Apex 430 cap replacements

antichef

pornk rock
I'm an enthusiastic and electronics-skill-free mic-modding newb -- so far, I've removed a mic transformer, replaced several mic transformers, and tensioned three ribbons. Now, I think I'm ready to move on to a condenser, even though I'm really not. I wound up with an Apex 430 that is essentially disposable, and I've been hoping to learn on it. I believe this is one of the "Shanghai" mics that is suitable for the "Dorsey mod", and information abounds, but I have yet to find a complete guide (the online reproductions of the article have important bits missing, and the reprints of the magazine seem unobtainable.

But no matter - I don't really want to do the Dorsey mod (or, I'm not up to it, in any event), I just want to replace some caps. I've found lots of info here, but no circuit board has looked just like mine, so here's my post with pictures.

I bought some caps at a local electronics store, getting several different types that I was fairly sure were not tantalum or ceramic, which my research indicates are bad to use for the signal path. I got a bunch at the .001uF value, and another set with a 1uF value. Here's the first group (actually, the orange one of these came out of the Apex 430):

caps.jpg


can anyone say what type of caps these are? The 1uF set (not pictured), is largely the same, but I have a 1uF "foil" cap - is that good for anything?

Next, here's the circuit boards from the mic. As I hinted, I couldn't wait and already switched out a cap (C5) from the orange one above to the green-ish one above:

board1.jpg


and here's the other board (other side of the mic):

board2.jpg


and lastly, here's the back of the first board, with the C2 cap (I think) - is the "capsule coupler" cap, and does it look like a polystyrene one? (I had set out to change this one, until I saw it):

board1back.jpg


for good measure, here's the schematic, that I got from the Apex website:

schematic.png


so: 1) can/should I use any of those caps in the picture? 2) If so, where should they go? 3) if not, is it because they're the wrong value, or the wrong type, or both?

I like the change from the orange one to the green one -- seemed to take some of the harshness of the HF out. But again, I really have no idea what I'm doing.
 

PhilGood

Juice box hero
EDIT: D'oh! Guess my internet is slow tonight! It took me a while to get pics!

Doesn't look like you could do much to me besides maybe removing C14 & C15. I believe those are just RF caps, but you may need them.
 

antichef

pornk rock
If the pics are coming in slow, it's probably my server that they're hosted on -- very busy tonight for some reason (not those pics).

I'll try pulling those out -- thanks! I got the mic used -- does it look like someone already changed out the caps?
 

PhilGood

Juice box hero
If the pics are coming in slow, it's probably my server that they're hosted on -- very busy tonight for some reason (not those pics).

I'll try pulling those out -- thanks! I got the mic used -- does it look like someone already changed out the caps?

No, it looks like they used some pretty good ones in the first place. C2 on the back was probably replaced. They don't use polystyrene stock usually. I think you probably did a good thing by replacing C5, but I don't know what was there before. The tantaliums on the back side are all for phantom power.

How does it sound by itself? You could probably replace the capsule with something nicer and make a big improvement.
 

PhilGood

Juice box hero
I wonder if these have those standard 2:1 transformers. Cinemag makes a 4:1 that I don't think would be too outside the rules for use. Might even improve the low end.

Sowter has a great paragraph on their website about mic/line pres and transformers, and it made me think about mic transformers and if it applies.

Maybe mshilarious, Marik, Gus or someone with serious background could comment on the idea. The paragraph is as follows:

"WHY 600 OHMS? There is a lot of history and some confusion here. The ideal impedance for driving an audio line is zero ohms and the ideal input impedance for connecting to it is infinity. The actual wire does not need to have any particular "characteristic impedance" nor does it need to be terminated like radio frequency cable. 600 ohms is a nominal value used to describe an environment.

In summary it could be said that a line driver should have an impedance no more than 600 ohms and a receiver should have an impedance no less than 600 ohms. If both driver and receiver were both 600 ohms however, half the signal would be lost in the driver. In a small system the designer may try to make the receiver impedance a factor of 5 greater than the driver but in a large or very noisy environment a factor of 10 might be attempted."

I don't know how apt it is to apply this to mics, since we're talking line level, but I think it's important to examine it since we are talking low impedance audio output.

Discuss?
 

antichef

pornk rock
What's the value of C08? (.47uF?) I think that's part of the feedback.
I think you're right -- looks like a typo on the schematic, the "C" and the "8" are separated, and one looks handwritten, but the value there is .47uF. The actual cap is one of those mustard-colored blobs, and has tiny numbers: 475 25+

To tell you the truth, I hadn't listened to the mic too much - I got it for real cheap, ($30 for it and an Art toob preamp) and threw it into the "to-be-modded-and-perhaps-accidentally-destroyed" category in my mind. Now that I listen to it, it's not something I'd use very much -- somewhat raspy highs and thin lows, but it doesn't have that muffled boxiness that I've come to associate with my least favorite cheap condensers. I have a couple other candidates that I can take up the cause with.

Here's the transformer:

tranny.jpg


a little beefier-looking than I expected, but I have no idea how to tell the ratio without actually measuring it, which is something still outside my skillset.

Wish I could say something intelligent on the subject of impedance here. I do use a variable impedance preamp, and so if I wound up with a decent sounding mic with a weird impedance, I bet I could still use it.

I guess I'll move this mic into the "to-be-modded-with-capsule-and-hopefully-saved" category, and revisit it when my skillset has broadened. I'll have a look at my MXL 990 - I got that new, and it sounds muffled and boxy :)
 

antichef

pornk rock
One other question that was bugging me -- you'll notice the blue plastic toggle switch on the first circuit board picture -- it's totally enclosed by the housing, but appears to be functional. In the schematic, left hand side, you'll see two switches -- S1, and S2. S2 is clearly a cardioid/omni switch, and my mic doesn't have that (I think the Apex 420, which shares the schematic, does), so I'm thinking the switch we see is S1 -- would that be a bass rolloff? That's what I think it is, based on messing with it.
 

ausrock

Well-known member
The 420 and 430 are apparently internally identical, it's just in the 430, the switch is hidden. Here's a couple of alternate pics...........;). I notice in your pics, they've conveniantly put a QC sticker over the switch operation symbols.

:cool:
 

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PhilGood

Juice box hero
One other question that was bugging me -- you'll notice the blue plastic toggle switch on the first circuit board picture -- it's totally enclosed by the housing, but appears to be functional. In the schematic, left hand side, you'll see two switches -- S1, and S2. S2 is clearly a cardioid/omni switch, and my mic doesn't have that (I think the Apex 420, which shares the schematic, does), so I'm thinking the switch we see is S1 -- would that be a bass rolloff? That's what I think it is, based on messing with it.

Yup. Lift the sticker and you'll see the markings.
 

Gus

New member
Parts look OK.
R11, C10 interesting

I was told some of the early MXL 2001s came with better caps I have not checked that yet.

The transformer bobbin looks different than some china transformers I have seen, note the tabs to help hold the lams together. The lams look more refective and the tape is not yellow like other china transformers I have seen.

I would use it stock before changing anything. Take notes what you like or don't like.
 
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