MK7 - tube mic project

[EEMO1]

ok,

well... I guess it's cool. looking at ioaudios m7 adapter/holder, I started to wonder if that even fits with the screws on top of the capsule.

i need one of those holders btw.

 

[ioaudio]

yes, my DIY m7 holder fits. it´s just a brass strip, with a M3 rod to connect to the rubber part. the screw on top for clamping the capsule is M2, M3 would not fit on into the headbasket.
jonkan, which measurement do you need? chinese capsules are 32mm in diameter.

as been mentioned, the capsule sitting high is also part of the acoustic environment.
http://gwagner.50webs.com/U47_transparent.jpg
edit: no direct link of the pic possible, check http://www.wagner-microphones.com  there is a transparent pic showing the capsule height.

the g7 psu is not suitable, too much ripple on the heater supply.

 

[bradb]

What if we applied the mods you suggested for the tbone to the G7 supply?  Would that tame the ripple?

 

[EEMO1]

i've had a bit of hard time finding brass strip in my local hardware store... Guess i got to go deep for this one. 

 

[bradb]

max, your U47 capsule transparent image link isn't working... can you double check it?

EDIT:
here's something that shows the capsule height, sorta:

http://audiotuts.s3.amazonaws.com/33_studiomics/neumann_u47tube.jpg

 

[MATTI]

http://www.groupdiy.com/index.php?topic=30397.0 and http://www.groupdiy.com/index.php?topic=30126.0 ,
lewilson also has mounts to the orignal specs

Matti

 

[ioaudio]

the brass strip holder is ok, you need to file off the head of the m3 screw and make it flat enough so it does not interfere with the ring of the m7. the screw should stick in the brass strip, so you still can turn it for the orientation of the capsule, 
a nice holder as linked above is better/easier to use (while working with the capsule!)

i fixed the link above.

 

[dissonantstring]

hi max,
in light of a possible "custom" body/headbasket GB in the works in the other thread we would need to build a PSU for the MK7 from scratch.

i was wondering if you could provide information on the PSU:

secondaries voltage? (i'm assuming something like 120VAC and 6.3VAC)

can you provide the cap and resistor values of the RC network (4 caps and 4 resistors) where the values are not listed on your PSU schematic on the B+ side?
thanks!
-grant

 

[ioaudio]

the schematics from the modded thomann mic psu show values only for the modded part.
the B+ : caps are 22 or 47µF 250/400V, and some resistors in between dropping voltage, pretty standard, plus two 75V zener in series for limiting the out voltage to 150Vdc. (edit: updates)
if you build a psu from scratch there are more possibilities.
as already mentioned, i could come up with a schematic for a really nice psu, using a choke (i´ve seen a good one from hammond, shouldnt be expensive)

-max

 

[dissonantstring]

hi max,
thank you very much for the information - most helpful.

if you build a psu from scratch there are more possibilities.
as already mentioned, i could come up with a schematic for a really nice psu, using a choke (i´ve seen a good one from hammond, shouldnt be expensive)

-max

that would be awesome.  no rush - it would be great to have that option.
many thanks!
-grant

 

[bradb]

Max, you rule.  I'd be very interested in a custom PSU.

Could your PSU design be made strong enough to power 2 MK7s?

 

[plumsolly]

Got mine today - looks awsome. thanks, max

 

[stitch-o]

What if we applied the mods you suggested for the tbone to the G7 supply?  Would that tame the ripple?

As I have a couple of G7 PSUs here, I am very curious as to this...

Otherwise, I'm in for a custom ioaudio PSU build!

Cheers!

 

[ioaudio]

updated first post, please reload the schematics & parts list.
the modded psu is fine now.

 

[ioaudio]

What if we applied the mods you suggested for the tbone to the G7 supply?  Would that tame the ripple?

As I have a couple of G7 PSUs here, I am very curious as to this...

sure, use what you already have, especially when you mount it in a bigger box and space is not an issue. it´s the same lm317, just compare the schems, dont forget to change the the surrounding resistors accordingly (i choose them so that even with the wiper open the output voltage should not go higher than the specified 10v for the big caps) .


capacitive coupling for the caps can be a problem, so do not mount the 10000µ close to the power transformer.
when you start from a higher rectified voltage (loaded), you can dial in a higher voltage from the lm317 (and use caps with a higher voltage rating) use bigger resistors for the 3,3 and 2,2 ohm.
you can find a calculator for RC filters here:
http://www.pentodepress.com/calculator/RC-ripple-filter.html

exploring possibilities, you can also add a choke to the schematic. allied has the Triad C-40X 0,3H 500mA 10ohm for $10.97
together with on 10000µF thats 61.4dB attuenation with a 3 volt drop at 300mA/100Hz

http://www.pentodepress.com/calculator/LC-ripple-filter.html

search for "ripple" from user prr for very good psu information.

if B+ differs from 150v re-calculate the resistors 50k for the pattern and 1,4M in the mic.

 

[natek]

the schematics from the modded thomann mic psu show values only for the modded part.
the B+ : caps are 22 or 47µF 250/400V, and some resistors in between dropping voltage, pretty standard, plus two 75V zener in series for limiting the out voltage to 150Vdc. (edit: updates)
if you build a psu from scratch there are more possibilities.
as already mentioned, i could come up with a schematic for a really nice psu, using a choke (i´ve seen a good one from hammond, shouldnt be expensive)

-max

I would be interested to see what you come up with for a custom PSU for this mic, i like the idea of having a specifically designed PSU to go with this great Mic concept.

 

[Linus]

Is there another name or model number for PF86 tubes?  The voltages are different than EF86, correct?

 

[ioaudio]

i just realiced that the parts list was showing only the pf86, i updated that.
the heater voltage and current is different. nominal 4,5v@300ma for pf86 and 6,3v@200mA for the ef86.

 

[ChuckD]

Hey Max,


Any chance of just getting a PCB set for this project and I could use a BV8 clone by cinemag instead of your transformer? Then if you ever make some more  transformers I could swap that in?
I am currently putting together a bunch of mics and would love the chance to try this design out.

Thanks!

-ChuckD

 

[ioaudio]

hi chuck and all who emailed me,
i do not have pcbs or sets/transformers left for sale at the moment. please be patient, i´m working on it.

-max