Official C12 Clone - Build and Support Thread

[chunger]

Since the PSU connections were already shrink tube wrapped, I decided NOT to cut the connectors and rewire. Does Alctron not use high quality cable, or is it perfectly ok to re-use most of the cable connections? Same thing in te mic. I kept the B+, heater, and polarity control wires in tact. I added my own silver teflon for ground and bias. I did not shrink tube around the connections, but I bought some on Amazon just now, and will re-do those connections if need be.

The mic works as well. I am home for Thanksgiving and have no audio interface, but my brother is here with a portable stereo recorder that has an XLR input, so I know the mic passes signal fine. Polar pattern switching is not working, but I realized I forgot to bridge the rear and front backplate of the tester Alctron capsule, so I assume that would be why. I assume no damage would arise from my mistake, right?

I did not pay attention to which transformer wires went where. I still don't fully understand how you would keep track of polarity in regards to the transformer. All I know is Red goes to XLR and blue goes to the PCB. I will test the polarity when I get back to my studio and swap the blue wires if need be. That's all that matters, right? I noticed the Alctron was inverted polarity compared to my other mics in general, and I did not want to swap the audio wires in the PSU XLR connector since they were nicely shrink wrapped already,

I will probably install the Tim Campbell capsule tomorrow. Why do we test heater voltage at the mic, while we test B+ and Bias in the PSU? Shouldn't we test everything at the mic?

I'm also still confused about the capsule teflon stand-offs. Since the metal pin goes through the teflon and makes contact with the PCB, how does the teflon have any effect whatsoever? Why would it even matter to float those capsule connections, and why are we using the teflon standoffs? It seems all we're doing is wrapping teflon around the connection that is made to the PCB. How is this different from using teflon wire?

Stock wires should work fine in the PSU as long as you remember to unground the bias pin and add a wire which you did.  Heat shrink probably optional especially since the surrounding pins all have the original heat shrink still.

The teflon pins are supplied in the kit just in case you want to isolate the hi Z connections. . . if so, you can drill out/enlarge the holes and press fit the teflon pins.  Then, make the required connections with teflon wire.  Also, pins are convenient because you will not have to clean the PCB again when you change capsules. . . which most people will do at least 1x in the build process.

 

[Category 5]

Stock wires should work fine in the PSU as long as you remember to unground the bias pin and add a wire which you did.  Heat shrink probably optional especially since the surrounding pins all have the original heat shrink still.

The teflon pins are supplied in the kit just in case you want to isolate the hi Z connections. . . if so, you can drill out/enlarge the holes and press fit the teflon pins.  Then, make the required connections with teflon wire.  Also, pins are convenient because you will not have to clean the PCB again when you change capsules. . . which most people will do at least 1x in the build process.

I changed out all my wires for the teflon ones and found many of the original wires cold soldered to the connectors so don't let the heat shrink give you a false sense of security.  Continuity between the pins and wires was okay even with the bad joints but in the long term you could certainly see a premature failure of those connections if yours are as bad as mine were.

Here's a tip if you do rewire them.  Plug the mic cable into the connector while you clean the pins of old solder and solder new wires.  The plastic that holds them melts easily and you could end up with crooked pins.  The cable will hold them in place and help dissipate a little excess heat too.

Do you happen to know the correct drill size for the standoffs for a tight fit Chunger?  Just for reference.

 

[Matador]

I did not pay attention to which transformer wires went where. I still don't fully understand how you would keep track of polarity in regards to the transformer. All I know is Red goes to XLR and blue goes to the PCB. I will test the polarity when I get back to my studio and swap the blue wires if need be. That's all that matters, right? I noticed the Alctron was inverted polarity compared to my other mics in general, and I did not want to swap the audio wires in the PSU XLR connector since they were nicely shrink wrapped already,

Polarity really only matters if you want to use two mikes in close proximity and don't want to worry about them being out of phase.  However there's little reason to do this with two of the same mike.

Testing can be done by placing two capsules in close proximity and clapping your hands while recording both, and making sure the waveforms move in the same direction when zoomed way in.  Even better is to use a sine wave generator direct to the tube grid on both mikes, and make sure both signals move the same way.

It's really pedantic though, I wouldn't worry about it too much.  Phase issues can always be solved by adjusting the position of one of the mikes (which should always be checked and done anyways) or by using a polarity invert switch on the preamp.

I'm also still confused about the capsule teflon stand-offs. Since the metal pin goes through the teflon and makes contact with the PCB, how does the teflon have any effect whatsoever? Why would it even matter to float those capsule connections, and why are we using the teflon standoffs? It seems all we're doing is wrapping teflon around the connection that is made to the PCB. How is this different from using teflon wire?

The standoff still isolates the connection point from contamination when soldering, and makes the impedance to ground consistent from mike to mike.  It's an extra guarantee against noise and for mike-to-mike consistency.

The reasons why we float high impedance connections, and why they aren't strictly "floating" in this design were already covered previously in the thread.

