MK7 - tube mic project

[MATTI]

From memory...I don´t have the project here on my table while waiting for more parts like the body, what´s the good place to ground the transformer?

Matti

 

[Jonkan]

I just placed a small spacer between the socket and the pcb, and tightened the whole thing alot. Measures just fine on my multimeter, so i think im good.

I did try to scrape away some of the green stuff under the socket to expose the ground more where the socket lies flush with the pcb, but that didnt work as well for some reason.

Anyway, two of my amps are ready now so i started working on the psu.

Is it really possible to mod this with the big 10000uf caps without rebuilding it on perfboard?

The only place where i have room for the electrolytics is either: behind the transformer screen using extended wires to connect to the pcb. Or lying on top of the already existing electrolytics that filter the B+.

What do you guys would be the better choice here? Id prefer not to build it on perfboard from scratch if possible, since i didnt get components to do everything from scratch (big hassle unsoldering all the existing components to use them).

Any chance of seeing a picture maybe from someone how they managed to get everything into that tiny box? If anyone actually used the stock pcb that is...

Or maybe i should just get what i need and build from scratch....hmmm *scratches head*.

/J

 

[bradb]

i build the max pcb, was quick and easy, and i'm more confident that it will work!

 

[bradb]

there's that solder tab on the tranny and a pcb ground hole almost underneath it.

 

[bradb]

i want to make sure this sonics testing process makes sense:

I've got some cheapies for the output cap... does it make sense to do the sonic testing (which roll off I want) with the cheapies, settle on a value and then get a good output cap in the correct chosen value?

 

[bradb]

Some progress pics...

yes, its friday night....


http://img9.imageshack.us/img9/7757/dsc05076h.jpg

http://img16.imageshack.us/img16/4740/dsc05073.jpg

http://img17.imageshack.us/img17/774/dsc05078y.jpg


I think I'm in a pretty good spot, since the PSUs are done.

Waiting on Skylar's case, connectors and bodies

Still need:  EF86s, tubes, Capsules, cabling

 

[bugfight]

lookin good.

i was waiting on those cases to get started, but maybe i'll go ahead and dive in too...
still need tubes, sockets, psu and the high value resistors

 

[0dbfs]

Some progress pics...

yes, its friday night....


http://img9.imageshack.us/img9/7757/dsc05076h.jpg

http://img16.imageshack.us/img16/4740/dsc05073.jpg

http://img17.imageshack.us/img17/774/dsc05078y.jpg


I think I'm in a pretty good spot, since the PSUs are done.

Waiting on Skylar's case, connectors and bodies

Still need:  EF86s, tubes, Capsules, cabling

Looking good!

From the snaps it looks like this is the socket you used:
http://tubedepot.com/sk-b-vt9-st-2.html

I was just wondering whether you were able to source the 1n and 10n styroflex caps in NA?

Have not yet assembled the mk7 boards yet. Still need to acquire: body, PSU/enclosure, socket, tubes, & styroflex...

Plus, I'm thinking that i'll end up sourcing a couple of the different output cap variations and do some A/B "tuning" between the two mic's I am putting together... But that's icing. Gotta get these babies thumping some cones first and foremost.

Thanks!
-jonathan

 

[bradb]

That is the socket i used.


the source for those styroflex is i my bom... in max's first post... a lot in that bom needs to be changed, but the styroflex is good.  I think imo pointed out where those could be obtained.  Memory is fuzzy.


yeah, why not get started!

 

[0dbfs]

Thanks! I hadn't looked at that in a while and was just going by the parts list in the first post...

Here's the link for surplus sales:
http://www.surplussales.com/Capacitors/Poly-Unelco.html

And Banzai:
http://www.banzaieffects.com/Styroflex-c-827.html

Cheers,
jonathan

 

[plumsolly]

for the styroflex/polystyrene caps, PartsConnexion, Michael Percy Audio, Justradios all have them, but i think mostly in 630v. I got some from justradios and they aren't to big.
-Ben

 

[Jonkan]

How many pf86 tubes do you think i should get for 4 mk7 mics? Im thinking of ordering a lot of 10 NOS  VALVO pf86 tubes from germany, completely unused,  that the seller just tested for me to see that theyre indeed working. If im lucky, will that be enough do you think to find 4 of them that are relatively low noise? Im not that picky with noise, as i mostly record rock´n´roll, but they have to be atleast useable for lower spl sources aswell.

