Apex 420 modifications

[crazydoc]

It's still a little hard to read the schematic, but it looks like C7 is 4700P, which would be 0.0047uF, and C5 is definitely marked 0.47uF on the schematic. C7 passes the high frequencies, and when you switch in C6(?) this would pass the lower frequencies, and I'd expect this to be a larger value. What value is C6(?), the one in series with the switch S4?

Since the supply voltage is rated at 33V, I'd expect that 50V caps would be adequate.

 

[Andybot]

apex 420

Hi Crazeydoc, thanks for the laminate info and part number.

I read the value of C7 as 4700pF as well, in reality the caps C7 and C5 are both
470n which i beleive is 0.47uF.

Looking at the mic I can see that the cap in series with the switch S4 is suppossed to be C8 but this part of the circuit is not actually present , no switch, no capacitor.

The mic I have is obviously a little different to the schematic that apex sent me.


I wonder why this part of the circuit is not present.

Thx, A

 

[crazydoc]

It's the high pass switch, which apparently your mic doesn't have. That's why that cap is 0.47uF, to pass all frequencies. I'd say replace it with a good quality polypropylene of the highest value (0.47 or greater) that you can fit in there, as Marik suggested above, to extend the bass response.

 

[Andybot]

apex 420

Thx Crazeydoc,
they must have redesigned at some point, this mic does have a high pass and
pattern select on it. Some apex mics have turned up with the high pass inside( which is where this switch would be, directly on the circuit board)

Thx for the help, A

 

[Andybot]

apex 420

Hi,
could someone help me work out which way my transformer goes back in, when i took it out it came out before i could mark its position.

The windings read 50 and 150 ohms respectivelly so I guess I need to know if this transformer is stepping the signal up or down, or is it doing something else in this position.

Any help is appreciatted.

Im getting some samples of the laminations sent to me from magnetic metals, they were very helpfull, did not have the exact type but found a suitable replacement for me.

Andybot

 

[Flatpicker]

I guess I need to know if this transformer is stepping the signal up or down, or is it doing something else in this position...

Steps down. 150ohm ---- 50 ohm.

 

[Andybot]

apex 420

Thx Flatpicker.
So am I right in thinking that the transformer is being used to obtain the correct output impedence?

Or something else?

Thx, A

 

[crazydoc]

It converts the unbalanced signal to a balanced one.

 

[Flatpicker]

So am I right in thinking that the transformer is being used to obtain the correct output impedence?...

Yep. Plus what Doc said.

 

[Andybot]

mic mods done

Hi,
i did all the mods, changed out the laminations and replaced some the caps etc
and it does sound better so thx.
One problem im having is hiss at high gain, I compared it to mics with equivalent
noise floors and its certainly noisier than those and a little to noisey right now to use.

So my question is what might be causing this....age, capsule , transistors
i did clean the board carefully of flux checked my joints.

One thing is that where a polystyrene cap was recommended I have a 1000pf polyester in right now, might this cause more noise?

Hope I can solve this as I really quite like the mic on my friends fender princeton
so any help is appreciated.

Thx

 

[BigHighLonesome]

I have the same mic, so I am following along closely here. I dont mind it stock. WHat are people general opinion of this Mic ?

I may make a mod...

 

[Andybot]

mic mods

Hi BHL,
i like the 420 alot and am sure the noise is something that is caused by a fault and not usual to these mics. I dont really have alot of experience with the mic so ill just say I like it.

I did get a apex 435 condenser and changed some caps on it and il like it alot.
I recorded some guitar with it alongside a rode nt5 mic and liked the apex more
which for 45us I thought was amazing.

Ill be using it more soon so ill see how it works out on voice/bass etc.

Thx

 

[Andybot]

mic mods

Oh, forgot the most important thing. It was suggested that I change the laminations in the transformer which I did and it really helped with definition.
If you can I would do it.
A

 

[Flatpicker]

...I compared it to mics with equivalent noise floors and its certainly noisier than those and a little to noisey right now to use.

There is probably still some microscopic moisture around the FET. Open it up and let it sit under a lamp, approx 12" below a 40W bulb for ~12 hours, exposing the FET and circuit board to dry air.

Oh, and I don't recommend using a heat gun unless you want to risk melting your diaphragm!

 

[Andybot]

mic mods

Thx Tim,
i will try out the bulb thing.
I appreciatte all your help.
Andybot

 

[BigHighLonesome]

Is there any easy instructions ro picture to help me relaiminating. I have exprience with making my own effects (hobby) so I have the skills. I just need to know how.

I like the 420 a lot as well. Great bang for the buck value and very versitile.

I LOVE my Rode NT-4 as well, but they are both for different applications.

 

[Andybot]

mic mods

Hi BHL,
the relaminating will be no problem once you have the transformer out, the laminatioms are held in by a wax and you can just carefully pull them out and replace them with the new ones. You do sorta have to commit to the project as you have to get to the transformer to find out the lams you need, size width etc.

If you unscrew the end of the 420 and pull of the body youll see a plain rectangular metal box....the transformer is under there. I used a soldering iron and braid desoldering to remove all the solder where the cover is soldered on and it will then pull out. It will be the same for the transformer but dont do what I did and not mark where everything goes back.

Good luck, just ask.

Andybot

 

[Andybot]

mic mods

Hi,
i tried out the tanning bed but it did not improve the noise any.

I decided that maybe because the mic is older the diagragm may be the problem so I swapped diagragms with another apex which only showed that
the diaphragm was not the problem.

I have no idea where to go from here except to clean up the board.

One thing I noticed that may or may not be the problem is that the switches pop really loudly when I switch them, so I have to mute, what might cause this
and might this add to the noise of the mic.

Thx, A

 

[crazydoc]

I assume you didn't change the FET? Make sure the solder connections are good where you soldered the new caps near it. (I guess you did according to your post .) You could put the original C1 back in to see if this makes any difference. Next I guess would be to change the FET and see if that makes any difference. I can't see what the part # is on the schematic, but probably any 2SK170 type would be OK, at least to see if that made a difference in the noise.

 

[paddyponchero]

Hi,
i tried out the tanning bed but it did not improve the noise any.

I decided that maybe because the mic is older the diagragm may be the problem so I swapped diagragms with another apex which only showed that
the diaphragm was not the problem.

I have no idea where to go from here except to clean up the board.

One thing I noticed that may or may not be the problem is that the switches pop really loudly when I switch them, so I have to mute, what might cause this
and might this add to the noise of the mic.

Thx, A

Check the polarity of that electrolytic, my guess is it's in backwards

EDIT: If it's not that, have a loot at the connections on the transformer again - you mentioned earlier that you forgot the way they went - second guess is that you have one wire from the 'primary' and one from the 'secondary' connected to the mic.