******* WARNING WARNING WARNING *******
LOOK out for the "FAKE 47 Gold"
Beware of sellers on EBAY
We have seen microphones being sold that imply they are coming from us. They are not. The first clue is the text of the ad seen below.
"...we have changed the 6922 valve for much better NOS military spec 6n1p-ev. Every mod on this page has been performed except the transformer and capsule."
We ALWAYS change the capsule and transformer on this mic. That's the whole point. And the stock tube in the mic is NOT a 6922. So it is likely the writer has never seen the inside of an a5500.
If you are not buying a FAR 47 GOLD from Fox Audio Research, then you are not getting the real deal.
FULL STOP
Contact us at the email below for details or clarification
******* WARNING WARNING WARNING *******
The 47 "Gold"
The Aurycle A5500 kit is great value
See: http://www.aurycle.com
*NEW! 47 Gold Special Edition
See bottom of page
"Got to say the 47mod has done a world of difference with this mic. ATM its only hooked up to an mbox 2 for voice over work. It sounds wonderful. With the increased head room and increased max SPL it also sounds great for trumpet too. Can't wait to get it into the HD studio. All the strange behavior at moderate SPL is g...one. DC issues are gone. Great improvement in the usability of this $125 mic. I'm impressed!"
Quote from Clifford Brown III, Brown Audio Solutions & Services Partner San Francisco, California and KRML On Air Peronality, Carmel, California
We have come across a great upgrade platform from a company called Aurycle. (http:/www.aurycle.com)
This microphone is the cheapest path we have found for the home studio to get a u47 sounding microphone
The folks at Aurycle sell a microphone kit for only $139 USD which gives you a working microphone platform that can be simply upgraded. The basic mic. is Cardiod only, but since that is the way most people use a u47, it is little inconvenience.
We make some serious changes to the basic microphone and get some serious results in return.
The response chart below shows the mid-range lift in the FAR 47 with the Peluso capsule and the gentle roll-off about 10KHz that creates the warm u47 type sound.
Far 47 Gold , typical acoustic response at 0,5 metres, with the Peluso K47 capsule
FAR 47 Gold Sound Examples
The link below lets you hear the FAR 47 Gold in action. It was used on the Flugelhorn and the sax , the Bass and as the "under the sound board" mic for the piano
Far 47 Gold SE, Male vocal w/ LA610, NO EQ
New Capsule ... 
Starting with the Aurycle A5500 microphone kit we replace the stock capsule with a centre terminated capsule similar to the one used in the u47. We use the Peluso P K47, Gold sputtered 34x14 mm, 6 micron, dual diaphragm capsule shown above.
It is built to have a much flatter response than an AKG style capsule and it begins to roll off the high frequencies above about 14Khz. It has a slight lift in the upper mid- range that adds a unique "grit" to the sound. It seems to just cut through a mix and sit there.
Options for the cost conscious:
We are now selling the RK47 capsule for those who want a u47 sound but have a budget to follow. It has a very similar response.
New Circuit ... 
(Actually it's an old circuit from the u47)
First we cut. In fact we do a lot of cutting. On the circuit board that is. Then we connect both halves of the tube in parallel. That's right parallel. This doubles the power output we get versus the stock circuit, so a 3dB headroom improvement right there.
Another reason we parallel the tubes is to lower the Plate Resistance (Rp). The VF14 tube in the u47 has a low Rp. On the order of 8,000 ohms. The little 6072 is 20K for a single triode. By putting both triodes in parallel we lower Rp to about 10K. Much closer to the VF14. This allows the tube to drive the transformer harder and shows up in the sound world as improved low and high frequency response.
We remove the input capacitor and connect the capsule diaphragm directly to the tube's control grid pin. This is exactly the way the input circuit is wired on the u47. This is also the secret to the extended low frequency response and the famous u47 "proximity effect" sound.
Then we replace the critical capacitor in the audio output path using a polypropylene dielectric capacitor. Polypropylene capacitors are preferred in audio paths for their wide bandwidth and much more transparent sound.
