Apex 460 Mod - FAIL

P

pureaudiouk

New member
Hi.

Just modded the 460 with a PK47 kit from Canadian Audio Distributors. (without the transformer, cos I've ordered a cinemag which has not arrived yet)

The kit seemed great.

I tested all my connections to see if they functioned without shorting. They all seemed to. I did the following

1) - Wired a PK47 capsule in.
2) - Changed C8 with a philips .68 Mylar cap
3) - Changed the tube

now, the mic is dead. D'oh!!

the tube warms up and glows a lovely orange. But no sound at all.

When I was soldering, I knocked out the capsule ground, which I though had come from c10. So i soldered it back on.. Would this cause a problem?

Are there any other ideas people have. I've looked and looked and I can't see any loose wires!!

Does the polarity of the Capsule matter? ie - if I wired the wrong side of the mic up, would that make it fail??

ack!

Paul.
 
You have to be very careful with the wires in the Apex. Some are very stiff and you can get a broken connection that doesn't LOOK like a broken connection. You also have to be careful with soldering in there. Excess solder can touch another pad and short it out. Another VERY important thing is to make sure excess flux is cleaned off the boards. Its a high impedance circuit and flux can cause problems.

The polarity does matter. It's a multi pattern mic and you have 3 surfaces of a capacitor as the transducer. Check the wires and make sure they are soldered according to the schematic.

Change tubes first to see if it isn't just the tube. If you can't figure it out, let me know and I could probably fix it for you.
 
Looking at the schematic, yes, putting the mic ground at C10 would be bad. That's on the opposite side of the transformer. There should be an open ground near the top of the board and the front diaphragm lead should be soldered to that. The backplates should be soldered to the standoff junction of C4 and R10, and the rear diaphragm should be soldered to the junction of C5 and R9.

That's probably the cause.
 
ah! I actually meant the ground is on R10, not C10.

when you say the stand off junction. Does it matter if I connect on the front or the back of the PCB (there are junctions either side)

Electronics is definitely not my strong point :) but it doesn't make sense that it'll make a difference...

I'll switch the pk47 wires around and switch the tube back and get back to you...

thanks for your response!!!
 
First off, what do you mean by "ground" off R10? Do you mean the backplates?

R10 is nowhere near the ground. R10 leads to the B+ voltage from the power supply. The front diaphragm lead should be soldered to ground. You can solder to either side of the standoff. That's what its designed for. It has teflon or ceramic as the insulator to keep stray capacitances from running through the PCB.
 
you're right of course.. The backplates. I Don't know why I thought it was ground.

ok. So I have all wiring where it should be for the Capsule. I assumed the capsule didn't really matter if it was wired front or back. So I wired it however it appeared in my hand. Is that an error?
 
So long as the backplate connection is correct the diaphragms are interchangeable. It just won't be the front of the mic if you swap them.
 
ok. So..

changing tubes makes no difference (the old tube was working before).

The tube is amplifying. ie- I get hum etc. and I get the satisfying clink when the tube is tapped. So I'm guessing it must be some short somewhere?

Should I get a multimeter and try to find a short? if so... what's the best way to do this? ie- what setting should I set it to? I had it on the beep setting (ie- find a circuit) but it wouldn't detect stuff over a resistor/cap.

(I told you my electronics skills are terrible)
 
Since you're a bit confused, could you take pictures of both sides of the mic and post them? I think we might be able to spot the potential trouble spot if we could see what you've done.

Craig
pureaudiouk said:
ok. So..

changing tubes makes no difference (the old tube was working before).

The tube is amplifying. ie- I get hum etc. and I get the satisfying clink when the tube is tapped. So I'm guessing it must be some short somewhere?

Should I get a multimeter and try to find a short? if so... what's the best way to do this? ie- what setting should I set it to? I had it on the beep setting (ie- find a circuit) but it wouldn't detect stuff over a resistor/cap.

(I told you my electronics skills are terrible)
Click to expand...
 
pureaudiouk said:
ok. So..

changing tubes makes no difference (the old tube was working before).

The tube is amplifying. ie- I get hum etc. and I get the satisfying clink when the tube is tapped. So I'm guessing it must be some short somewhere?

Should I get a multimeter and try to find a short? if so... what's the best way to do this? ie- what setting should I set it to? I had it on the beep setting (ie- find a circuit) but it wouldn't detect stuff over a resistor/cap.

