Building a Vintage-style U87 Mic Is Easier and Cheaper Than You Think (Video) April 30, 2013 11:43 35 Comments

In the video below, guest vlogger Matthew Jenkins walks us through his build of a vintage-style Neumann U87 clone. What some viewers may find surprising is that at no point during the video does Matthew perform any black magic or mortgage his home. As you'll see, a soldering iron, some attention to detail, $350-500 USD, and a free afternoon are all that's required to complete this project. And, thanks in large part to Microphone-Parts and Vintage Microphone PCB, all of the components that go into an excellent U87 reproduction are now available off the shelf. The components Matthew used are:

• Microphone body ("donor" bodies range between $100-200 used or new)
• RK-87 capsule from Microphone-Parts ($109)
• D-U87 PCB Set from VintageMicrophonePCBKit ($20)
• PCB components from Mouser ($20)
• Cinemag CM-2480 from Cinemag ($43)

That puts Matthew's total at $342. Your cost will vary depending on the donor body, capsule, and components you choose. Other options include:

• Donor Bodies
• Behringer B2 (all switches)
• MXL 2010 (all switches)
• Aurycle A460 (no pickup pattern switch)
• MCA SP1 (no pickup pattern switch)
• CAD GXL2400 (no pickup pattern switch)
• Carvin CM87S (no pickup pattern switch)
• Gauge ECM 87 (no switches)
• Nady SCM 900 (no switches)
• Capsules
• Microphone Parts RK-87 ($109)
• Peluso P-K87i ($255)
• TSKGuy U87 ($250)
• Transformers
• AMI T13, designed specifically as a replacement for the original U87 transformer ($95)

Please ask questions or share your experience with building a U87 in the comments. And let me know of any donor bodies or components I may have missed.

5-Minute Project: How to build a "Circuit Sniffer" March 13, 2013 18:24 12 Comments

Here's a fun little noise-maker you can build for under $5 in under 5 minutes: a "Circuit Sniffer." Just as microphones pick up vibrations in the air and turn them into an alternating electrical current, this little device picks up the magnetic fields emitted by electronic devices. You can get some pretty brutal sounds by just plugging it into an amp and probing your household appliances. Check out the video below (4:09) to see what it does and how to build it.

Sourcing component(s)

There is only one component involved here, an inductor. Inductors are measured in Henries; the higher their value, the greater a voltage they can induce from the same change in current. What this means for us is that higher value inductors will have a louder output and need less amplification. I used a 1000uH inductor in the video which is about the minimum value I would suggest to maintain a useful output level. Healthy-sized inductors often pop up in electronics surplus stores like All Electronics or Electronics Goldmine for less than a dollar each. Here are a couple that are available at the time of writing:

• Electronics Goldmine G18221, 1000uH, 4 for $1
• Jameco 5800-103-RC-VP, 10000uH, $0.69

Besides our inductor, all you need is a cable to get the signal to an amp. The standard choice here is an unbalanced 1/4" which can be found at any Radioshack or music store in the world. Happy probing! If you stumble upon any especially crazy sounding devices, please share you findings here. Many thanks to Nicolas Collins, author of "Handmade Electronic Music" for turning me on to this idea.

How to Add a Guitar Pickup Emulator to Your LINE2AMP July 25, 2012 14:46 4 Comments

Note: This article is about an old, discontinued version of the L2A Reamplifier. The instructions below do not apply to the current kit.

The PPE mod equips your LINE2AMP reamping kit with a classic, single-coil pickup output which, in addition to providing a new tonal option, allows it to interface more "authentically" with vintage guitar amps and effects.

While browsing Jack Orman's excellent "Lab Notebook" series, I came across his drawing of a simple guitar pickup emulation circuit. This article and the Passive Pickup modification for the LINE2AMP are greatly indebted to Orman's article. There are three electrical properties we must recreate to mimic a guitar pickup: inductance, impedance, and capacitance. Accordingly, our passive emulator circuit consists of only three components--you guessed it: an inductor, a resistor, and a capacitor. Together, these components form an low-pass filter with a resonant peak that is largely responsible for the unique tonal signature of a passive pickup.

