Somewhat Different Mic Circuit

[skipwave]

Roddy, I have one paired with the Royer 5840 cathode follower circuit that sounds great to me. I think they need lower bias voltage than is considered acceptable by some.

 

[rodabod]

That's interesting. I wonder if the lower tension might reduce the nastiness. I've heard this capsule in a Sony C37 mic with standard polarisation, and it was not nice.

 

[zebra50]

It's been said before but the quality control on these is bad. I've seen two faulty ones in new mics, one with a ripple in the membrane, and one with a 'twist' or skew at the centre terminal. Maybe there are some good ones around.

(Having said that the gold circle in my TLM49 diaphragm is off-centre!)

 

[Rossi]

Are you guys talking about Chinese capsules in general or about these particular SE ones. I'm not exactly crazy about SE, but their capsules looked better made than average Chinese stuff. I've yet to see an SE capsule with ****** up membranes. They're certainly not as good as a Neumann capsule, though. And you hear it clearly, when you back up and get more ambient sound. There's more off-axis coloration. Their circuits are crap, though.

Apart from these two, I have a SE2200A. Out of the box is is excessively sibilant. I put in a different circuit using the same transformer and then tweaked the response with passive filters. I got it to sound really nice, actually, but it won't stand very high SPLs; I suppose the simple RCL filters (to ground) make the output stage drive pretty hard. Anyway, that's why I wanted to try a different kind of filtering scheme. BTW: The 2200A has a 32 mm capsule, though. I've yet to find a reason why they build 34 and 32 mm capsules which are essentially very similar.

I haven't tried those capsules with higher voltages, yet. My impression so far is that they are built for lower voltages P48-derived voltages. They put out quite some level, you don't need a DC/DC converter for self noise in the 12-14 dB A region (or even lower, I haven't measured my modded mic yet)

Zebra, the off-center gold circle may look disturbing, but it shouldn't change the sound at all. What I didn't like so much about the TLM49 is that I got the impression that they use a fixed low cut in the circuit. It certainly sounded nothing like my (K47 equiped) U47. I'd also prefer a cleaner circuit. I also don't like tube stuff, when it gets too dirty (except in guitar amps, of course). Almost clean tube is about my favorite flavor. Good clean transistor is fine with me, too.

 

[zebra50]

Are you guys talking about Chinese capsules in general or about these particular SE ones.

The mount in my SE mike was loose, rattling about, and the capsule had a ripple. But I did get it off ebay sold as not working so it may have been dropped by the first owner.

Zebra, the off-center gold circle may look disturbing, but it shouldn't change the sound at all. What I didn't like so much about the TLM49 is that I got the impression that they use a fixed low cut in the circuit. It certainly sounded nothing like my (K47 equiped) U47.

Yeah, I know it won't make a difference, but it surprised me and made me wonder if Neumann use 'class b' capsules in their lower end mics. That's idle speculation on my behalf, and would probably have me kicked off less tolerant forums (fora!). Actually I know it's not a fashionable opinion but I find the TLM49 to be a useful mic - clean, very quiet, maybe a tad boring, but often that's what you need. It is sold as 'optimised for vocals' so your low cut theory could be right.

 

[Gus]

I have a number of MXL microphones that have the 32mm capsule.  Many have new or changed circuits inside them solid state and tube and combinations.  One circuit that sounds good(to my ears) with a MXL32mm it is +140VDC B+, 100K plate resistor, 1K cathode resistor bypassed with a good 470uf cap, 1 gig grid to ground, capsule direct to grid, 60VDC charge voltage, MXL 32mm, 5840 tube wired as a triode, 5.7VDC heater, 1 uf cap to jensen DB like the Royer 2001, in a MXL2001 body, different clean power supply I built.

It is a lot like the Royer 2001 circuit. I like it with the grid to ground resistor instead of no resistor like the Royer.

Other circuits help or hurt the 32mm.  I have built a lot of microphone circuits and tested changes to the circuits stock and changed.  You can work with the 32mm but you need to try different circuits and transformers.

 

[Rossi]

Yeah, I know it won't make a difference, but it surprised me and made me wonder if Neumann use 'class b' capsules in their lower end mics. That's idle speculation on my behalf, and would probably have me kicked off less tolerant forums (fora!). Actually I know it's not a fashionable opinion but I find the TLM49 to be a useful mic - clean, very quiet, maybe a tad boring, but often that's what you need. It is sold as 'optimised for vocals' so your low cut theory could be right.

I'd be surprised if Neumann would even consider this. Apparently the K47 production is so consistent, that they quit distinguishing betwen K49 (both sides matched) and K47. The capsule in the TLM49 is different, though, in that only the front diaphragm is gold sputtered. At least in the one I opened. I think I'd really like this mic if they'd put in a simple clean FET circuit. It's not a bad mic as is, but I found it a little bass shy. I prefer to cut the bass in the DAW. The 49 style mic grille is really nice. Open, yet very protective. Plus it looks good  ;D.

 

[Rossi]

I have a number of MXL microphones that have the 32mm capsule.  Many have new or changed circuits inside them solid state and tube and combinations.  One circuit that sounds good(to my ears) with a MXL32mm it is +140VDC B+, 100K plate resistor, 1K cathode resistor bypassed with a good 470uf cap, 1 gig grid to ground, capsule direct to grid, 60VDC charge voltage, MXL 32mm, 5840 tube wired as a triode, 5.7VDC heater, 1 uf cap to jensen DB like the Royer 2001, in a MXL2001 body, different clean power supply I built.

It is a lot like the Royer 2001 circuit. I like it with the grid to ground resistor instead of no resistor like the Royer.

Other circuits help or hurt the 32mm.  I have built a lot of microphone circuits and tested changes to the circuits stock and changed.  You can work with the 32mm but you need to try different circuits and transformers.

I did something fairly similar with an Oktava MK-319. That was my first tube mic project, and it turned out very nice right away. I put in a 5840 circuit that pretty much follows the U47 schematic, so it is lower voltage than yours. I used the Oktava transformer, which is about 8:1. The capsule (60V) is wired direct to grid, the grid resistor is only 60 meg (built from the 50 and 10 meg resistors in the Oktava  low cut), similar to the U47. The resulting bass loss is very small. DC heaters at 5.9V. The mic sounds nice and is very low noise.
I'd like to try that circuit with a Dale M7.

Did you put in some kind of HF-filtering? I don't think I would like a Chinese capsule with a linear head amp, tube or transistor. I think these capsules need at least a little 10k reduction.

I don't like to spend much money modding low cost mics. I think that money may be better spent on a more expensive mic. So I don't think I'd ever put a Jensen in a Chinese mic. Hence my preference for those small Neutrik NTE transformers. Even though they're tiny, they don't sound that bad, actually. At least I don't get the impression, these transformers are necessarily the weakest part in the chain, if you use them in a circuit that doesn't push them to their limits. I also tried the NTE10/3 in a KM84 type circuit for an MXL603, and it sounded quite nice.

 

[Gus]

I have built circuits with a LP filter yes that can help.  The circuit I posted does not sound that bad at all with out a LP filter and a 32mm. 

 

[mitsos]

Nice to see a non-tube mic circuit around here. Thanks for posting!