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Copyright



2008 FiveFish Studios

www.fivefishstudios.com

SC-1mk2 Microphone Preamp Kit

STEP 4. Next, we need to adjust the trimmers of the onboard voltage regulators. Basically, the ex/-20V to +/-24V
regulated power supply you feed to the preamp board will be further regulated down to +/-18V.

There are two test points on the preamp board labeled TP+ and TP-. Hook the negative probe of your voltmeter to Ground.
Connect the positive probe of your voltmeter to the TP+ terminal, adjust the top trimmer (turn the screws) until you get a voltage
reading of +18Volts.

Do the same for the TP- terminal. Connect the positive probe of your voltmeter to the TP- terminal, adjust the bottom trimmer
until you get a voltage reading of –18Volts.

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Summary of Contents for SC-1mk2

Page 1: ...is 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 ...

Page 2: ...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...

Page 3: ...z 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 recom...

Page 4: ...d 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...

Page 5: ...here 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 ...

Page 6: ... 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 ...

Page 7: ...itive 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 indu...

Page 8: ...ed 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 ...

Page 9: ... 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...

Page 10: ...is 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 ...

Page 11: ...e 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 ...

Page 12: ...ps 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 Rea...

Page 13: ...just 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 Ch...

Page 14: ...ng 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 ...

Page 15: ...hile 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 le...

Page 16: ...t 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 Buil...

Page 17: ...itch 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 ...

Page 18: ...ut 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 ...

Page 19: ...es 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 20: ... 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 ...

Page 21: ...l be further regulated down to 18V There are two test points on the preamp board labeled TP and TP Hook the negative probe of your voltmeter to Ground Connect the positive probe of your voltmeter to the TP terminal adjust the top trimmer turn the screws until you get a voltage reading of 18Volts Do the same for the TP terminal Connect the positive probe of your voltmeter to the TP terminal adjust ...

Page 22: ...2 IC3 and IC4 Make sure the orientation of the IC chips are correct Make sure all the legs of the chips are inserted properly in their corresponding IC sockets STEP 6 TURN POWER ON AGAIN See if any smoke comes out Feel the IC chips and check if they re hot They should not be Touch the other components to see if they re hot None should be hot Maybe the voltage regulators can be a little warm but no...

Page 23: ...hone 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 If using a condenser mic turn phantom power switch to ON position Check to see if the LED lights up Wait a few seconds and your condenser microphone should start working ...

Page 24: ...few seconds before I can hear sound This is normal This is due to the soft start phantom power It takes anywhere from 15 seconds to 30 seconds to stabilize and reach full power I m not applying the full 48V at full blast to your expensive mics Rather I feed phantom power to the mic gradually and raise the voltage gradually It also protects your speakers from the thumping sound and your expensive m...

Page 25: ...yright 2008 FiveFish Studios 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 2007 FiveFish Studios ...

Page 26: ... C32 C33 2 10uf 63V C34 C35 2 1uf 100V LED1 1 LIGHT EMITTING DIODE Z1 Z2 Z3 Z4 4 12V ZENER DO 41 1 0W D1 D2 D3 D4 D6 D7 D8 D9 8 1N4004 D5 1 1N4148 IC1 1 THAT 1510 IC2 IC3 2 OPA2134P IC4 1 THAT 1646 IC5 1 LM317T IC6 1 LM337T L1 L2 2 78F3R3J RC Q1 1 BC546B NPN transistor All resistors 1 4 watt metal film when available RLP 1 2K67 R10 R26 2 3K32 R2 R3 RLS 3 6K8 R4 R5 2 4R7 R6 R7 R9 3 10K R8 R29 R30 3...

Page 27: ... R33 R34 2 5K TRIMMER R35 R36 2 220R XLR IN 1 Neutrik XLR Female XLR OUT 1 Neutrik XLR Male IC Sockets 4 8 pin IC socket 300 GOLD SW1 1 GRAYHILL 1 DECK 12 POS SWITCH SW2 1 RIGHT ANGLE TOGGLE SWITCH JP1 1 Conn Header 2Pos 0 100 vert SHORT1 1 Conn Jumper Shorting Tin HS1 HS2 2 Heatsinks TO 220 T1 1 INPUT TRANSFORMER optional ...

Page 28: ... you re not using any INSERT jacks make sure to put jumper JP2 back on the board Construction Notes If you re using the INSERT jacks please keep a couple of things in mind 1 The SEND signal is unbalanced Therefore it is recommended that this cable be kept as short as possible 2 The RETURN signal is also unbalanced Therefore it is recommended that this cable be kept as short as possible The signal ...

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