Can anyone help me make this mic better?

[Guest]

I havent seen anyone talk about this one yet. The name of it is the Luna, I wont mention the company... The sound is "harsh and agressive", thats the best way i can describe it. Also, the noise is a bit high. I tried to be very careful with my tracing, but the pcb is soldermasked and the traces are very small, so if something dosen't look right, I can check it. Hopefully the schematic is clear enough. Any and all thoughts are welcome. I'll take the files down in a bit, or atleast the schematic.

www.jcmaudio.com/Luna_Schem.jpg
www.jcmaudio.com/Luna_Front.jpg
www.jcmaudio.com/Luna_Back.jpg
www.jcmaudio.com/Luna_Transformer.jpg

Thanks guys... I'll try to get some pics of the capsule.... i used a scanner for the boards.

 

[Gus]

first off I think the lams need to go in the transformer. Check your microphone circuit against the 2001/ v67/.......china schematics it does not look correct as a standard china microphone. Tim H. has nice ones drawn mine are hand drawn.

The 2nd fet might be a PNP EF

I tried one in a store and put it back I think there is to much grill mesh in the capsule grill to much refections for my ears that crappy hollow sound. The grill does kind of look like the cool looking gefell um900. The basic circuit sucks because of some of the the stock parts.

It also IIRC the 797 audio capsule with the plastic back backplate cardiod only model. Does not sound as good as a the two skin 797 audio capsule.

 

[Guest]

Thanks Gus, I'll check it friday evening... It was a real pain to trace, but I think it is pretty close. Probably a very good thought on the grill, it does have very thick mesh and I think I can open it up a bit. I'll also upgrade some of the caps, starting with the film cap... I am pretty sure the capsule is actually a dual, with a dummy membrane on the back, I looked at it some time ago and I'll have to open it again to make sure my memory is correct.

 

[Gus]

There will be a back skin even witht the plastic backplate. What you want to look at is the the backplate If it is the plastic one I don't like that as much as the real brass backplate.

Different porting etc does not sound as good to me.

I think it might be modeled in someway after the TLM103 capsule

 

[dale116dot7]

The TLM103 capsule has no back skin, it uses different porting to simulate the loading of the back skin. U87 and M7 'clone' capsules do need that back skin, though.

 

[Gus]

I think it might be modeled in someway after the TLM103 capsule.

I should have been more clear the backplate of some rodes and other 797 capsules have no blind hole just thru holes. I am guessing that the back skin is more for a dust cover with the 797 cardiod only capsules.

The 103 is not 1/2 of a 87 style capsule wired cardiod only to my ears and the cardiod only 797 are not 1/2 of the 797 dual skin capsule mult pattern capsule wired cardiod only to my ears.

 

[Bo Hansen]

Hi JCM audio,

Yes Gus have right, the Q2 must be a PNP emitter follower (not a N-FET) as a transformer driver.

There are also a missing ground that shall be connected to the junction between Q2 collector, transformer primary low end, R4 and R3.
And of course the XLR pin 1 must also go to ground.

Here is some other wild guesses:

The R6, C7 is a unnecessary RC-link, and are a remains from a low cut filter there C6 (not mount) are the second filter capacitor and the link between C5, C7 and R7 is now insted for the low cut switch.

The D2 and D3 are probably zenerdiodes, but maybe they shall be connected between the R10, R11 and C11 (zener ground end is ok)

BTW, the first improvment for this type of Chines mike amp is to fix a better bias point for the emitter follower, it can be nice to have aprox. the half B+ (the voltage before R10) on the Q2 emitter, to get best headroom to drive the output transformer, and it can be done with a extra resistor around 1 to 2 Mohm connected from the Q2 base to B+ voltage rail.
(to add this resistor on amps with low cut filter, the cutover frequency will be a bit lower)

--Bo

 

[Gus]

had some time to look a t the schematic. I redrew it .

Ae there pad or roll off switches

Looks kind of like a super lux build looking at the jpegs. Need to look at the capsule.

C7 and R6 I need to think about some more need to know what the 2nd transistor is fet or bjt

Is the junction of R4,R7 and one of the transformer wires connected to ground?

I don't know the electros would need to test them.

If you deside to work on the microphone I would work on the grill first. If that helps then the circuit. Worst case you build a new circuit with good parts.

For giggles take a look at the brauner C schematic.

