Official C12 Clone - Build and Support Thread

[Matador]

One thing to check for is if anything is touching the mic casing?  Is it buzzing as loud as your other condensers with out the body tube or is the buzz also reduced in level?

I get a lot of hum without the body tube...?

THanks!!!

This is normal.

Can you post a clip of what the mike sounds like?

 

[Matador]

I have the intention to build a C12, but I still have one question:

The capsule boosts the higher frequencies (just like a K67 capsule).
In the schematic there is no de-emphasis or other frequency correction.
Won't this microphone sound 'over bright'?
Would it be an idea to add a capacitor between the anode and ground (just as in the ELA M251) to roll-off the HF a bit?

(Sorry, but I did not read all 247 posts...)

The C12 response peak is significantly higher in frequency that a K67.  It should sound fine in a flat response circuit.

The cap-to-ground trick will work, but not the default 100pF ELA M251 value.  I would suggest 470pF as a starting point to reduce  a K67-ish peak down (although you'll be making a very different mike as compared to a flat C12 circuit/capsule combo).

 

[robomatique]

Can you post a clip of what the mike sounds like?

THanks for getting back to me! I just recorded a few word. I have attached the file as a txt file, download and change the ending to mp3 and it should work (?).

By the way, would R1 and R2 be ok as .1w resistors?

Thanks!

 

[Randallizer]

Okay, so last night we completed work on our kit with an immaculate original c12 capsule. We also picked up a NOS GE 5 star 6072.

Today we gave it it's first run out and the results were....


Unbelievable!!

Hopefully in the next couple of weeks we'll give it a shoutout against an original C12, but at this stage we aren't too worried about how it'll measure up because we've clearly got a fantastic mic on our hands.

Huge credit and appreciation to Chunger and Matador for their work on this project and I have no reservation in recommending others to give it a go.

At this stage I would also recommend to others with old 414s to not be scared of using the capsule in this project. The results are pretty spectacular.

I'll post a clip in the morning.

 

[Matador]

Can you post a clip of what the mike sounds like?

THanks for getting back to me! I just recorded a few word. I have attached the file as a txt file, download and change the ending to mp3 and it should work (?).

By the way, would R1 and R2 be ok as .1w resistors?

Thanks!

Borderline:  those resistors have about 1mA, which is 0.001*0.001*91000 = 0.091W.  You can probably get away with it due to the sandbagging by the manufacturer, but those really should be 0.25W parts if you want to count on them for the long haul.

 

[BryanJHarris]

Getting ready to dive into this project pretty soon, but I was wondering who used the Beesneez k12s and what their thoughts were about them?  I doubt I have to patience to hang around until Tim is taking new orders so this seems like a potentially good option. 

Bryan

 

[Aaronrash]

Hello Matador,

I have a few questions for you. I've been talking with Andreas Grosser recently about building a U47 with a EF12 tube. He sent me the schematic and it's a pretty straightforward build. Seems pretty simple and he cleared all the mystery of using a EF12 with a U47 up for me.

The EF12 heats off of negative voltage. The power supply you designed for the C12 actually seems like a perfect candidate for the U47 build with a few modifications. I need +A 120V that will be sent to a voltage divider in the mic and then it will polarize the capsule and power tube operations. Then I need -6V for the heater and that's it, I'll be good to go.

I spoke with Chunger about this and he suggested that turning the diodes and capacitors in the the filament section on the power supply along with a LM337 regulator should give me the -6 for the heater. And I can use the adjustable 200V line for the +A120V. I just wanted to run this by you as Chunger suggested and see what your thoughts are. Hopefully it will help other people in the future looking to build a U47 with a EF12 as well.

 

[jplebre]

Hi guys

the mic is alive and sounding stunning, even with the stock alctron capsule.
I'm hoping with the more accurate edge terminated capsules that cheap feeling on the transients will get improved


I have a few questions, I'm not sure if this is normal:
- with no body cover on, the microphone is incredibly hum-y. Enough to bury signal (if signal is spoken words, low level singing).
- With body cover on, mic is spotless clean!
I know some members mentioned hum problems and other people answered to put the body on, but I still feel it's weird there's SO MUCH hum without the cover.

- the voltage takes a while to ramp up to 120v (a few minutes at least) and takes a very long time to ramp down (+10min).
in fact, the mic stays "operational" for 2-3min before start loosing signal.
Is this normal? I'm used to seeing bleed resistors on PSU designs but not on this one, so I'm unsure if it's normal.
(I don't think R6 - 470kOhm qualifies as bleeding resistor?)

