Q: WHO MAKES THE BEST PREAMPS FOR THE MONEY?
A: YOU DO.
Seventh Circle Audio provides professional quality electronic kits and support to handy audio recording engineers. Our flexible, modular preamp kits provide a full range of "colors" suitable for any application and are in daily use by recordists world-wide.
Assemble your own world-class microphone preamp by combining a CH02 or OneShot chassis and up to eight of our superb amplifier modules.
Customize your system to suit your current needs and expand as your studio grows. We currently have five preamp modules available, each with its own distinct personality, as well as a 2-channel active instrument DI!
Improve your skills as an engineer by learning about electronics, or order fully-assembled units to save time and still save money.
Impress your clients with what you can build, not just what you can buy.
Save money! Stretch your studio budget by investing your down time in DIY.
Each kit is thoroughly documented with assembly instructions, bills of material and schematics. All the documentation is freely downloadable so you can be ready to go before your kits arrive. If you get stuck or have questions, support is available via e-mail and the message board. We guarantee you won't be stuck with a non-working kit!
Q: What all do I need to buy to get started?
A: You need to purchase at least one module (kit or assembled) and a chassis/power supply. Either the up to 8-channel CH02, or the single channel PC01.
Q: Will the newer modules work in my older CH01(Beige or Cream-colored) chassis?
Answer: YES! As long as the power supply has a 6-pin connector.
Q: If I have the older chassis (CH01), do I need to buy the black subpanels/faceplates?
Answer: NO! The black faceplates are specifically for the CH02 chassis! They MUST be purchased if you are installing them into a CH02 chassis!
Some Assembly Tips...
Like all AC line-operated devices, our kits can present a potential shock hazard if basic safety precautions are not followed. Don't attempt any of our kits unless you have a basic understanding of electrical safety.
Only apply power to the PS03 when it is installed in the chassis, never when loose on your workbench. Never touch any of the line-side components while the supply is plugged in. If you ever need to measure voltages on the PS03, use clip-on probes and keep your hands away from the board while the AC cord is connected.
Always work on your chassis with the AC cord disconnected. Simply switching off the power is not enough.
Never work with electricity under the influence of drugs or alcohol, or while overly fatigued.
Take your time! Don't rush!
None of our kits are recommended for absolute beginners and all assume some prior experience soldering on printed circuit boards (PCBs). This experience is easy to get, however, by building a simple kit or practicing with surplus parts on a piece of copper-clad perfboard.
You should own and understand the proper use of a digital multi-meter (DMM). You should have at least heard of Ohm's Law and understand the difference between a volt, an amp, and an ohm. You shouldn't have to ask where to put the probes to make a basic voltage measurement.
Probably more important than any acquired technique is the attitude you bring to the project. Electronics assembly demands an attention to detail that does not come naturally to some. It's not good enough to do a decent job on 99 out of 100 solder joints, or to get 9 out of 10 diodes installed the right way round. It's not like playing horseshoes. But if you're the sort that enjoys working with your hands, has a curiosity about the inner workings of complicated machinery, and has the patience to read and follow directions, success is virtually guaranteed.
You don't need fancy or expensive tools to do great work, but trying to save money by skimping on tools is false economy. Here's a list of tools that we use daily and can recommend without hesitation. They're not the cheapest, but they'll last for years. If you can't find them locally, they're easily available from the sources listed on our resources page.
Soldering Iron - It's possible to do a decent job with a cheap 25W pencil iron, but we strongly recommend a temperature-controlled unit from Weller, Hakko, Pace, Metcal, or other quality brand. Make sure that the tip is electrically grounded and the handle dissipates static buildup.
Hakko 936-12 or similar
Hakko 900M-T-0.8D chisel tip
Pliers - It's good to have at least two pairs on hand, one larger and one smaller. You may also find it useful to have both serrated and smooth jaw versions of the same tool. For electronics work we usually prefer pliers with spring-loaded jaws. Xcelite, Erem, Plato, Xuron, and Lindstrom are some other quality brands to look for.
Klein - Needle-nose plier D335-51/2C
Klein - Long-nose plier D307-51/2C
Diagonal cutters - Again, it's useful to have larger and smaller versions on hand. Don't abuse small precision cutters on heavy gauge wire or thick component leads.
Klein Miniature semi-flush D219-4C
Klein Standard 5" D245-5C
Lead benders - These are specialized but very inexpensive tools that will make any electronics assembly job easier and more professional looking. We strongly encourage you to prepare resistor leads using a lead bender!
Magnifier Lamp - If you plan to build a lot of kits and have trouble seeing small type, you may want to consider a magnifier lamp. Luxo is the premier manufacturer, but in recent years decent knockoffs have appeared which are fine for occasional use.
