[rodabod]

Also I was thinking of using the second switch to switch C8 output cap between the 1uF (C24 value) and 0.5uF (C12 value).

Meh, I'm not sure if this is worthwhile really. Try either and see if you notice much difference.

I'd maybe set the pad cleverly so as to reduce the gain of the triode stage in order to give more headroom for really loud sources, otherwise a preamp pad is just as effective. Depends how many poles your switch has as you don't want to upset the balance between the chosen anode and cathode resistor values.

Roddy

[ChuckD]

Ok I'll just go stock C24 then here it is
Can someone check this over for me?

I think I will just dump the 2 original PCBs and either do a point to point or a new small pcb that allows better caps. actually I will gut the whole mic but still is a super deal!




-Chuck

[Marik]

marik, i dont understand: 200v on grid?

the c12 is set up with a "fixed bias". the negative bias voltage comes through a extra wire (pin4, ignore the fat line on the schematics) from the psu.
note the 1kiloohm resistor on ground of the HT supply. it creates a voltage drop when loaded with the microphone, with the point before (on the left of) the resistor being negative relative to ground.
 
http://www.coutant.org/akgc12/c12schem.jpg

Hey Max,

Dat's rite, but if you look at the schemo Chuck drew originally, the grid bias derived straight from B+.

Best, M

[ChuckD]

based on my C24 drawing I came up with this. I left the 1uF cap off assuming to move that down by the transformer where there is more room for a nice audio cap.



Can someone go over my proposed schematic ? Will this work well with a Cinemag 2480 / 6072A / CEK12


Chuck

[rodabod]

Can someone go over my proposed schematic ? Will this work well with a Cinemag 2480 / 6072A / CEK12

Chuck, the schematic looks ok to me. Yes, it should work well with Cinemag/6072/CEK12.

I might suggest you still use the original PCB though - it's easy to remove and replace components and the boards mount fine.

Also, if you do use a new PCB deign, pay attention to the Hi-Z area from the capsule to the grid. Often the capsule connection here is floating on a standoff so that the 200M resistance doesn't get shunted through dirt or flux on the board.

[Gus]

ChuckD.

Whats the B+? the heater voltage?

First thing I would do is install a NOS 12at7 and check out the microphone

  First look at all the tube microphone schematics you can find.
Next read the microphone meta link in the darker blue meta meta at the top of the pages.

What microphones do you like that your heard, not what you read about on the web.

What capsule will you use? What microphone body?  Then you can buy the tube and transformer etc to add to the capsule and grill.

If you leave it cathode biased you can reuse the stock PCB.  I have two nady 1050s that have new circuits on the stock PCBs.

Don't believe some of the stuff you read on the web about part changing in microphones.  And if you change stuff don't limit your testing to your voice.  Voice sometimes does not "show up" higher end harshness.

The stock schematic is an interesting one how the pad is done etc I have not seen that before in a China made microphone.

[Marik]

Will this work well with a Cinemag 2480 / 6072A / CEK12

As Roddy has said, it will work. I am however wondering why such a boring selection?

Best, M

[Gus]

Marik
 I think people like boring because they read it on the web.

[ChuckD]

Geesh !

I already had a 2480 ,  and a nice 12AY7.
I wanted to use a Pel-CEK12 since I already building a G7 with a DALE-M7 and a cinemag BV8

Don't assume. Everyone has different goals. I wanted something to compliment the U47-G7 type such as a C24/C12 type. Since the circuit was derived from this it seemed like a good idea.  


 -Chuck

[rodabod]

I think people are arguing about something being a boring DIY, as opposed to being boring sounding. It's good to try the standard well-known circuits.

A good selection of parts like those you mentioned should sound good. I've used the Cinemag 2480. It's easy to fit in the mic you have chosen, and doesn't seem to have much effect on the sound, although I have not tried it on extremely loud sources yet.

[Marik]

Geesh !

I already had a 2480 ,  and a nice 12AY7.
I wanted to use a Pel-CEK12 since I already building a G7 with a DALE-M7 and a cinemag BV8

Don't assume. Everyone has different goals. I wanted something to compliment the U47-G7 type such as a C24/C12 type. Since the circuit was derived from this it seemed like a good idea.  

