Modifying the Rode K2 mic Part 1: Tube Change

I originally intended to replace both tube and capsule on this mic, but after experimenting and comparing I ended retaining the original capsule but with a replacement tube. In this post I’ll describe the simple tube change and give some audio examples. In the next post I’ll go over the capsule change. To be clear, the capsule upgrade made the mic sound different, rather than better, and based on what I already had in my mic locker I chose to return to the original capsule.This highlighted the importance of following your ears rather than what you read on the internet!

Okay, so here’s what you need:

A Rode K2 valve microphone ( I got mine second hand off EBay for £300 which is a fair price). These are decent mics and are very useable straight out the box. They are multi-pattern, very well made with a good quality power supply, cable and shockmount (unlike the Chinese valve mics often used for mods such as the Apex 460). The case is a bit tacky but you can’t have it all.

A NOS (New Old Stock) Telefunken E88CC (6922) valve or equivalent

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I learned a lot about the vintage tube market whilst researching these. Firstly, they are not cheap! You have to be careful as there are a lot of rip-offs out there, people trying to pass off newer tubes as vintage ones but fortunately there is a wealth of info out there to help as well as several reputable dealers that get recommended by many different people. I paid approx £125 for one from NOS Tube Store , their service was great and the tube was as described. This particular one is a sought-after Telefunken made in West Germany in the 1950’s. There are many other fine vintage tube options but I didn’t have the time and money to experiment, and this tube was highly recommended by a lot of people. If you want to know more and have time to burn, just check out the forums. Different tubes will impart a different sonic character to the mic so the ultimate test is to use your ears!

How to do it

This is very easy and I would recommend you try this first and see if you like the way it sounds. I recommend you record some different sources with the stock tube before you proceed, so you can compare afterwards and understand for yourself how the mics character has changed.

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Firstly, undo the metal retainer ring at the base of the mic and remove it. Then undo the metal sleeve that forms the main body of the mic (hold the mic by the grill end and unscrew). It should then slide off to reveal the tube and circuitry of the mic as shown in the picture.

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The tube is secured in position by a plastic clip which sits on top of the tube (pointy end) and the clip is held in place by 2 screws. Using a Phillips screwdriver, loosen both these screws and fully undo 1 of them to flip the plastic clip up and out of the way.

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The tube can now be pulled carefully from its socket, a slight amount of wiggling (of the tube, not you) may help!

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Carefully insert your new tube into the socket, it only fits in one orientation, make sure it is fully engaged. Replace the plastic retaining clip over the top of the tube and tighten the screws.

To my ears the NOS Telefunken tube makes the mic more mid-focused, the low frequencies are still clear, warm and big, the highs are a little less bright and sharp but the mid presence makes the mic cut through the mix more. I also find it more pleasant to listen to than with the stock tube, but it may not suit every application. I’ve presented some comparisons here to give you an idea of the difference. All clips were recorded via the preamps on my UA Apollo interface, I’ve endeavoured to maintain the same conditions and distances between mic and source for each comparison, but there may be small variations.

Firstly, male voice (don’t worry, I’m not singing)

Stock Tube

NOS Telefunken E88CC

Female voice

Stock Tube

NOS Telefunken E88CC

Double Bass

Stock Tube

NOS Telefunken E88CC

Judge for yourself and decide if this mod is worth the money, for me it’s a yes, but I will qualify it by saying I have other flavours of mic tonality in my locker, this adds something different, and it does it rather well.

In the next post I’ll describe changing the capsule and post some examples of the difference that makes.

 

 

 

 

AKG C414B Hum problems

I thought I’d write a quick post on this in case some of you experience a similar problem, it may save you hassle and expense.

I have a pair of AKG C414B mics, they are real workhorses and as the cliche goes, the studio Swiss army knife. On top of that they are solidly built and very reliable. But sometimes things go wrong. I recently did a bit of drum recording for myself and was listening back when I noticed a faint but distinct mains frequency hum on the overheads (my 414s). I had them running through my home made Neve preamps and then into a pair of line-level inputs on my UA Apollo interface. I automatically assumed the hum was coming from my home-made preamps rather than the solid, Austrian-engineered AKG mics. I duly set out to test, swapping cables, microphones and trying various configs of phantom power on / off on each channel, until it was clear that the problem lie with one of the 414s.

