The FAR 460 Mini-Mod
(The APEX dirty little secret)
Testimonial on the FAR 460 Mini-mod
Oh, WOW! That's more like it! This mic really sounds amazing, Brian. You were right: I'm completely happy with this mic, plus some! This once lifeless, spineless, cheap-sounding mic now sounds brilliant, creamy, and --dare I say--could hold it's own on some much more expensive well-known name brand mics in my collection. Plus, not only did you work on the mics, you also took the time to put together the documentation to explain what you did and demonstrate the results. Sheesh. This thing hurts it sounds so good.
Paul Nixon, Announce/Producer, Austin Texas
Hear Paul tell the story his way with his FAR 460 Mini-mod.
Click the logo to hear the Mini-mod preamp in action using a 32mm capsule and the Apex 460 stock transformer
The APEX 460 microphone is one of the favourites among the do-it-yourself microphone modding set. The reasons are simple. It's a simple mechanical package. All parts are accessible. It's mechanically strong and it's well documented, described and discussed ad nauseum on the internet.
Interestingly enough it is also used by a number of professional microphone manufacturers as the platform for their products. Most notable in the group are Peluso, Telefunken, Avantone, Advanced Audio and many others.
And of course yours truly provides a couple of mics based on the APEX 460 as well.
The number of problems that one can read about are interesting. Below are a few that I have read on blogs.
- The mic sounds "esssshy"
- The capsule has at 3Khz peak
- The mic is too sibilant
- The cathode follower circuit sounds terrible
- The transformer is "shrill"
A Solution for the Home Studio
So we set out on a research path that moved in a direction that no one else seemed to pursue. The FAR 460 Minimod is a "Do-it-Yourself" project that gives the most improved sound for lowest cost.
Questions:
- What is really wrong with the APEX 460?
- What are the simple changes one can make to an APEX 460 that make it sound "good"?
Assumptions:
- The capsule is not damaged (wrinkled diagphragm)
- The capsule has a typical 32mm capsule response
"A" is for APEX, "S" is for Sibilant
To help us determine where to start we decided to accummulate some facts that we have measured that might help explain the things people complain about.
- The mic sounds "esssshy"
- The capsule has at 3Khz peak
- The mic is too sibilant
A large number of complaints are around sibilance, lack of warmth and "esshy" sound. By "esshy" we mean the sound of the letter "S" is distorted and does not sound natural.
Well it is well known that the 32mm Chinese capsule has a rising response in the high end. It varies from capsule to capsule but tends to be a 6 to 7dB boost centred at about 11 Khz. By itself this should NOT cause "distorted 'S'" sounds.
We believe it is more complicated than that. The stock preamp is actually making things worse.
There are two incorrect value caps (C9/C10) in the 460 and many other low end mics that are supposed to reduce RF interference that could get into the mic through mic cable. Unfortunately these caps are .1 uF when they should be no more than .001 uF! This causes the nasty audio side-effect of boosting the high end 2 dB at 20Khz to 25Khz as you see below.
The graphs below are made by injecting a transformer isolated signal (Hammond 850G) into the mic preamp. The capsule is effectively short circuited by the 150 ohm output impedance of the transformer and the coupling cap.
Oh and if you change the tube to a 6072 the boost goes 1 dB higher! :-)
Note that with the 6072 the gain is 2dB less NOT 6dB less as many believe.
And to make matters worse the distortion caused by poor capacitors and starving the tube of current is really very bad and guess what? The distortion peaks at 11Khz too!
Put all that together and you have your smoking "esh".
When you mod the mic properly you can see the distortion drops enormously. In the graph above both mics are outputting the same signal level. The 6072 needs 2 dB more input due to the gain difference from 12AX7B.
And remember, the transformer was not changed for the graphs above. These are just circuit improvements.
The Cathode Follower Sounds Bad?
Well this one is a weird one. The Cathode follower tube circuit has the lowest distortion of any tube amplifer configuration. It does very little to the signal except allow it to drive a lower impedance load. The cathode follower does so little to the signal that some people don't understand why you would ever need it!
