Category: Blog

Musician’s Friend has resurrected their “Stupid Deal of the Day” promotions where they pick some mass-produced music thing and sell it very cheap. Recently, the SDOD was an MXL v250 Mic for $59.99 I saw this promotion being shared all over Facebook and one of those people contacted me and asked if it would make a good donor mic to mod.

The v250 is a typical low-cost transformerless MXL mic. It has a Small Diaphragm Capsule (despite looking like an LDC) and a mass-produced Schoeps-style circuit board. The body is essentially a BM-800 but with a very nice Headbasket. It also features a threaded base which can screw into various Spider type shockmounts. The mic comes stock with a hard mount only.

For this mod, I did a straight-up rebuild using the jaSb board with the optional internal pattern switch. The capsule was replaced with my usual k47 style using my own mounting cradle. I could also transformerize these with my new BFM board and transformer mounting system.

To The Bench

The rebuild was pretty straightforward. Being a brand new mic, I wrapped the body cylinder in paper to avoid scratching the (very thin) finish. The old guts were removed and the new stuff went in. I already had one or two jaSb boards built so this went pretty quick and easy.

The final Assembly was simple too. I really like the nice big headbasket on the v250. Everything fit just fine and the initial technical and listening tests were done with no issues.

Off to the Studio to do an “After” recording

While letting mics burn in, I like to record something with them. Usually, I do an Acoustic Guitar recording to just see if they have the sound. This one’s got it for sure.

The v250 is a fine mic to mod. As BM800 style bodies go, this one is nicer than the typical.

I recently bought yet another cheap MXL 910 on ebay. As I was considering what flavor to make it, I noticed a box of long-forgotten CK12 style capsules on the parts shelf. Earlier on, I was working on a CK12-ish flavor of my transformerless mics. I quickly ran into quality issues with these capsules. They sounded great – when they worked. But at one point, I had only two out of a batch of five that were useable. They are made at the same factory which makes my extremely high quality k47 style capsules, so it was a disappointment. Anyway, I sort of abandoned the “12 flavor” – maybe until now.

The key thing that sets the CK12 apart from the k47 is that it is edge terminated. As you can see below, there is no wire coming off the center of the diaphragm. Instead the white diaphragm wire is attached to the edge of the capsule. The classic AKG-ish sound of these capsules is an extended smooth and silky top-end.

CK12 style capsules do not always fit that well in some BM800 style headbaskets because of the height of the stand-offs for the backplate wires. The MXL910, however, has a nice big headbasket which easily accommodates a CK12.

Transformer or Non?

But, should it be a transformerless mic? Or should I go transformer-coupled? While pondering that decision, I thought about the results I’ve had with the Tab-Funkenwerk transformer I’ve been using. They have a very fat low and low-midrange and can tend to sound a little “dark” overall. But a CK12 is a brighter capsule! So maybe a CK12-style capsule in a transformer coupled mic with the Tab-funk tranny could be pretty cool!

What we have here is a mic with a CK12-style capsule, a KM84 style circuit and a T12-style transformer. Will it be an abomination of nature or maybe something special?

These Go to Eleven

As soon as I plugged this in to my test mixer at my workbench, I knew I was onto something. The fatness and fullness in the lows and low mids of the Tab-Funkenwerk tranny combined with silky bright top end of the C-12 is pretty amazing. After one quick test on acoustic guitar in the studio, I’m pretty excited. It has lots of everything. Full lows without being boomy. Silky highs without being harsh. And a nice bit of transformer crunch/compression that I expect from the AMI transformer. The mic output is hot! I might experiment with a fixed 3 or 6db Pad. On the other hand, that strong signal is probably contributing to the extra crunchy saturation of the transformer so maybe I’d opt to pad these at the preamp on loud sources. As always with my test recordings, this is straight into a CAPI vp312 preamp with no EQ or other processing at all. The Guitar is mic’d from about 20 inches away with the CAPI preamp gain on the 2nd from lowest setting.

A Worthy Addition

This is not the most versatile mic I make. I’d say my good ol’ transformerless mics with the k47 style capsules take that prize – they work great on anything. But this mic would be beautiful on vocals, acoustic guitar (and other stringed instruments) and percussion. I would probably not reach for it to use on a guitar or bass amp or kick drum. For sure, it’s another fantastic flavor and this particular one will find a home in my personal collection.

Not sure yet if I will add any CK12 flavor mics to my list of standard offerings in the store. Although this particular capsule is working fine, I’ve had a bad experience with them in the past. Maybe I had a bad run of them. Maybe not. I want to see how this one works over the long term for a while and maybe try another build or two before I start offering them to non beta-testing customers.