Faced with an expensive repair, I thought, well, let’s open it up and see if anything obvious was up with it.

Hmmm, lots of surface mount components and no obvious signs of trouble. A quick Google search led me to this post. Not exactly the same problem but similar, so I read on. Turns out that the grill / mesh of the mic connected to ground via pin 1 of the XLR forms a Faraday Cage, which helps shield the high-impedance capsule from EMI noise in the room. The mesh makes contact mechanically and if this connection is a little dodgy, it won’t work and there will be noise. I tested the resistance between pin 1 on the XLR and the mesh, it was a variable which immediately suggests a problem. I went about gently squeezing the base of the mesh in an attempt to improve the mechanical connection. Checking again, the resistance was now consistently minimal, so time to test. I put the body back on and plugged it in, powered it up and hey presto, no noise. Phew!…. So if you’re having this kind of issue, try this first, the mic is easy enough to open , just remove the 2 screws on the base (star driver or a flat head screw driver will do) and the smaller cross head screw in the XLR connector base and then slide the body off.

Flying mics and ominous cymbals

I recently read an article on the flying mic technique – not sure where, may have been TapeOp – but being a fan of the more esoteric side of recording, I thought I have to try that out.

The idea is simple, you suspend a mic from a pulley via a length of string which allows you to smoothly raise and lower the microphone. You then record a source and vary the mic position as the source sound decays, allowing you to pick up more of the detail in the decay of the sound.

This technique is particularly interesting with cymbals. If you have the mic too close, the initial attack will likely overload it so you won’t capture the detail in the moments immediately after the transient, but with the mic far away you can’t readily pick up the fine details of the decaying sound. And it’s in that decaying sound that a lot of the interest lies; cymbals produce lots of non-harmonic tones, i.e. frequencies not related to each other nor a fundamental pitch by integer multiples as we find with strings or pipes.

I set up a mic stand over my ride cymbal and improvised a makeshift axle from the clamp for a reflection filter, this would function as a pulley and allow a length of string to travel freely over it and up and down over the cymbal. For the microphone I chose my trusty Oktava MK-012  (modified by Micheal Joly) with an omni-pattern capsule so that I could get really close into the cymbal without the proximity effect. I tied the mic to one end of the string and made sure there was enough free XLR cable to allow the mic to travel freely up and down.  With the other end of the string in my left hand and a drum stick in my right, I practiced striking the cymbal whilst simultaneously lowering the mic. It took a few goes to get the timing right but eventually I could ride the mic in just after the initial hit and get it very close to the cymbal surface for the decay.

I also experimented with moving the mic around the cymbal surface to capture different harmonics. Monitoring on headphones also allowed me to get the movement right in terms of riding the volume.

So here are some results:

I think there’s some great scope for sound effects and soundscapes using these. With that in mind, here are a pair of hits reversed, hard panned and with an added splash of reverb to create an eerie, ‘something bad is about to happen’ kind of sound:

Happy experimenting…..

 

Piano Re-Amping

I recently watched a brilliant online recording masterclass with Sylvia Massey courtesy of Creative Live, very inspiring and it reminded me of something I’d lost sight of, the spirit of experimentation. During the class she records a band live and demonstrates some of the techniques she uses as well as her creative process. What struck me was how playful it was. Among the many things she did (including vocal feedback delay using 2 mobile phones a mic and a monitor speaker,  and passing a guitar signal through a power tool), she re-amped a snare by passing the recorded track back through a speaker with a snare strapped to it. The recorded sound of the re-amp was blended with the original snare to get fatter drum sound. This got me thinking, what else could you apply that too?

I’ve been doing a few tracks recently where we’ve used midi piano, I’ve been using the sampled grand piano in Ableton which isn’t bad at all (to my ears at least), however, it’s still a sampled piano and lacks a little dimension. I had the idea of re-amping the piano by passing the sampled piano track back through a speaker playing into the body of the upright piano I have at home, then micing the piano to get a new piano track. The idea being that this new track contains the string and body resonances of the real piano. The final piano track would then be a blend of the 2.