 

[chrissugar]

I hope the one [Luna] I received for testing was defective because it was the worst sounding LD condenser I ever tried.
Or maybe it was ok and this mike just sounds bad.

chrissugar

 

[Gus]

Chris I think it might be the microphone design build no one I know that tried one liked it.

I tried one at a store because it looks cool with the big grill, kind of like the UM900. Evenat the store it did not sound good. If it was maybe $100.00 USA I would have bought it and worked on it but for $199.00 no way.

FWIW I have bought 6 or 7 MXL v67s as things to mod and work onthe circuit looks kind of like the luna. I think they were about $70.00 dollars on sale one time. I don't like them stock but they were cheap and good to learn on

If the microphone gets better with a grill mod the electronics can be replaced or improved. Can't realy see what make the capsule is maybe the capsule is not that good.

I also think the stock 2001/v67/ etc (one with the same circuit and parts used and 32mm capsule)china microphones stink stock. You would be better off with a sm57,58 and a good pre.

 

[chrissugar]

I'm not interested anymore in china mics because it's a waste of time and money.
Although I'm open minded so if a good and cheap capsule or mic will be available I will try to build something.

Sorry Gus, I still had no time to write down the values for the Phantom C.
I hope to do it in the near future.

chrissugar

 

[Gus]

Chris

I have no desire to make the phantom C circuit. I was just wondering what the operating points of the fets are. No rush at all. I see nothing new in the C circuit.

 

[zebra50]

Latest luna schem sketch, curtesy of gus is at...

http://www.omnipressor.com/MicSchLib/luna.GIF

it's a bit too big to insert in the thread.

cheers!
Stewart

 

[Gus]

Stewart

Thanks. It is just a redrawn one of the top link

www.jcmaudio.com/Luna_Schem.jpg

It has a few guesses in it from other china microphones I have been inside.

The 1 gig going to the top of the 3.3k would be a little different than it going to ground. Not realy sure what R6 and C7 are for. Guess 2:1 alot of china microphones use a transformer like that at 2:1

I might try removing R6,C7,R7 and C5 and connecting the base of the PNP to the drain This is if Q2 is a PNP.

Is the input cap a Mylar replace with better if so? and it looks like two of the doides are zeners.

Upgrade C9 and C10. Upgrade C3 try a 100uf at 10V. Upgrade C4 to 22uf at 50V. Try to use Low good ESR electros that you like.

I would work On the grill first.

 

[fum]

Here's the marketing drivel on this:

The new Luna professional condenser microphone is truly a work of art inside and out. Luna delivers vintage look and sound combined with modern electronics for the best of both worlds. The large diaphragm cardioid design is perfect for professionally capturing vocals, guitar, piano and just about anything else. Simply put, Luna eclipses the competition

So, what's there to improve? :wink:

 

[Flatpicker]

Why go to the trouble to make a mic that sounds like crap? They must've thought the looks would sell it - and looks like they were right!

 

[alk509]

[quote author="fum"]Luna delivers vintage look...[/quote]

Now what the **** does it matter if a mic "looks" vintage??? Now I'm not buying their **** fo' SHO'!

Peace,
Al.

 

[Bo Hansen]

Gus,

I might try removing R6,C7,R7 and C5 and connecting the base of the PNP to the drain This is if Q2 is a PNP.

Yes, this is the best solution if not the low cut circuit will be use.
But maybe the R3 must be adjusted if not the input FET have right bias point it self.

--Bo

 

[Rossi]

I had a Luna for review, and the one I had sounded absolutely okay. Nothing spectacular, but definitely better than say an MXL2001. The capsule is all brass, btw. The Luna is actually pretty much the same mic as the Groove Tubes GT55. Same electronics except for pad and low cut switches (if i remember correctly). The GT capsule has their special HF-disk at the center terminal. I acutually preferred the Luna without the HF-Disk. I don't think the grill is so badly designed. You can actually unmout the two disks and cup your ears with them to see if the sound changes.

 

[Gus]

Need to see a good picture of the capsule.

If m-audio is using the same company as GT/m-audio microphones was, it might be a Tenlux/superlux capsule 3 or 6 micron from the looks of the circuit build?

I did not see how to get inside the grill of the luna. FWIW the sampson CL7 I looked at seems to have the grill assy glued to the frame of that microphone.

If the luna can be helped with the grill one could fit a Royer style circuit inside I think.