legs.
STEP 12: Solder the Bourns potentiometer. Make sure the component is flushed to the board. Solder the middle leg first, check
alignment, and then solder the other 2 legs.

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SC-1mk2 Microphone Preamp Kit
STEP 13: Solder the Grayhill selector switch. You really need a magnifying glass to make this work easy and accurate. The pins
are very close together and you don’t want to short these pins… otherwise, your gain dB steps will be all wrong.
Build Notes:
a. Solder one of the end pins of the Grayhill switch, and then check if the switch is still flushed to the board, straight and not
crooked. . If crooked, re-heat the pin and straighten the Grayhill switch while the solder is melted. (DO NOT STRAIGHTEN THE
COMPONENT AFTER THE SOLDER BECOMES HARD. You’d risk ruining the PCB or breaking the part.)
If the part is flushed and straight (look at it from all angles), then solder another pin located on the opposite side. Check if the
device is still flushed and straight. If it is, then solder the remaining pins.
b. Installing the stop pins. The Grayhill switch will come with a metal stop pin rod, and a sticker to keep this rod in place. Use
tweezers to hold this pin rod and push it inside the 12:00 position hole as shown in the photo below. Then put the sticker over
it. The pins may not go all the way in, that’s fine. Re-attach the washer and the nut and tighten the nut by hand. This will push
the pin side and the sticker will keep it in place.
If you lost the included stop pins, don’t worry. Just use some cut leads from a resistor.
STEP 14: Solder the LED to the PCB. Observe proper orientation of the LED. Otherwise, the LED lamp will not light up.
Build Notes:
a. One leg of the LED will be longer than the other leg.
b. The LONGER leg of the LED is soldered nearest the Grayhill selector switch (i.e.
long leg = top position)
c. You need to bend the LED leads to form a right angle as shown by the photo on
the right. Set the height of the LED so it is aligned with the DPDT switch. Again, solder one leg of the
LED and see if the height is correct before completely soldering the other leg.
STEP 15: Insert the IC chips, IC1, IC2, IC3 and IC4. Be careful inserting the chips, and make sure all pins go in properly into the IC
socket holes.
Build Notes:
a. ANTI-STATIC WARNING: Ground yourself before handling the chips. Touch a metal gear to
discharge any static electricity on your body. Avoid touching the metal pins of the IC chip. If you
have a wrist ground strap, use it.
b. Perform the pre-flight check adjustments first before inserting IC chips IC1 to IC4. See
PRE-FLIGHT CHECK Section below.

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SC-1mk2 Microphone Preamp Kit
STEP 16: Solder wires to the +48V, V+, GND, and V- pads. Connect the wires to your power supply (or PSU-1848/2448 If you
also bought the PSU kit). All pads are 0.1” pitch on center, so you can use standard Molex 0.1” headers and connectors with the
SC-1mk2 board.
STEP 17: Solder XLR Jacks to the PCB using hookup wires. Solder pads 1, 2 and 3 to XLR Pins 1, 2 and 3 respectively. Do the
same procedure for both the input XLR and output XLR jacks. All pads are 0.1” pitch on center, so you can use standard Molex
0.1” headers and connectors with the SC-1mk2 board.
PAD 1 = XLR Pin 1 = GROUND
PAD 2 = XLR Pin 2 = HOT
PAD 3 = XLR Pin 3 = COLD

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SC-1mk2 Microphone Preamp Kit
STEP 18: The Input Transformer is OPTIONAL. It is not required for normal operation. But it gives additional “sound flavor” to the
preamp. If you prefer a clean/neutral/clear sounding preamp, you can omit the use of the Input Transformer.
If you are NOT using an Input Transformer, solder the 2K67 resistor in the RLP location. Also, Make sure to jumper the terminals
as shown in this photo.
If you are USING an Input Transformer, solder the 6K8 resistor in the RLS location.

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www.fivefishstudios.com
SC-1mk2 Microphone Preamp Kit
STEP 19: Solder the power connector wires. The power connectors are standard 0.1” pitch pads. So you can use any standard
0.1” Molex header and connectors. From left to right, the pins are labeled 1 to 4.
Pin 1= +48Volts
Pin 2= V+ (see STEP 3 of PRE-FLIGHT CHECK ADJUSTMENTS for further instructions)
Pin 3= GND
Pin 4 = V- (see STEP 3 of PRE-FLIGHT CHECK ADJUSTMENTS for further instructions)

Page 19
Copyright 2008 FiveFish Studios
www.fivefishstudios.com
SC-1mk2 Microphone Preamp Kit
PRE-FLIGHT CHECK ADJUSTMENTS:
It is a good idea to wear Safety Goggles when working. Especially when powering a circuit the first time! Buy one of those Safety
Goggles at HomeDepot or Lowes or other hardware places. Safety Goggles are cheap… Your eyes and eyesight are
irreplaceable!!!!
Also, do not work (especially without safety goggles) very close to a powered circuit. Remember my warning about electrolytic
capacitors being inserted wrongly backwards? They can explode. And if your face is right above the PCB, inches away, looking
down at it, guess what could happen…. YOU HAVE BEEN WARNED!
STEP 1. DO NOT APPLY POWER YET! TURN OFF POWER.
STEP 2. Review your work. Finished reviewing it? Good…. Now REVIEW IT AGAIN! It’s easier and less stressful to review your
work now before any “smoke” comes out of it!
To be specific, make sure components are inserted in the right locations.
Make sure all the diodes are pointing in the right direction.
Make sure all the electrolytic capacitors are inserted in the right direction.
Make sure there are no SHORTS or COLD SOLDER in your soldering job.
STEP 3. Since the SC-1mk2 Mic Preamp has on-board voltage regulators, you can feed it a regulated voltage higher than +/-
18Volts. The ideal thing to do is feed the preamp an input voltage somewhere in the +/-20Volts to +/-24V supply (regulated).
TURN ON POWER. (Remember, wear your safety goggles.) Stand back…. Wait a few seconds. Did it smoke? If yes, turn off power.
If not, good!… Proceed cautiously.