I set about doing this, it was relatively simple. A spaced pair of AKG C414s aiming inside the top of the piano, close in on the strings, and then a speaker placed at the bottom of the piano aiming into the body (I used my Avantone Mix Cube for the job).I removed the lower panel of the piano so the speaker could play into the body (see photo)

Using a real piano to enhance the sound of a sampled piano
Using a real piano to enhance the sound of a sampled piano

Once all this was set up, it’s just a case of pressing play and record. In the mix, just blend the original with the re-amp track according to your taste.

Here’s the original sampled piano track:

 

Here’s the re-amped track:

 

Here’s a blend of the 2:

 

You can hear how it adds a depth and dimension to the sampled piano without recourse to loads of plugins.

I’ve also tried passing other signals through it, including vocals and guitar tracks,it lends an interesting colour.

I’m liking the natural colouration you get with re-amping, it’s something I’m definitely going to explore more.

 

 

DIY preamps continued….

As promised in the previous post, here are some sound samples to demonstrate the sonic differences between the DIY EZ1290 Neve-style Mic preamps and the stock preamps on the Universal Audio Apollo firewire interface.

The setup for this was pretty simple, a remote drum recording session where the drummer (the fabulous Mr Mark Whitlam) was given a score and a backing track to record the drum part to. The session was carried out in Marks garden studio cabin, a compact but decent sounding purpose-built space that has been acoustically treated.

Listening to the stye of the track and how the drums sounded in the space I decided to go for a simple 4 mic setup: 2 overheads placed more out in front of the drums to get a more balanced picture of the kit as a whole, supplemented with kick and snare close mics.

The drums themselves were:

Vintage 1960s Zildjian A 14″ hi hats, 22″ Istanbul Agop Azure ride (next to hats), Bosphorus 21″ medium thin ride and an 18″ bosphorus thin crash. Drums …. Snare: Canopus Zelkova, 1960’s premier Olympic 20″ bass drum and 12″ Tom, modern premier 14″  Tom

Of course, all properly tuned…..

On the overheads I used 2 Oktava MK-012 modified by Micheal Joly at Oktavamod, on the kick an Electrovoice RE20 and on the snare a cheap and surprisingly cheerful Audio Technica AT2020 (high SPL handling, nice response, good rejection).

On the following audio examples you are listening to just the overheads so you can hear more clearly the differences between preamps. Note that these are different takes, although the drummer is incredibly consistent, so the comparison is not entirely precise.

Firstly, through with the UA Apollo preamps

 

And then with the EZ1290 preamps

 

You can hear the subtle differences, especially when you listen to that ride cymbal from about 10 seconds in. The Apollo preamps are very good, very clear and crisp, but the EZ1290 has a smoother sound, more open and somehow with a better sense of space.  What do you think?

This is the only direct comparison I’ve done but I’ve been working a lot with these preamps on voice and guitar and really like the sound I’m getting, I’m finding I’m using less processing further down the line to shape the sound. I’ve particularly enjoyed the combination of this preamp and the modified Apex 460 valve mic mentioned in a previous article.

 

DIY Sub Kick

The concept of a sub kick is very simple, take a large speaker and use it in reverse as a microphone specifically for picking up low frequency information, from a kick drum for instance. This can be used in the mix to reinforce the sound of the kick alongside another kick drum mic,  providing additional depth to the sound due to it’s focus on the sub 100Hz frequency range. The subkick won’t pick up much spill from other parts of the kit either, and a good trick is to use it to trigger a gate on the internal kick drum mic, to get a very tight and clean kick sound.

Various companies make them, the  Yamaha SKRM100 for example, which is essentially a 6.5″ woofer mounted in a small drum shell, with mesh either side and a built in stand. The price, £350, quite a bit for speaker on a stand! Over the years I’ve seen various DIY versions in studios around the way including an NS10 woofer clamped into an old worktop vice as a base, all these incarnations functioned well, and cost significantly less than £350 to make. Time to get the tools out I thought.

This is an easy DIY project, it involves mounting a woofer speaker into a suitable frame (in this case a tambourine shell), and then a little soldering to attach an attenuator and a male XLR connector.