Since the last entry, I’ve got a handful of Transformer Coupled builds under my belt including three Sterling ST55s and two RS/47Ts. This led to some minor tweaks to the circuit boards – mainly for fit and layout and a few new build tricks. I love these mics!

Wanting to try some higher end transformers, I finally got my hands on a Tab Funkenwerk T12 from AMI (USA). I still had no luck getting anyone from Cinemag to return emails trying to buy their product. The AMI was in stock and I had it within a week of ordering it. This thing is pretty pricy so I’d been very curious about what it would bring over the Chinese transformers I’ve been using.

Is it worth the money? Depends. Read on…

Data

I wanted to get some idea of how these guys perform in a clinical situation on the workbench with test signals. First, answer “why are transformers cool?” Everyone likes to throw around words like “warm” and “mojo” and such when they talk about this stuff. To me, what’s going on is mostly about the harmonic distortion you get from a transformer. Generally, Transformers are pretty clean in higher frequencies. It’s the low end where they get “funky”. So what do the harmonics look like?

As expected, both transformers have the most harmonic distortion in the low end. Where they differ however is that the Chinese 3rd and 4th harmonic fall off pretty quickly at higher frequencies, but they stay more constant in the AMI. The CN T8 has a stronger 2nd harmonic in the mids and highs but most of the other harmonics were stronger in the AMI. I’m not showing it here, but when I displayed the higher order harmonics (up to 8), the same trend continued. The CN T8 harmonics dropped off more in the mids than the AMI which stayed more constant over the whole range. My guess at this point is that the AMI is going to have more mojo (ok, here we go with the words).

Note that the response of the fundamental rolls off more in the low end on the CN tranny. Let’s look at that closer…

The CN T8 transformer definitely has a bit of a High Pass effect going on. It’s down 3db at 35 Hz. It’s subtle but meaningful as you will hear below. As a sanity check, I temporarily doubled the size of the coupling cap to see if this rolloff was because that was undersized. It made no difference. The rolloff is definitely from the tranny. I think it’s clear that this is one reason the CN transformer is one fourth the cost of the AMI.

Listening

I was anxious to compare these two transformers so I quickly finished up another RS/47T that I had in progress. Also some fresh PC boards arrived today, so I was able to use the latest version of the transformer adapter board. It still needed a little adjustment with a dremel tool. Next rev will be perfect! Anyway, I set up the two mics over/under and recorded some acoustic guitar. As always, both mics went through identical CAPI vp312 preamps and levels were trimmed to within a tenth-ish of a dB. There is absolutely no processing on either mic.

My impression is that the AMI has a lot more going on in the lows and mids. And there is almost a subtle compression happening on hard strums – like a tiny bit of mxr dynacomp was switched in! The extra lows are not too surprising given the response curves above, but the stronger mids are probably due to the extra strong 3rd,4th (and higher) harmonics that the AMI seems to produce from its lowest frequencies. Both mics were hand-biased for minimum THD when they were built so the differences must be mostly from the transformers. The mic with the Chinese T8 feels lighter and brighter with more of a silky top end and it does not have quite as much thickness in the lows and mids. I think they both sound lovely. If I were wanting one of these for bass drum or bass or electric guitar amplifier, I think the AMI would probably win the day. But for voice, acoustic stringed instruments, percussion I think either mic could work wonderfully and the one with the Chinese T8 might even be preferred in some cases.

Listen for yourself here. The piece plays through twice. First time is with the Chinese T8 and the second is with the AMI. After that, there are some short loops repeated 4x with each transformer. The CN followed by the AMI

Every so often, I get contacted by someone interested in an rebuild of a Transformer Coupled Microphone such as an MXL2001 or Sterling/Groove Tube ST/GT55. My only solution has been to put a mic parts kit in those mics. This is by no means a bad solution. I’ve built a T84-55 kit from Mic Parts for my own ST55 a while back and the results are fantastic. The idea behind that kit and several other similar DIY project kits is to use the circuit and transformer from a Neumann KM84 in a large diaphragm mic (hence the “T84” in the kit name). The KM84 is an early phantom powered small diaphragm condenser (SDC) mic with an incredibly simple circuit. Despite that, if you can find a vintage 84, it will cost you four digits to acquire it. The KM series of Neumann mics is named for Klein Mikrofon or “Small Microphone” hence these are all SDC pencil style mics. The schematic for the KM84 is no secret and is incredibly simple. It has to be in order to fit everything in that tiny pencil mic (this is from long before surface mount components came along).

The Audio Path of a KM84 consists of just a few parts: An FET, two capacitors and a transformer. Because there are so few components, each one matters quite a bit. In fact, if you can find a vintage BV107 transformer from an original KM, it will cost you almost as much as the mic! When adapting this circuit to an LDC we get to lose one of those capacitors because the capsule is normally not grounded in an LDC. Therefore the audio path becomes even more minimal! And, because we have more room in an LDC, we can add a few non-audio path things to make the circuit perform better. The short version is that the KM84 circuit makes for an excellent transformer coupled LDC!

