Can anyone help me make this mic better?

[Guest]

Thanks for all the responses guys. The capsule is all brass, and there are no pads or rolloffs on this mic. I havent had any time in the past few days, but I'll look at Gus's schematic and hopefully get something solid worked out. Also, I'll post some pics of the capsule and grill later this evening. There is plenty of room for a royer type circuit if I decide to go that route... For now though, I'll take gus's suggestion and start with the grill. The one thing I will say about these mics, is that I have two and they sound nearly identical. I'll keep one as a controll so that some comparisons can be done.

 

[Guest]

www.jcmaudio.com/Luna_Capsule_Front.jpg
www.jcmaudio.com/Luna_Capsule_Back.jpg

These were done, like the others, with a scanner... I'm going to try to get a digital cam and take better ones. The capsule is sealed with tape along the edge.

I removed the inner, finer mesh of the grill and it is an improvement. A more natural and open sound to my ears. I believe that the capsule is limited by the electronics...

 

[Gus]

The pictures are good news. That looks to be a superlux capsule not a bad capsule from the little time I worked with a sampson CL7. I think it is the same capsule as Tim C. posted about.

I have been thinking about this. After your grill tests, try cap upgrades and leave the possable transformer to last first cap to change the one between the capsule and fet. It might use a better lam alloy than other china microphones it is shiny it does look to be the 25 size

 

[Guest]

tried to post this before... but something got messed up. Now to retype... argh! :evil:

Thanks to everyone fro your help, I have played around with changing caps, and it is getting better :grin: A smoother, less gritty, sound. I have done a little reading and I do believe Q2 is a pnp... If I remove R6,C7,R7 and C5 and connect the base of the PNP to the drain, how can I tell if I need to adjust R3 for proper biasing? If I do this, I should still put 1/2 the B+ voltage, as Bo suggested earlier, to the Base of Q2 then, right?
Also, are C3, and C4 essential to the circuit? I am not sure what they are really doing...

I'll try to get an updated schematic, layed out and labeled a bit more clearly like gus did (thanks gus!), uploaded this evening. also I'll try to get some better pics with my new digital cam. :razz:

 

[mcs]

[quote author="fum"]Here's the marketing drivel on this:[/quote]
Just read the marketing drivel on my new mic in the brewery. It's not only good - it's perfect! :green:

Best regards,

Mikkel C. Simonsen

 

[Guest]

Ok, so I removed R6,C7,R7 and C5 and connected the base of the PNP to the drain... and it works! How can i test the bias to see if things are biased properly?

 

[Guest]

If I take the junction of R4, the PNP emitter, and the transformer to ground, then do I need an extra resistor between the emitter of the PNP and ground? Aslo can I take the 1G resistor going to the top of R4, and put that at the bottom R4 as well, and then to ground? This is all assuming ( i hope correctly) that the PNP is an emitter follower. If I am way off tell me please.


Thanks guys

 

[Gus]

By removing R7 the 1 meg Base to ground you have a direct coupled EF. The emitter should be about .6 V higher than the drain of the FET measureing from ground.

What you have now is about as simple as you can get. There is one more trick. Two more parts can go a cap and resistor however you will need to change the wires from the capsule, Think neumann U47. Look at my simple FET stage based off the KM84 circuit.

You still need C4 you don't want DC in the output transformer.

 

[Guest]

Ok, I think I follow you gus... This has all been a HUGE improvement on the mic... I highly reccomend modding it if anyone has one... comparing the stock and modded mic, the modded version is MUCH cleaner and clearer... the "grit" is gone. Also, it has a more "open", less stuffy sound. Its turning into a nice little mic. :razz: Thanks, of course to you guys.


The Lab - The best education I never paid for. :green:

 

[Gus]

did the removing the mesh make the most difference? Question what is the voltage at the source of the fet to ground? look at the low output microphone thread for a link from the meta.

 

[Guest]

Actually, I think that changing the cap near the capsule to poly prop. for now (had to use what I had, going to order some polystyrene), and removing R6,R7, C7 & C5 made the biggest difference. You can really hear alot more detail in the sound now. I prefer the more open grill it seemed to be less stuffy sounding but the difference was most noticible in the electronics... though, now that I think about it, the grill change might be more obvious now that the electronics are better. Before I mod the second one, I'll try the original 2 layer mesh on the modded one to see what the difference is. I'll also put up a short sound clip of the final modded mic v.s. the stock one. I'll get the voltage for the FET up tomorrow evening.


Oh, btw, the cap near the capsule is 1000pf... no surprise I am sure... I misread/labeled it on my schematic.

 

[Guest]

ok... capsule rewired... voltage at source is .775v

Drain = 17.2v
Emitter = 17.85v so its about 6.5v higher, which seems pretty good to me.

 

[Svart]

yeah keep it polypro, polystyrene can make a mic sound more open but thinner. in your opinion would this mic be a good modding mic? looking to get another LDC to play with..

 

[Gus]

So how does the "final" version sound?

 

[Guest]

I haven't had a chance to give it a good comparison, and I am thinking I am going to relam the transformer, but from my initial listening, it is less harsh on the high end, clearer, and there is more "resolution" to the sound. The stock mic sounds grainy compared to the modded one. Also, it seems less noisy though I am not sure about that. I will put some sound clips up of the stock and modified mic... Probably wont get to it until wed. though.

I like the sound of this better than the mxl2001... I am guessing its the capsule. It has a more natural sound to it.

Svart, I actually rewired the capsule (gus's suggestion of course), so there is no cap between the capsule and gate.

I'll try to give a slightly more coherent opinion once I have done more recording with it. Now, to find some lam.... and a :guinness: :green:

 

[Flatpicker]

[quote author="Svart"]yeah keep it polypro, polystyrene can make a mic sound more open but thinner...[/quote]This might be because higher voltage polypro?s have a thicker dielectric than the polystyrenes. Just curious, but where did you find 1000pF polypros and what voltage rating do they have?

 

[Guest]

Tim, I'll get back to ya this evening on the capacior...

So I am going to attempt to relam the transformer with superperm 80 EE and I'm a bit clueless... I am still not exactlysure what I need. any advice? Also, any places that sell it? I found some at www.magmet.com lots of different kinds though... forgive my ignorance, still a beginner with transformers. Thanks

 

[Svart]

digikey has em: P3102-ND 50v.


gotta search for them in micro farads, so 1kpf= .001uf. you can also parallel some 470pf and get close enough to try it out.

:thumb:

PS: my polystyrene are also 50v. i've used 100v for both with no difference that i can tell, but that doesn't mean that on a scope you wouldn't *see* a difference..

 

[Flatpicker]

[quote author="Svart"]digikey has em: P3102-ND 50v...[/quote]Yep, there it is! Funny but I missed these (or just forgot about them) somhow. I knew they'd be listed as uF, but couldn't find any with voltage ratings that low. Thanks. :thumb:

 

[Gus]

I am interested about the lam part.

The superlux built microphones I have(I think the GT33s and GT44 I have look like superlux builds) or have seen inside look to have different aloy lams stock than the lams of other china built microphones I have been inside..

Also from what I heard working on a CL7 microphone and what Tim C. posted about the capsule. I would like to compare a reworked Tenlux/superlux against my modded MXL2003 both are 3 micron capsules.

Did anyone have a chance to measure the outside diameter of the superlux capsule in mm, 32nn or 34mm?

The grill looked to be glued in place on the cl7 I worked on it was not mine so I did not remove the grill.

Edit fo fun read this thread again add compare my guess at the schematic
http://www.groupdiy.com/index.php?topic=3024&start=15