Solder Sucker - We hope you'll never need it, but it's a good idea to have one around to augment your solder wick. The Edsyn Soldapullt is an industry workhorse, but low-cost versions also work well.
Wire Strippers - Always handy to have, especially for stripping transformer leads. Make sure to get one with a range of wire gauges appropriate for the work you're doing.
Hot Air Gun - Not absolutely essential, but definitely helpfule with the heat shrink tubing used in the chassis kit. A small, light-duty unit is best for occasional electronics use.
Chemicals and Supplies
Solder - In recent years the electronics industry has been revolutionized through the introduction of lead-free solder and components. Removing lead from large-scale manufacturing will undoubtedly produce long-term benefits for the environment and workers in the industry, but lead-free solders make life more difficult for the electronics hobbyist and repair technician due to their higher melting points. If you're uncertain about your soldering skills and don't plan to be soldering eight hours a day for the rest of your career, we recommend you use traditional leaded solder. If you already know what you're doing, it's probably better to embrace change and get used to working with lead-free solder since it's not going away.
Solder Wick - Also known as solder braid, this clever stuff acts like a solder sponge when applied to a joint and heated. Use it to clean up excess solder or remove parts from the board. It's easy to overheat the board and lift a pad, however, so use solder wick with care.
Flux Remover - If you use the recommended solder you won't need to deflux the board, but it's good to have a can on hand just in case.
Flux Pen - It's unlikely you'll need this since your kit will contain new parts with fresh, clean plating, but it's useful for stubborn joints or components with oxidized leads.
Silicone Adhesive - Makes for a better job of mounting the front panel trim control.
Dow Corning 684
Thread Lock Adhesive - Use on output transformer mounting screws, especially if you plan to use your chassis in a mobile rig.
Loctite Threadlocker Blue 242
Canned Air - If you don't have a compressor, a can of this non-flammable aerosol is useful for cleaning and drying your finished boards.
Toothbrushes - Used to remove any loose solder blobs or wire snippets from the solder side of the board.
DMM - It's absolutely essential to have a decent DMM (digital multi-meter) to build any of our kits, and if you continue with electronics you'll likely find your meter to be the most valuable tool you own. Buy the best one you can afford, but make sure it has the proper feature set for electronics testing. A 200mV DC range (lower is better), 2M ohm resistance range (higher is better), and diode tester (transistor Hfe is better) is essential. Frequency counting and capacitance measurement are also quite useful. RMS AC voltage measurement is very desirable, but not necessary. We've listed three suitable models below, but there are many others that will also work.
Probes - In addition to the standard test leads that come with your DMM it's helpful to have a few additional probes. At the very least, get a pair of Pomona "mini-grabber" type test leads for no-hands measurements.
Pomona 3782-36-0 black
Pomona 3782-36-2 red
Jumpers - A set of "mini-grabber" or alligator clip jumpers can come in handy if you find yourself doing a lot of troubleshooting.
Oscilloscope - An oscilloscope produces a visual representation of a voltage versus time, or one voltage versus another voltage. It is definitely not necessary to have a scope to construct any of our kits, but if you're considering investing in an oscilloscope here are a few possibilities for new units. Many new oscilloscopes are digital, and their small size, light weight, color displays, and extensive signal processing functions make complex testing much easier. There are also many excellent scopes available on the used market. Look for at least a 20MHz bandwidth (higher is better) and two input channels. External triggering is also useful. Convenience features such as on-screen cursors and built-in metering functions are nice to have but not necessary.
Tenma 72-6805 - includes function generator
It's also possible to use a DAW to visualize waveforms, but not for making calibrated measurements.
Signal Generator - It's also not necessary to have a function generator to successfully construct any of our kits, but a simple generator is very handy to have in any studio.
NTI (formerly Neutrik) MR1
Gold Line GL1K
It's also possible to use a DAW for test signal generation.
Components and Component Handling
One of our goals when designing kits is to use as many standard parts as possible. Consequently, you can find detailed information and datasheets for most of the components at manufacturers or distributors web sites. Simply google the manufacturer's part number for quick access to a wealth of component data. You can also check prices and order extra parts directly from the distributors listed on the Bill of Materials (BOM) using either the manufacturer or catalog number. Apart from poor soldering, the main reason kits don't work is because a part has been installed in the wrong place, or installed incorrectly. Components like electrolytic capacitors, diodes, transistors, and ICs are polarized and must be oriented correctly. Installing these parts backwards will prevent the board from working, destroy the component, or both.