The component values in the LINE2AMP (pictured above) recreate the performance of a standard single-coil pickup. The inductor and capacitor set the cutoff value for the low-pass filter at 5.5kHz, while the resistor damps the ringing of the resonant peak. This creates a filter with a smooth bump around the resonant frequency and a gradual LPF after.

Approximate Frequency Response

Performing the Passive Pickup Mod

1. Mount both output jacks in the chassis. This will keep the work steady and allow us to better gauge the wire lengths needed.
2. Trim the leads of the inductor and a length of black wire according to the distance between the jacks.
3. Place the 820pF capacitor between the two pins of the Passive jack.
4. Place one of the inductor leads in the Tip pin and one end of the black wire in the Sleeve pin of the Passive jack. Solder the inductor, capacitor, and wire in place. (Illustration 1)
5. Solder the remaining leads of the inductor and wire to their respective pins on the switching side of the Active jack.

 

How to Build a Boutique Passive DI June 29, 2012 19:12 31 Comments

Note: Full kits for our our passive DI project, the FE2, are now available in the store.

If you can solder one component to a couple of jacks, you can make the best passive DI money can buy. That's no exaggeration--at it's core, every passive DI is just a transformer, and some of the best winders in the world, Cinemag, Sowter, Lundahl and Jensen make transformers designed specifically for direct box applications.

Passive DI Basics

Let's start from the top: a DI, or "direct inject" or "direct box," is a device that allows one to plug an instrument output directly into a microphone preamp. A DI achieves this by doing two conversions: 1) from high impedance (Hi-Z) to low and 2) from unbalanced to balanced. Electronically, there are two ways (at least) to perform these conversions: 1) actively, with buffering/balancing circuitry or 2) passively, with an audio transformer. Active DIs are fairly complex, require power (usually in the form of +48Vdc "phantom power"), and are ideally suited for hi-Z signals such as those from passive guitar and bass pickups. Passive DIs are extremely simple, require no power, and are best suited for lo-Z inputs such as synthesizers and active pickups (however, they have been known to sound great on passive sources such as the "Billy Jean" bass line).

Why Go Passive?

From a technical perspective, active DIs outperform passive DIs in almost every respect, and at a fraction of the price. The performance of passive DIs is restricted by an inherent property of transformers: the closer you bring the input and output impedances to their ideal values, the more signal you loose. An active buffer, on the other hand, can present an exceptionally high input and low output impedance while maintaining unity gain. Yet here I am telling you how to build a passive DI. Pourquoi? They sound good. A good passive DI will thicken and smooth the sound in a way that a transformerless, active DI will not.

The DI Transformer

In terms of sound quality, the only component that matters in your passive DI is the transformer. And, unlike a reamping box where a budget transformer performs admirably, a direct box is a sensitive application that demands a high-quality transformer. There are a couple of essential features that take quality DI transformers out of the "budget" range: 1) mu-metal case for magnetic shielding and 2) Faraday shields to isolate each winding.

Building Your Direct Box

Gathering Components

Nothing exotic here. Transformers must be custom ordered from the manufacturers and the remaining components are standard at Mouser, Digikey, Farnell, etc. Depending on the transformer you choose, the entire BOM will cost you between $75 and $115 plus shipping from at least two locations.

Qty	Value	Note	Approx. Price
2	1/4″ TRS jack	Solder terminals	$1
1	SPST (or SPDT) Toggle Switch	Solder terminals	$1.25
1	DI Transformer	Cinemag CM-DBX, Lundahl 1935, Jensen JT-DB, Sowter 4243	$55 - $85
1	Male XLR jack	Solder cup terminals	$3
1	Aluminum chassis	Hammond 1590N1	$11.50
1	Ring Terminal		$.25

Assembly

Wiring

The schematic and wiring instructions below are based on the color coding of the Cinemag CM-DBX. However, the circuit itself applies to any DI transformer with a mu-metal case and shield wires for each winding. This includes offerings from Jensen, Sowter, and Lundahl.

