Possible mods/improvement for Fame tube mic?

[Lale]

Hi!

Few years ago I got LDC multi-pattern Fame tube mic off from a net auction. Mic is Fame SKEA002/W and I haven't been able to find any useful info about it. Soundking has been selling this mic at some point also. Mic is discontinued and was originally cheapish (apprx 400€) mic. I paid 80€ (!) for it and thought that I give it a go and see how it is. Case seems sturdy and build quality is suprisingly good. But soundwise the mic isn't anything special, it lacks detail, sounds "lazy" and is somewhat noisy. I tried swapping tubes, stock tube had really harsh highs, and I ended up using a GE JAN 6072A. I really couldn't get rid of the noise by tube swapping and the sound of the mic itself is still a bit dull and not interesting. It's somewhat decent, but I never end up using it. I try it every now and then but in the end it goes back to the closet and stays there.

Here you can see the pics of the mic:
http://www.bror.fi/tubemic/
I can provide more detailed pictures if you wish to see, just ask.

I'm not really skilled to see what type of tube mic this is, if someone could tell me somehing about it, i would appreciate it.

I'm also interested in trying to mod the mic to see if there was some potential. I have skills to do soldering well and basics of electronics, been building stompboxes and amps etc. Could you be able to point me the most potential procedures of modding this particular mic? Upgrading transformer? Capsule? PSU? Individual components? Should I just dump the whole innards and rebuild it from the scratch?

EDIT: almost forgot to mention, grille is build with two layers of mesh, outer is very typical thicker mesh and inside theres a second layer of denser mesh with thinner wire. No any foam of fabric used.

Any info is appreciated, thanks a lot in advance.

- Lale

 

[dgatwood]

No way to know without seeing the circuit sketched out, really. I can't even tell where the coupling cap is unless it's that polystyrene-looking capacitor on the top board. There was a post on one of the other boards that suggests it might be from one of the Chinese mic manufacturers and would probably sound better with a better capsule, but this is mostly speculation....

 

[Lale]

No way to know without seeing the circuit sketched out, really. I can't even tell where the coupling cap is unless it's that polystyrene-looking capacitor on the top board.

Thanks for the reply! Basically, I was hoping that there was someone who has seen this mic before and had straight info about it. I can try sketch the circuit, but it will take some time.

Actually, I took a second look at the mic and there is anothere polystyrene looking cap on the top of the top circuit, its hiding there and that's supposingly the coupling cap, it's the first component after the capsule. I'll take another pics, top circuit removed, to reveal this.

There was a post on one of the other boards that suggests it might be from one of the Chinese mic manufacturers and would probably sound better with a better capsule, but this is mostly speculation....

Was this discussion about Soundking or Fame mic? I can't find anything using google.. Would you be able to provide a link or tell what/where to look for?

 

[Lale]

Ok, I accidently bumped into info about Apex450. Exactly the same mic. This was purely a lucky coincident and now I have at least some info. Mic is somewhat similiar as Apex460 (lots of info on that) but there are some differencies.

Unfortunately 450 is discontinued and there isn't that much info about it either.

I found a page about repairing Apex450
http://www.deeringamps.com/workbench/apex450.htm
and info about transformer of 450 and 460
http://www.foxaudioresearch.ca/transformers1.htm

Apex460 schem is readily available and I'll try to use that to trace the schem of my mic. I'll also try to trace the PSU.

 

[dgatwood]

Thanks for the reply! Basically, I was hoping that there was someone who has seen this mic before and had straight info about it. I can try sketch the circuit, but it will take some time.

Actually, I took a second look at the mic and there is anothere polystyrene looking cap on the top of the top circuit, its hiding there and that's supposingly the coupling cap, it's the first component after the capsule. I'll take another pics, top circuit removed, to reveal this.

I could be wrong, but for a multipattern mic, I would think there would need to be one coupling cap per side of the capsule.

Was this discussion about Soundking or Fame mic? I can't find anything using google.. Would you be able to provide a link or tell what/where to look for?

Wasn't much of a discussion. What I said was almost the entire discussion.

http://www.prodigy-pro.com/diy/index.php?topic=40645.0

 

[PhilGood]

Standard Alctron/Ningbo cathode follower circuit. Pretty standard for these mics. I don't even need to trace it, I've seen it and variations of it so many times. Its pretty much the same as the Apex 460, but with high pass filter and a pad.

The noise is most likely from a capacitor on the signal path or the capsule itself.

Some things you could do to make the mic better: Change the tube biasing method. Replace the capsule. Remove the filter caps on the transformer and of course, upgrade the transformer. Upgrade the transformer coupling cap. Easy enough to find, just trace the transformer leads back to the first 1uF you find. luckily the polystyrene up by the capsule is a good fit, but if its bad that could also be the source of the noise.

Also look for stray flux on the tube socket.

I wouldn't alter the grill. Reason being that its only a 2 layer grill and the finer mesh helps tame some of the highs. Its a good shape and size, too. Similar to the U47's dimensions. That's a good thing.

Also, the circuit was designed for a 12AX7, not a 12AY7 or a 6072A. Changing the tube type isn't necessarily going to benefit anything. Wrong tube in the circuit can change how the transformer is driven. If you're good at electronics, one thing you could to would be to rewire the tube socket (you'd have to replace the PC board) so that it could use a tube like an EF86. Then you could use a lower turns ration transformer. I did this in a Nady TCM 1050 and was tickled by the results!

 

[PhilGood]

Oh, one other thing you could do: Find the 2 270k ohm resistors (the voltage divider for capsule bias voltage) and replace them with 470k, 560k ohm or even 1M ohm resistors. That might help a bit with detail. Then again, you could suck the diaphragms into the backplate, so be careful.

And you could adjust the B+ voltage.

 

[Lale]

Phil, great info, thanks a lot!!

Good to know about the tube..
I recently got some 60's RCA 12AX7A's and I will try them to check the noise and performance. Old RCA's seem to be on a bright side (in a guitar amp) and I'm not sure if I'm going to like this mic brighter than it is now
On the other hand, RCA's highs are so sweet that it might work anyway. We'll see. Any suggestions for good 7025/12AX7A tubes in this kind of application?

I'm not sure if I'm bothered to try the EF86, more willing to try a better transformer (any suggestions? - should i go straight with cinemag?) and do tweaking here and there, I got very good info on that already - thanks again, Phil.

 

[PhilGood]

If you have the space? I'd go with Lundahl. You'll get better windings, better laminations & materials, good shielding, plus a larger core.