Into The Rabbit Hole

I decided to design my own LDC KM84 style board. I call it the “BFM” because this is for a BIG F’n Microphone, not a Klein Mikrofon. I’ve made two footprints of the board: One that will fit the Sterling/Groove Tube ST/GT55 and another “800” shaped board that will fit most low cost MXL bodies. The boards are called the BFM-T-55 and BFM-T-800 respectively. The T-55 will support the Pad and HPF switches on the Sterling/Groove Tube mic. Both the T-55 and T-800 versions have an optional internal pattern switch to allow switching into Omni Mode.

That Capacitor

The one capacitor in the audio path has to be a pretty big one. The 7:1 transformer is going to nominally present about a 10k Input Impedance to the FET stage so we’re going to need at least a 1.0uF cap to ensure a flat response down to 20Hz. That may not sound huge, but it wants to be a very high quality film cap and they start to get big and pricy at that value. Mic parts uses a Sonicap product which costs about $10.00! Being a bit of a Capacitor Skeptic myself, I couldn’t bring myself to spending ten bucks on a 1uF cap. I opted instead for a $3.09 ‘FastCap‘ from Solen. They say “France” on them so they must be good.

The Problem With Transformers

The only thing hard about building Transformer Coupled Mics is… getting transformers. The high-end goto for transformers these days is Cinemag. Their CM5722w is ideal for this circuit as it is a pretty faithful recreation of the original BV107. However, actually acquiring one of these mythical transformers has proven to be difficult.

The Mic Parts kit comes with a transformer which they have custom wound for them. I do not have such clout, so I’m out trying to score a seven-ish to one microphone output transformer. For my testing and development, I bought a 10:1 transformer from Analog Classics. It’s about $45 compared to about $80 for the Cinemag. I also bought a 7:1 Chinese transformer for about $22. These are in endless easy supply so it would be nice if it doesn’t turn out to be awful.

To The Bench

I had enough parts and bare boards to build a couple of prototypes. I also had to come up with some way of determining the ideal value for the FET bias resistor (R3) for each individual mic. FET Bias is extremely critical in this circuit! I purchased a 20K Bournes Precision 10-turn pot and mounted it in a box with some wires that can be clipped into the circuit. The trick is to determine the value that yields the lowest harmonic distortion, best gain and most symmetrical clipping. Next, I read the actual value of the pot and install a low-noise fixed resistor that is as close as possible to the pot. This has to be done individually for each mic (each FET actually).

I use REW (Room EQ Wizard for the THD analysis). So you dial it in with the pot and then measure the actual value that got you the goods. For the first two mics, I came up with 7K7 and 8K1 for the R3 resistor values. I didn’t have those exact values in low-noise Vishay/Dale resistors, so I put a couple in series to get close enough for now (I’ve since ordered a whole series of Vishay/Dale resistors between 5K and 8K.

First Tests

After my prototyping phase, I had three mics to work with:

• Sterling Audio ST55 with Mic Parts board and Transformer
• Another Sterling Audio ST55 with my BFM board and an Analog Classics 10:1 transformer
• A prototype BM800 body with the Chinese T-8 Transformer.

The first thing I did was fire up REW and did a sanity test comparing my two builds with the Mic Parts kit just to see if we’re in the same ballpark. We are. The Sterling with the 10:1 Analog Classics Tranny had a significantly lower output than the Mic Parts mic. I expected it to be lower but not by the 6.5dB that it was. Oh well it still had plenty of gain and great signal to noise ratio. The 800 with the Chinese transformer was within a half dB of sensitivity to the Mic Parts mic.

Next, I set up a shootout rig with the Mic Parts ST55 as the compare-to mic and one of my prototypes under it. They both went into identical CAPI vp312 preamps. My main interest is to evaluate the two transformers I have managed to acquire against the Mic parts mic. Apart from that, we are using the same FET, similar Capsules and the circuit is pretty close to that of the original KM84.

I recorded some acoustic guitar with various combinations and took some time to listen to the result. To be fair, we’re comparing several components here: Capsule, Transformer primarily but also FET and ok sure… that fancy capacitor. I printed the MP ST55 against each of the prototypes. That Chinese capsule that I was supposed to hate so much actually turned out quite nice. In fact, I went back to the bench and swapped it into my Sterling ST55 and recorded some more. Here is a short loop of that recording. I am switching mics on every CM7-Em. The entire sequence of three mics happens twice. I won’t say which is which, but suffice to say, I don’t think this chinese T-8 Transformer is a compromise at all. But I still really want to get my hands on a Cinemag to try!

