MXL 603s... crappy capsule?

[Category 5]

[quote author="dasbin"]Someone on another forum mentioned that bypassing the DC/DC converter in this mic will lead to a clearer sound. Any comments on this? And if you recommend it... well.... how do you go about doing this?

Thanks for putting up all this detailed info guys, I'm going to be modding my stereo pair with new caps soon!
Also I should note that I've had trouble in the past getting these mics open. The screws in the body are HELLISHLY tight on mine. Jewler's screwdrivers didn't give me enough torque so I tried some different slightly larger screwdrivers, which didn't catch and pretty much flattened the heads of the screws Guess I'm drilling them out...[/quote]

My 603s dont have the screws, the body screws off itself after you remove the capsule.

If you have the older ones, or the mxl600 the screws in the body don;t work in the conventional way. To remove the bosy you turn the screws IN instead of out and then the sleeve slips off. to put it back on you line up the holes with the screws and back them out until they are tight. This is the opposite of how normal screws work.

Shane

 

[Marik]

Today I put into 603 a 6111 tube, wired as a direct coupled CF. The output trafo is a 1:10.5 Cinemag 2840, which is just the right size to fit the body. As I thought and said before, the capsule is actully very very good and I like the mic.

 

[Category 5]

[quote author="Marik"]Today I put into 603 a 6111 tube, wired as a direct coupled CF. The output trafo is a 1:10.5 Cinemag 2840, which is just the right size to fit the body. As I thought and said before, the capsule is actully very very good and I like the mic.[/quote]

Yes Marik! I was thinking of using Royer's mod to do this. Can you show us pictures? With the Royer circuit you have to keep the transformer in the power supply. How about wih yours?!


Shane

 

[rafafredd]

[quote author="Marik"]Today I put into 603 a 6111 tube, wired as a direct coupled CF. [/quote]

What do you mean by "direct coupled CF"?

As I understand you take the signal from the cathode directly into the transformer primary, without a cap.

But if it´s true, you have DC current on the transformer primary windings, and with a nickel alloy small mic transformer this would be a problem.

So, what´s that all about?

 

[b3groover]

[quote author="Marik"]Today I put into 603 a 6111 tube, wired as a direct coupled CF. The output trafo is a 1:10.5 Cinemag 2840, which is just the right size to fit the body. As I thought and said before, the capsule is actully very very good and I like the mic.[/quote]

Details, please!!!

 

[Marik]

Yes Marik! I was thinking of using Royer's mod to do this. Can you show us pictures? With the Royer circuit you have to keep the transformer in the power supply. How about wih yours?!

First of all, you don't have to keep it in PSU. The reason is a trafo's size.

What do you mean by "direct coupled CF"?

As I understand you take the signal from the cathode directly into the transformer primary, without a cap.

But if it´s true, you have DC current on the transformer primary windings, and with a nickel alloy small mic transformer this would be a problem.

Rafael,

Direct coupled CF is one, where first stage is an anode follower, followed by CF, and there is no coupling cap between these two stages, but of course, there is a cap between CF and trafo.

Details, please!!!

Let me tweek it and play with different component values for a few days, and then I will post it.

 

[zebra50]

Sounds intriguing, Marik.

6111? Sub-mini twin triode, and neither rare nor expensive - same price as 5840, I think.

Presumably 1st stage for gain, second as buffer/impedence converter.

10:1 is a lot higher ratio than I've used in my CF mics (2:1), which are based on the 'royer' CF article. I've had good experience with the cathode followers actually - they sound pretty good to my ears. In theory 2:1 should be fine for z-matching to a 'normal' (circa 2kohms) mic pre input - but I think you have another idea about this :wink:

the output trafo is a 1:10.5 Cinemag 2840, which is just the right size to fit the body.

Now I'm listening! Small good trannies would be very welcome.

Keep us posted - I'm trying 10:1's tomorrow......

[

 

[bradzatitagain]

6111 tight element spacing could cause microphonics. Shield might help, Leeds Electronics has shields for sub-minis, and sockets too, believe it or not. Anyone ever tried 5703WB medium mu triode? Charcteristics are slightly different than 5703, which is high mu, but it seems to be in plentiful supply and relatively inexpensive. I bet nuvistors would fit in this mic body too, 6cw4, 7586, et al. Tricky finding sockets. Did GUs say, at one time, this is the same capsule as a Nady CM90? On eggshells here, not making claims, just trying to recall...

 

[Gus]

cm90 is 3 micron

 

[rafafredd]

[quote author="Marik"]
Rafael,

Direct coupled CF is one, where first stage is an anode follower, followed by CF, and there is no coupling cap between these two stages, but of course, there is a cap between CF and trafo.
[/quote]

Thanks, Marik.

It´s just that I remenber you once talking about a CF with the output transformer inside the cathode circuit, with no blocking cap, and a current source, if I remenber right...

