The Xaudia Blog

09-10-2012

Trash-caster recycled Nashville guitar (part 1)

I have wanted a Nashville tuned guitar for some time, and saw an opportunity when I found a Jazzmaster / Jaguar style body and neck going cheap on a well know auction site. Time to put a guitar together! I’m calling this the Trashmaster (or Trashcaster?) as it is assembled from reused bits and pieces.

Hello Kitty? My pink guitar!

The guitar parts arrived last week, and although the body and scratch plate looked in good shape, the neck was from a different instrument and played like a cricket bat! The body is a sort of vintage pink – not sure if I like it or not. Well, for £56 all in, one can’t complain too much.

I had a spare neck kicking around from last year’s Telemaster project, which played much better but didn’t quite fit in the body socket either. Judicial application of a plane, fret file and some abrasive paper quickly solved that problem!

Things almost fit together, but not quite!

The scratch plate has two cut-outs for pickups and three switches, and covers most of the guitar’s routing. A metal plate from a Jazz bass covers the rest, and again this almost fits, and a hacksaw and file made some unwanted corners disappear.

The pickup holes are also slightly bigger than standard Strat or Tele single coils, and so custom pickups were made. This was pretty simple – using flatwork boards from StewMac, I cut out boards for the top and bottom of the bobbin, and drilled to make room for the magnets. This board is pretty useful stuff – it feels like cardboard but works like plastic. It drills easily and can even be turned on the lathe!

Custom pickups made in the Xaudia workshop

The board was the glued to Alnico 5 magnets, and then the bobbin wound with 42AWG wire, and finished with string before potting in the wax bath. I put 9350 turns on the first pickup, but suffered a wire break about half way through making the second. Problems can often be turned into opportunities, and so in this case I ended up with a tapped 5000+5000 turn pickup for the neck. I have also been scatter-winding, so this should be interesting!

Wiring the guitar with scratch built pickups

The switches on the scratch plate can thus be used for phase and coil tap duties. Try to be neat with the wiring!

Fender-looking Trashcaster, and Telemaster

So, time to put the guitar for a bit together for a moment and see how it looks. Not too bad, but I’m not so sure I need a pink guitar in my life! More here….

30-09-2012

Fostex Frankenphone

The Fostex printed ribbons are rather odd microphones, using a membrane with a metal track suspended in a magnetic field to generate the signal. Although they have a natural figure of 8 response, their sound is more like a moving coil dynamic than a ‘true’ ribbon microphone.

This one was probably once used as a donor mic to fix a broken one – it arrived without a capsule assembly.

Fostex printed ribbon mic

Sadly, Fostex UK were unable to supply a replacement part, so for now at least it has been converted into a Frankenphone ribbon mic.

Another Frankenphone!

I used a spare ribbon frame from a Reslo mic, with a pair of small neodynium magnets glued to the frame, which gave a field of around 6000 Gauss (normal Reslos are around 4000 gauss). The new ribbon assembly fitted neatly into the old mount, needing just two strips of foam to hold it in place.

Fostex transformer and switch unit

The Fostex transformer and filter switch were still present, but were designed for the Fostex printed ribbon capsule, and are unsuitable for a ‘real’ ribbon microphone. I wound a custom 1:34 transformer for the job, which works nicely. The mic has a full range output and sounds pretty good!

29-09-2012

MOTM Reslo SR1 studio ribbon

Reslo SR1 studio ribbon microphone
This month’s MOTM is the Reslosound SR1 Studio microphone, which was a big brother to the RB models, and was Reslosound’s top of the range ribbon microphone. They are nice sounding figure-8 ribbon microphones, and are very much less common than the RBs, and have become quite desirable amongst collectors and studio engineers. Often they came in a stunning bronze colour with matching plug, like the one above. 

The advertising at the time claimed 30Hz to 20kHz – although doesn’t qualify that with a dB range.

Reslo SR1 (top) and RB microphones

Extra sensitivity comes from using a longer ribbon and an extra magnet, and the mic is consequently about 1/3 as long again compared with the more common RB. By necessity the SR uses a different ribbon frame from other Reslo microphones. The mic below came complete with its original fibreglass stuffing –  which protects the ribbon, damps any ringing of the shell, but seems to muffle the sound a little.

Inside the Reslo SR1
Reslo SR1 output connector

The RB microphones are quite notorious for grounding problems, as the mic body is only grounded through mechanical contact at the plug. The SR1 deals with grounding in a better way. The output socket has a hole drilled in the centre with a small wire pushed down and soldered to one of the lugs (see photo, by the green wire). When the mic is reassembled, the long screw that secures the connector makes firm contact with both the mic body and the central wire, giving a good solid ground. This works well, and I now use this approach to ground troublesome Reslo RBs too.