Sorry, did not intend to offend. Once again, it will work, but you asked if it will work well... I think it is OK, and since you already have 2480, of course, go for it.

I however, have my own reservations about combining parts you mentioned.
2480 has a very small core and gets away with early saturation because it is a DU core (no "I"). To get some primary inductance it has lots of turns of pretty thin wire, so it has high DCR (which of course, loads the signal), and still does not have enough pri L. To me it sounds pretty boring, uninteresting, with poor bass, compare to the bigger core brothers. To get a somewhat better bass response you should use it with a lower mu and Rp tubes, which will also help to keep the transformer out of saturation.

Gus has already suggested 12AT7 and as you see there is a good reason for that.

Also, if it is your intention to get C12/24 type of sound I don't quite see a good reason of using CEK12. Yes, it is an edge terminated capsule, but it is about where the similarity ends. It's been many times noticed that the CEK12 backplate construction and hole pattern is exactly like K67/87 type, so don't hold your breath to expect it sound anywhere close to a five chamber CK12.

Hope it helps.

Best, M

[ChuckD]

Thanks! Great  info!
 
I don't have to use the 2480 I can just pawn it off in the Black Market, and get something better at Funkenwerk or.... Got any suggestions?

I already ordered the CEK12. Too bad I didn't know that it was so different.

-Chuck

[Gus]

I suggest you change the tube first maybe adjust the heater voltage
 then the capsule,
 then maybe the output cap and maybe grid cap and caps between stages
What types are in the places I posted?
 Try it with the stock transformer and hear what the grill and capsule might work with for a circuit.

Good larger transformers can cost a bit of money

[rodabod]

Has anyone tried a 12AU7 in any of the Chinese mics yet? Just wondering if it might couple better with the standard transformer.

I should really borrow an audio test-set from work and test some different setups.

[Marik]

Has anyone tried a 12AU7 in any of the Chinese mics yet? Just wondering if it might couple better with the standard transformer.

Yes, I did. Sonically, I like them by far the best out of 12...7 family. The problem is out of many NOS brands I could not find even one with more or less satisfactory noise level... and I mean it--all of them were unusable.

Best, M

[Marik]

Thanks! Great  info!
 
I don't have to use the 2480 I can just pawn it off in the Black Market, and get something better at Funkenwerk or.... Got any suggestions?

I think our Max (Ioaudio) had some good stuff.

With 12AT7/12AY7 I used Oliver's BV314, with good results. His customer service is not the best to say the least, and build quality is quite sloppy. The transformer comes with no any paper work, or even color code, so you will need to figure out the pri and sec windings, as well as phasing yourself. However, they sound very good.

Best, M

[rodabod]

Has anyone tried a 12AU7 in any of the Chinese mics yet? Just wondering if it might couple better with the standard transformer.

Yes, I did. Sonically, I like them by far the best out of 12...7 family. The problem is out of many NOS brands I could not find even one with more or less satisfactory noise level... and I mean it--all of them were unusable.

Hi Mark,

I may try to get the noise-selected ECC802S which I have heard may be good enough to use in a microphone.

I also just bought a military equivalent CV4003 so I will check its noise performance too and report back.

Roddy

[Marik]

Hey Roddy,

Please let me know if those work out and what do you think.

Best, M

[rodabod]

I also just bought a military equivalent CV4003 so I will check its noise performance too and report back.

I'm just testing and burning this in just now. It seems to have lower noise than the noise-selected GE 6072 which I was using although it is hard to compare since the output levels are different.

Sound quality seems fine, and low-end extension is fine too. What I'd really like to do though is take a Lindos test-set and compare responses using the different valves I have.

For reference, the CV4003 (ECC82) is a Mullard with a KQDD stamp and has the date code 85-09 which I think makes it a late production. They also made an ECC802S which is noise-selected.

Roddy

[mushy]

I have a pair of 5751s on their way to me now for my ACM-1200s.

Also, has anyone ever tested the Edcor's in the ribbon mics?  At half the price of the Cinemags, it certainly makes you think.

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