 

[Melodeath00]

Thanks for the answers everyone! I'm back at my studio now. It turns out polar pattern switching IS working after all, despite the backplates of the stock K67 not being bridged. Not sure how that's possible. Anyway, the mic sounds decent as is. A little bass-light. I think that's just an issue with this stock k67. The mic is also very quiet, despite this just being a "tester" 6072 tube. I will put in Tim Campbell's capsule tomorrow night and report back. Luckily polarity is the same as my other mics, so I will not have to mess with the transformer wires

 

[Woot]

Hey Guys,

So after rectifying my n00bish mistake of missing the two underside ground pads, one of the mics has fired up perfectly but the other is still not working.

Still have no output when the preamp is up really high.

I have had a read through the thread and changed c13 as it looks to have sustained a minor burn during capsule change but stil no love. I have double checked all connections and the trafo wirings.

Interestingly the mic transmits body noise when the amp is dialled up ie if I tap on the mic body lightly it comes through headphones nice and clear.

My voltages on the PSU are spot on.

The voltages on the tube are:

5: 6.3v
6: 67.3v
7: -0.9v
8: nil reading
9: 0.5mV

Any advice on where to start would be great.

Kind Regards,

Matt

Hey, just wondering if anyone can give me some pointers where/how to start trouble shooting this mic.

Thanks!

 

[Melodeath00]

Woot, by the "two underside ground pads," are you referring to the two pads for support "beams" for the horizontal tube board? I did not even use those, so I doubt they could be a source of your problem, as I'm not dealing with any problems. They seem to connect to the upper two ground pads anyway

 

[MicDaddy]

I still haven't sorted out my noisy mic :'(.  Waiting on 6072a from TubeDepot to swip swap with the GE from BOWIE.  Will be both happy and sad if that is the issue.  If it does not solve my problem I'll build a second mic circuit from Chunger and attempt to swip swap with the existing, paying special care to not use heavy rosin flux, and will clean the circuit meticulously before installing.

Regarding polarity, there must be a 'correct' way to wire this.  From the schematic XP1 --> TX primary --> TX secondary --> XLR pin2.

A kick drum hit should cause the speaker driver/woofer to push, not suck in. 

 

[Matador]

Hey, just wondering if anyone can give me some pointers where/how to start trouble shooting this mic.

Thanks!

Do you have any way of injecting a signal into the grid of the tube?

 

[Woot]

Do you have any way of injecting a signal into the grid of the tube?

Unfortunately no, a scope etc is on my buy list...

 

[Woot]

Woot, by the "two underside ground pads," are you referring to the two pads for support "beams" for the horizontal tube board? I did not even use those, so I doubt they could be a source of your problem, as I'm not dealing with any problems. They seem to connect to the upper two ground pads anyway

Hi Melo, not the pads for the horizontal beams but 2 of the pads on the board itself (the third one being obscured under the tube socket) there was a post a ways back saying they were needed to complete the ground path.

 

[Melodeath00]

Woot, by the "two underside ground pads," are you referring to the two pads for support "beams" for the horizontal tube board? I did not even use those, so I doubt they could be a source of your problem, as I'm not dealing with any problems. They seem to connect to the upper two ground pads anyway

Hi Melo, not the pads for the horizontal beams but 2 of the pads on the board itself (the third one being obscured under the tube socket) there was a post a ways back saying they were needed to complete the ground path.

Do you have a picture of the pad you're talking about? I guess I'm still not sure, and now I'm worried i didn't take care of that either

By the way, I just referenced the first page build photos again and it appears the bottom two holes below the tube deck are not used. Is that correct chunger or Matador? They are for optional support braces?

 

[Woot]

Do you have a picture of the pad you're talking about? I guess I'm still not sure, and now I'm worried i didn't take care of that either

 

[Woot]

2nd one

 

[Melodeath00]

Gotcha. I did not solder those. Maybe Matador can chime in? All of my ground points seem to be corrently groudned when I test with a multimeter.

An update on my build: Installing the Tim Campbell capsule was much more difficult than I expected. Those are some of the tiniest screws I've ever dealt with, and I wouldn't be shocked if I legitimately spent an hour just trying to screw the capsule into the holder. Thank goodness Tim puts those plastic covers on the capsule as well, or I would have flung solder right onto the diaphragms, if not scratched them with my screw driver. I know; I get chills just thinking about the possibility.

Regardless, my C12 sounds FANTASTIC. I'm using an early 1960s 6072. The mic is not noisy. Great frequency response. Plenty of bass. Actually, it's very similar to my U47 in terms of quality of sound, but to give some comparison, the C12 has a 1-2db cut in the mids around 2kHz to 5kHz, and then a nice 2-3db boost around 7kHz up to 11kHz. The frequency response rolls off at about 15kHz.

The C12 actually seems to have a tiny bit more low-end as well, but it depends greatly on how close I am to the mics.

On my particular voice, that cut in the mids and boost in the air makes me sound more "there" in your speakers. It's remarkable. I suspect my U47 having more audio energy at 15kHz and above than the C12 is not especially "authentic," but they both sound sensational. I'm happy!

 

[micaddict]

Congrats, Melodeath00!
You've come a long way in a short time.
This should be an inspiration for others, including me.


