Official C12 Clone - Build and Support Thread

[Melodeath00]

You can heat telfon wire all day with a soldering iron and not effect it:  that's why it costs more than PVC insulated wire (which "shrinks away" as it's heated, making the stripped section twice as long as you cut it).

Hey maybe I wouldn't mind that actually. It was sort of a nightmare trying to strip that 28 gauge wire for the capsule connections. I need to find a smaller wire stripper. Mine only goes down to 22 or so. I had to redo a couple of weak connections caused by bad stripping that caused physical breakage at the connection points. Actually, I got a couple of strands of silver threaded through my thumb while trying to strip the wires. That wasn't fun having to pull out of my skin.

This is the side of the board opposite to the tube socket.  The heater trace runs from the middle pad here up to the heaters.  This means that if the non-tube socket side "middle pad" is soldered to the main PCB you are good to go for the heater + connection.

The ground connections however are on the socket side.  So soldering the side opposite to the socket (on the left and right) only provides mechanical strength with no electrical connection.  You must solder the pads on the socket side on the left and/or right.

If you left the middle pad unsoldered on the socket side (under the socket) it's fine:  it's just for mechanical strength.

I would go back and resolder all pads with the exception of the middle one under the tube socket and you should be good to go.

I'm definitely good on the heater. I will verify the underside pads tonight, although I suspect I "accidentally" have them connected on the left side. Thanks!

 

[Melodeath00]

Matador,

Sure enough, my underside pads appear to be accidentally soldered. I am getting continuity between the mic body and the underside pads, so it appears they are fine. However, then I noticed I am also getting continuity between Ground and Heater. Mic connector Pin 7 and Pin 2 have continuity. That seems odd. Is it expected? There also seems to be continuity between Ground and XP2.

When I turn the mic on, I still have continuity between Ground and the under pads, but continuity is lost between Ground and Heater. In fact, I suddenly get a "Low Battery" signal when I tried to measure continuity between Ground and Tube Heater. Any idea what's up with that?

Also, my Bias measure -1V from inside the PSU, but at the mic I am getting -0.755V. Is this acceptable, or should I tweak the Bias in the PSU?

Thanks a lot for your help

 

[Matador]

Matador,

Sure enough, my underside pads appear to be accidentally soldered. I am getting continuity between the mic body and the underside pads, so it appears they are fine. However, then I noticed I am also getting continuity between Ground and Heater. Mic connector Pin 7 and Pin 2 have continuity. That seems odd. Is it expected? There also seems to be continuity between Ground and XP2.

When I turn the mic on, I still have continuity between Ground and the under pads, but continuity is lost between Ground and Heater. In fact, I suddenly get a "Low Battery" signal when I tried to measure continuity between Ground and Tube Heater. Any idea what's up with that?

Also, my Bias measure -1V from inside the PSU, but at the mic I am getting -0.755V. Is this acceptable, or should I tweak the Bias in the PSU?

Thanks a lot for your help

The heater continuity is meaningless, as it's the output of a regulator.  So long as you have 6.3V WRT ground you are fine.

XP2 should be grounded, as it's the transformer primary return path.

Bias cannot be measured at the tube grid itself, as the meter current will drop across those huge 30M resistors.  The closest you can measure it is right at the P4 connection as it enters the mike.  There is no current draw through the tube grid so measuring it anywhere in the chain is fine (unlike the heater, which is a sizable current that will drop across the wiring resistances).

 

[Melodeath00]

Thanks for all your help Matador! I do find the "Low Battery" indicator intriguing when i tried to test the continuity to the heater when the mic was on. Hopefully no damage was done to the tube. I wondered if maybe the tube was pulling DC from the batteries of the Multimeter and getting heated too much, but I have no idea if this is even electrically plausible. I'm revealing my ignorance here here.

I received my Loctite Go2 Glue today. I'm not sure how it possibly arrived so soon, as I could swear I received my tracking number today and it already arrived. Regardless, in preparation to work on the headbasket, I put on my Blackspade 2-layer 251-esque headbasket and did the "tap" test for resonance. This 2 layer headbasket makes the same ping sound as the single layer. I am debating whether using glue to dampen the headbasket is necessary, as it appears to be perhaps a feature of this mic body tube size. What do you guys think?

I also tried to do a frequency response test to see how the 2-layer effects things, but without an anechoic chamber/scientific setup, it's hard to be positive the mic didn't move at all between recordings of pink noise. IF the mic did not move at all (and that's certainly a big if), then I can tell you the 2-layer Blackspade design starts rolling off high frequencies at about 8kHz, with up to 4dB difference at 15kHz compared to chunger's single-layer, taller C12 design. I hope to come up with a better testing solution at some point so I can get a more accurate figure/comparison. Even the slightest accidental angle shift could have a drastic effect on the highs

 

[teacat]

Also, I have a batch of capsules coming in from China due in early December

Chunger, can you give us some more details on this? I was trying to decide between the RK-12 and the AK-12. How will your offering be different or similar to either of these?
On a side note I noticed Oliver Archut has a cheap c12 capsule for sale but every time I've emailed him about purchasing one he doesn't respond.