(I told you my electronics skills are terrible)
Click to expand...

Check the brass eyelets on the side of the backplate. Make sure its not touching any other metal. If you're running it through the mount, make sure the screw is long enough to make contact with the backplate.
 
Thank the lord!

After following your instructions, I realised that the screw holding the connector for the backplate "may" not have been screwed tightly enough.

I noticed that without the head basket on, the mic seemed to work, though only with TONS of noise. As soon as the head went on.. Poof. Nothing. So after a bit of testing I realised that the basket was too small for the oversized capsule, so I ripped a layer of mesh out and... Voila! pimped Apex 460.

Thank you so much for all your help. these kind of online communities are rarely as accepting, or as useful as you guys.

You've made me Phil/feel Good!

I'm going to mess around with my capsule alignment (ie - It is slightly off centre.. ) but that should just be a cradle ammendment..

Paul.
 
You're welcome! Check back if you want. I have newer suggestions on how to improve on the standard web "Apex 460" mod. There are some things most folks aren't doing that makes a difference!
 
thanks Phil.

After doing some rooting around, I think I've got a list of recommended further upgrades...

Starting with the basics (as included with a mod kit)

1) new capsule - Peluso sound good, CK-12? (or in my case the PK47)
2) new transformer - Cinemag 2480 works great
3) C8 - Replace .68 1uf Mylar
4) Replace tube with 6072a
-----

Other mods.

4) C6 - Replace with same spec - Blackgate/Nichicon
5) C1, C2 - Replace (with what?)
6) Cathode follower removal - Is this now recommended or not?
7) short tube pins 6,7+8 together and ground. (Marik Mod)

DO NOT REMOVE C6 + C7

Does this pretty much cover it? I thought it would be useful to compile these in one list..
 
Besides what you've already listed:

Replace R3 and R4 with either 470k ohm or 500k ohm.

Replace C4 with .01uF (at least 250v) polystyrene

Replace C5 with 4700pF Polystyrene or good film cap.

Remove C3

Remove C9, C10

Remove R1 and jumper

Remove R5 and move wire to other pad or jumper it.

Replace R6 and R10 with low noise 250M ohm.

Replace C6 with Black Gate or Nichicon Muse 100uF 16v




Someone else posted some of these on another forum, but when I was going over the schematic for the C12 I noticed a lot of similarities. I was in agreement that this puts the circuit much closer to a C12 and sounds really good!

Going this far is not for the faint of heart! Do it a step at a time so you can correct if you make a mistake along the way.
 
C8 can be anywhere from .47 down to 1.5uF. I'm at the point where I only use mylar (polyester) if nothing else suitable for audio is available. Polypropylene is better, Paper in oil if it will fit in the space I'm working on.

The sound with those is much more defined and musical.

Stay away from carbon composite resistors and the noise will be better.
 
blimey. that's quite a list.

No wonder you painted over Apex on your mic. It's nothing like the original.

Do you know if any of the mods are interdependent? ie- they only make an effect if made in combination.
 
No, each one has its own effect on the sound, each one an improvement to it own. I find that changing capacitors has a significant effect. Things like increasing the B+ drain resistors (R3,R4) helped quite a bit as did upping C4 to a .01uF. The quality of caps is quite important. The fewer the resistors also. The purest sounding mics to me have the least components. The most significant changes to be made are the capsule and transformer. Once you get it there the rest just gets it closer and closer to "world class". I really don't know if it could ever be considered that, but close. I think the only real improvements beyond the available mods would be to wire it all point-to-point.
 
Another thing going lately is that Marik and I have been exchanging emails regarding the Cinemag 2480. It's like the original T14/1 AKG transformer and although that worked pretty well in the C12 and Ela M series its rather small and doesn't leave much dynamic room and can be pretty lifeless. The first Ela M had a larger transformer and had a bigger sound. He has been making transformers for a while now and may have a pretty good larger core transformer in the works with really good laminations. Probably could breathe even more life into the mic. Probably cost a pretty penny, but I'm sure more than worth it in sound.

We'll see what he comes up with.
 
Holy MACKEREL!!!

just tried this for the first time in a session...

BEAUTIFUL! The vox just "sits" in the mix like a high end mic should.

Comparing to a Violet design globe, 414 and neumann... this not just holds it's own, but spanks them on the vocal I was recording..

I honestly was not expecting the capsule/mods to sound this good. I may have to order another one...
 
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