Henk

 

[jandoste]

It's amazing !
Thanks Matador and Chunger!

 

[Matador]

Gotcha. I did not solder those. Maybe Matador can chime in? All of my ground points seem to be corrently groudned when I test with a multimeter.

An update on my build: Installing the Tim Campbell capsule was much more difficult than I expected. Those are some of the tiniest screws I've ever dealt with, and I wouldn't be shocked if I legitimately spent an hour just trying to screw the capsule into the holder. Thank goodness Tim puts those plastic covers on the capsule as well, or I would have flung solder right onto the diaphragms, if not scratched them with my screw driver. I know; I get chills just thinking about the possibility.

Regardless, my C12 sounds FANTASTIC. I'm using an early 1960s 6072. The mic is not noisy. Great frequency response. Plenty of bass. Actually, it's very similar to my U47 in terms of quality of sound, but to give some comparison, the C12 has a 1-2db cut in the mids around 2kHz to 5kHz, and then a nice 2-3db boost around 7kHz up to 11kHz. The frequency response rolls off at about 15kHz.

The C12 actually seems to have a tiny bit more low-end as well, but it depends greatly on how close I am to the mics.

On my particular voice, that cut in the mids and boost in the air makes me sound more "there" in your speakers. It's remarkable. I suspect my U47 having more audio energy at 15kHz and above than the C12 is not especially "authentic," but they both sound sensational. I'm happy!

This was covered in post #624.  Both sides of the tube PCB should be soldered in order to make sure that the tube board receives ground and heater voltages properly.  Having the tube support wires soldered in is a bonus to transmit ground to the tube PCB board.

I have to think about it some more, but I think the tube will transmit a thump without the heaters being lit.  For anyone not seeing the mike amplifying please make sure both sides of the tube PCB pads are soldered to the main PCB (both front and back).

 

[Category 5]

Mat.  The third middle one underneath can not be soldered if the tube socket is installed first so obviously the two side ones are the imperative ones.  Is there any reason to solder the middle too and then install the tube socket after?  I followed chunger's steps therefore the bottom middle pads are inaccessible.

 

[Melodeath00]

Congrats, Melodeath00!
You've come a long way in a short time.
This should be an inspiration for others, including me.


Henk

Ha! I have definitely learned quite a bit over the past year, although I'm not sure I would consider myself an inspiration. When are you going to post a build thread, Henk? I think I'm building a U67 next, but funds are low and I'm waiting for chunger's new body.

Gotcha. I did not solder those. Maybe Matador can chime in? All of my ground points seem to be corrently groudned when I test with a multimeter.

An update on my build: Installing the Tim Campbell capsule was much more difficult than I expected. Those are some of the tiniest screws I've ever dealt with, and I wouldn't be shocked if I legitimately spent an hour just trying to screw the capsule into the holder. Thank goodness Tim puts those plastic covers on the capsule as well, or I would have flung solder right onto the diaphragms, if not scratched them with my screw driver. I know; I get chills just thinking about the possibility.

Regardless, my C12 sounds FANTASTIC. I'm using an early 1960s 6072. The mic is not noisy. Great frequency response. Plenty of bass. Actually, it's very similar to my U47 in terms of quality of sound, but to give some comparison, the C12 has a 1-2db cut in the mids around 2kHz to 5kHz, and then a nice 2-3db boost around 7kHz up to 11kHz. The frequency response rolls off at about 15kHz.

The C12 actually seems to have a tiny bit more low-end as well, but it depends greatly on how close I am to the mics.

On my particular voice, that cut in the mids and boost in the air makes me sound more "there" in your speakers. It's remarkable. I suspect my U47 having more audio energy at 15kHz and above than the C12 is not especially "authentic," but they both sound sensational. I'm happy!

This was covered in post #624.  Both sides of the tube PCB should be soldered in order to make sure that the tube board receives ground and heater voltages properly.  Having the tube support wires soldered in is a bonus to transmit ground to the tube PCB board.

I have to think about it some more, but I think the tube will transmit a thump without the heaters being lit.  For anyone not seeing the mike amplifying please make sure both sides of the tube PCB pads are soldered to the main PCB (both front and back).

Thanks Matador. I noticed that the left underside pad MIGHT be soldered on mine. There is a small gap between the tube PCB and the mic PCB by accident, and it looks like some solder slipped under to the underside. Perhaps that is why I'm not having issues. I will check with a multimeter tonight and solder the right underside pad as well. The middle is inaccessible due to tube socket, as mentioned. I hope the fact that my tube PCB not being flush against the mic PCB is not causing some OTHER issue.

I do have a bunch of cable underneath the tube. Do you think there are any repercussions to tube heat having teflon wires resting against it? Obviously the tube wont be melting the teflon.

I'd also like to note that while my headbasket has a distinct "ping" when you tap on it, this sound is completely unnoticeable during normal usage of a microphone. Regardless, I have some Loctite Go2 on the way to fix the issue and feel more comfortable.

 

[Matador]

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).

As for soldering the tube PCB's:  for the heater connection, if you look closely at the tube PCB:

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.