1. Begin by twisting the brown and red transformer leads together. (Making differential wires a twisted pair can reduce electro-magnetic interference.)
2. Mount the transformer and jacks on the case. Stretch each transformer lead to where it will be soldered and trim the leads, leaving an extra 1/2" for wiggle room. Strip and tin the leads.
3. Trim, strip, and tin two lengths of heavy-gauge wire for the ground connection. We'll call this wire "Green".
4. Solder the leads to the jacks in the following configuration:
   • Yellow -> Input Tip
   • Orange, White, Black -> Input Sleeve
   • Gray, Green -> XLR 1
   • Red -> XLR 2
   • Brown -> XLR 3
5. Solder the green wire from XLR 1 to the center pin of the ground switch. Solder one end of the remaining length of green wire to one of the other pins of the ground switch, and the other end to the ring terminal.
6. Fasten the ring terminal to the case to secure the chassis ground connection.

Looking for a full kit? We now offer the FE2 Passive DI kit in our store.

How to Add L/C/R Switches to a Passive Summing Box June 25, 2012 15:28 7 Comments

The theory of operation is simple: instead of each input being hard wired to either the L or R bus, the inputs go first to a switch which then sends the signal to either a) the L or R buss or b) both buses (or "center"). The wiring, however, is not so simple. Assembling these switches requires considerable point-to-point wiring skill and a good deal of patience. The following guide assumes you have an Endless Summer kit, however the general method can be applied to your own passive summing project.

Components

1. Sort the 6.8k (blue, gray, black, brown, brown) and 9.53k (white, green, orange, brown, brown) resistors included in your kit. Each switch will use four 6.8k and eight 9.53k resistors.
2. Trim two black and red pieces of hookup wire according to the distance between your switch and the jacks being switched, with a little extra length to account for the twisting. Strip and tin the ends of each wire.

Populating the Switch

1. Place the hookup wires in the center row of pins, alternating black and red. Solder the wires to the pins and trim the leads. (Picture 1)
2. Twist the pairs of hookup wires together tightly, leaving a 1/4" at the ends. (Picture 2)
3. Place two 9.53k resistors in each pin of the bottom row so that the leads point out from the switch (away from the center row). Solder the resistors and trim the leads. (Picture 2)
4. Do the same with the 6.8k resistors in the last remaining row of pins. Use only one resistor per pin. (Picture 3)
5. Solder the hookup wires from the switch to the pins of the input jacks being switched. Solder the red wire to the Tip pin and the black wire to the Ring pin. (Picture 4)

Connecting the Switch to the Bus Wires

1. Identify the two columns of pins associated with the each input jack. You will solder the 6.8k resistors from these columns to the bus wires that run directly above their respective jacks. Solder the resistor in the same column as the red wire to the "hot" bus wire and that in the black wire column to the "cold" bus wire. If you have already soldered the other, non-switching jacks to the bus wires, follow the standard you set regarding which wire is "hot" (Tip) and which is "cold" (Ring). Once you are done soldering, trim the leads. (Picture 1)
2. Solder the 9.53k resistors in the same columns as a black wire to both of the "cold" bus wires and those in the red wire columns to both "hot" bus wires. At this point the wiring will become a bit of a rat's nest, and you may want to insulate the resistors from each other with the provided heat-shrink tubing. (Pictures 2, 3, 4)

How to Build a DIY Passive Summing Box December 8, 2011 12:13 105 Comments

I've been curious for a while about the fuss surrounding analog summing. But with commercial boxes priced $600+ I wasn't that curious. Luckily, passive summing is a pretty simple concept and one that's very wallet- and DIY-friendly to achieve. Check out the video above for a quick run-through of how I built my 16-channel summing box.