 

[chunger]

Also, I have a batch of capsules coming in from China due in early December

Chunger, can you give us some more details on this? I was trying to decide between the RK-12 and the AK-12. How will your offering be different or similar to either of these?
On a side note I noticed Oliver Archut has a cheap c12 capsule for sale but every time I've emailed him about purchasing one he doesn't respond.

I don't have any specific data on the build specifications the other venders have for their edge terminated capsules but I am sourcing a 6 micron k67 based capsule.  Similar to the 35mm center terminated capsules I already get, these capsules sound surprisingly good, but there is variation from unit to unit and it is not top tier in terms of construction quality.  I am also working on sourcing a top tier Chinese capsule with high manufacture consistency and quality control but pricing may not be favorable enough to justify stepping down from a premium type backplate correct capsule so I have not pulled the trigger on that yet.

The screw pattern and general appearance of the capsules I am importing does not track with other capsules that I have seen on the market right now.

 

[Spencerleehorton]

HI Guys,

What sort of output volume should i expect from this C12? on my allen and heath GS3000 desk i go into the valve channel and have the gain about 2o'clock and go into a line in on another channel which gain is about 12o'clock, so to me its a fairly low output i get from the mic.
In comparison with a Apex 460 to which i have all the gains way down and there is loads of volume.
Is there a way of testing the output level correctly?
Have tried a 2.2uf cap in there and didnt like it so have gone back 1uf and sounds good.
Is it just the transformer which controls the output level? or  is there other tweaks available?

regards

Spence.

 

[Matador]

The gain in the tube common cathode stage is about 30dB.  The transformer (assuming a 10.5:1 transformer like the Cinemag CM-2480) looses about 20dB, which means the net gain is about 10dB.  A 12:1 transformer like the AMI T14 looses 21.5dB which means overall gain is 8.5dB.

The C12 circuit is meant to be high-headroom:  the input can take signals approaching 3 V peak-to-peak without clipping.  The net gain is modest, probably by design.

The Apex 460 is CCDA, which means that a much lower ratio transformer can be used.  For example using a BV8 type at 6.5:1 or even 5:1 means there is 4-6dB more signal coming out of the mike.  I think the stock Chinese transformer in the Apex might be a 5:1.

Aside from converting the mike to CCDA (which can be done with a few resistors and by activating both sides of the tube) and changing the transformer, the only way to get more gain is to move to a higher mu tube like a 12AT7.  You can get a few more dB out of the circuit that way.  Also, increasing the plate resistor and picking a higher-current bias point can gain a dB or two as well.  You can also experiment with increasing the capsule polarization voltage perhaps 10% or so, however you are probably getting into shakier ground.

However I've found that most preamps have 50+dB of gain which is more than adequate of getting the output to line level even on the quietest of microphones.

 

[Spencerleehorton]

HI Matador,

I think my problem with gain is my transformer, i think maybe I'm using a 4:1 or 5:1 ratio which would account for the slightly low output.
My Apex 460 has a Sowter 9610 which is 10:1 in there so i think its best to swap these transformers round and see what I get?

what do you think?

regards

Spence.

 

[Category 5]

HI Matador,

I think my problem with gain is my transformer, i think maybe I'm using a 4:1 or 5:1 ratio which would account for the slightly low output.
My Apex 460 has a Sowter 9610 which is 10:1 in there so i think its best to swap these transformers round and see what I get?

what do you think?

regards

Spence.

Other way around.  Lower ratio will have higher gain but also higher output impedance.  Not sure the tube will like it.

 

[Matador]

Too low a ratio will load the tube down and you'll loose signal even before the transformation happens.

Do you know the input impedance of your desk channels?  If they happen to be 600 ohm, a 5:1 will present a 15K load to the tube, which will clobber the signal.  A 12:1 looks like 86K which only loads the tube by 15% or so.  A more modern 1K balanced input will be even better.

I think you'll find the signal much hotter even moving up to a 12:1, especially if your desk is 600ohm input impedance.

 

[Spencerleehorton]

HI Matador,

My Allen & Heath GS3000 desk is as follows:

INPUT IMPEDANCES
Mic inputs 2k ohm balanced
Line inputs 15k ohm balanced
Tape inputs 22k ohm balanced
Guitar inputs 470k ohm unbalanced

so just to be sure will it be better that i use the sowter 9610 10:1 ratio or the other 4.5:1 ratio one from cathedral pipes?
could i put two of the 4.5:1 ratio transformers in series to get 9:1? or even three to get 13.5:1?
or is that not a good way?
I dont have any other ratios at the moment.

regards

Spence.

