Official C12 Clone - Build and Support Thread

[Winetree]

The Triplets are fine and are resting
waiting for new capsules.

 

[tonycamp]

good to see these successes! I'll be joinin ya"ll shortly

 

[Matador]

Both sets are measurements with no C10

tube socket pin 1= 117v at psu 131v
"        "        pin 2= -0.55 at psu 1.1v
"        "        pin 3=grnd grnd
"        "        pin 4=6.3 at psu6.5

with the p4 at the entry of the mic shorted to ground

tube socket pin 1=113v at psu 125v
"      "        pin 2=0.56 at psu .040
"      "        pin 3 grnd grnd
"      "        pin 4=6.3 at psu 6.5

thanx
T

So let's summarize so far:

1) Shorting the grid at pin 2 causes the current to shoot up:  correct
2) Shorting the turret where C10, R11, and R15 join causes the current to shoot up:  correct
3) Removing C10:  current changes: incorrect
4) Removing C10, shorting right at P4 where it enters the mike:  not much current change:  incorrect

DC bias current should not change when C10 is removed:  it is a filter only.  C10 is suspect.

So let's narrow down the rest of the components at these nodes (which are R11 and C13).

Pull C13.  Leaving C10 out, short the same node as step 2 above and make sure the current still increases (meaning pin 1 drops).  Then short P4 as it enters the mike:  if R11 is ok, you should see the current increase the same way as it did shorting the turret as in step 2.

 

[tonycamp]

Both sets are measurements with no C10

tube socket pin 1= 117v at psu 131v
"        "        pin 2= -0.55 at psu 1.1v
"        "        pin 3=grnd grnd
"        "        pin 4=6.3 at psu6.5

with the p4 at the entry of the mic shorted to ground

tube socket pin 1=113v at psu 125v
"      "        pin 2=0.56 at psu .040
"      "        pin 3 grnd grnd
"      "        pin 4=6.3 at psu 6.5

thanx
T

So let's summarize so far:

1) Shorting the grid at pin 2 causes the current to shoot up:  correct
2) Shorting the turret where C10, R11, and R15 join causes the current to shoot up:  correct
3) Removing C10:  current changes: incorrect
4) Removing C10, shorting right at P4 where it enters the mike:  not much current change:  incorrect

DC bias current should not change when C10 is removed:  it is a filter only.  C10 is suspect.

So let's narrow down the rest of the components at these nodes (which are R11 and C13).

Pull C13.  Leaving C10 out, short the same node as step 2 above and make sure the current still increases (meaning pin 1 drops).  Then short P4 as it enters the mike:  if R11 is ok, you should see the current increase the same way as it did shorting the turret as in step 2.

Hello Matador,

Ok, pulled C13 and jumped left turret at r15 to ground, C10 still out

tube socket pin 1=97v at psu=119v
"      "        pin 2=-0.50 at psu=-1.15
"      "        pin 3=grn
"      "        pin 4=6.3 at psu=6.5

Removed jumper at R15 and jumped p4 to grnd entering the mic

tube socket pin 1=97v at psu 119v
"      "        pin 2=0.544 at psu 0.039
"      "        pin 3 grnd
"      "        pin 4 6.3 at psu 6.5

?

thanx
T

 

[Matador]

Ahh...that is now correct.  Either C10 or C13 is suspect.  C13 could be leaking polarization voltage on to the grid, or C10 is leaking to ground and causing a bias across R15.  If C10 was leaking, this should try to pull the grid higher which would make the current higher, which isn't what you are seeing.  If C13 was leaking, then it would drop across R15 which would make the polarization voltage lower which would cause the current to drop (which you are seeing).  So I'm leaning towards C13 but you should check both.

Do you have any non-styrene 1nF and 5nF caps you can try in these positions? 