In some ways it can be thought of as an electronic stepdown transformer that has very little voltage loss but still gives you the current boost. (A weird concept but pretty accurate) The output signal voltage is a little lower than the input and the phase remains the same.
But just to put things in perspective, the cathode follower circuit is the ONLY circuit in the famous Sony C 37 microphone and the AKG c12A.
The transformer is "Shrill"
In fact we have seen above that the Stock 460 preamp is "shrill" but it is actually caused by the combination of two wrong caps and the transformer resonating together.
What happens when you remove those two bad caps? You get an amplifier that passes audio almost perfectly.
The stock circuit (CCDA) with the stock transformer in the 460 is flat within .1 dB from 30Hz to 30Khz and it's only down .5dB at 40Khz!
One BIG Wild Card
As it turns out the Chinese 32mm capsules come with lots of variation. One common problem that I have seen is a poor response below 300Hz. (even in expensive mics from manufacturers who shall remain nameless) This cannot be fixed.
This is the actual response of a client's 460 capsule
The only solution for that is get a good 32mm capsule. The Peluso CEK89 is one such product. But you can even buy capsules from E-Bay and try them until you get a good one.
CEK89 capsule
The FAR 460 Minimod
So what is the minimum you can do to make this mic. sound good? Turns out it's simple.
1. Remove C9 and C10 to remove the 25Khz peak resonance in the high end.
2. Change the caps in the signal path: Polystyrene input and 1uF polypropylene output (C8)
3. Change the tube to a 6072 or a very good 12AT7
4. Add a tiny EQ cap like that found in the ELA m251 design, between the Anode pin of the 1st stage tube and ground. ( I like 200pF myself but it depends on your capsule, sometimes 330pF is a better sound)
Optional:
5. Change the cathode bypass cap from 100uF to 22uF to reduce low frequency rumble and distortion.
6. Change the cathode bias resistor to 1.8K to increase plate current in both tubes and improve biasing on the 2nd stage.
7. Remove the two inner layers of mesh from the headbasket
8. Optional : Add a *220K damping resistor to the output circuit across the transformer primary coil. (after the capacitor) This resistor makes a cleaner low end by damping the remaining transformer/capacitor resonance.
* We had published this as 47K which is correct for the BV11P transformer. For the APEX transformer it should be 220K.
Results
Below is the ACTUAL response of a FAR 460 Minimod measured at .5 metres. The response is showing 60Hz to 15Khz. After 15K the response falls slowly and smoothly.
APEX 460 Mini-mod sound sample
Chinese 32mm capsule and someone fooling around in our studio
A Mini-mod Done by a Customer
Richard Byrd sent me this email after having purchased and installed a mini-mod kit. He also installed an RK12 capsule to round out the modification. Because he did not install the EQ capacitor, this combination is similar to our FAR 12 Basic mic, except that it does not have fixed voltage bias.
"Loved your page super helpful. I bought your fox sg upgrade and did the 460 mod here are my results. I did not use the elam capacitor, this is just straight into the computer from a focusrite saffire pro dsp 24 into reaper. I have never made a mic before or done a mod but i can promise you I will only be building my mics from now on.... this took me a total of 4 hours to do and just a sodering iron. the first take is stock then the second is your mod with the rk12 capsule. its just so much creamier. so professional. "
Here are the before (1st sentence) and after (2nd sentence) results in one file:
If you cannot hear the sound, your computer or browser doesn't support the sound format. Or, you have your speakers turned off :)
Conclusion
So when all is said and done what's the result. Well it turns out that the Chinese APEX 460 has all the goods to create a great sounding microphone. The capsule has it's own characteristic sound, but when you "tame" it with the right circuit you get a mic that sounds surprisingly good!
Do It Yourself MiniMod Kit
To help all the do-it-yourselfers on a budget, we have put together a kit and with schematic diagram , photos, instructions, a new tube and parts. It only costs $95 USD and improves the APEX 460 amazingly in our opinion while keeping the expensive parts un-changed.
To order your 460 MiniMod Kit contact us at:
(If you would prefer us to do it for you just ask!)
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