I got very curious about it, and I´m still is. Maybe it´s a subject for a new thread???

 

[Marik]

[quote author="bradzatitagain"]6111 tight element spacing could cause microphonics. Shield might help, Leeds Electronics has shields for sub-minis, and sockets too, believe it or not. Anyone ever tried 5703WB medium mu triode? Charcteristics are slightly different than 5703, which is high mu, but it seems to be in plentiful supply and relatively inexpensive. [/quote]

No. I did not encounter any microphonics. In fact it is a very rigid construction tube. Enough to say its body temerature can go up to 200C, and its cathode to heater insulation is 200V. This is the very tube Neumann uses in M149. I don't have 5703, but have a 6021. The reason I chosed 6111 over 6021 is that it is a lower mu tube, so in my mind it would work better with smaller sized core output trafo.

I bet nuvistors would fit in this mic body too, 6cw4, 7586, et al. Tricky finding sockets.

Were you talking about 6111 microphonics? :wink:
Also, in this design I wanted to try a direct coupled CF, so twin triode would be the way to do it.

BTW, I got Nuvistor sockets in Antique Electronic Supply, a few years ago.

 

[bradzatitagain]

Charcteristics are slightly different than 5703, which is high mu,

My mistake 5703 is low mu.

Were you talking about 6111 microphonics? :wink:
Also, in this design I wanted to try a direct coupled CF, so twin triode would be the way to do it.

Doh! Didn't read far enough backwards. into the thread, mia culpa

 

[dale116dot7]

I've used 5703, also 5840, 5744, and 5702 for mics. They all work ok, but slightly different sounds. I find almost all of these tubes are microphonic. Mounting arrangements seem to solve most of those problems, though. A bit of damping material (such as an O-ring) around the tube seems to prevent a lot of 'ringing' of the tube's glass envelope from appearing on the output.

 

[bradzatitagain]

You can sometimes line a spring type shield with a thin layer of felt to cure some microphonic woes. IERC shields might also help. Can be acquired here:

http://www.leedselect.com/parts-sockets.html

Leave a few for me!

 

[Marik]

As I understand these shields are mounted on a socket. Although sub-miniature tube socket is a cool idea, I prefer not to use it in microphones, as any contact oxidation will result in noise increase. If you deside to use the socket anyway, I'd suggest to leave grid open and solder it directly to a capsule cap, or directly to a capsule, depending on your circuit. The same applies to "normal" 9 pin tubes. Also, keep this path as short as it is humanly possible.

Using tube dumping, Dale was talking about, would be quite sufficient. In fact, using rubber mounts and big O-rings, I had good results even with Nuvistors, although I had to select them for lower microphonics.

 

[bradzatitagain]

[quote author="Marik"]As I understand these shields are mounted on a socket. Although sub-miniature tube socket is a cool idea, I prefer not to use it in microphones, as any contact oxidation will result in noise increase. If you deside to use the socket anyway, I'd suggest to leave grid open and solder it directly to a capsule cap, or directly to a capsule, depending on your circuit. The same applies to "normal" 9 pin tubes. Also, keep this path as short as it is humanly possible.

Using tube dumping, Dale was talking about, would be quite sufficient. In fact, using rubber mounts and big O-rings, I had good results even with Nuvistors, although I had to select them for lower microphonics.[/quote]

The IERCs do have a sprung, mmm, collar that can slip over a bayonet type socket. They're unlike bayonet socket shields in that they're double layered, the inside layer is slotted the length of the shield and grips the tube so it'll stay in place w/out a socket, similar to the older single layer sprung shields that didn't need a shield socket. As such they also act as a heat sink and can lengthen the life of the tube. Probably not as effective as the sinks Gus hipped us to in Dulka's C800G thread tho. I can shoot a jpeg to somebody that's hosting if you want to take a gander right away; it'll take me a minute otherwise I don't have my homepage set up at the moment. Either way I'll get back here w/a snapshot.

& there might not be enough room anyway; the socket would glom lots of real estate. FWIW I keep myself in groceries building houses in earthquake country, it kinda bleeds into all my methodology. I'm almost done w/an over engineered rocking horse for my brand new nephew. <g> Safer than a Volvo.

 

[Marik]

Brad,

I would be interested to see this shield. If it's not much trouble, please email me the pics, and I will host it:

markfuksman(at)comcast.net

 

[bradzatitagain]

[quote author="Marik"]Brad,

I would be interested to see this shield. If it's not much trouble, please email me the pics, and I will host it:

markfuksman(at)comcast.net[/quote]

Can do, this shield cozies an EL86, tall 9-pin, but they're all constructed alike.

 

[Marik]

Here they are:

 

[dasbin]

Does anyone know a suitable substitute for the .22uf caps that I can find at Mouser? I'd like to buy all the parts from the same place to save on those big handling and shipping charges... thanks guys