Reslo SR1 transformer, being re-wound

winding arrangement for SR1 transformer

The SR1 was available in both 30/50 ohm and 250 ohm versions, and used the same laminations and bobbin as the later RB transformers, but with a more sophisticated winding configuration. The SR1 transformer has a 5-winding construction, with two primary windings alternating between three secondary windings.

We can supply reproduction SR1 transformers on request.

Thanks to David Pumple for sharing photos and information. The SR1 advert is from http://reslosound.blogspot.co.uk/.

21-08-2012

ElectroVoice EV RE20 vs RE320

Everyone who has worked with me will know that I am a big fan of the EV RE20 / PL20 microphones.  Although perhaps most famous as a radio presenter’s mic, they are used throughout studio-land for kick drum, horns and vocals – Thom Yorke from Radiohead is one famous user.  In our studio, they are the go-to dynamics for pretty much everything that makes a loud-ish sound –  kick drum, toms, bass, guitars, horns, vocals, percussion, organs, science experiments, and so on. We have three, and I could happily use more.

From top. EV RE20, PL20, RE320 and another RE20.

I don’t really like severe EQ’ing, particularly with digital EQ, and so the idea of having an RE20 that is voiced for kick is particularly seductive. So, I was very eager to get my hands on the new EV RE320, which is an RE20-shaped thing that is specifically designed for kick drum. But wait! It is also specifically designed for vocals and instruments. How does that work?

EV RE320 switch with kick drum (left) and ‘flat’ settings.

Whereas the original RE20 has a switch which operates a high pass filter circuit, the switch on the RE320 gives different voices for different applications, giving access to ‘flat’ and ‘notched’ settings.

So, what are the differences between an RE20 and an RE320? The most obvious thing is that the RE320 is very black…. supermassive-black-hole black. in fact. And it comes in a zipped reinforced thing that is a hybrid between a box and a bag. This is a big improvement on the crappy plastic boxes that the RE20 came with, which tend to snap at the first opportunity. The RE320 is also about £150 cheaper than the RE20, and is ‘assembled in China’, whereas the RE20 is ‘made in the USA’.

RE320 snug in its little box-bag

More importantly, what about the sound? Here is a frequency plot of a ‘normal’ RE20, recorded in the Xaudia test chamber at 20 cm from the source. The blue line is the flat setting, and the green is with the HPF switched in.

RE20 response (blue) and with the HPF (green)

I had hoped that the flat setting of the RE320 would be be the same as the RE20, but in fact the new model is brighter and louder. Here is the RE320 in ‘flat’ (red) and ‘kick’ (green) modes, along with the RE20 in blue as a reference….

RE20 (blue), RE320 in flat (red) and kick (green) modes.

The RE320 has a higher output in both positions, and also has a peak around 4 to 6 kHz, which may brighten up some vocals. And there is other stuff going on too! A more revealing way to look at the behaviour of the ‘kick’ position is as a difference plot…

RE320 – difference between the flat and kick drum settings.

This plot shows a complex filter network being applied, with a low shelf boost, a -4dB cut at around 350 Hz, and a +5dB boost at 3.5 kHz.

Despite the differences, the RE320 does sound like it belongs to the same family – in fact it sounds rather similar to an RE20 with a +5dB boost around 4-5 KHz. I guess that makes sense!

Only time will tell if I will love this as much as the RE20, but it is a decent dynamic mic and will certainly find uses. I will report back once I have used these on a real recording session.

Stewart, Xaudia

A typical day at the office

RCA 77DX under test at the Xaudia microphone workshop.
I think I always wanted my bench to look like the inside of the Tardis. Signal generators, oscilloscope, LCM meter, frequency counters, distortion meter, microohm meter, home built impedance bridge, and lots of other gadgets. And an RCA 77DX, of course! 
20-08-2012

Straightening a dented mic grill

Here’s a rather deformed grill from a Beyer ribbon mic…

And here’s how we straighten it using a doming block….

Simply pick the nearest radius curve from the block, and push out the dents with a suitable doming ball….

Voila! The end result…

🙂

11-08-2012

Rogue Cadenzas

I have come across a couple of Cadenza ribbon microphones recently that are not what they seem.

The microphones came from different sources, but both had been modified in the same way. The mods were performed long enough ago that the foam had started to disintegrate.

In both cases the ribbon element has been replaced by a dynamic element. and the mic stuffed with pink foam. Both mics are painted black with a silver top, and in both cases the stand adapter is fixed to the microphone rather than being removable.

Rogue Cadenza with dynamic element

There are clearly a few of these floating around. The stand modification looks well done, and I suppose it is just about possible that this was done at the factory, perhaps as a budget alternative to the ribbon mics, although I have not seen any documents to support that.