Resistors come in many shapes and sizes, but the resistors used in SCA kits are generally of two types, 5% tolerance carbon film and 1% tolerance metal film. The tolerance specifies the most the actual value of the component can vary from its marked value. For example, if you measure a 1% tolerance, 1K ohm resistor, the actual value can be anywhere between 990 and 1010 ohms. A 5% tolerance, 1K ohm resistor could measure anywhere between 950 and 1050 ohms. Keep this in mind when you're sorting parts. Resistors are marked with a standard color code. Since there are many descriptions, examples, and tutorials explaining the color code on the web, we won't repeat that information here. A quick google search will turn up more than you'll likely want to know. Resistors are generally quite rugged, but they can be damaged by improper insertion into the board. That's why you should invest a few dollars in a lead bender and prepare the resistor leads properly before you install them. Never bend the leads at the resistor body and force the resistors into the board. Even though resistors are not polarized and will work happily when installed in either direction, it's good practice to install them with the tolerance bands pointing in the same direction. This not only makes the board look more professional, it makes the resistors much easier to read when testing and troubleshooting.
Capacitors come in all shapes and sizes and vary greatly in their internal construction. These internal details result in properties that often make certain capacitors better suited for certain applications, which is why your kit may contain both 1uF film capacitors and 1uF electrolytic capacitors, for example. Capacitors are specified by capacitance (measured in Farads) and maximum working voltage (usually marked as WV). You can almost always substitute a capacitor with a higher working voltage for one with a lower working voltage, but never the other way round. Electrolytic capacitors are usually large enough to have their values printed directly on the case and don't need to be deciphered, such as 100uF / 63WV for example. Except for special types, electrolytic capacitors are polarized and must be oriented on the board correctly. If they're not they have an annoying tendency to explode, so be very careful to observe the markings on the board and the capacitor during assembly. Almost without exception the negative lead of the capacitor is indicated with a colored stripe down the side of the case. Tantalum capacitors require special care in handling. Because of their extremely thin dielectric, they are more susceptible to damage from static discharge and reverse polarity than other types. It's a good idea to check tantalum capacitors for shorts before installing them on the board. Tantalum capacitors may be marked differently than aluminum electrolytics, so be sure you understand how the capacitance, working voltage, and polarity are designated. Ceramic and film capacitors aren't polarized, but as with resistors it's good practice to orient the markings so they read in the same direction. The markings on these parts usually consist of a 3 digit code such as "104" and possibly a voltage rating or other manufacturer codes. The 3-digit code indicates the size of the capacitor in picofarads. The first two digits are "significant" and the third indicates the number of zeros following the significant digits. So "104" indicates 100000 picofarads (100000 pF), which is the same as 100 nanofards (100 nF) or 0.1 microfarads (0.1 uF).
Inductors are simply loops or coils of wire, usually wound on a form and packaged for easy insertion into a circuit. Like resistors and capacitors, they come in all shapes and sizes, each suited for a particular application. They're also very rugged and reliable, but need to be treated with the same care as other components. Inductors wound on sintered ferrite cores, especially, can break if dropped or crushed. Use a lead bender to prepare inductors for insertion into the board. Never bend the leads at the inductor body and force the part into the board. Most small inductors are marked with a code similar to the resistor color code. Values are denominated in microhenries (uH) of inductance. For example, an inductor marked with brown, black, and red stripes would have a value of 1000 uH.
Semiconductors include all of the so-called "active" components such as diodes, transistors, and integrated circuits. These days, they're almost always made from silicon that has undergone a number of elaborate chemical manipulations. Considering their complexity, most semiconductor devices are remarkably rugged and durable but they must be treated with care, especially when they're loose on the workbench. Even small static discharges can damage them, so be sure to keep them in their static-dissipative pink bags until needed. Make sure to discharge any static buildup on your body by touching an electrically grounded object before handling semiconductors. Virtually all semiconductors must be installed with the proper orientation to function properly, so pay close attention to the silkscreen outlines and component designators on the board. Also, semiconductors come in standard packages and can only be differentiated by actually reading the part numbers. Your kit will be guaranteed not to work if you swap the positive and negative voltage regulators, for example. There is no way to tell these components apart except by reading the part numbers.
The largest, heaviest, and most expensive component in your kit is likely to be a transformer. Since they only pass AC, transformers can provide DC isolation between two circuits, or between two parts of the same circuit. They are also used to match impedances and signal levels by trading voltage for current and vice versa. Audio transformers are high-precision electromechanical devices and must be handled with care. Use the least amount of heat possible when soldering leads to a transformer terminal board. Excessive heating of the pins can damage the internal connections. Excessively long transformer leads can both receive and radiate noise and must be trimmed to the appropriate length as described in the assembly instructions, but don't trim them too short. Don't put any unnecessary strain on the transformer leads. Hold the leads with pliers while stripping them. Brace the pliers against the bench to avoid jerking the lead as you strip the insulation. Pulling too hard on the leads can cause internal shorts or break the leads entirely. Don't tighten the nuts on the mounting screws too much. Use a drop of Loctite to keep the nuts from working loose over time, especially if you plan to use your completed kits on the road.
There are a number of excellent guides to basic soldering technique on the Internet, a few of which we've listed on our resources page. If you don't have a lot of electronics assembly experience (and even if you do) they're worth checking out. Here are the basics most relevant to SCA kits.
Make sure you have good lighting and ventilation. If you have trouble reading small print, get a magnifier or magnifier lamp like those listed above. Set up a small fan to blow smoke away from the work area.
While sorting and preparing the components, make sure the leads are free from oils and oxidation. Clean the leads with flux remover if they appear suspect. For stubbornly oxidized parts use a bit of emery cloth.
Use a lead bender to prepare the components for insertion into the board, especially the resistors. Orient the resistor tolerance bands in the same direction for a more professional looking board and to make troubleshooting easier.
Install and solder the lowest profile components first and work your way up to the larger parts. Install all components of the same height at the same time. Flip the board over onto your bench using a piece of stiff cardboard or foam to keep the parts in place.
Don't bend leads to keep the parts in place. This technique is fine for many projects, but our boards can be densely populated and have relatively small pad sizes. Bending the leads only makes it harder to get at all the pads and easier to create an inadvertent short.
To make the solder joint, heat the lead and pad at the same time. Allow a second for the joint to heat thoroughly and apply a tiny bit of solder just where the tip of the iron comes into contact with the lead and pad. Then apply enough solder to complete the joint. The whole process should take no more than 2 or 3 seconds, and the finished joint should be smooth and shiny, not rough, coarse, or dull looking.
Don't use too much solder! Apply enough solder to form a small volcano-shaped fillet around the lead. If the solder on the lead is higher than the PCB pad is wide, you've applied too much. The solder should also penetrate the holes and appear on the component side of the board. Don't worry if the fillets on the component side aren't perfect.
Keep your iron's tip clean by wiping it on a damp sponge every few minutes.
For most components, cut the leads flush with the top of the fillet. Don't cut into the solder fillet. Don't bother trimming leads unless they protrude more than 1/8" or so from the board.
Make sure all components are mounted flush with the PCB unless specifically instructed otherwise. You don't want space between the board and the parts in most cases. For multi-lead components like switches and ICs, check the fit after soldering the first lead. Reorient the part before soldering the rest of the pins.
After all the components have been installed, brush the board with a stiff toothbrush to remove any stray solder blobs or bits of component lead. Clean the board with flux remover if desired, but if you use "no-clean" flux this step isn't required.
Always wash your hands thoroughly after handling solder that contains lead. And even though it may look delicious, don't eat it.
If you take reasonable care during assembly you shouldn't have to worry about desoldering, but sometimes mistakes happen and you'll need to desolder and remove a component. Don't forget that the populated circuit board itself is more valuable than any single component you may have to remove, so it's often better to sacrifice the part completely than risk damaging the board. Too much heat will eventually cause the copper cladding to delaminate from the PCB substrate, so always work quickly and use as little heat as possible.
For two-lead parts like resistors and capacitors, heat one lead at a time and rock the part out of the holes. Be sure the solder is molten before you start pulling on the part. Use as little force and work as quickly as possible. Clean the holes using wick or a solder sucker.
For ICs, snip all the pins as close to the component body as possible. Heat each pin and remove it with pliers or tweezers, then remove the remaining solder with wick or a solder sucker.
For multi-pin parts that can't easily be cut off, remove as much solder as possible using wick or a solder sucker. Heat all the pins simultaneously using a hot air gun. With patience and care you can remove the part without destroying the board.
If you damage the board while removing a part, all is not lost. There are really only a few things that can go wrong: damaging the hole plating, lifting a pad, and breaking a trace. All of these can be repaired with a bit of care and patience.
If you notice a little brown collar of material attached to a lead you've just pulled out of the board, you've probably damaged the hole plating. This is only a problem if the plating is needed to connect a trace on the bottom of the board to a trace on the top. If there's only a connection on the bottom side, simply install the new part and solder as normal. If there are connections on the top and bottom, install the new component and solder the lead on both sides of the board. If the component covers the top pad and you can't solder it with the part installed, see the next paragraph.
If you lift a pad or break a PCB trace while removing a component, you can restore the connection by adding a jumper. If the trace is intact and only the pad has come loose, carefully scrape about 1/4" of solder mask from the trace and attach a small jumper to the pin. Carefully solder the jumper directly to the exposed copper. Verify the connection by testing for continuity with your DMM.
If the trace is badly damaged, it may be necessary to jumper between component pins. Follow the broken trace and consult the schematic to see which pins should be connected. Use a length of small gauge solid wire to connect the pins. Follow the broken PCB trace as closely as possible. Verify the connection by testing for continuity with your DMM.