MXL 603s... crappy capsule?

I have been playing with a MXL 603s, trying to get it to sound good.... or at least better. I rebuilt the circuit, and that was somewhat of an improvement, but it seems like the capsule isn't good at all. I hear filtering that i think is caused by the rather thick rim around the edge of the diaphragm. Also, it seems like the acoustic resistance network is causing some weird phasing. Making it an omni is somewhat of an improvement... Anyone else played with this capsule? I know I am probably just wasting my time on a crappy capsule... :?

That is not what I have experienced. The capsule is actually pretty good. Supposedly it is a KM84 knock off. What do you think is wrong with yours?
I played with MXL603 a lot. To make it sound more or less presentable you should change all the signal caps for good quality polystyrenes, or polypropilenes. One from capsule--use around 1000pf polystyrene.
If you want to get a better bass, you should use for signal caps from FET (two 0.22Mf) at least 1Mf, and finding right size films to fit might be tricky. If you absolutely cannot find them, try 2.2Mf small Black Gates there.
Also, I like bypassing DC converter, but you get some signal loss.

If you make an omni out of it, IMO it doesn't work right, as omnies require much higher tuning resonance frequencies (to the top of the band)than cardioids. Since this capsule was designed as a cardioid, you get a HF roll off, when seal back chamber. Since this capsule has very simple, but smart design, you can easily take it apart and reskin it with higher tension mylar. Just don't bust it--use another ring, as a mylar frame.

I can't get my two modded 603's back from a friends studio. Like Marik posted change the input ceramic to a 1000pf polystyrene, the two .22uf to the output transistors to good films and the output RF caps .022ufs to .01uf good films. Its the S circuit IMO there is nothing wrong with the stock circuit it just needs some parts upgraded.

Have FUN finding good films to fit.

I have two nady cm90s almost the same circuit but 3 micron not 6 micron like the 603. A modded 603 is a very good SD microphone. You need to be very careful working on them you need to keep the parts very clean.

FWIW some people like the modded 603s better than 184s

I spend more time cleaning up after the soldering then the changing of the parts.

Thanks for the response guys... I don't know what it is that I am hearing, but it seems to me that as you get off axis, the freq response starts to get odd... There seems to be a "bump" where this happens... Unfortunately I have destroyed the capsule in fiddling with it, unless i rebuild the acoustic resistance network.... it is now an omni. luckily they are cheap. Unfortunatley as well, I spent some time rebuilding the circuit with a simpler schoeps design so that i could fit some larger caps in there... :sad: Any thoughts on saving it, i.e. is reskinning practical? If not I guess it'll just go in the talkback mic bin. Thanks again guys... Still learnin.

I don't know what it is that I am hearing, but it seems to me that as you get off axis, the freq response starts to get odd...

Click to expand...

It is a wide cardioid mic, but even omnies have "srtrange" off-axis things.

Any thoughts on saving it, i.e. is reskinning practical?

Click to expand...

Well, if it sounds good to you, leave it as it is. If you want to try to reskin, find a similar to original ring, unwound a cap as a film donor. You will need some kind of jig--a larger ring would be probably OK. Glue (or clamp) the mylar on the jig and heat the mylar, so all the shrinks will disappear, let it cool down, and repeat the process. Also, the heating will make the mylar more stable in a long run--the process called "cold flaw relaxation", known from mic capsules and electrostatic speakers manufacturing. Tune the mylar to about 8KHz open air--togeher with small back chamber, it will probably give you about 16KHz tuning resonance. Because of diffractions, the capsule should be linear probably up to 20-22KHz. You can also play with different volume of back chamber (make sure the spacer ring is very thin) for different bass response. Also, when sealing back chamber, make sure to leave a tiny hole, called equalization vent, so inside the chamber pressure will be the same as outside one.