In order to isolate between the two, you can try:

1) Leave P4 grounded and both caps out.  You should see pin1 at ~97V just like you already have.
2) Insert C10 back in.  You shouldn't see pin1 change from 97V, as the cap should not effect the DC bias level.
3) If on inserting C10 you see pin1 jump back up to 120V, then C13 is suspect and should be replaced.
4) Assuming #2 is successful (pin1 stays at 97V after C10 goes back in), re-insert C13.  If you see pin1 shoot back up to 120V then C10 needs to be replaced.

If either of those two caps are leaking DC current then it will cause foul-ups of the bias (due to the astronomically high impedances of the bias resistors).

 

[tonycamp]

Cool Matador,

and then there were 2!, i do not have any caps to use as substitutes, I am going to frys right now tho get some new soldering tips, i'll look for a couple of the caps while i'm there(prob wont have), i will follow your instruction when i return. Do you by chance know the manufacturer of the styrenes in the kit, or part #'s, so i can order new ones?

again, thanx a lot for guiding me through this buddy
T

 

[Matador]

I got the original styrene parts from www.justradios.com:  I think Chunger may have as well.  Go to their cap page, and look for the section titled 'Polystyrene Film "Tubular axials"'.

You should be able to find 1000pF and 5000pF (or 1nF and 5nF, or maybe even 0.001uF or 0.005uF) ceramic caps at Frys for testing.

 

[tonycamp]

Ahh...that is now correct.  Either C10 or C13 is suspect.  C13 could be leaking polarization voltage on to the grid, or C10 is leaking to ground and causing a bias across R15.  If C10 was leaking, this should try to pull the grid higher which would make the current higher, which isn't what you are seeing.  If C13 was leaking, then it would drop across R15 which would make the polarization voltage lower which would cause the current to drop (which you are seeing).  So I'm leaning towards C13 but you should check both.

Do you have any non-styrene 1nF and 5nF caps you can try in these positions? 

In order to isolate between the two, you can try:

1) Leave P4 grounded and both caps out.  You should see pin1 at ~97V just like you already have.
2) Insert C10 back in.  You shouldn't see pin1 change from 97V, as the cap should not effect the DC bias level.
3) If on inserting C10 you see pin1 jump back up to 120V, then C13 is suspect and should be replaced.
4) Assuming #2 is successful (pin1 stays at 97V after C10 goes back in), re-insert C13.  If you see pin1 shoot back up to 120V then C10 needs to be replaced.

If either of those two caps are leaking DC current then it will cause foul-ups of the bias (due to the astronomically high impedances of the bias resistors).

C10 back in, tube socket pin 4 holds at 97v
C13 back in, tube socket pin 4 jumps to 120v to 130v! acted very erratic!

DAG NABBIT!!! C10 IS THE VARMINT!!!

Is it normal to want to smash it with a hammer now?

You know, i'm thinking i should just replace all 3 styrenes now that i've ironed them a bunch of times(i did heat sink clip them every time)? Also as i've been thinking about it, pre tinning the outside of turrets and wrapping around would allow an ultra quick contact with the iron, vs filling the turret which gives more mass for the heat to hang onto longer, maybe i did toast it? we'll never know ???

Thanx again for all your help Matador, if i can return the favor someday(obviously outside the realm of electronics), it would make me happy

T

 

[Matador]

C10 back in, tube socket pin 4 holds at 97v
C13 back in, tube socket pin 4 jumps to 120v to 130v! acted very erratic!

DAG NABBIT!!! C10 IS THE VARMINT!!!

Just to make sure:  if it goes wonky with C13 back in, then C13 is the culprit...not C10. 

Was that just a typo?

 

[tonycamp]

C10 back in, tube socket pin 4 holds at 97v
C13 back in, tube socket pin 4 jumps to 120v to 130v! acted very erratic!

DAG NABBIT!!! C10 IS THE VARMINT!!!

Just to make sure:  if it goes wonky with C13 back in, then C13 is the culprit...not C10. 

Was that just a typo?