 

[Spencerleehorton]

Hi Matador,

done a little test today with the C12 and the Apex460 (modded caps and sowter 9610 transformer with mullard tube)

setup both mics, c12 normal vocal position, apex460 above the c12 upside down, put the phase button in on one of them.
apex 460 with mic gain on GS3000 on -10 (mic gain goes from -10 to 60)
C12 on 30 and levels are about the same.
Definetly hear that the C12 is cleaner and less muddy the midrange just need to get the output up, so im gonna swap the transformers and repeat the test.

regards

Spence.

 

[Spencerleehorton]

Hi Matador,

Have swapped the transformers the one in the apex460 was actually a peluso BV11P, now have similar levels from both outputs of mics.
sounds great now. Gains up around half way for drum overheads, for vocals a little more, havent tried yet for acoustic guitar but will later.

update

Just seen that the peluso BV11P ratio is 5:1, so thats not ideal either, i will pull a 10:1 9610  out and try it as i think i still havent got this right, as the apex 460 output is well down on what it was with the 4.5:1 transformer in it, i must have it the wrong way round.

regards

Spence.

 

[Matador]

So it's going to be hard to compare the two in a transformer swap.

The output impedance of the CDDA stage in the Apex 460 is low:  like on the order of hundreds of ohms.  So moving from a 5:1 to a 10:1 lowers the gain and ("hand waving here") doesn't effect the frequency response, all other things being equal (e.g. similar winding inductance, capacitance).  This is because it's almost impossible to "load down" a follower stage.  The two sound pretty similar, just one is quieter than the other.

C12 won't behave the same:  it's high output impedance means that it's very easy to load down the stage, and since the output impedance of the tube forms a low-pass-filter with the transformer primary capacitance, the frequency response can change drastically as the ratio of the transformer is changed.

Due to loading effects, moving from 5:1 to 10:1 in the Apex 460 will cause a 6dB gain loss.  The same swap in the C12 will only cause a 4dB gain loss, since the loading effects on the tube are drastically reduced.  The higher ratio transformer will probably sound clearer and have more presence in the highs as well (ultra important on a C12).

 

[Spencerleehorton]

HI Matador,

Just to be clear then, the APex 460 will be better using the BV11P transformer which is 5:1
The C12 will be better using a 12:1 transformer? i do have several transformer which i maybe able to configure to have a 12:1.

regards

Spence.

 

[Spencerleehorton]

Hi Matador,

I've put in a Sowter 9610 10:1 and the mic sounds good, lovely bottom end and crystal clear top end , it as a 6072 tube in it, it is still lacking in output when compared to the APex 460 modded as per Fox with a BV11P transformer in there and a Mullard tube.
But gain at half seems to match apex 460 output and similar S/N from both.

regards

Spence.

 

[Category 5]

Hi Matador,

I've put in a Sowter 9610 10:1 and the mic sounds good, lovely bottom end and crystal clear top end , it as a 6072 tube in it, it is still lacking in output when compared to the APex 460 modded as per Fox with a BV11P transformer in there and a Mullard tube.
But gain at half seems to match apex 460 output and similar S/N from both.

regards

Spence.

I don't think you will ever get the gains matched between the C12 and Apex.  The C12 needs to trade some of its gain for drive capability (current).  The Apex uses the second triode as a cathode follower so it has tremendous drive capability already.  That's why it behaves so well with a low ratio transformer.  Think of a CCDA as a plate follower feeding a cathode follower.  You will always need less gain with the 460 unless purposely increase the transformer ratio with the intent of lowering gain. 

 

[tskguy]

Hay everyone! I wanted to mention on this thread I am starting to take orders for my new fully chambered ck12 capsule. Th HK12. Check out my white market thread fro pricing and time frames. I also have some clips of the capsule against some original C12's...

http://groupdiy.com/index.php?topic=49859.0

Please pm with any questions... I only have a very small number at first so they may go fast.

Thanks
Tskguy

 

[chunger]

Hay everyone! I wanted to mention on this thread I am starting to take orders for my new fully chambered ck12 capsule. Th HK12. Check out my white market thread fro pricing and time frames. I also have some clips of the capsule against some original C12's...

http://groupdiy.com/index.php?topic=49859.0

Please pm with any questions... I only have a very small number at first so they may go fast.

Thanks
Tskguy

I'm very excited that this is moving forward.  We've been working tightly with tskguy in development work on this capsule in our kit mic referencing against a very nice vintage original C12, and I believe the prototypes have performed impressively.  I have actually purchased 10 units in the 1st production run to finally realize my original goal of having complete premium kits available for purchase with one click.  Tskguy has been taking his time on the dev work on this capsule, and as always, the machining standards that he holds are impressive.

This is a huge announcement!

Also, Chinese edge terminated capsules have been completed and are shipping to me right now!  Along with a batch of NOS Mullard 12AT7's meticulously tested and selected to a premium noise/tone/microphonics standard for microphone application, fully burned in and tested by Christian Whitmore.

Good things are in the pipeline in C12-clone-land if there is such a place.