newbie builds ioaudio MK47 microphone

[chunger]

OK. . . a lot more hacking last night.  I was just thinking Zayance has a nice power supply PCB and Dany at http://www.collectivecases.com has a pre-drilled case that probably would have been a good idea, silly me decided I wanted to "learn something" and here we are 

ok. . . onward.  Next I go for the back side of the PSU case with the power switch and IEC power jack.

I get an accurate measurement of the hole I need.

Use painter's tape to mark the location and use metal cut-off blades on a rotary tool to cut my square hole.

Fits.

I go ahead and use the part to guide the drill for screw holes.

Next, I center punch the hole for the power switch.

small hole to start.

and follow with a Nieko unibit purchased on amazon.com .  This tends to walk a bit less than a drill bit for the bigger holes.

smooth!  I like this bit a lot.  Cuts the mild steel with ease.

Next, I locate my toroid's final position.

And mark center with a pencil.  There is a lot of room to spare here, so I do not need to be very precise.

and drill my mount hole for the toroid bolt.

back side is drilled.

quick test fit to see how things look in place and verify clearances.

. . . and it looks like we are ok.

Next, I move to the front side and position my components.  LED bezel, pattern rotary switch, input 7 pin XLR, and output 3 pin XLR.

component locations marked.

Next, I center punch and drill with a small bit to start,

. . . and follow with the unibit to bring the holes to final diameter.

LED bezel fits nicely.

Next, the pattern switch.

For the XLR D-type Neutrik connectors, I will have to use a large unibit to bring the holes up to diameter.  Note, this large diameter bit can buck something fierce if it catches and fling your work piece across the room, bend the case, and/or injure your wrist particularly if you are using a high torque drill like I am using here, so please clamp the piece securely and make sure you are in a position with lots of mechanical advantage and stability when drilling these holes.

Bam!

Repeat for the other side.

I use a ruler to position align the XLR jack with the enclosure.

tape it down with painter's tape and use the jack as a drill guide.

and repeat for the other side.

Perfect!

and front side holes are bored.

One last important hole in the enclosure .  My star ground point.  I choose to ground near the 1st capacitor after the choke because I read somewhere on the internet that that is a good position for my primary star ground.  I'm using a #36 bit here and will tap for 6-32.

I grab some 220 sandpaper and wrap it around a pencil eraser.

and "erase" some of the powder coating surrounding the ground point so my tab will make solid contact with the enclosure.

and screw my solder tab to the star ground point.

more flat head 4-40 screws and locking nuts secure my Neutrik input/output jacks.

back-side power components in position.

I re-install the turret board.

And the heat sink assembly.  Now, all components are in position and I just need to wire the connections.

Humans Win!

 

[HellfireStudios]

So close... I bet you can taste it.

 

[David R.]

Hi all, I hope you would suffer a newbee question, but I am really trying to learn and not electrocute myself in the process.  I am building my power supply for ye olde mk47 using the Zayance board and the Antek AN-05T200 transformer.  Here is a link for the spec sheet.  http://www.antekinc.com/pdf/AN-05T200.pdf  I also bought a fender style jewel lamp, to make it pretty.

My question is wiring the transformer.  Here is what I think I should do, can anyone confirm or correct?

Primary:
Tie Red to Red, connect to switch
Tie Black to Black, connect to - (N) on the IEC (with built in fuse)
Connect other side of switch to + on IEC.
IEC ground to star ground

Secondary:
Yellow to board (1)
Tie Grey to White, connect to board (2)

Lamp:
Tie Green to Green, connect to lamp
Tie Blue to Blue, connect to other side of lamp.

Do I have it?  Thanks!

Chunger - great documentation of your build.  I am learning all kinds f stuff here.

-David R.

 

[kante1603]

Hi David,

For primary seems to be correct if you're in 115v land.
Secondary is wrong:Either you tap off the 180v or the 200v,isolate the left-over with some shrink tube or so.Don't connect them to each other.
Lampon't know the specs of the lamp you want to use,but paralleling the two secs seems overkill to me,that's 4 Amps at 6,3 vac......

Cheers,

Udo.

Editlease ask further general questions here:
http://www.groupdiy.com/index.php?topic=41379.0
...just to keep chunger's thread clean

 

[wave]

David,
You use one pair of blue and green for the lamp. There are 2 6.3VAC secondaries each utilizing a blue and green wire.
DO NOT tie the two greens and two blues together.