How It Works

Most analog summing designs take a number of mono inputs and assign them to the stereo bus via either pan pots or L-C-R switches. This route, while superior in functionality, is rather complex and expensive. The design below leaves out panning/assigning and makeup gain in order to avoid the need for power and forgo toggle switches (≈$7.50/channel). What we end up with is a passive bus mixer: 4 or 8 stereo pairs are summed via L and R buses, which are then sent to external microphone preamps for makeup gain. This basic design has been proposed by "New York Dave" and Fred Forsell, and can be found in the monitor section of old Neve consoles.

The greatest benefit of this approach, in my opinion, is the tonal flexibility. Every pair of preamps will impart their own sonic signature on your mix.

Inputs are summed to the bus wires via resistors. All of these resistors must be the exact same value with as low a tolerance as possible. Recommended values are between 5-10k ohms depending on the input impedance and volume drop you're aiming for. The value of the shunt resistors depends on the number of inputs used and the value of your summing resistors. NYD gives us the formula for calculating it, where I is the input impedance, R the desired output impedance, and N the number of channels: (I/N)*R/((I/N)-R)

Putting It Together

Building a passive summing box always seemed like a bit more of a hassle than it should be for such a simple circuit until I found Rhythm in Mind's idea for mounting everything on a front panel. It's a great approach for this project, as all of the components weigh in at a grand total of around 3 lbs. Simply drill a panel as I've drawn below (or order one!) and mount components right to the panel as shown. I used nylon standoffs to suspend the bus wires with lock washers to hold them taut.

I've had no problems with noise or interference with this setup. But if you do find it to be noisy, you can always add a case.

Bill of Materials

Qty	Value	Note
8	1/4" TRS jack	Panel mount, solder terminals
2	182Ω for 16ch 165Ω for 8ch	Metal film, 1/4 watt, 1% tolerance resistor
16/32	6.8kΩ	Metal film, 1/4 watt, 1% tolerance resistor
4'	Bus wire	At least 24 AWG thickness
6	1 3/8" Nylon standoff	Female->male, 6-32 or 4-40 thread (must match other standoff)
6	3/8" Nylon standoff	Female->male, 6-32 or 4-40 thread (must match other standoff)
6	Machine nut	6-32 or 4-40 thread (must match standoffs)
6	Lock washer	#6 or #4 size (must match standoffs)
2	Male XLR jack	Solder cup terminals
4	4-40 nuts and bolts	For mounting XLR jacks

Using It

Since the inputs of our summing panel are hard wired to either the L or R bus, you can't simply send a mono signal (unless you want it panned R or L). Rather, assign your tracks to a number of stereo buses and then send those buses to the summing panel as shown below:

Update: Adding Mono Inputs

Since posting this article, I've received a lot of questions about adding mono inputs for tracks like lead vocal, bass, kick, and snare that are often panned dead center. Luckily, this is really easy to implement with just a little more math. Of course we know that in the world of stereo, a signal that is "dead center" is actually two identical signals of the same volume in each channel. So instead of sending our mono inputs to either the L or R buss wires, we will send them to both. However, by doubling the signal, we've made our mono input 3dB louder than the others. We can rectify this by changing the input resistor values for the mono channel to 1.4x the value of the regular input resistors (1.4:1 being 3dB expressed as a ratio).

DIY Kits

We now stock the SB2 Passive Summing Mixer kits in the DIYRE store. The SB2 accepts 8 or 16 balanced inputs via D-sub jacks and puts out two balanced, microphone level outputs. The kit contains everything you need to build a passive summing mixer. SB2 Passive Summing Mixer Kit $49

I.J. Research 4KCC Build Guide November 22, 2011 16:30 12 Comments

The IJ Research 4KCC is now sold by Ramshackle Recording.

Introducing: LINE2PRE Re-Preamp November 18, 2011 19:19 13 Comments

The LINE2PRE is a tool for sending your pre-recorded tracks through your mic preamps for additional harmonic saturation. Why hasn't anyone thought of this before?