Ok, i'm replacing all three just to be safe, you did say c10 on number 4. above though

T

 

[Matador]

Also, if you are going to order new ones from JustRadios, buy a couple of all of these following types (since you only need two values, 1000pF and 5000pF, and they are all less than $1):

1) 500V 5% Dipped Silver Mica Capacitor
2) 630V Metal-Foil Polypropylene "Orange Dip" Capacitors
3) 630V Metalized Polypropylene Film "Tubular axials"
4) 630V Polystyrene Film "Tubular axials"

For C11 and C10 it's not as critical, as they are just filters that dump noise to ground.  However audio does pass through C13 and you might find slightly different "mojo" with the above types.

 

[Matador]

Ok, i'm replacing all three just to be safe

T

Understood:  when you get them, I highly suggest putting them in one at a time in a process like you just did, and you can test each one in turn and make sure they are ok.

 

[tonycamp]

will do all of the above Matador, thanx a million

Edit 8 months later; I just noticed i never resolved on this thread, even though i've had this mic working for 8 months now, somehow i must have burned a polystyrene cap..C10(i think it was), i replaced all three, put in the Tim Campbell capsule, and  amazing mic!

thanx Matador and Chung

 

[Matador]

Got one working today. It seems that the meter drags down the readings on the B+/Bias circuit. So the only way I was able to get it adjusted is by taking quick readings followed by an adjustment, repeated until I got it into the correct range. I'm assuming this is normal.

Yes.  If you use a DVM with 1M input impedance, it will draw 120uA of current from B+.  This will drop an additional 20V or so from the B+ supply.

If you have a DVM with 10M input impedance, or a scope with a 10x mode, this is preferred.  Otherwise, you can not stuff the 470K bleeder resistor until after you have made the circuit adjustments, and then place it back in after the mike is set up.  The bleeder will substitute for the meter, so the voltage will by definition not be higher due to the effect of the meter.

 

[Ericbazaar]

Hi at all,

first to my Person, i am absolutely new in Mic Building and I'm from the area Ribbon Mic. I am from Germany and please excuse my bad English.
I saw a few weeks ago the studio page 939 and I knew I will build this microphone. I ordered everything.
I build the Mic in last 2 Days.
I have some questions. Is it even possible to make a test with the stock Tube and the stock Capsule? I still waiting for the right Tube and Capsule. The shipping takes a long time from the USA, unfortunately. The values ​​of the PSU are normal.
Unloaded B+ = 195V
Heater          = 6.5V
Bias              = -1,0V
Is it possible to test the microphone without a right tube and a right Capsule? Unfortunately I have ever started a recording and this micro does not sound good, extremely quiet level, it hums, it has no bass, sounds harsh.
Please do not scold me, I should not have to make, I know...
I only have the stock tube, so can I measure values​​ with it? I have ordered a 6072A gold by Electro Harmonix. Should I rather wait for the tube?
How are the values ​​at the micro body and how can I measure, without tube?

Many Thanks

Eric

 

[HellfireStudios]

I would not do any calibration without the intended capsule and tube, but a functionality test (make sure it outputs sound) could be done with the the original capsule and tube.

-James-

 

[Ericbazaar]

Hi again,

here are a few pictures. The SMD is unfortunately not in the middle of the contacts, are there problems? Have I done everything right?
https://www.dropbox.com/s/pjuybi39d2v5s4n/IMG_9591_DxO.jpg
https://www.dropbox.com/s/16lcztrhe1d5nzt/IMG_9593_DxO.jpg 
https://www.dropbox.com/s/oh81wvr3lrqgmok/IMG_9594_DxO.jpg
https://www.dropbox.com/s/l798dj43an0tped/IMG_9595_DxO.jpg
https://www.dropbox.com/s/8yw2yav3pxgwy9z/IMG_9596_DxO.jpg
https://www.dropbox.com/s/zybzkoq6upfteqm/IMG_9597_DxO.jpg
https://www.dropbox.com/s/4jthrjxmvjfv61o/IMG_9598_DxO.jpg
https://www.dropbox.com/s/ar7tbit50kjgjqi/IMG_9599_DxO.jpg
https://www.dropbox.com/s/ty6cflqsv0t9dlg/IMG_9600_DxO.jpg