The 200VAC you get from using the yellow and white lines. Put some shrink tube on the end of the grey line. It is unused

Dave

 

[David R.]

Udo and Dave, thanks much. I am looking at the trafo specs and understand. I am in the US and the lamp is 6.3 volt. 

And now back to pictures of Chunger's build.

 

[chunger]

Hey guys,

I'm at the stage now in the project where I could burn the house down so I'm going to take a step back, make a nice drawing of my proposed wiring so people who actually know what they're doing can verify that it's correct and the grounding will be optimal, etc.  Learning how to draw in google Layout. . . always takes longer to learn new software to make a simple drawing, but it'll pay off down the road.

Note, I have secured a direct source for Alctron microphones and will be using the Alctron GT-2B body for this build which should be very similar to the Nady TCM1050.  The mk47 guts should fit like a glove.  I will have many (ok, maybe a bit more than "many") extras and will make those available if anyone out there would like a nice quality, reasonably-priced Alctron body with no logo for their build.  Lead time 2 months, so probably 2.5 months including logistical groundwork.  My liaison on the ground in China will QC these before they ship to me, so hopefully all will be in order.

Feeler thread is in this forum.  Please ping the poll on the feeler thread here http://www.groupdiy.com/index.php?topic=49290.0 if interested so I can get a rough gauge of interest and quantities.

 

[Matador]

Hey Chunger, you might consider investing in a Greenlee punch for the XLR connectors.  It makes a very clean hole that's just the perfect size for the Neutrik panel Mount XLR connector.  The correct size is 15/16" and the part is Greenlee 730BB-15/16.  It can go through up to 14 gauge steel, and makes a perfect, burr-free hole every time.

I ended up buying two others in addition:  one for 9-pin tube sockets, and one for 8-pin octal tube sockets.  Worth every penny!

 

[chunger]

Well Shoot!!!  That greenlee punch would probably have made life a bit easier and the XLR holes a whole lot less exciting to drill.  That would have been the smart way to go.  Oh well.  Next time.

OK, I was wondering if anyone who actually knows what they are doing can look over my proposed internal wiring to make sure I'm not going to blow something up.  I must warn you. . . I do not know how to draw schematic type drawings, so there likely are mistakes here.  I'm just googling symbols as I go and drawing things willy nilly.

I'm particularly unsure about how I'm coming to the star ground with the audio grounds and the 7 pin xlr ground.  I chose my star point close to the 1st capacitor after the choke. . . wondering if it would be quieter to use a secondary star point upstream from the choke a bit for the grounds coming in from the XLR's. 

I'm also unsure about whether I have indicated to wire the rotary pattern switch properly.

As for the 7 pin XLR pinouts, it seems there is no consensus as to how that should be wired up.  That being the case, I went ahead and wired it to be compatible with the Chinese Apex 460 (Alctron HT-11A) because those are very likely future projects for me (C12-ish build) and if these cables I'm building cost $50 each (Gotham 7 conductor cable and Neutrik connectors) I'm hoping to have as many tube mics as possible use cross-compatible cables in the studio.  I'm hoping I am correct to assume the heater and the large +voltage typically utilize the 2 wires with the larger conductors.  Since it seems the MK47 does not have a dedicated heater voltage, I will retain the same pinouts that would be compatible with an Apex 460, but put the 48V pattern on the 2nd large wire for the mk47.

 

[mulletchuck]

I am an expert by no means, but isn't any point along that ground connection (green line) electrically equivalent, and thus won't be affected if it's before/after the choke?  As long as the star ground is connected to that heavy-duty ground wire you custom-bent, that'll be fine, right?    Consider this post a sidebar question, anyone who replies.

 

[chunger]

Hmmm. . . reading back through the build support thread, it seems people using this transformer are switching the 680R 10W chassis mounted resistor to 1k-1.5K and substituting 1K 5W potentiometer for the 500R 5W for voltage adjustment.  I should probably start at those values to begin.  I have 1K resistor and 1K pot already purchased "just in case".