- Bias: I'm using a fluke 175 but I'm not sure I'm measuring Bias accurately. Every time I probe P-ground and P-Bias, the voltage shown is lower (-1.3/-1.5v) and creeps up to -1v where I've set it previously. Is this normal? if so, should I aim for the DMM-free voltage or loaded by the DMM?
If it's not normal, any ideas?

- there's a windy sound but I'm 100% sure it's my room and windows and computer and etc. I'm in the studio 3 days this week so I'll be able to try that out.

If you have rumble and hiss noises, try ditching the stock altron capsule. even a £10 EH6072 is free of most of those issues and sounds quite acceptable.

 

[Matador]

The EF12 heats off of negative voltage. The power supply you designed for the C12 actually seems like a perfect candidate for the U47 build with a few modifications. I need +A 120V that will be sent to a voltage divider in the mic and then it will polarize the capsule and power tube operations. Then I need -6V for the heater and that's it, I'll be good to go.

Do you have a schematic?  I bet you can use a positive heater supply just fine.

 

[Matador]

I have a few questions, I'm not sure if this is normal:
- with no body cover on, the microphone is incredibly hum-y. Enough to bury signal (if signal is spoken words, low level singing).
- With body cover on, mic is spotless clean!
I know some members mentioned hum problems and other people answered to put the body on, but I still feel it's weird there's SO MUCH hum without the cover.

The air is awash in 60Hz radiation, and even microamps of noise current across very high impedance sections will generate significant noise voltages that be happily amplified by the tube.

In short, completely normal, the the entire reason why the circuits are encased in metal tubes in the first place.

- the voltage takes a while to ramp up to 120v (a few minutes at least) and takes a very long time to ramp down (+10min).
in fact, the mic stays "operational" for 2-3min before start loosing signal.
Is this normal? I'm used to seeing bleed resistors on PSU designs but not on this one, so I'm unsure if it's normal.
(I don't think R6 - 470kOhm qualifies as bleeding resistor?)

The time constant of each filter section is 9 seconds:  there are 3 cascaded together, so it takes a few minutes to charge up.  Yes, R6 is a bleeder, and yes it takes quite a while to ramp down.  One of the side effects of a high-impedance supply!  You can lower the bleeder resistance but all of the passive networks need to be retuned.

I have a 1K/10W discharge resistor on alligator clips for this exact reason.  When I shut off the PSU, I clip the resistor to the B+ supply and it discharges quickly enough to do immediate work on the supply.

- Bias: I'm using a fluke 175 but I'm not sure I'm measuring Bias accurately. Every time I probe P-ground and P-Bias, the voltage shown is lower (-1.3/-1.5v) and creeps up to -1v where I've set it previously. Is this normal? if so, should I aim for the DMM-free voltage or loaded by the DMM?
If it's not normal, any ideas?

Where exactly are you measuring?  If you measure at the tube plate it is expected.  The best place to measure is in the PSU (at the 5-pin connector block), or right where P4 enters the mike.  If you measure on the "other" side (or tube side) of R11 then the meter impedance will foul up the measurement.

- there's a windy sound but I'm 100% sure it's my room and windows and computer and etc. I'm in the studio 3 days this week so I'll be able to try that out.

If you have rumble and hiss noises, try ditching the stock altron capsule. even a £10 EH6072 is free of most of those issues and sounds quite acceptable.

Wind noise typically means the tube needs more burn-in time.  Leave it on for a few days and check again.

 

[jplebre]

Hi Mata!

Thanks once again for your patience!

Where exactly are you measuring?  If you measure at the tube plate it is expected.  The best place to measure is in the PSU (at the 5-pin connector block), or right where P4 enters the mike.  If you measure on the "other" side (or tube side) of R11 then the meter impedance will foul up the measurement.

I am actually doing this at the PSU molex terminal Pin4 and P6 (I think.... ground one...), using the tightening screw as the probe point.

Also, I see you left provision for ground wiring. Chunger never mentioned adding extra ground wire.
Is the little jumper between the Xlr Pin 7 and the ground tab really enough?

Cheers

 

[Aaronrash]

The EF12 heats off of negative voltage. The power supply you designed for the C12 actually seems like a perfect candidate for the U47 build with a few modifications. I need +A 120V that will be sent to a voltage divider in the mic and then it will polarize the capsule and power tube operations. Then I need -6V for the heater and that's it, I'll be good to go.

Do you have a schematic?  I bet you can use a positive heater supply just fine.

Yes here's the schematic from Mr. Grosser. He also said it's the same schematic Flea uses in their U47/EF12 mics. However he emphasized on how important the -6V is 

Here is also the EF12 data sheet: http://www.hifitubes.nl/weblog/wp-content/telefunken-ef12.pdf

Edit: I removed Andreas schematic because a member here messaged me telling me Andreas doesn't want his work posted anywhere publicly, although Andreas didn't tell me not to post it anywhere I've taken it down anyways.

