Apex 460 capacitor change?

  • Thread starter Thread starter EdgeGuy
  • Start date Start date
I posted a reply at SF also. C4 is a polystyrene that is mounted to the back of the board in the 460, which is why you don't see it in photos.

The ceramic must have been in very early versions.

Lucio
 
Just an update regarding C6 and C7.

DO NOT remove them!!

After trial and error I found that they are very important to the sound and helping the mic sounding fat and full. Without them the mic sounds hollow.

If at all possible, replace C6 with a Black Gate or Nichicon Muse, but otherwise leave them in or put them back. The mic will sound thin without them.
 
Exactly what I've found too! It almost sounds like a broken toy without them.
 
ok have any of you tryed replaceing the zeners with a 3.3uf 400v cap
 
I just wanted to bump this thread with my own experience. I built one of Lucio's (ish) mics with other ideas from JJ Audio and other posters, myself, etc. I loved it so much I had to build a mate, now I have a pair. I think these are the best sounding and most versatile mics I now own, and I can't wait to put them through their paces.

I used this schematic

Apex460_CEK-12_NEW_schematic_1237x882modbyLTD2Luciofor460onstudioforumscomcathodefollowerdismissedreferencevoltagesrecommendedvaluesandbrand.jpg


with the following changes: C8 .56 uF Axon capacitor from Parts Connexion, transformer Peluso T14/1, polystyrene .001 in C4 I found at Newark, I had to use different brand of resistors in a few places but same values as the schematic, and for C5 I used a polypropylene film capacitor of taiwanese origin from Mouser, I think the brand was CDE. EH 6072a from the Tube Depot tested for low noise / low microphonics, peluso CEK-12. I lowered the PSU voltages using zener diodes of a lower value and replacing R6 to 100K to correct the pattern voltage (described earlier in this thread). I removed all the inner headbasket layers. I also got some much nicer spider mount shockmounts from Acme Distributors / Q-Mic. Model QM-16 but they require some modification to get small enough for the 460 body (bend the metal ring out, saw off the excess, drill a new hole for the thumbwheel screw).

the sound with a panasonic polyester at C1 was good, but, I prefer the openness of the polystyrene cap (which I silicon glued to the pcb as insurance against microphonics). the polyester cap gives a nice subtle rounding of the tone, but, I was going for vibrancy.

the sound with a 1 uF or 1.5 uF C8 was pretty good too but I found it slightly "tubby" on most sources. the lows were outweighing the highs. the .56 tightens things up brilliantly, and, is about what was used in the AKG C12 originally

these cap changes made subtle differences, but that's what this type of thing is all about, so they were significant. The Axon (I also liked Mundorf) C8 cap was no accident either... I had a 1uF CDE polystyrene cap in there and it sounded a lot brighter than the Axon/Mundorf of the same type. Got the idea for these brands from JJ Audio who does a Dutch microphone based on the 460.

thanks to Lucio and everyone in this thread for the inspiration and direction. I just can't believe what I was able to accomplish for $500ish per microphone...incredible! They sound great (amazing) on voice, acoustic guitar, tambourine and shaker, bass amp at a distance in fig 8 or omni (Paul McCartney/Geoff Emerick trick) and that's all I've had the chance to try so far. Can't wait for drum and piano opporunities.

The acoustic guitar sound, for example, is just...classic. Like a Grizzly Bear record or something. That super warm yet realistic "big" kind of sound...nothing like a typical small diaphragm condenser. Vocals are very bright and cutting.

On every source there is just this subtle soft compression sort of sound that makes me think I'm tracking to tape or something. I'm just so floored right now, ok that's enough of a post!

gearandstufnewpedalsBOLLWEVIL020-1.jpg
[/IMG]
 
Last edited:
Thanks Monk ..... Gonna give it a once over.

Was the inner head basket removal a big change?
 
