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FiveFish Studios SC-1mk2 Assembly

Mic preamp kit; solid state, dc-servo, balanced mic preamplifier with input transformer option
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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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Summary of Contents for FiveFish Studios SC-1mk2

  • Page 1 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.
  • Page 2 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 2 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.
  • Page 3 Page 2 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...
  • Page 4 Page 3 SC-1mk2 Microphone Preamp Kit Multitester – A simple meter/tester to measure resistance, and voltages. A digital read-out is a big help. Soldering Lead – 60/40 lead or lead-free solder Magnifying glass – to see what you’re doing! Especially when soldering IC pins and the Grayhill selector switch.
  • Page 5 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.
  • Page 6 (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.
  • Page 7 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.
  • Page 8 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.
  • Page 9 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.”...
  • Page 10 +/- 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.
  • Page 11 Page 10 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.
  • Page 12 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.
  • Page 13 Page 12 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.
  • Page 14 Page 13 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.
  • Page 15 Page 14 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.
  • Page 16 Page 15 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.
  • Page 17 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...
  • Page 18 Page 17 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.
  • Page 19 Page 18 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.
  • Page 20 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).
  • Page 21 Page 20 SC-1mk2 Microphone Preamp Kit STEP 4. Next, we need to adjust the trimmers of the onboard voltage regulators. Basically, the external +/-20V to +/-24V regulated power supply you feed to the preamp board will be further regulated down to +/-18V.
  • Page 22 Page 21 SC-1mk2 Microphone Preamp Kit If you cannot adjust the voltages to +/-18Volts no matter how you turn the trimmers, something is wrong. POWER OFF and re- check your work. (Note: I’m assuming you’re feeding the Mic Pre board with a voltage more than 18Volts coming from your power supply).

  • Page 23: Audio Testing

    Page 22 SC-1mk2 Microphone Preamp Kit AUDIO TESTING Connect a dynamic microphone to the input XLRs, connect a monitor speaker to the output XLR, turn power ON, set the gain switch, adjust volume and you should hear sound come out of your preamp.
  • Page 24 +/-24V (or higher) will be good. I still recommend a regulated power supply. Using a cheap power supply, or unregulated power supply will cause hum problems. Add to the mix the high gain capability of the SC-1mk2 and you can be amplifying problem hum by 100x, 500x, 1000x, 2000x or 4000x time.
  • Page 25 Page 24 SC-1mk2 Microphone Preamp Kit SC-1mk2 PCB Component Layout Guide Copyright © 2008 FiveFish Studios Copyright  2008 FiveFish Studios www.fivefishstudios.com...

  • Page 26: Light Emitting Diode

    Page 25 SC-1mk2 Microphone Preamp Kit SC-1mk2 Parts List Rev5.2 Part Qty Value Custom SC-1mk2 PCB C1,C2 470pf/50V 47pf/50V C4,C5 47uf / 50V C6,C7,C8,C9,C10,C11,C16,C17, 16 0.1uf / 100V C19,C20,C24,C26,C28,C29,C31,C39 C12, C13 10uf / 50V NON-POLAR C14, C15 100pf / 50V...
  • Page 27 Page 26 SC-1mk2 Microphone Preamp Kit 100R R31,R32 NOT USED R33,R34 5K TRIMMER R35,R36 220R XLR IN Neutrik XLR Female XLR OUT Neutrik XLR Male IC Sockets 8-pin IC socket .300 GOLD GRAYHILL 1-DECK, 12-POS SWITCH RIGHT ANGLE TOGGLE SWITCH Conn Header 2Pos 0.100 vert...
  • Page 28 Page 27 SC-1mk2 Microphone Preamp Kit How to use the included TRS jack to function as an INSERT jack This diagram explains how to wire aTRS jack to function as an INSERT jack. [insert photo here…] UPDATE PHOTO Do not forget to short the two terminals on the jacks as shown in the photo above. This connects the SEND connection to the RETURN connection completing the circuit if there is no TRS jack inserted.