We replace the electrolytic caps with Nichicon. We change the cathode bias circuit to a fixed bias *method that emulates the circuit in the original u47 more closely.
*For the purists out there we don't use the u47 filament current method but we use a **Gallium Arsenide diode. That's a fancy way to say an Infra-red LED. They provide infinite Bass response and maximize the tube gain. George Neumann couldn't dream of this in 1947, but I bet he would have liked the way they perform.
**News!
We have recently done some A/B testing comparing IR LEDs with two 1N4148 signal diodes in series and the signal diodes sound better. The IR LED is not fully saturated at the 600uA current we are running in the 6072 tube but the 1N4148s do turn on fully. This makes the bias voltage solid and the mic. sounds crisper. That's the best way we can descibe it.
We are updating all drawings to use two 1N4148 diodes.
New Tube... 
Our standard replacement tube is an Electro Harmonix EH6072. These tubes are made in Russia, are available all over the USA and Canada so there is no problem to find replacements.
We also have at any given time a short supply of vintage 6072 tubes from various manufacturers. To be very honest when we electronically measure the gain and noise level difference between new and old tubes there is generally very *little difference. There can be a slight sound difference with the old tubes which is best described as a less edgy top end. It is perhaps due to higher input capacitances but we have not proven that.
*Editors Note: I stand corrected. We recently got in a package of JAN 12AY7s (military spec). They sound thin right out of the box but improved the longer I let them run. I want to understand that better.
The tube change, from the 12AX7 that comes with the kit, improves the signal to noise ratio by about 6 dB. It also reduces the gain by about 6 dB which gives us more headroom going into the output transformer. 12dB of total benefits there.
New Power Supply ...
We replace the two regulating Zener diodes in your power supply so that the output voltage is 120 volts. That in turn sets the capsule voltage to 60 volts. This is the capsule voltagerange shown on the u47 schematics of various eras.
Transformer Required
Note:
We have recently discovered that the Aurycle A5500 transformer is designed with "de-emphasis" built in to compensate for 32mm Capsules. We previously thought our first 5500 was defective but it is actually designed with a notched response. This makes the a5500 transformer incompatable with K47 capsule and so we must change the transformer.
Low Cost Option: APEX Standard (KCM)
We have done measurements on the transformers from China, that are used in the APEX 460. We have to say they perform very well. The distortion is as good as the CM-2480 and the high end response is actually flatter!
Don't be confused the 460 transformer has a yellow wrapper around the coils. The Aurycle wrapper is green. They look the same but are VERY different.
The APEX 460 transformers are a single bobin design and use iron rather than exotic alloys of Nickel and cobalt. However there are aspects of iron transformers that are better than fancy alloys. See our page on transformers and if you want to really get down with transformers, read this PDF of "Audio Transformers" (3 Mb) a book by Bill Whitlock of Jensen.
Below is the response of the KCM transformer from 20Hz to 40Khz. It's very good with the 6072 and as good as the original u47 with the 6922 tube!
T8 Transformer: Higher Output and Brand Quality
For those who hunger for more, the good people at AMI TabFunkenwerk make a transformer that has a ratio that is closer to the u47 BV8 transformer but it fits in a small package. It's called the T8 and is just the ticket to make your FAR 47 Gold sing at 4 to 5 dB more output and therefore have more sensitivity.
The 47 Gold Special Edition
With the help of our Dremel tool, we have fitted the Pelsuo BV8HR ("Historical Replica") transformer into the 47 Gold. This brings the "Gold" into close proximity to the classic u47.
To properly drive this BIG IRON, high ratio (6.5:1) transformer we use our parallel 6922, LED biased preamp circuit which has a very low output impedance.
The combination of the K47 capsule, the 6922 preamp and the BV8 transformer make a mic that makes you say Ahhhh. That's the sound I was looking for.
Three Great Models
47 Gold BASIC, with RK47 capsule and KCM transformer
47 Gold Standard, with Peluso K47 and the T8 transformer
47 Gold Special Edition, with Peluso K47 ultra low distortion and low noise 6922 tube and BV8HR transformer.
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