Official C12 Clone - Build and Support Thread

[dmp]

Now I've listen the audio samples from Tskguy - there is also present - it's a kind of a pink noise wich can be clearly hear on the HK12  samples but NOT on the C12 samples ( it's harder to hear it on speakers, but on headphones, it's easy - especially on the end of the vocals and ac guitar samples : on the C12 samples you can hear the console's hum but no pink noise, on the HK12 samples - console hum PLUS pink noise) - well, to be more exact, when A-Bing tracks, C12 samples do have a very little self noise wich is normal, but when switching to HK12 track - then seems like  adding a "spoon" of pink noise to the signal.
I first blame my tubes - a nos JAN GE6072 and a nos Mullard 4024(the second build it's a Elam251 mod and use 12at7), but hearing it on every sample I listen I think it's something else - maybe a PSU issue?
I saw that in the original C12 schematics there aren't any var-resitors on the B+ rail, nore any IC on the Heater rail. Could those components be the source of the noise? Or what else?...

It sounds like you've already identified it as noise from the HK12 capsule?

Since the PSU is passive and well filtered, I have trouble thinking it is a PSU problem. But a quick test is to shut off the PSU while recording and see if the noise ceases. I had a tube mic build where I did identify a psu problem with this test.

You could also replace the capsule with a 50pf capacitor and see if you can hear the noise. This will eliminate all sources but the capsule.

 

[bsatriani]

It sounds like you've already identified it as noise from the HK12 capsule?

NO! Please don't induce conclusions that I didn't make!
I don't blame the HK12. I use a RK12 and find the same noise.
All I wanted to know is if someone knows the source of that noise and if it's any way to get rid of it.

You could also replace the capsule with a 50pf capacitor and see if you can hear the noise. This will eliminate all sources but the capsule.

Tried it , not to check the noise, but to check the response from the audio circuit wich I find out to be very good (I like a little more presence so I swapped the Erse .56ut with a ClarityCap .47uf)

 

[bsatriani]

Here is the signal source that was passed through the audio circuit and an overall image(funny isn't it?)....

One more mention: I also played a track through it and I find out that the output is warmer and clearer in the highs than the original - and like it so much!- instantlly made me think of this circuit also being great as an amp for my diy summing box.

I also think the results are not precise as the mic is not being close  - but I've done the test just to make an ideea.

 

[Category 5]

This is not a noisy circuit.  I think the hiss you hear is regular tube noise and obviously the older tubes will have more of it, especially used and abused ones.  I do not find the noise objectionable at all. They mics are plenty quiet for all but the quietest of sources (classical) but I would be reaching for a fet mic in those situations, not a buttery tube mic. 

You can probably bury the noise a little further down by using the 6201/12at7 instead since the gain will be a little hotter and require less from the mic pre. 

 

[dmp]

NO! Please don't induce conclusions that I didn't make!

Jeeze, relax. I was trying to help you.

 

[bsatriani]

NO! Please don't induce conclusions that I didn't make!

Jeeze, relax. I was trying to help you.

I am relaxed and apreciate any help, so thank you!
Your question probably refered to the capsule I use, but as you mention ''HK12'' I don't want to suggest anything about it, therefore my early reaction.
I use the RK12. I will try the stock capsules and also a RK47 I have to see what happens.

 

[Melodeath00]

FWIW my C12 is not noisy. It has about the same level of noise as my point to point U47 build. Do you hear the "pink noise" in the acoustic guitar clip I posted?

Can't tell from the clips you posted, they are edited(cutted) so short. Leave a few seconds before or after the recording source and then I might hear it,...or not....
Now, don't imagine that my builds have a hurricane inside them wich I call "kind of a pink noise", it is something subtle, but it is! 

Any mic has noise, but actually, I found my Sennheiser e906 was much noisier than this tube mic once I turned up the preamp gain to get it as loud as the C12.

Turning up the preamp gain increases preamp self-noise and so will increase noise in every mic(at least this happens with my preamps : SCA, JLM, DAV). A fair comparison would be done at the same preamp gain level/output level, and then lowering the loudest mic level into your daw to match levels.