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First start with a speaker, I went for an 8″ Wharfedale woofer of EBAY (approx £18), you can use anything from 6″ up, though some say it doesn’t work as well with larger speakers. I’m not sure about that, the 8″ seems to work pretty well. Most important is the speakers frequency response, it should go down to about 20Hz to get all those sub bass frequencies.

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I thought a lot about how to mount it, I wanted something that would isolate it and look good, but not cost too much. The cheapest and most elegant solution I could think of was to use elastic hairbands to suspend the speaker within the circular frame of a tambourine (without the jingles of course). So I ordered a 10″ tambourine (£7 Ebay) and removed the jingles by pulling out the nails holding them in place.

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Slip the elastic hairbands through the screw holes in the speaker, then feed each end through one of the slots in the tambourine rim and push the upper loop (the one that goes over the rim) round and under so the 2 loop ends overlap. Take the nail that used to hold the jingles in place, push it back through it’s location hole so that it pegs the 2 loop ends of the elastic in place. Push all the way in so it’s secure. That was probably the trickiest step in all of this, required a lot of patience to get the elastic and the nail to all go in the right place. Repeat this for the remaining screw holes.

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The next challenge was figuring out how to mount the the subkick using a normal mic stand. I happened to have a broken mic stand lying around so I took the pivot mount from it (the bit that screws onto the top of the vertical part of the stand and allows the boom to attach to it and swivel up and down). The advantage of using this was that it had a standard screw thread on the end which meant I could attach it to a regular mic stand (as shown in the picture above). The pivot mount itself attached to the tambourine rim with a nut, bolt and a couple of washers (through one of the existing slots in the tambourine).

Next step is connecting it up to a mic pre-amp. The output of the subkick is pretty hot, an attenuator (or pad) is recommended to bring the signal level down to the region expected by most pre-amps. You can buy an inline attenuator that connects between the subkick and the XLR cable to the pre-amp, or you can knock together a basic potential divider circuit to do the job for you. I opted for the latter as you probably guessed. Another point worth mentioning here is that I’m going to use an unbalanced connection, providing the environment isn’t to (electrically) noisy and cable runs are short, this shouldn’t be an issue. If you wanted to go for a balanced connection, you would need to wire in an audio transformer, and to get one that has good sub-sonic frequency response isn’t going to be cheap. You could also use a DI box, again, a good quality one with good bass response would be preferable.

Circuit 1

The schematic for an attenuator circuit is shown above, I used a simple potential divider, the values I chose for the resistors R1 and R2 are:

R1=680 Ohm , R2 =150 Ohm

There are many combinations you could use and they also depend on your speaker, Google “attenuator for Subkick” if you want to get lost in that world!

 

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With the resistor values chosen, I soldered them directly to the speaker terminals and covered them with heat shrink. Easiest way I found was to solder one end of R2 to the speaker – terminal, and one end of R1 to the speaker + terminal, slide a sheath of heat shrink over each resistor then twist the exposed ends together, before applying heat to shrink the insulation (see above).

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I then soldered a short length of guitar cable to the speaker – terminal and the exposed resistor ends, ensuring I had a sleeve of heat shrink in place to insulate the connection.

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Finally I soldered the male XLR connector onto the end of the cable, (Pin 1 to Speaker -, Pin 3 to the resistors, Pin 2 unconnected). I had a retaining clip lying around so I used that to secure the connector to the frame, so as not to put too much mechanical load on the soldered joints.

So there you have it, a fully functioning subkick that doesn’t cost an arm and a leg, doesn’t look to shabby, and is not to difficult.

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Here is a quick audio example of the subkick in action. The audio is as follows

Bars 1-2 : Internal kick mic only

Bars 3-4 : Subkick only

Bars 5-6 : Internal mic + Subkick

Bars 7-8 : Internal mic + Subkick (with gate on subkick)

Bars 9-10 : Full kit, no subkick

Bars 11 – end : Full kit with Subkick

https://wijproductions.files.wordpress.com/2014/10/example-subkick.mp3

Modifying the T.Bone SC1100 mic

Modifying the T.Bone SC1100 Large Diaphragm Condensor Mic

T.BONE SC1100

I bought one of these mics a while ago on the recommendation of a vocalist friend. Considering it cost about £100 from Thomann it was a good deal; 3 patterns, transformer coupled and smooth-sounding with none of the top end harshness of other mics in this price bracket. It also came with a nice metal case and decent shockmount. However, it is still flawed, there is a distinct scooped sound to it which can be flattering but also leads to lack of clarity, and the low frequency response is muddy or ‘woofy’, which is probably a lot to do with transient response.