So, look out when buying old microphones – what you see is not always what you get.
Caveat Emptor!

31-07-2012

MOTM Mystery 74B clone

It is said that imitation is the sincerest form of flattery. If that’s true then the RCA 74b junior ribbon was one of the most flattered microphones ever made!

In the middle is a ‘real’ RCA 74b and on the right is a 74b made under license in Italy by Magneti Marelli. But what’s that on the left? It’s our microphone of the month, and I don’t know what it is.*
When I first saw this I thought it must be another rebadged or licensed 74b. The outer dimensions are almost identical to the real thing, and it even has a red ‘meatball’ badge, although this time with some unidentified Eastern-looking symbols – perhaps from somewhere in South East Asia.** It even has a good copy of the swivel stand mount.
Inside the 74b clone
But inside the mic there are some differences. The ribbon has similar dimensions, but the magnet assembly is quite different, with two large, strong horseshoe magnets providing the field through a pair of U-shaped pole pieces.

Rear view with horseshoe magnets
In a ‘real’ RCA 74b, the magnets are at the front and bevelled, with a rectangular frame at the rear.
‘real’ RCA 74b microphones inside
In the photos above the transformer is a replacement. The original transformer, below, was faulty, probably due to insulation breakdown. Again, the marking on the transformer looks very Eastern in style, and appeared to have been written with a brush, in eastern style.
Perhaps the oddest thing about this microphone is that it has been shot! There is a pellet embedded in the side of the mic. Perhaps it was used as target practice. Or just maybe it was in use at a radio station in the last days of Saigon….
*Thanks to John Gooding!
** I have tried to identify these but no luck yet!


—————-

Update, 13 August 2012


A couple of readers have sent in messages about the provenance of this microphone….


“My friends here in Thailand says the symbol is almost definately Chinese. It is certainly not Thai, Vietnamese or Cambodian. By most stuff here has been made in China since China started making things, so your Saigon theory is still the best.” James Browne, Hungry Ghosts


“Hi Stewart. Sent picture to my factory in H.K, the marking is definitely Chinese,” Andy Hearn, ECM


—————
Update, 15 June 2022 (ten years later…)

Thanks to Adam Pan from Taiwan for providing this additional information and photographs.
“The first photo left one ribbon mic is make by Shanghai Microphone Factory in 1940’s. 
After a long time looking for some China made microphone. when I move to live in Shanghai China from 2001, I found two ribbon microphones in China, one is the same as yours, the logo is the word “Ding”(鼎) in chinese, that is “tripod” the meaning is “one word is as heavy as nine tripods”. Reminder to “keep your word”. And the other one’s logo is “He-Ping”(和平)，That meaning is “Peace”. 
A few years ago, I helped Superlux develop some products, and I met an older engineer who is retired, He was involved in the manufacture of Type 74 microphones at the Shanghai Microphone Factory.”

15-07-2012

Hexapup hexaphonic pickups now available.

One of the great things about being a micro-business is that you can act quickly! There is no management structure, no liaising with a marketing or accounts departments – we don’t have them! And best of all, no office politics! This means that if we have a good idea, or even a stupid one, we can do it straight away.
Hexapup in a Gretsch-style ‘toaster’ cover

Last month we made a stereo guitar pickup prototype, and it was fairly clear from our customers and comments on forums that a few people might want one. So now, six weeks later, we have a ‘production’ version in a humbucker sized* can – the Hexapup!

Hexapup – hexaphonic guitar pickup

Hexapup guitar pickup

The hexapup is actually made of six small pickups, and can be wired for mono, stereo or hexaphonic output

Mono
When wired as a conventional mono pickup, the hexapup has a bright single coil tone. But it also has hum rejection (humbucking) properties because the coils on one side are reverse wound, with reverse magnet polarity.

Hexapup – serial number 002 with 43AWG wire



Stereo
There are two obvious ways for stereo wiring. Either bottom-and-top, or alternating strings. Put another way, the lowest three strings can be sent to one output, and the highest to the other, so power chords could have one sound, and solos another. Or, the E, D and B strings sent to the left, and A, G & e to the right. This makes for nice stereo width, and is great for multi-tracking chords, and chorus type effects. I have my guitar wired this way!

Hexapup being mounted to a customer’s guitar



Hexaphonic
Each coil can be given its own output, volume and tone control which, with series / parallel and phase options gives a staggering number of combinations. Each string can be sent to a different distortion or delay to  get strange new sounds, and could even be auto-tuned or pitch shifted separately – that might be weird. With six outputs, imagination is the only limit!

We currently have some big introductory discounts on the first production run, so please get in touch if you want one.

I’ll be writing a bit more about the technical specs in a couple of days, so stay tuned.

* Actually a little deeper than a normal humbucker, but most guitars have plenty of space.