The Hi Pass Filter on the Sterling

This took a few tries to get right. There is a balance here because you want the filter to remove low rumble or other unwanted tone from some instruments and voices. But on the other hand, a transformer does all its cool stuff in the low end, so you don’t want to cut too much. After three different capacitors (and two Mouser orders), I settled in on a cap that gives a great Lo Cut for this mic. Here is the in-circuit response with and without the filter

In Part Two, I dive in to comparing a couple different transformers.

There I was surveying my wonderful recording studio which I had been doing numerous upgrades to of late. I had the coolest mic and mic preamp collection I could ever hope for. My console layout looks and works great. I have these amazing Focal monitors. The rooms sound amazing.

But why? Why bother with all this? What am I going to record? I’m not in a band. Covid has everyone isolated. As our Japanese Exchange Student used to say: What’s the goal?

While you’re here, check out our custom microphone modifications and rebuilds. If you have a neglected MXL 990, MXL 910 or similar mic in your locker, we can very affordably turn it into a “go-to”.

A Call from the Home Town

My buddy Jeff Stachyra, in addition to being a great musician and songwriter (and leader of The Dirt Farm band), has an amazing studio near Binghamton NY called Newclear studios. His site speaks for itself, but it’s really a sweet mix of modern digital and vintage analog gear and instruments. Anyway, he had a client who was working on a solo album and had a few songs that he wanted some additional vocals and other stuff on.

And there was the answer to what’s the point? Rick Iacovelli is a local musician and artist in the Binghamton area known for his eclectic musical and visual arts style. Also just a very cool dude. With a few emails back and forth, and some details on how to transfer the tracks, I was set up to work on four of the songs from Rick’s upcoming album. And now the reason for having all this cool gear was in sharp clear focus! Remote Music Collaboration is a reality!

The common thread for the four songs was adding background vocals. For most of them, I did three or four tracks double-tracked. Back in the day, I used to do this sort of thing for lots of my clients, but it’s been a while. Between not playing live for a long time (and my last band being an instrumental surf band called Tsunami Of Sound), I was a little out of practice. The last few years, I had particularly lost the ability to do any high falsetto harmonies. Determined to turn that trend around, I took one lesson (so far) from Eden Casteel here in Rhode Island. I would have continued, but this was just before sailing south again for the winter. Anyway, she gave me some great tips, exercises, general information and encouragement that got me on the road to recovery.

Now that I had this variety of mics and preamps, I decided to try and avoid the all one dude on one mic sound and do different parts with different gear.

I used the matched pair of modified MXL990 and the modified MXL910. The 990s have the RK12 capsules in them and are very AKG-ish “hi fi” with a flat, extended response. The 910 has a K47 style capsule in it which has that upper midrange edge of a Neumann. One of the 990s is set up low and facing up. This was for the falsetto parts as I do them more easily if my head was angled down a bit (the Bee Gees finger in the ear trick was helping too).

Preamps used were:

• UA 4-710D in half tube/transistor mode with a little of the FET comp,
• Sound Skulptor MP573 Kit
• Rupert Neve Designs 511 (which I have since sold)

MoDs On ThE RuN

I liked all the tunes very much, but this one was especially fun. It’s a clear nod to The Who and Rick was wondering about getting a Baba O’Riley-ish sequencer on it. The drums were played by the incredible Mike Ricciardi. In addition to being a great drummer, Mike is also an accomplished photographer with a very unique style. To do a sequencer part, I needed to build a tempo map to the reference track provided by Jeff. This turned out to be very easy because Mike is so good!

Most of my parts are “Ahhs” and that is what you see where there are six tracks. In the middle, I’m singing eight tracks of “Mods… we are Mods… we are the Mods on the run”. I tend to avoid copy-paste background vocals and prefer to sing each repeated part each time it appears in the song. I may have broke that rule a bit on the falsetto parts because I am still struggling a bit there. When I got a part that worked, I tended to copy those!

For the Sequencer, I used what is becoming one of my favorite synths: Waves Element. I absolutely love this synth. It’s complex enough to do anything, but simple enough to easily program great patches from scratch. It brings me back to my Korg Polysix days. I built a patch I liked, set up a pattern in the built-in sequencer and it played perfectly to the tempo map.

The Result

Here is MoDs On ThE RuN released to youtube. Enjoy Rick’s animations while you listen!

Check out the rest of Rick Iacovelli’s Youtube Channel here. The other tunes and much more of his cool animation are there. Give him a like and a subscribe while you’re at it!

The Other tunes I contributed to are listed here. Vocals on all of them, but a guitar or keyboard here and there as well.

• But I Ain’t Got You
• Wishing Well
• Dandelion Today

Thanks again, Rick for the reason why.