I did some research to see if anyone had performed a mod on it, but very little came up, until I came across a this thread on the Advanced Audio Europe forum:

“…The SC1100 has a discrete class “A” transformer coupled circuit based on the original AKG 414 from the early 70’s. This circuit has 14db more headroom than a U87.

The capacitors in the SC1100 are already high quality tantalum and polypropylene. R10 can be changed to a 2.2K which will increase the output level and headroom by 3db.

The SC1100 has a dc to dc converter board similar to the U87AI in order to polarize the rear diaphragm via the pattern switch with 110 v dc for FIG 8.

The SC1100 has a low tech single winding transformer that works remarkably well when driven from the much lower output impedance of the 414 circuit.

We can supply a 2.25:1 transformer with dual bobbin windings and bi-metal laminations for $59. Our 2.25:1 transformer will take 6db more level than the stock transformer and recover much faster from percussive transients.

The SC1100 has no pre-emphasis and there is lots of room in the head grill for either our AK47 or AK67 which will both work well with that circuit.

The AK47 will give it a more U47fet tone but with 3 patterns and the AK67 will give it a more U87 tone but with more headroom….”

Looks like someone else had the same idea, I contacted Advanced Audio and they supplied me with a new capsule (AK67), transformer and resistor to perform a relatively simple upgrade to this mic.

The result? A clearer, more precise mic with nice tight bass response. You can opt for a different capsule of course, and this will change the character of the mic, they recommend their AK47 or AK67 capsules. I found the AK67 added back the mids that seemed scooped in the original, giving a lot more presence to recorded sources, I’ve included some quick audio examples at the bottom of this post.

The basic cost of this mod was 145 Euros plus p&p for the AK67 capsule BV2.25 transformer, and they very kindly threw in the 2.2k resistor as well.

If you’re interested in performing this mod yourself, then I will outline the procedure I followed. I would say this is an easy to medium mod, you will need to be confident with soldering and desoldering components (see here for some good tutorials), and not be squeamish about completely dismantling the microphone!

Disclaimer: Be aware that you could damage your mic if you get this wrong! I am in no way responsible for any damage that may occur as a result of following my guide. Use common sense and take care and you should be fine, if in doubt or lacking confidence, find someone who can help!

You will need:

  • Suitable replacement capsule , transformer and resistor (many suppliers can provide these components, I found Advanced Audio Europe to be very helpful in recommending the right parts, get in touch with them here)
  • A temperature controlled soldering iron with a fine tip
  • Desoldering pump
  • Audio quality solder (4% silver)
  • 1mm dia. heat shrink
  • wire cutters / strippers
  • Set of small Phillips screwdrivers
  • 99.9% Isopropyl Alcohol, a toothbrush and / or cotton buds (for cleaning the solder joints afterwards)
  • (optional) A crocodile clip to use as a heat sink when soldering near heat sensitive components.
  • (optional) A camera

Time required is about 1-3 hours depending on how skilled you are (took me about 3 and I’m not that skilled!)

1) Prepare your workspace

Not essential but this is how I like to work: have a clear, clean workspace with good lighting ready, warm up the soldering iron and lay your tools out. I grounded myself for ESD protection, not sure if it’s strictly necessary but I did it anyway, I have a wire connected to the radiator pipe which I wrap round my finger.

I took photos every step of the way so I could refer back to see where wires were connected or how things fitted together, very useful and no hassle these days with camera phones.

2) Dismantle the mic

– Unscrew the base of the microphone, slide off the body sleeve and put both parts to one side.

unscrew the microphone body

-With an appropriate screwdriver, undo the 2 screws either side of the head basket and then remove the basket and he plastic locating ring that mounts the headbasket to the inner metal runners.

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– I’m not sure if it’s strictly necessary, but I found it easier to completely dismantle the mic to work on it, so I removed the 4 screws on each PCB that hold them to the frame, and the 6 screws holding the transformer case and XLR connector to the frame too.