Hopefully someone who knows what they're doing might be able to take a look at the wiring diagram and see if things need to be changed.  I forgot to insert the LED as well, so I think I'll make the changes to the diagram now to reflect anticipated differences.  Would it be better to switch the 2 previous 1K 10W resistors to slightly higher values instead of the latter resistor and trim pot?

 

[Sredna]

Would it be better to switch the 2 previous 1K 10W resistors to slightly higher values instead of the latter resistor and trim pot?

You just have to try, it'll depend on your trafo, the mike and your local voltage differencies.

With an 1k pot you'll have a larger voltage span.

My trafo gives out a lower voltage so I ended up with 4*500R (no choke) and 5 * 68uF and an 1k pot.

 

[chunger]

Ah. . . also, quick question.  I was wondering if someone can offer a mouser part number for a test-mode switch that would fit here without hacking so I can update the first post's BOM to offer a slightly cleaner build.

 

[mulletchuck]

I'm particularly unsure about how I'm coming to the star ground with the audio grounds and the 7 pin xlr ground.  I chose my star point close to the 1st capacitor after the choke. . . wondering if it would be quieter to use a secondary star point upstream from the choke a bit for the grounds coming in from the XLR's. 

Any connection point along your ground wire to the star ground should be electrically equal.    right, everyone?    Or are you referring to the actual physical placement of the star ground in the chassis?

 

[wave]

Ah. . . also, quick question.  I was wondering if someone can offer a mouser part number for a test-mode switch that would fit here without hacking so I can update the first post's BOM to offer a slightly cleaner build.

Chunger,
Here is the switch I used. It's PC mount as I did a PCB for mine.

http://www.mouser.com/Search/ProductDetail.aspx?R=100SP1T1B1M2QEHvirtualkey61200000virtualkey612-100-A1121

Part #612-100-A1121

Dave

 

[Matador]

For grounding, the answer generally is, "it depends"!

A few suggestions:
1) The largest ripple current is around the rectifier and in the first filer cap.  I would isolate this ground point and have it's own wire to the star ground (basically, cut your ground bus here between the first two caps, and run two wires to the star ground point, one for each)
2) The cable shields (pin 1 for a normal XLR, not sure which one on the 7 pin connector) can be tied directly to the chassis right at the connector.  These can be thought of as extensions of the chassis, so do not need individual wires back to the star ground point.
3) Audio 0V should be tied to the star ground itself, and no place else!
4) The IEC connector ground should be tied directly to the chassis right at the IEC inlet with a dedicated bolt and lock washer

The Rane article is very good, as is the "proper grounding techniques - right as Rane" thread here on GroupDIY.

 

[chunger]

Hmmm. . . a few slight mods.  So the only real critical star ground is my audio 0V and that absolutely needs to go directly to star ground and not hit anything else prior.  The other grounds including output jack pin 1 can just go to chassis, but I'm assuming it doesn't hurt to take those to star.  Technically, I should bore another ground point exclusively for IEC safety ground very close to the IEC, but perhaps depending on proximity to selected star point, it might be ok?  Well, I definitely had the XLR grounds a little wonky so this should be better.  Debating whether to cut that pretty ground bus I worked so hard on 

revised PDF:

https://docs.google.com/open?id=0B5bvhqkG9T7fX29zdFg3ZGpwc1U

Ahhh. . . shoot. . . why not just go all the way and do it proper?

https://docs.google.com/open?id=0B5bvhqkG9T7fVlhTeV9Id1lUY0k

 

[Matador]

You might try it out first.  The distance between your star and the bus is likely pretty short, so cutting the bus may not make much difference for this design.

You can always cut/tune it later should there be a problem!

 

[chunger]

Yeah. . . the ground bus is clean the way it is, and it's only a 2 min. operation to change the ground scheme in a totally accessible area of the case without moving anything else should I have a noise problem.  Given the generous distances I have between the noise-inducing components in a generously sized enclosure, I doubt it will be an issue.

Another quick question.  Is it ok for me to use 2 LED's in parallel here?

 

[dmp]

Another quick question.  Is it ok for me to use 2 LED's in parallel here?

You can generally aim for about 1 mA for an LED. Less if you want it to not be as bright.
The resistor in series with the LED sets the current (I=V/R). If you have two LEDs in parallel they will be sharing the current.
I'd suggest putting the LEDs in series, however. Then they would have the same amount of current and you wouldn't have to adjust the series R.