Or should I get less than 10... or more even?

What do you think?

I also have three ef86 tubes, of which 2 are ok in noise to my ears. Problem is that theyre not the same brand, and id like the mics to be atleast "semi" matched soundwise.

/J

 

[ioaudio]

tube sellers cannot really test the tubes for our application, where the tube is running at very low power with very high grid resistance.
testing tubes for mics works best in the mic itself.
i had good success with valvo pf86´s, you should be fine with 10 nos tubes.

 

[bradb]

Everyone's been quiet here for awhile.

I'm ordering some parts at redco.com for other tasks and figured I'd throw in some mic cable for the MK7.  The Mogami W3172 has 6 conductors, the Gotham Audio mic cable has 7 conductors.

Looks like we only need 6 conductors for the mk7...  so I'm thinking of going with 20' of the mogami for each mic. 

any comments or feedback from anyone?

 

[Davo]

You're fine with either... I ended up getting the gotham, using 5 conductors and the shield for ground... I'm sure the mogami is just as good ;D

 

[imo]

I'm curious to hear peoples impressions of their builds on this mic. It is a wonderful design, and i've enjoyed it quite a bit.
I recently rebuilt the power supply to the more traditional choke based supply. It gets the voltages where the need to be so i can go back to the original bias, which i think sounds better. I used a Mylar M7 capsule, a pretty low noise EF86. I have experimented with various output caps, using a .47 right now . The mic sounds really nice though i do find it to be a bit lighter in the low end than my Pearlman TM1. Not bad, closer to the U67 in some ways, but I am wondering if this is the nature of the circuit in general.
I have tried using larger output caps, but it doesn't sound as nice.
I am anticipating putting this circuit in one of Skylar's 47 bodies when they are done, and i know there is a lot to be said for mesh, body resonance, etc
If anyone feels on shedding some light on the nature of the 86 style tube pushing this type of output transformer(BV8). how does the transformer respond to the 86 as opposed to a VF14?
Any thoughts on sound, usage, etc?
Best
Ian

 

[bradb]

Imo,

What capsule did you use?  Thiersch?

what brand of output cap did you choose?

what kind of tube, NOS or old or new?

good to hear from someone that's completed the build....

i'm kinda waiting on getting the bodies before i source the tube and capsule... no real reason.

 

[imo]

I used a mylar M7 capsule (Neumann), a Xicon polyester .47 cap(tried other values as well)..I used a NEC EF86, a japanese variant that was smoother and less noisy than any of my other options. I am currently using the "Tbone" mic housing, though i have plans to replace it with the 47 body in the works. DId a bit of experimenting and enjoy the mic. I know Paul(PH) on the forum is really enjoying his mic as well. We did a bit of an unscientific shootout at my studio a few weeks ago. His MK7 sounded quite nice on acoustic and vocals, again similar to the way a 67 has a more focused mid-forward sound. It didn't have the lowend of either my Pearlman TM1 or my Soundeluxe 251. I guess i'm curious if one wanted to chase that down (trying to grab more lowend) are there other avenues than the output cap? Paul and I are using 2 different capsules (his is the Dale M7) different brands of EF86, and different output caps and the mics seem pretty similar in terms of soundstage.
Ian

 

[Jonkan]

I just measured my two finished modded psu:s and im getting these voltages unloaded:

HT: I can trim between 5.9-8v aproximately, so that seems fine.

B+: 145v

Pattern: 112v, 55v, 0v measured directly on the switch were i mounted the voltage divider resistors.

Is that ok voltages?

I just hope that ill have better luck than IMO with my modded psu:s, since im building 4 mics.

/J

 

[ioaudio]

a lot depends on the characteristic of the capsule. try switching capsules and mic amps/circuits if possible.
a couple of things to try:
sometimes you can achieve more "modern" lowend if you try a higher valued grid resistor ~1Gohm instead of 68Mohm.
also "modern" would be the use of a much bigger output cap (~2µF).