Reamping boxes like the LINE2AMP are a great studio tool for those who have a lot of amps, pedals, and other guitar-level gear lying around. Well, I dunno about you, but, being a recording engineer, I've invested a lot of more in awesome mic preamps than in guitar gear. And as well all know, a preamp that overdrives nicely is one of nature's finest signal processors. So I put together this little box that basically performs the same function as the LINE2AMP, but with a little extra volume reduction, an output impedance tailored to mic preamps, and an XLR output jack. Exceedingly simple, but it does it's job quietly and with pretty much zero sonic fingerprint.

 

Full kits and assembly instructions for the LINE2PRE will be available in the store in early 2015.

Test Driving the DIYAC RM-5 Ribbon Mic (+how to build your own for <$100) November 7, 2011 12:28 7 Comments

A couple of weekends ago, I attended a friend's birthday at the Latvian society of Philadelphia. Knowing almost nothing about Latvia except the excellent microphones of Juris Zarins (Violet) and my friend Artur Fisher (which I'll get to in a second), I picked the bartender's brain about his home country while I sipped my first Latvian beer. Turned out Latvia's history was fascinating enough to keep me riveted to my bar stool for an hour or two while the party raged at increasing volume around me. For instance, did you know that the class that entered university this year were the first to have been born in the modern state of Latvia?

But I digress... this post is about microphones! My unplanned introduction to Latvian culture and beer turned out to be of the fortuitous kind, as just the week before I had received one of Artur Fisher's RM-5 ribbon microphones to try out. Artur's microphones are made by hand (in Latvia, of course) with his own RE-154 ribbon motor. Visually, the RM-5 is right up my alley: elegant, simple, utilitarian, and unbranded. Sonically, it delivers everything I had imagined a high-end ribbon mic should: rounded, almost tape-esque transients, a full low-end, and detailed, but gentle reproduction of the high-end. The track below was recorded with the RM-5 only, with no EQ and very moderate compression. So what does this mean for DIY? You can build your own microphone with Artur's RE-154 ribbon for about $100. Here's what you need:

• Artur's RE-154 Ribbon Motor $59
• Edcor RMX1 Transformer $22.77 (same transformer used in the RM-5
• Male XLR Connector ≈$3
• Microphone body, be creative!

As you heard above, you'll end up with a great mic. Being able to build it for the price of an SM57 is, to my mind, almost absurd. Absurdly awesome. Long live DIY! 

How to Build a DIY Reamping Box October 3, 2011 13:52 30 Comments

One of the most powerful tools for expanding your sonic pallet in the studio is a reamping box--a box that converts the output from your mixer/interface/tape machine to an instrument-level signal. Suddenly, all of your guitar amps, effects pedals, and synthesizers become effects for any signal you can throw at them. A reamping box is a great first-project for DIY beginners: it's totally passive (you can't shock yourself), there are a limited number of solder joints to make, and there's plenty of room to make those joints. For a better idea of what's involved in this build, check out the following video on how to make a simple reamping box: Full kits for our popular reamping box, the LINE2AMP, are available from the store. For full assembly instructions, please see the LINE2AMP assembly guide.

How to Make Your Own XLR Mic Cables September 3, 2011 19:28 12 Comments

Soldering your own microphone cables is one of the most satisfying DIY projects you can undertake. No kidding! There are few things more gratifying than slicing through the soft rubber coating with an x-acto knife and joining the conductors to the connector with perfectly shiny solder joints. On top of that, building cables is a great way to get your feet wet soldering, and it's one of only DIY projects that is guaranteed to save you money. Check it out:

• A 20' Monster P500M20 XLR Cable from Sweetwater costs $59.95.
• A higher quality DIY cable using Canare Quad Core and Neutrik XLR connectors costs less than $12.

That's almost $50 saved on one cable! Imagine how much you'll save over a lifetime simply by learning to solder your own cables.