 

[Matador]

That would be trivial to convert to a positive heater supply (much like the U47):  far easier than converting the C12 supply to negative heater:  mainly because the LM337 and LM317 don't share a pinout, and the heater supply has a fixed ground connection to the plane which would be difficult to break (lots of cutting and dicing).

If you are interested I can show you:  it will end up looking very much like a G7 in fact and should sound exactly the same.

 

[chunger]

Hey Matador,

Are you able to provide a bullet point list of component flops and trace re-routes that need to happen in order to change over to negative voltage heater? 

I'm personally interested for U67 PSU application.  I have a dremel and am not afraid to use it  ;D  I figure the LM337 is easy enough to switch by mounting it upside down in the heatsink and running individual wires down to the PCB.  The rest of it might get a bit more involved, but I'm good with my hands and reasonably confident I can execute even extensive re-routes on the board.

From a cost perspective, it might still be advantageous to use this PCB and OEM Alctron donor PSU for the project.

I know.. . it's probably the same thing. . . easier to change the mic over to positive heater on the U67 circuit as well. . .    But I want to build both the kit provided PSU in Dan's enclosure as well as our modified PSU to compare side-by-side to validate.

 

[robomatique]

Can you post a clip of what the mike sounds like?

THanks for getting back to me! I just recorded a few word. I have attached the file as a txt file, download and change the ending to mp3 and it should work (?).

By the way, would R1 and R2 be ok as .1w resistors?

Thanks!

Borderline:  those resistors have about 1mA, which is 0.001*0.001*91000 = 0.091W.  You can probably get away with it due to the sandbagging by the manufacturer, but those really should be 0.25W parts if you want to count on them for the long haul.

THanks Matador, I will get some new resistors!

Did you ever have a chance to listen to the clip? Did it say anythiung to you?

THanks again for all your help!!!
Robert

 

[Matador]

Hey Matador,

Are you able to provide a bullet point list of component flops and trace re-routes that need to happen in order to change over to negative voltage heater? 

I'm personally interested for U67 PSU application.  I have a dremel and am not afraid to use it  ;D  I figure the LM337 is easy enough to switch by mounting it upside down in the heatsink and running individual wires down to the PCB.  The rest of it might get a bit more involved, but I'm good with my hands and reasonably confident I can execute even extensive re-routes on the board.

From a cost perspective, it might still be advantageous to use this PCB and OEM Alctron donor PSU for the project.

I know.. . it's probably the same thing. . . easier to change the mic over to positive heater on the U67 circuit as well. . .    But I want to build both the kit provided PSU in Dan's enclosure as well as our modified PSU to compare side-by-side to validate.

Makes sense:  I'll take a look.

 

[Aaronrash]

I'm definitely interested in going this route as well

 

[scott_humphrey]

The EF12 heats off of negative voltage. The power supply you designed for the C12 actually seems like a perfect candidate for the U47 build with a few modifications. I need +A 120V that will be sent to a voltage divider in the mic and then it will polarize the capsule and power tube operations. Then I need -6V for the heater and that's it, I'll be good to go.

Do you have a schematic?  I bet you can use a positive heater supply just fine.

Yes here's the schematic from Mr. Grosser. He also said it's the same schematic Flea uses in their U47/EF12 mics. However he emphasized on how important the -6V is 

Here is also the EF12 data sheet: http://www.hifitubes.nl/weblog/wp-content/telefunken-ef12.pdf

Edit: I removed Andreas schematic because a member here messaged me telling me Andreas doesn't want his work posted anywhere publicly, although Andreas didn't tell me not to post it anywhere I've taken it down anyways.

This seems a bit off topic, and I agree that you shouldn't post Mr. Gosser's schematic without his permission. I'll bet that there is a simple way to accomplish the same thing without having to modify the board. I'm glad to explain. If you're interested just PM me.

I've used the power supply board from this project for another home brew mic with good results. It's great in that you can easily adjust the B+ and bias voltage, so you theoretically could use this board with a variety of different tubes. I'm using it with a 6ak5w and Beesneez K7 in an Equinox body and am very happy. I'll post this separately once the circuit is finalized.

 

[chunger]

Important Note!!!

The new revision 1.2A PCB's have a screen printing difference from rev. 1.1A.  The indicator for "cath" was originally at the C10 junction in the older pcb and is now at C11.  Both nodes are ground points and will work for connecting the wire, but the build documentation reflects connecting at C10.

 

[jplebre]

Yikes! I was actually running to my mic before I realise that if the cathode was not plugged in I would have noticed

Matador, did you have any thoughts on the Bias measurement drift?