Thanks marik... reskinning seems a bit involved for the end product, at least at the moment, perhaps I will find a use for it... Also, whats the best wat to get to the capsule without damaging it? As far as the capsule being a km84 knockoff, it may very well be, though it is quite different... In the km84, there is much less distance between the edge of the casing, and the diaphragm. I think this would contribute to better off axis response...
Too bad I don't have a couple grand for a pair...

Gus, Marik, anyone,

Do you know what the trim pot inside these mics is for?

Stewart

I think it is for adjusting the fet bias point. The s circuit has a 1meg with notes for adjusting the + to drain voltage to a certain value.

[quote author="zebra50"]Gus, Marik, anyone,

Do you know what the trim pot inside these mics is for?

Stewart[/quote]

FET bias.

Hey Gus,

We were writing at the same time. But you were first :thumb:
:guinness:

[quote author="Gus"]...Have FUN finding good films to fit...[/quote]Yep. It's a tight fit just getting those .22's in there.
[quote author="Gus"]...I have two nady cm90s almost the same circuit but 3 micron not 6 micron like the 603...[/quote]How do the Nady 3-microns compare to the MXL 6-microns soundwise? Are the Nadys worth messing with?

Thanks! I have a pair to play with - was going to sell them but will investigate further.
Stewart
:thumb:

The Nadys are cheap they sound ok. they don't have the trim pot otherwise the circuit is very close to the 609s

FWIW

I bought one of those $200 matched pairs of 603s as a beater mic pair, and have decided that these are my current favorite SD mics...as is.

the pair is a really good match two. Inverting the phase on one completely cancels the other out.

To me they sound extremely close to a KM84 on acoustic and mandolin. They are really nice mics, especially for the price. I'd upgrade mine, but I like them just fine as they came. I also use a pair of MC012, and have just ordered a single AKG 451. I think the 603's will get some wear and tear in my studio though.

I may get another one to do he royer mod with. I imagine a tube circuit would sound pretty nice. The 3 micron version (mxl600 - Nady SD) is nothing like the 603s. The capsule is what makes these mics. the 603s' capsule is a very good copy of a KM84...although I am sure they aren't all as good as the other. Originally MXL had some consistency problems, but supposedly since they set up their own Chinese factory they have eliminated the problem. I think they are more selective with their capsules now as well. I hated the original MXLs, but the 603s and the cheapo 990 have blown me away! I hear the V77 and V69 are pretty nice as well, and have heard excellent recording that were made with both.

Shane

I love these microphones. I think stock they are very usable. I have two pair, one for live work and one for the studio. I definately want to try the cap mod!

Thanks for posting this!

I was thinking more about this. What would those who have done the mod say is the biggest difference between the stock 603s and the modded one?

The stock circuit uses ceramic caps. The first cap capsule to input has the biggest effect because of the voltage difference across it Ceramic caps in microphone circuits give a grit to the music. With ceramic caps it almost sounds like more bass is there. The grit is a loss of claritiy to my ears.

Flatpicker and I have had a few phone conversations about this. The cap between the capsule and circuit can have the biggest effect of the parts used in microphones IMO. I intend to try a paper in oil in that place.

In our local store I was able to find 3Mf film cap, which fits perfectly, when lying on bottom of PCB. The bass is much improved, as the sound overall. Here is a pic of the cap, installed into Oktava 012:

http://home.comcast.net/~markfuksman/OktavaCap.bmp

[quote author="b3groover"]I was thinking more about this. What would those who have done the mod say is the biggest difference between the stock 603s and the modded one?[/quote]You have to do it! It really opens up the sound. :thumb:

[quote author="Flatpicker"][quote author="b3groover"]I was thinking more about this. What would those who have done the mod say is the biggest difference between the stock 603s and the modded one?[/quote]You have to do it! It really opens up the sound. :thumb:[/quote]

Are you talking about just replacing the one cap? If so, where can a suitable substitute be found that wille asily fit into the existing enclosure?

Also, what effect will the cap mod have on a matched pair of mics? Is it likely that the mics will no longer patch exactly?

Shane