Official C12 Clone - Build and Support Thread

[tonycamp]

Hey Chung,

when are the pcbs and component kits going to be available? (sorry if i missed it somewhere)
I'm going to the metal supply house on monday next week to try to hunt down some appropriate tubing, I pretty much have a simple method worked out for offset and extending rails as well, I'll let you know how I make out next week.

T

 

[chunger]

I just confirmed general function and calibration on final revision PCB's and parts kits.

pcb's, parts kits, and AMI transformers are now officially available on the webstore http://store.studio939.com

 

[Tommy Radonicus]

I'm going to the metal supply house on monday next week to try to hunt down some appropriate tubing, I pretty much have a simple method worked out for offset and extending rails as well

I've been researching this myself locally (In Australia) as well .. Curious to see how this goes.  8)

 

[chunger]

Just finished up posting the complete build procedure.

A package has been sent to Tim Campbell yesterday for evaluation.

I wish I had a new capsule to show the assembly procedure, but unfortunately, I had to scavenge a capsule from a previous prototype so the picture sequence does not perfectly represent a new build.  I may go back in and re-visit various sections of the build later to clean things up when I have a chance, but in general, I think I've covered everything with enough detail that most people should be able to get through the build.  I also think the new headbasket looks stunning and am very pleased with the proportions of the new mic even though it's too tall now to fit in the original donor mic's pleather baggie.  It still fits in the hard case with room to spare though.

I received a lot of orders for pcb's and parts kits.  I am just finishing up bagging up the kits.  Orders may experience a bit of delay due to volume right now.  Thanks for all your support!

We are running a bit low on HT-11A microphones at this time, but a new order is being worked on to replenish stock and this time I will be ordering significantly more units so we will be able to stay in stock for a while when that arrives.

 

[Matador]

Wow I almost ran out of popcorn for this build. That final version looks stunning, and the build pics are gorgeous.

Many thanks to Chunger for doing all of the really hard work for this project:  sourcing bodies and parts from China, getting custom head-baskets made, arranging component kits, talking to Tim and Oliver, driving prototypes and parts all over Northern California, making detailed CAD renderings of all of the internal mike dimensions, etc, etc, etc.  The very first prototype literraly dropped right in and every screw hole lined up perfectly on the first try due to the attention to detail.  In my 20 years in the electronics industry, this has never happened to me before.  I can guarantee to everyone here that designing the PCB's was the easiest part of this entire project.

I hope every gets a chance to build one of these mikes and hear it in their studio, and will be impressed as we were.

 

[EvLoutonian]

That's a good wrap!
I have to admit, it gets my interest piqued!

 

[chrispsound]

Could I just jumper RB and FB at the board or does there need to be another wire attached to the capsule backplate and connected to the PCB?  I am asking this because I already have a Apex 460 with a microphone parts rk12 in it that I would like to use with your PCB and I am pretty sure the two backplates are not isolated.  Thanks, Chris

 

[Matador]

Could I just jumper RB and FB at the board or does there need to be another wire attached to the capsule backplate and connected to the PCB?  I am asking this because I already have a Apex 460 with a microphone parts rk12 in it that I would like to use with your PCB and I am pretty sure the two backplates are not isolated.  Thanks, Chris

Yes.  Electrically, they are the same net.  The isolated backplate feature is really only used on the ELA M25x that has the on-body polar pattern switching.

 

[tonycamp]

Just checked out the final build! MataChung! You guys just killed this! Absolutely awesome! Imagine how insane it would have been if the pcb was black :-\....... ;D  I got my shipped notice today, cant wait to build my "Sweetbaby". Thats gonna be her name, my Mk47 is named "Badboy"! Corny yet appropriate?

thanx fella's, again awesome job!
T

 

[Winetree]

Got Power Supply built. On voltage adjust the Bias will go down to -2.6 VDC
but I can only got it up to 0VDC and I run out of turns. Small range. It says you can adjust unconnected to mic.
I have the 502 (5K) Bias trimmer placed correctly. Regulator feels cold. Does it regulate bias?
Other voltages in ballpark.
Any suggestions.

 

[JessJackson]

It should be -1vdc (negative one)

Got Power Supply built. On voltage adjust the Bias will go down to -2.6 VDC
but I can only got it up to 0VDC and I run out of turns. Small range.
I have the 502 (5K) Bias trimmer placed correctly.  Everything else OK.
Any suggestions.

 

[Winetree]

Thanks, Human error Misread read Build Guide
Heater can now be adjusted to 6.3 VDC.
On to Mic Build.

 

[Matador]

There needs to be a return current to establish the bias.  If you don't want to use a mike, a 180K resistor is perfect, because the tube is meant to be biased to 0.7mA with -1V on the grid (and a 120V plate supply).  The 180K resistor goes between the B+/120V node and ground.

Otherwise, the only return current is through the 470K bleeder resistor, so the bias will jump after a tube is installed.  Keep in mind that the B+ and bias voltage are not regulated:  they require a current in order to establish themselves.

 

[JessJackson]

Matador, Speaking on this... does anyone think it could be worth building a rectified, choked PS like erics here:

http://www.groupdiy.com/index.php?topic=50834.40

My problem is that different studio locations have different fluctuating voltages and with a passive PS the heater can be anywhere from 5.7-6.9.

 

[tonycamp]

Hi fella's,

I built my Matachung C12 clone this weekend! Was really fun and looks great! The quality of all the parts is outstanding. I will be waiting on a couple of Tim Campbells little darling's now. In the meantime, i THINK i found one discrepancy in Chungers build thread regarding audio pins 5 and 6. They are referred to as pin 5+ pin 6- in one post, and pin 5- pin 6+ in another post?(attached)
I just wanted to point this out so there are no wiring out of phase issues for anyone. I will double check this tmrw, to see if i'm confused about it, i just wanted to make sure it was noted.

I BELIEVE IN STOCK WIRING CONFIG, pin 6 IS + I am a dimwit though, so double check me

T

 

[tonycamp]

2nd post

 

[chunger]

Good catch. . . I've corrected the discrepancy.

Pin 5 -
Pin 6 +

 

[tonycamp]

Hey Chung,

unplugged mic, B+ wont go below 175V!? my bias doesn't move from 0 when turning down? Do you know of a simple reason for this? or did i get the B+ and bias trimmers backward? The Heater is at 6.30v perfect.

 

[Matador]

The heater supply in this design is regulated to the adjusted voltage.

The stock transformer has a 9.5V secondary.  That's about 12.7V after the rectifier diode.  At 600mA heater current, another 2.82V is lost across the 4.7 ohm filter resistor, bringing us down to 9.88V at the regulator input.  The regulator must maintain about 1.5V forward bias so that means the voltage feeding the rectifier cannot drop below 6.3V + 1.5V = 7.8V. 

That gives us about 2V of margin, or about 20% of the secondary voltage ratio:  that means the incoming 120V line voltage would have to be grossly out of spec before the heater voltage started to lower (and this is completely ignoring the fact that the heater has 10-15% tolerance all by itself).

As far as the plate voltage goes:  the tube will operate correctly with anything within 20V or so of the trimmed voltage:  the bias supply might suffer a bit, reducing capsule sensitivity if the voltage were to loose, but again the mains voltage would need to be way out of whack.  If it was good enough for AKG...

I'm not sure there would be much benefit to a choke in the B+ line:  this circuit doesn't pull a lot of current, and the single tube current range is pretty small (from about 0.1mA to about 2mA).  The PSU caps are more than capable of supplying this between charging cycles.  This is unlike a guitar amp that might have 50-100W output power swings, this design is essentially operated as a high-impedance "constant current source".

 

[Matador]

Hey Chung,

unplugged mic, B+ wont go below 175V!? my bias doesn't move from 0 when turning down? Do you know of a simple reason for this? or did i get the B+ and bias trimmers backward? The Heater is at 6.30v perfect.

You really need a test load to set B+ and bias:  put a 180K resistor between B+ and ground right at the 7-pin cable jack on the PSU.