Screen Shot 2014-09-23 at 11.12.11

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– desolder from the PCBs the 3 wires coming from the capsule. I found it better to do this than cut them as the blue wire on the replacement capsule was not quite long enough so I had to exchange it for the one from the original capsule. (Use a heat sink on the leg of the capacitor to prevent damage when desoldering). If necessary, ensure you take a picture(s) of where the wires connect so there is no confusion when reconnecting.

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3) Remove the existing transformer

– As you’ve seen, the transformer is located in the metal can at the bottom of the mic, open this and pull the transformer out, it is usually stuck to the lid with an adhesive pad.

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– cut the wires to the transformer fairly close to the transformer itself, the replacement has short wires and you will need to splice them to the existing wires in order to reach the PCB.

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4) Install the new transformer

-The replacement BV2.25 transformer is dimensionally quite different, you will need to install it lying on its side in order for it to fit in the can. I wrapped the metal core of mine in electrical tape, not sure if it’s necessary but the original was wrapped up too so I figured it might be useful to do. Route the wires through the 2 entry holes on either side of the transformer can.

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– Prepare the ends of each sets of wires for soldering (strip and tin where necessary), place a sheath of heat shrink on the long wires leading to the PCB and push down out of the way.

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– match up the colours of the wires from transformer to PCB and solder them together, you may need some clamps to hold the wires in place as you do this.

– slide the heat shrink sheaths over the joins and apply heat till they contract, ensure no bare wire is exposed.

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– relocate the wires in the metal runners and assemble the transformer can and XLR connector back into the frame. Replace the 6 screws taking care not to pinch any wiring in the metal runners.

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5) Swap the resistor

– Locate the resistor labelled R10 on one of the PCBs, flip over and locate the solder joints corresponding to this component.

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– using the desoldering pump, desolder and remove the resistor (I will assume you know how to do this, but if not sure then here is a good guide: http://www.tangentsoft.net/elec/movies/)

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– fit the replacement resistor, solder and trim the terminals

6) Capsule swap

– If your not intending to re-use the existing capsule, then you don’t have to be so careful about handling it. With the new capsule, only hold if from the sides and don’t pull on the wires connecting to the front and rear faces of the capsule.

– remove the existing capsule from the plastic saddle by removing the 2 holding screws either sideScreen Shot 2014-09-23 at 11.59.53

-Take the new capsule from it’s case and locate it on the saddle so that mounting holes are aligned with those on the saddle. Using the screws provided with the capsule, screw the new capsule in place and tighten, ensuring there is no play.

– feed the capsule wiring through the holes in the top plate of the microphone leading to the PCBs. If the blue wire appears to be too short, then you can remove the blue wire from the old capsule by undoing the retaining screw and swap it with the wire on the new capsule.

– to avoid accidental damage to the exposed capsule, I slipped the metal sheath from the mic body over the capsule, this is particularly usefull when it comes to soldering the wires onto the PCB as any spurts of solder could potentially damage the diaphragm

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– resolder the capsule connections, the blue wire goes to the shared terminal with the capacitor (use a heat sink to protect the capacitor), and the red wires go to the terminals on top of the other PCB. To avoid confusion, the PCB with the 3 way pattern select switch is mounted on  the front side of the mic, the wire from the front side of the capsule goes to the right hand side connection when looking at the back of the PCB.

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– clean the back of the PCB and all new solder connections with the isopropyl alcohol20140829_145823

 

7) Re-assemble and Test

– re-attach the PCBs using the screws, be aware of the capsule and avoid damaging it, replace the plastic ring and headbasket, now you can relax a bit as the capsule is protected! slide on the body sheath and tighten the base, the black backing plates to the pattern select and filter switches are likely to have come off and will need inserting before you put the body back on.

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– plug it to your preamp, apply phantom power and test, speak into it first and make sure you are getting signal, then try it on a range of instruments or vocals and see how you like it.

Good luck, I hope you enjoyed and / or have found this useful, I’ve made 2 of these mics now and am very happy with the recordings I’m getting from them. Here are some quick audio examples to illustrate the change in character of the modified mic compared to the standard version: