MK-U47 - build thread

Hi Max,

Understood thx !

I'll check with Cat5 tonight and them email you to let you know status.

Perfect, i think it's better to have a second set of eyes on the mic now.
Thanks Cat5 for helping out!

mk-u47 has landed !

Thanks to Cat5, Stefan and max, got everything dialed in tonight its working fine at 105.1v on the dial.  I put in the 408a and will let them cook for a couple of days.

I had mis-wired the b+ at the binder connector and yellow and green at tube sockets.

I redid my pcb like stefan and redid my gotham cable too

though my eyes were playing tricks on me when the tubes started glowing !

Can't wait to try it out; have the Thiersh blue cap !

Glad you did it - you got me a litlle worried there for a moment!
And a big thanks to Cat5!

ioaudio said:

Glad you did it - you got me a litlle worried there for a moment!
And a big thanks to Cat5!

Click to expand...

All good Max!

I understood the danger and that I was doing build at my own responsibility.

I had only psu on power bar and never touched psu without ground probe in place and only holding plastic ends of probes.

Originally i wired up cable with an additional ground and had star ground in psu also !

Thanks again to you, zayance and Dan for making these great diy kits possible !

Wow do these things sound great.  I put a Blueline in Cowboy's mic and put the Redline in mine and have to say the choice is not as clear as I expected.  The Blue has a sweetness to the mids and top but the Red is bigger on bottom (like i expect from a 47) and possibly a touch more mid forward.  I can't pick a clear winner.

Also,  the Philips tubes were pretty quiet right off the bat.  Certainly quiet enough to use right away.  A pair of RCAs I tried next were even quieter from the start, and a little rounder down low.

Got some NOS WE 408a's however and MAN.  What's the deal with these suckers?  Static central from the start.  These things will really quiet down after burn in?  Do they really sound that much better than the Philips or RCAs?

Haven't installed the GE's I got yet, but so far the Philips and RCA are both winners from first power up.

Any other tube ideas out there?

EDIT - Wow.  I'm surprised to say that even after only a few hours running signal through the tube the noise has calmed down almost completely, and yes, the Western Electric tubes sound great.  Each brand of tube so far has it's own character and the WE seems to have the most build up on the transients (which is consequently a feature I love) and fantastic smoothness.  They are still not as wide on bottom as the RCAs, but definitely a contender for a permanent spot in the MK-U.

Thanks for the review on tubes! I used the Phillips most of the time, their noise level should come down even more after 48 hours of use.

-Max

Here's the schematic for the VF14 version:

Also check out the thread on real-gear forums: http://realgearonline.com/thread/1585/mk-u47

Currently long time testing my "Mini-Passive" PSU - the original NG PSU in a small footprint:

ioaudio said:

Currently long time testing my "Mini-Passive" PSU - the original NG PSU in a small footprint:

Click to expand...

Would like a couple of these!  That's a great looking little design Max! 

Will there be kits or just finished supplies?

I'm not 100% sure because of the housing etc.
Here's the mini version at prototyping stage, still waiting for the chassis mount resistors but voltages are good
and the noise level/hum is very low.
The circuit is the same as the original.

Max,

I hope it's not too late:
I built my power supply with resistors in a TO-220 case.
The advantages:
- No wires - solderable to the PCB
- op to 20W Heat dissipation when mounted to a heat sink
- comperatively small size

I'll put up a picture tomorrow.

To get the idea look at this
http://www.reichelt.de/Dickschichtwiderstaende-TO220/RTO-20F-1-0K/3/index.html?&ACTION=3&LA=2&ARTICLE=89475&GROUPID=4336&artnr=RTO+20F+1%2C0K

I know they exist, but i prefer the wire wound resistors over the thick films to keep it closer to the original.

twin-x doesn't work currently...

...number two

...number three.

The heatsink ist sandwiched together witch the breadboard containing the capacitors and the rectifier diodes.
The pictures should give you an idea.

@Max do you wind the power transformer yourself? If so would it be possible to wind one with  stepped HV tabs (110, 140, 160, 180, 200V) and a 12v Tab. This would be an excellent tranny for this and other tube mic projects.

No, i don't wind power transformers.
Nice, modern take on the PSU, Chef! Are you getting any noise from the thick films during warm up?

When switching on there is a short built up of noise for about 5-10 sec, after that it dissapers again.

Cool, i had some noise issues when i tried those resistors, but they where probably from a different brand.