I didn't do a thorough before/after comparison. I just removed the mesh because I wanted it to be as similar to an AKG C12 as possible, a mic that only used a single layer basket. I guess I missed a learning opportunity, oops.

When I build my ELAM 251 style microphone, I will be leaving in some of the inner mesh, since that was part of that mic's sound.

I don't know exactly what sound the extra mesh has, but, I remember someone in this thread earlier saying it makes the mic sound "more U47ish" so I'm guessing it might soften the highs a bit.

With all the mesh removed, at least, this microphone is exceptionally clear sounding.
 
Dave Thomas sells replacement headbaskets for these mics. FYI.
 
I think michael joly does too, reworked to be much less affecting of the sound through removal of the sound-reflecting metal sections, or something like that.

Very cool mods either way, I'm going to be buying a c12 type cap soon for my current 460 project (which already sounds good after lots of circuit mods and a filter cap added to somewhat compensate for the k67 stock capsule). I can't wait - the c12 sound, very very slightly elevated highs and lows but not nearly enough to be considered "scooped" - is my favorite capsule for many things.
 
I think my next move is to try out some Tim Campbell capsules and see if that takes these to the "next level"
 
The Apex 460s I've described earlier (lucio-ish mods, Peluso capsules and transformers, etc) continue to please me greatly in sessions, so I'm going to leave them completely alone; they are perfect. Recently I recorded a female vocal and an acoustic guitar, with fantastic results. I do really want to build a third one though, with Tim Campbell capsule and 251 specs. After that I'm basically a U87 or two away from a world class mic locker, at least regarding LDCs.

I just wanted to write to raise an important point. I've been getting nasty zaps, pops, clips every now and then when recording with these, turns out it's the replacement cable's Neutrik plugs not fitting tightly with the power supply's cheapo chinese panel mount jack. The interruption of the high voltage makes nasty pops when jiggled or wiggled. I don't quite recall but I think these might have happened with the stock cables too, I'll have to check on that.

Temporarily, I have thickened the cable ends using a tricky combination of masking and electrical tapes to get just the right tightness. I have ordered some actual Neutrik panel mount jacks from Redco and hopefully these will be a tight fit with the plugs on my high end cables. That will be the final mods on this pair of mics, unless I get the guts to do the C12ish headbaskets at some point.

If you are getting nasty pops, this is a good probable reason why.
 
Ok, I got the Neutrik panel jacks, and they are very, very secure when the mic cable is inserted. Big improvement! No more nasty zaps and cutting out!

I finally got the chance to try these over the top of a drum set! While the sound is delightfully transparent, the high end is a bit too crisp for me, especially when the drums and cymbals are hit very hard...the sound kind of gets washed out.

Brian Fox at Fox Audio Research has been copying the C24 and ELA M 251 schematics where you attach a small 100 pF cap to the circuit to tame the high end a bit, except he recommends 200-330 pF with the super bright Peluso CEK-12, with 220 pF being his stated favorite value. He was kind enough to tell me all this. I'll attach a snippet of the schematic he sent me where you can see where to place this cap. You can see it in the AKG C-24 schematics, too.

So, I am going to play with caps here to get my mics a little less bright and balance the highs a little better with the mids. I guess I can report back next week after all that's done. You need a high enough voltage cap, I am going to use a 220 pF polystyrene at 600 V.

Just a tip for anyone finding things too bright with the CEK-12. Seriously a tambourine was kind of shredding my ears! Tube mics are so fun.
 

Attachments

Tube microphones are fun! ;)

I've had to switch out a few cheap panel jacks in the past ... took me forever to trace the problem down to them. Also gave away a few of the microphone cables that come with new microphone purchases - same problem.
 
Here's a picture of one of my power supplies with the updated Neutrik jack. The holes didn't line up with the old jack, so it's slanted a bit. Perfectly secure, however.

I also have spent the past evening and morning hunting down a faint 60 cycle hum that was driving me nuts. It turns out that when I lift the ground to pin 1 of the XLR on ONE only when BOTH are plugged in, that kills the hum and everything is perfectly silent. It also has to be one in particular, and not the other. I wish I understood why, but, at least there's a solution. Lifting the ground on both of them makes the buzz worse.

So anyway, both of my power supplies now also have a ground lift switch for the XLR output connector. Maybe someone else might find this handy? It was a very quiet buzz, maybe -65 or -70 dB, but I could hear it with the gain cranked up a lot on my preamps or speaker volume.
 

Attachments

  • GND 001.webp
    GND 001.webp
    722.8 KB · Views: 197
Yes, the 220 pF polystyrene caps made this mic "the shit" in my estimation. Immediately threw it into more of a classic, vintage, "warm" kind of tonality, better balance of lows and mids compared to the high range. Back to back listening to my new clips and "In Rainbows" (where you can see picture of a pair of C12s in use) are proving favorable. I'm not going to share all of my embarrassing tests, but you can hear a few before and afters here DIY "C-12"ish on drums, e604 vs 57 on amp - Gearslutz.com. I am liking it a lot on drum overheads now, probably the best I've heard out of what I own, and I just did a figure-8 vocal with acoustic guitar capture that worked pretty well also.
 
It never ends! I don't know if anyone in this thread has mentioned this specific tweak, but, the AKG C12 was fixed bias or so, where the ELA M 251 was cathode biased, like the Apex 460, with a resistor/bypass capacitor combination, using the typical "common cathode" circuit which I guess is mistakenly referred to sometimes as "plate follower." Which is what you achieve when you rewire the tube socket as described in this thread to remove the cathode follower stage.

Anyway, I wanted to get my mics sounding more C12-ish, so I read around and there's two ways to do it, you can use one of the unused pins, 4 or 7, in the cable to provide a negative voltage from the power supply, which requires cutting tracks and modifying the power supply, JJ Audio Mics uses this method, I have not tried it. I used Brian Fox, from Fox Audio Research, his method of using a diode to control the cathode bias.

You can simply wire up two 1N914 or 1N4148 (these days these are identical, just old names still floating around) in series, with the anodes of the diodes facing ground, and the stripe (cathode) of the diodes facing the tube cathode. This is in place of C6/R7/C7 remove all of those components first. Something about the way diodes conduct gives a fixed bias. You can also use an IR-LED (infrared LED) for the same purpose, Brian Fox claims a slightly softer sound, I'll be trying that next week. Small signal diodes and LEDs are not noisy like Zener diodes, so you don't need to use a bypass capacitor. And in fact, that makes it closer in practice to the C12 schematic. You lose several decibels of output this way, but, it's not a significant loss, just something to be aware of. I haven't experimented with adding back the bypass capacitor to increase gain, because I love the way it sounds now.

With my mic next to its mate, identically built, but with one converted to this "fixed bias," the sound is greatly changed. The cathode bias mic is thicker sounding, heavier in the low end, and sharper in the highs. The "fixed bias" (diode biased) mic is cleaner, cooler, airier sounding with a bit of a scoop. Amazingly like what I guess some of the differences would be between a 251 and a C12! I am convinced that this is a big part of those mics' difference, among other differences documented here: C12 v. ELA-M251 -- Differences?

The forward voltage of the diode(s) in question is I think the important thing? Somehow 1.5V of voltage drop average, or so, using the data sheet numbers, creates 1.1V on the grid as I measure with my multimeter, which is what you want, which is what the AKG schematic shows.

This is an extremely easy component swap and I would absolutely recommend to give it a shot in your mic and see which direction you want to take it in.

As an added bonus this clears up some physical space for me to cram in my Russian Paper in Oil caps that are coming in the mail for C8...

Think I'm nearing a stopping point with these! And looking forward to some actual recording use.
 
You must log in or register to reply here.
Back
Top