 

[Matador]

Hi at all,

first to my Person, i am absolutely new in Mic Building and I'm from the area Ribbon Mic. I am from Germany and please excuse my bad English.
I saw a few weeks ago the studio page 939 and I knew I will build this microphone. I ordered everything.
I build the Mic in last 2 Days.
I have some questions. Is it even possible to make a test with the stock Tube and the stock Capsule? I still waiting for the right Tube and Capsule. The shipping takes a long time from the USA, unfortunately. The values ​​of the PSU are normal.
Unloaded B+ = 195V
Heater          = 6.5V
Bias              = -1,0V
Is it possible to test the microphone without a right tube and a right Capsule? Unfortunately I have ever started a recording and this micro does not sound good, extremely quiet level, it hums, it has no bass, sounds harsh.
Please do not scold me, I should not have to make, I know...
I only have the stock tube, so can I measure values​​ with it? I have ordered a 6072A gold by Electro Harmonix. Should I rather wait for the tube?
How are the values ​​at the micro body and how can I measure, without tube?

Many Thanks

Eric

Kein Problem...your English is far better than my German.

You can test with stock tube and capsule:  however you'll have to re-do the calibration with your new tube.

As before, with tube installed, take voltage readings on pins 1, 2, 3, and 4 right at the tube socket with tube installed.  The stock tube is a 12AX7, which has too much gain for this circuit, so that may explain some of the harshness.

 

[Ericbazaar]

Hi at all,

first to my Person, i am absolutely new in Mic Building and I'm from the area Ribbon Mic. I am from Germany and please excuse my bad English.
I saw a few weeks ago the studio page 939 and I knew I will build this microphone. I ordered everything.
I build the Mic in last 2 Days.
I have some questions. Is it even possible to make a test with the stock Tube and the stock Capsule? I still waiting for the right Tube and Capsule. The shipping takes a long time from the USA, unfortunately. The values ​​of the PSU are normal.
Unloaded B+ = 195V
Heater          = 6.5V
Bias              = -1,0V
Is it possible to test the microphone without a right tube and a right Capsule? Unfortunately I have ever started a recording and this micro does not sound good, extremely quiet level, it hums, it has no bass, sounds harsh.
Please do not scold me, I should not have to make, I know...
I only have the stock tube, so can I measure values​​ with it? I have ordered a 6072A gold by Electro Harmonix. Should I rather wait for the tube?
How are the values ​​at the micro body and how can I measure, without tube?

Many Thanks

Eric

Kein Problem...your English is far better than my German.

You can test with stock tube and capsule:  however you'll have to re-do the calibration with your new tube.

As before, with tube installed, take voltage readings on pins 1, 2, 3, and 4 right at the tube socket with tube installed.  The stock tube is a 12AX7, which has too much gain for this circuit, so that may explain some of the harshness.

Hi Matador,

ok…Fair I between PSU/P6 and Mic Tube Socket Pin 1 so I have B + of 130V with a bias value of -1 volt. I change the bias to 0.0 volts B + drops to 90Volt on Tube SOCKT Pin 1, is this a correct response?
The Measurements are: PSU/P6        Tube Pin 1 = about 130V 
                                                      Tube Pin 2 = about -0,45V or ca 460mV
                                                      Tube Pin 3 = about 41,3mV
                                                      Tube Pin 4 = about 6,3V

                                                      Polar at Omni = 78V
                                                      Polar at Cardioid = 30V
                                                      Polar at Figure 8 = 0,0V
All with Stock-12ax7-Tube.

Thanks Eric

 

[Winetree]

I got 118.5 VDC with the stock capsules with all three C-12s.
Thought that would change with Tim's capsules
Looks like it doesn't. Does it 1.5 vdc really matter?