Yes, turning up the preamp will increase noise, but not as much as it will boost the actual audio signal, assuming the preamp is any good.

In the spirit of your posts, I decided to do a little noise shootout. C12 versus Sm7b. I leave a couple seconds of room tone, then play a short progression, then let there be room tone.

Test 1: Get the same volume going into the A/D. C12 pre is at 7. Sm7b pre is at 10. Don't adjust levels in DAW.

Which is noisier?
https://copy.com/DB70ztYx8Esx
https://copy.com/JEQ1fN8Q6TAx

Test 2: Same preamp gain. Turn the louder mic down in the DAW to the same volume as the quiet mic. Which is noisier?

https://copy.com/TKWY4jdXDp1Z
https://copy.com/2mZNiZAFA1Si

Should I do this test not with an SM7b? Unfortunately all of my LDC mics are tube-based, so i can't compare noise with a FET LDC. I wont post the files but I just did this same test with my DiY U47, and the C12 is indeed a tiny bit noisier. Not pink noise, but a more noticeable hum. Nothing compared to the Sm7b, though.

 

[Woot]

Hi Melo,

Thanks for the above posts - it's nice to have some comparison to my own C12 builds, as I've not utilised any tube mics before so don't have a reference point.

A/A2 certainly are noisier in the upper bits, but am listening on cans, so not sure if I'm missing some low end info.

These both sound similar to my C12 in terms of noise. Which capsule are you using?

Matt

 

[Melodeath00]

Woot,

Yes, A and A2 are quite a bit noisier. That's the Sm7b. My C12 is way quieter than the Shure. Maybe it's not fair since the Sm7b is a dynamic mic, but the point was to show the C12 is not too bad at all. And actually, I just discovered that my 6072 tube used in that test has a hum in it. I replaced it with another 6072 and it's even quieter now.

I'm using Tim Campbell's capsule.

 

[Woot]

Interesting, in that case then my C12 is quite a bit noisier than yours....

I'll do some samples and upload them for comparison

 

[Melodeath00]

Please do. For reference, my interface is a Focusrite Liquid Saffire 56, and the acoustic guitar was peaking at about -12dBFFS for the C12 at Preamp gain of 7. It's quite quiet IMHO.

 

[bsatriani]

Test 1: Get the same volume going into the A/D. C12 pre is at 7. Sm7b pre is at 10. Don't adjust levels in DAW.

Which is noisier?
https://copy.com/DB70ztYx8Esx
https://copy.com/JEQ1fN8Q6TAx

Test 2: Same preamp gain. Turn the louder mic down in the DAW to the same volume as the quiet mic. Which is noisier?

https://copy.com/TKWY4jdXDp1Z
https://copy.com/2mZNiZAFA1Si

Nice guitar sound!! thank you for the posts!

A and A2 clearly noisier than B and B2, and from your other post I see A,A2 is the shure, so B/B2=C12.
The c12 I built is not noisier than yours I think, or if is, not for much.

One more thing,...if you dialed 7 for C12 and 10 for SM7 to get the same volume going into the A/D conv, then the SM7 has lower output than the C12. Now, if test 2 was done at the same preamp gain, why did I had to reduce the A2 sample level in the daw to match the levels when I should have been reducing the B2?!...

Maybe this is going somehow crazy...

Once again, thank you for your clips!!

 

[micaddict]

My C12 is way quieter than the Shure. Maybe it's not fair since the Sm7b is a dynamic mic

Well, since it's a passive design the Shure basically doesn't have self noise (well, theoretically everything does a little, but you get the point). So, if there's noticeable noise, it likely is the preamp (or some other problem). Unless the pre is of high quality, it will struggle, especially in its upper range. I guess that's the reason you added test #2? I don't think that's watertight either, but it should help.

 

[Melodeath00]

Test 1: Get the same volume going into the A/D. C12 pre is at 7. Sm7b pre is at 10. Don't adjust levels in DAW.

Which is noisier?
https://copy.com/DB70ztYx8Esx
https://copy.com/JEQ1fN8Q6TAx

Test 2: Same preamp gain. Turn the louder mic down in the DAW to the same volume as the quiet mic. Which is noisier?

https://copy.com/TKWY4jdXDp1Z
https://copy.com/2mZNiZAFA1Si

Nice guitar sound!! thank you for the posts!

A and A2 clearly noisier than B and B2, and from your other post I see A,A2 is the shure, so B/B2=C12.
The c12 I built is not noisier than yours I think, or if is, not for much.

One more thing,...if you dialed 7 for C12 and 10 for SM7 to get the same volume going into the A/D conv, then the SM7 has lower output than the C12. Now, if test 2 was done at the same preamp gain, why did I had to reduce the A2 sample level in the daw to match the levels when I should have been reducing the B2?!...

Maybe this is going somehow crazy...

Once again, thank you for your clips!!

Thanks! About Test2 - In the DAW, I turned the C12 down, and the SM7b up to about the same level.  Did I make a mistake? Perhaps there was a misunderstanding? The Volume of Test 2 is totally separate from Test 1.

My C12 is way quieter than the Shure. Maybe it's not fair since the Sm7b is a dynamic mic

Well, since it's a passive design the Shure basically doesn't have self noise (well, theoretically everything does a little, but you get the point). So, if there's noticeable noise, it likely is the preamp (or some other problem). Unless the pre is of high quality, it will struggle, especially in its upper range. I guess that's the reason you added test #2? I don't think that's watertight either, but it should help.

Yes, cranking the preamp gain adds noise, but so does hitting the A/D with a lower signal. I agree Test 2 has problems too (hitting the A/D without a good signal will result in noise, too, after all). I wasn't sure how else to do the test, though, and I was following bsatriani's test protocol.

This test told me I would never use the Sm7b on guitar if I have other options available (due to both sound and noise). Maybe my Focusrite isn't as low-noise as I thought? It's their flagship Firewire interface still, so I'm not sure.

 

[mica]

AAAARGH!
Just got a replacement T14 trafo because the first one didn't have any reading om my DMM on the blue wires. (The red wires read around 22R on both) The new one is exactly the same..!! NO reading on any of my DMMs one blue wires.. Can you measure it wrong? I have tried everthing. I dont get it? I can't be that unlucky can i? Two in a row?

From the build doc:

My reading attached, and i of course have tried changing range: ohm, Kohm, Mohm etc.. still nothing..

 

[sr1200]

This might make me sound like a jerk, but based on the red wires... do you have any of the copper exposed or do you have the alligator clips just on the insulation?

 

[mica]

ohh haha the clips are touching the copper.
As mentioned the reading is fine if i do nothing more than change the clips to the two red wires..

 

[chunger]

AAAARGH!
Just got a replacement T14 trafo because the first one didn't have any reading om my DMM on the blue wires. (The red wires read around 22R on both) The new one is exactly the same..!! NO reading on any of my DMMs one blue wires.. Can you measure it wrong? I have tried everthing. I dont get it? I can't be that unlucky can i? Two in a row?

From the build doc:

My reading attached, and i of course have tried changing range: ohm, Kohm, Mohm etc.. still nothing..

HMMM. . . . it is possible you received 2 defective T14's, but the odds of this happening are very small.  Can you send both of them back to me just in case for some reason there is a problem with your DMM?  I will send another one. . . and test it before shipping.

 

[mica]

Ok.. Have tried just about everything. New batteries in the 2 DMM's i have, but no luck. The fact that the readings are spot on, on the red wires leads me to believe that the DMM's are ok.
I will send them both back to you tomorrow.

/Michael

 

[Category 5]

Ok.. Have tried just about everything. New batteries in the 2 DMM's i have, but no luck. The fact that the readings are spot on, on the red wires leads me to believe that the DMM's are ok.
I will send them both back to you tomorrow.

/Michael

That sucks man.  Have you tried passing a signal through the tranny just to see?