Here are the components I recommend using:

• Cable: Canare L-4E6S Quad Mic Cable
• Canare's quad core cable uses two conductors for each audio signal (hot and cold) and a woven shield to reduce noise and improve flexibility. You can go with Mogami cable if you're inclined, but I've found the Canare to be excellent for half the price
• Available from Redco Audio
• Connectors: Neutrik X-Series (silver contacts)
• Neutrik has an extensive line of connectors, but I stick with the X-series because they're what I've used in the past and they haven't failed me yet (plus they're the cheapest). I opt for the silver contacts because, while the gold is resistant to corrosion, the gold plating tends to wear off after a few hundred plugs and unplugs anyway.
• Available from Redco, Mouser, and pretty much anywhere components are sold.

Best of luck with your cabling endeavors. Please share this video with your friends if they're spending way too much on pre-fab cables!

Shure SM57 / SM58 Mods August 8, 2011 17:16 1 Comment

Unless you've been operating your recording studio from under a rock since 1965 (or are one of those curmudgeonly "haters") you've probably got an SM57 or SM58 in your mic locker. With their screw-open bodies, these mics are exceedingly simple and rewarding to mod.

Removing the Transformer (the "TapeOp Mod")

The stock transformer in the SM57 increases the output level by about 12dB, but it also contributes to the 57's somewhat pinched and midrangey sound. Taking it out is a quick and free way to increase the frequency and transient response of your mic. The video below walks you through the steps for this mod:

TAB-Funkenwerk Transformer Swap

TAB-Funkenwerk, maker of fine vintage condenser microphone kits, manufactures a replacement for the stock SM57/58 transformer. The T58 transformer is designed to maintain the basic SM57 sound while extending the high and low frequency response. T58s are available from for $80 each.

The Impedance Mod

Nowadays, most mic preamps and mixers present a rather high input impedance for condenser microphones. However, the SM57 was designed in the days of the standard 600ohm input and theoretically performs better when more heavily loaded (lower input impedance). By connecting a resistor across the preamp's input, we can increase the load on the SM57. In his Recording Magazine article (link below), Paul Stamler provides the following formula for calculating the resistor, where Rg is resistor to be strapped across the input, Rd is the desired input impedance, and Ra is the actual impedance of the preamp or mixer: 1/Rg = 1/Zd – 1/Za. The mod can be built into the male plug of an xlr cable or an xlr barrel connector by soldering a resistor between pins 2 and 3. Alternatively a simple box with a 1k linear resistor would provide a good range of impedances for different inputs.

Alesis 3630 Compressor Mods July 26, 2011 11:55 6 Comments

Touted officially by Alesis as the "most popular dynamics processor ever made," the 3630 is a bargain bin compressor that can be polished to resemble a professional one. The circuit employs some solid design fundamentals, but by all accounts suffers from inferior components and design choices. Various mods have been proposed over the years to considerably expand the sweet spot the 3630, lower its noise floor, and remove the snaps, crackles, and pops the stock unit is prone to. Collected here are those mods that have been deemed the most successful by the people who have tried them. Many thanks go to the originators of these mods who have shared their research with the DIY community.

"The 3630 is basically a dbx compressor. It uses dbx-designed RMS level sensors and VCA gain-change chips. Problem is, most folks have not taken the time to learn how to use this box, find the sweet spots for level setting, gain reduction, gain make up and attack / release times." -Michael Joly via Gearslutz

"I'm not saying that if you follow these steps that you'll have an 1176 or an LA3-A, but the quality of sound exiting the box will be vastly improved merely by swapping out a few components... No smoke? Then the chances are that you've just made your 3630 into something resembling what it should have been in the first place." -Peter Purpose via his GroupDIY writeup

"We have a really small compressor, the Alesis 3630, which is $300. That's the main one we used on Homework and Discovery." -Daft Punk via Mix Magazine

"This upgrade of the Alesis brings the VCA section up to the same spec as a DBX 1066." -"Icarus" via Sound on Sound

Please keep in mind attempting any of the following modifications will void your warranty with Alesis. 

Get a 3630

If you don't have one already, these comps can now be found for a pittance on eBay. With a little patience, you should be able to get one for less than $100. 

1. Beef Up the Power Supply

Make sure you're modded unit gets plenty of current by switching to a more robust AC adapter. This wall adapter from Line6 provides a hefty 2 amps. While you're in there, consider making these component upgrades to the power section:

Qty	New Component	Type	Position	Part #
2	220uf/35v	Capacitor	Power	C2,C3
2	2200uf/25v	Capacitor	Power	C4,C5
4	UF4001 fast recovery	Diode	Power	D1,D2,D3,D4

2. Upgrade the VCAs and Opamps

The VCA (voltage controlled amplifier) is responsible for controlling the compressor's gain and as such has a significant effect on the its sound and performance. The THAT2180 series of VCAs represent a high-quality alternative to the stock DBX2150s. Before you remove the stock VCAs, take note of their positioning so that you are sure to install the new ones with the correct orientation. The LF347N quad opamps can be replaced with a number of chips, the LME49740, MC33079P, LT1359. Make sure that the chip you order comes in the DIP-14 format. These upgrades were originally suggested by Peter Purpose in his GroupDIY article.

Qty	New Component	Type	Position	Part #
2	LT1359, LME49740, or MC33079P DIP-14	Quad Opamp	Input	U2,U6
2	2180BL08-U	VCA IC	VCA	U3,U7

Peter Purpose's modded unit. Note that the Burr Brown Quad opamps are now unavailable and must be substituted for one of those listed above.

3. Connect the Grounds

In his article on the 3630, Peter Purpose suggests connecting all of the input and output grounds via heavy gauge copper wire.

4. Replace and/or Upgrade Passive Components

Many of the passive components, resistors and capacitors, should be improved or changed to different values. The chart below was compiled by Sound On Sound forum member "Icarus" in this post.

Qty	New Component	Type	Position	Part #
2	100k metal film	Resistor	Input	R12,R54
2	1.69k metal film	Resistor	Input	R14,R56
4	2.2k metal film	Resistor	Input/VCA	R13,R42,R55,R72
4	6.2k metal film	Resistor	Input/VCA	R15,R41,R57,R73
4	240k metal film	Resistor	VCA	R27,R208,R69,R211
4	20k metal film	Resistor	VCA	R22,R23,R64,R65
2	470 metal film	Resistor	VCA	R26,R68
2	100 metal film	Resistor	VCA	R29,R71
4	33 metal film	Resistor	VCA	R209,R79,R212,R102
2	5.1k metal film	Resistor	VCA	R25,R67
2	5.6k metal film	Resistor	Knee	R83,R106
2	6.8k metal film	Resistor	Knee	R17,R59
2	2.2M metal film	Resistor	Level	R10,R52
2	10k metal film	Resistor	Level	R8,R50
2	22uf audio grade electrolytic	Capacitor	Level	C11,C29
6	10uf audio grade electrolytic	Capacitor	VCA/Level/Power	C16,C43,C6,C7,C33,C55
2	22pf metal film	Capacitor	VCA	C15,C32
2	150pf silver mica	Capacitor	Input	C12,C30
Remove	--	Resistor	VCA	R28,R70
Remove	--	Capacitor	Level	C42,C56

5. Disable the Gate

If you don't find yourself using the gate function on your 3630, you can send it and its nasty artifacts packing by simply snipping the two jumpers shown in the picture.

5 Ways to DIY With Discrete Opamps June 17, 2011 11:09 5 Comments

This week, I was lucky enough to receive a pair of GKL255 discrete opamps in the mail from Bearcat Audio, the newest vendor on the DIY Recording Market. (Thanks guys!) Even as I opened the parcel from Montreal, my mind was already thumbing through the projects in my DIY to do/wish list for a special place to socket these new DOAs. But first, a little overview of discrete opamps for the beginner:

An operational amplifier (opamp) is a single-ended differential amplifier. This means it takes two inputs, inverted (-) and non-inverted (+), and produces a single output which is many orders of magnitude larger than the difference between the inputs. Usually opamps are manufactured as monolithic integrated circuits (ICs); however, a few intrepid designers have created their own using discrete transistors, resistors, capicitors, etc. There are three classic DOAs that most DIYers have tried to clone, imitate, or "improve": the Melcor 1731, API 2520, and Jensen 990. Each classic opamp has it's own sound which, without getting into too much audiophoolishness, can summed up thusly:

• Melcor 1731 (1960's): Smooth highs and lows, beefy harmonics
• API 2520 (1970's-): Aggressive mids, solid lows, classic 70's coloration
• Jensen 990 (1980-): Low-distortion, fast transient response, wide open sound

1. Build an API or Jensen style mic preamp

The 2520 discrete opamp is at the heart of the "API Sound." And these days, there are a cornucopia of projects for the API-style preamp builder, including:

• Access 312 and Bicycle 312 are PCBs for 312-type preamps
• FiveFish X12, Seventh Circle A12, and Sound Skulptor MP12 are complete kits for building preamps in rack-mount enclosures
• Bearcat 412 a complete kit for building four 312-inspired pre's in a 1RU chassis 
• ClassicAPI's VP25, VP26, 312, and 312DI are 500-series replicas of API circuits

The 990 DOA was used in several very successful preamps, including Jensen's twin servo design, which utilized two Jensen opamps and transformers. Seventh Circle Audio's J99 kit is a version of the twin servo with SCA's own 990-type opamp and Lundahl and Cinemag transformers. It's also possible to create a Jensesque preamp with JLM Audio's Baby Animal Dual kits, using any 990-type DOA and Jensen transformers.

2. Concoct your own preamp design

One of the distinct pleasures of building with discrete opamps is that they have a common footprint and can often simply be swapped. This makes the basic transformer/single opamp preamp design a great platform for experimenting with new component combinations.

• JLM's Baby Animal kits provide such a platform with a pre-fab power supply and chassis so you can focus on transformer and opamp choices.
• The Bicycle 312 Hybrid PCB is also a great place to start if you want to build your units from the ground up.

3. Build a ClassicAPI "Missing Link" Console Channel

One theory about the lack of "mojo" or "warmth" in modern recordings is that we're simply not running audio through as many transformers and gain stages as they did in the days of the large-format console. Preamps, in other words, were only part of what made those consoles sound so good. ClassicAPI provides some consolation for the console-less in the form of the VC528 ST+ console channel for the 500-series/51x Alliance. The VC528 "completes" a preamp with a fader, filters, and an output amp, running the signal through two transformers and discrete opamps of your choice along the way.

5. Make a unique hybrid 1176 compressor

Igor's 1176-style compressor for the 51x Alliance/500-series, the F76 FET, provides the option to replace the original amplifier stages with DOAs. Why not be the only engineer in town--heck in the county, heck in the tri-county area--with an "API 1176"!? 

6. Upgrade the DIP8 opamps in your mixer, compressor, equalizer, converters, etc.

Until yesterday, June 16th, 2011, the sacrifice you made for using high-quality discrete opamps was not being able to use them in modern DIP8 format gear. AC Sound has begun briding this gap with a series of discrete opamps in the DIP8 format. The opamps will come in "tall" and "wide" formats and M, A, and J models (can you guess what the letters stand for?) AC Sound listed the first set of model A's on the market yesterday and plans take pre-orders the "J" and "M" models soon. Your cheap monolithic opamps had better watch their backs!

How to Perform the MCM DAC Mod October 26, 2010 07:10 13 Comments

Jim Williams of Audio Upgrades first tipped recording folks off to the MCM 50-7774, a "hidden treasure" D/A converter with a stellar DAC chip and a very low price tag. The design is an early version of the audiophile-endorsed Beresford TC-7510 that was licensed to OEM manufacturers. And, while it is marketed as a home hi-fi DAC, the 50-7774 has gained popularity among engineers as a professional mixing and mastering converter. The stock unit is impressive in itself (various Gearslutz members have said they prefer it to RME ADI8-Pro, Presonus Central Station, and MOTU 828 mkIII converters), but a couple of mods proposed by Williams and others can put it on par with really high-end DACs. The mods can be done in a couple of hours, and the whole project costs about $135 including the stock unit and premium replacement components.