MK7 - tube mic project

[Skylar]

Looks like its just a power thing not in the audio path.

It's definitely in the audio path! This cap can have a big effect on how your mic sounds, particularly in the low end.
I suggest trying a few things, but, ultimately, any film cap will probably give good results. You start to get into really subjective territory with the choice of output cap.

 

[Kingston]

seems to be some confusion here.

There's the 0.33-0.68uF (or something) cap between plate and output transformer. That one is in audio path, and can have a great effect on the output of the mic. If you want bass, use a higher value. If you intentionally want to cut some nasty proximity effect depending on your mic casing, use a lower value. This is a prime spot for a PIO cap, too, for "better definition" and "more 3d".

There's another 1uF cap in the mic that is for PSU smoothing only. Not need to use anything fancy here, any good film cap will do. Although audiophiles will tell you PSU caps have "tremendous" effect on audio.

 

[guavatone]

Revised: after 10 hrs of being on.

Finally got it going.  All voltages seem pretty spot on. Ht=155 VDC.  Patterns are 0,60, 120.

-Modified G7 PS with Beesneez capsul. big .5uF Russian PIO on output cap. Tung-Sol 806s tube

In MS the sound at front and back seem very different.  Front side has more proximity/bass than the rear in MS mode.  Maybe a burn in issue?  Maybe some capsule anomaly?

I do have a 10uF cap for the pattern decoupling cap to ground.  It seems this was changed to a 4.7uF.

This baby is also really sensitive to movement.  I am curious to see how it holds up with drums or percussion.

Quiet:I don't have an anechoic room, but somewhat quiet and can't hear any hum under the room noise.

-More testing.  I thought it was room noise, but some of it sounds like Hight Freq. diode hash.  I am using el cheapo bridge diode packages.
Then I filter out with HP filter 50-125 HZ, this takes away much of what I thought was room noise.  Possible getting a LF boost somehow.

I will try to post PS schematic

Thanks Max

 

[khstudio]

Hey Max,
I was talking to Gus last night & he recommended I check out your MK7 circuit & PS to use with one of my BeezNeez K7 capsules. I built the Arabella Circuit already which sounds great but wanted to try a circuit that was a little closer to the u47 with the "Fixed bias".

Where can I find the PCB's for this project... especially for the PSU?
If they're not available, could I get the files to etch myself?
Also, I noticed the "MOD" for the PS & that some in the US had noise problems... Gus had mentioned how critical the PS & especially a CLEAN heater supply is for the Fixed Bias... any updates to the noise problems, etc...?

Any advise or help would be great!

Thanks, Kevin

Oh, forgot to ask, what are the dimensions of the MIC Circuit?
Want to make sure it will fit in my body.

 

[Kamel]

Hello,
I've made a custom MK7 with that PSU
http://www.groupdiy.com/index.php?topic=46016.msg577183#msg577183

is there is some interest, and i can do a small batch of PSU PCB

 

[khstudio]

Hello,
I've made a custom MK7 with that PSU
http://www.groupdiy.com/index.php?topic=46016.msg577183#msg577183

is there is some interest, and i can do a small batch of PSU PCB

Very cool build, nice work.
Would you be willing to send me the PCB files so I could etch it myself?
Also, what are your voltages & which Power TX did you use?

Thanks,
Kevin
email:
kevin (at) khstudio (dot) us

 

[MatthisD]

Hello,
I've made a custom MK7 with that PSU
http://www.groupdiy.com/index.php?topic=46016.msg577183#msg577183

is there is some interest, and i can do a small batch of PSU PCB

kamel, if at all possible could I get two PSU boards from you?

Matt

 

[TheGuitarist]

So just finished my mic! Sounds ridiculous... like stupid good... BUT there is psu hiss (the hiss goes STRAIGHT away when i turn it off)

I only had a quick check of a couple of voltages and they seemed ok, so if i should do a comprehensive test i'll do that.
I'm using fixed bias with an ef86 (unless it could be a bad ef86 that has something to do with the PSU?)

So any suggestions? Just move over to self biasing? Do something to the PSU to try and clean it up?

Any suggestions would be great! Would love to use it on a session i have tomorrow night.

 

[djn111]

Hi,

You could try a inductor in the power supply instead of resistor, very effective for HF interference on the power supply line.

DJN

 

[tmuikku]

Yello! Seems like I've lost one of the three glass tubes. Any ideas where to source one (locally) or what to use as substitute? Max, do you have extras if I don't find anything to replace the missing one?

Edit: Well, checked out the thread and seems like I'm not the only one that lost a glass tube. So, going to check out some craft stores. If I don't find any I'll send email to max and ask him to send me a new one. Altough I could try to manage without one and figure out alternative insulating standof.

 

[guavatone]

So just finished my mic! Sounds ridiculous... like stupid good... BUT there is psu hiss (the hiss goes STRAIGHT away when i turn it off)

I only had a quick check of a couple of voltages and they seemed ok, so if i should do a comprehensive test i'll do that.
I'm using fixed bias with an ef86 (unless it could be a bad ef86 that has something to do with the PSU?)

So any suggestions? Just move over to self biasing? Do something to the PSU to try and clean it up?

Any suggestions would be great! Would love to use it on a session i have tomorrow night.

Leave it on for 24 hours with one tube.  See if burn in resolves it.  then try another tube if it is still noisy.  I had this issue with some EF86's

 

[guavatone]

So just finished my mic! Sounds ridiculous... like stupid good... BUT there is psu hiss (the hiss goes STRAIGHT away when i turn it off)

I only had a quick check of a couple of voltages and they seemed ok, so if i should do a comprehensive test i'll do that.
I'm using fixed bias with an ef86 (unless it could be a bad ef86 that has something to do with the PSU?)

So any suggestions? Just move over to self biasing? Do something to the PSU to try and clean it up?

Any suggestions would be great! Would love to use it on a session i have tomorrow night.

Leave it on for 24 hours with one tube.  See if burn in resolves it.  then try another tube if it is still noisy.  I had this issue with some EF86's

 

[dmp]

So just finished my mic! Sounds ridiculous... like stupid good... BUT there is psu hiss (the hiss goes STRAIGHT away when i turn it off)
I only had a quick check of a couple of voltages and they seemed ok, so if i should do a comprehensive test i'll do that.
I'm using fixed bias with an ef86 (unless it could be a bad ef86 that has something to do with the PSU?)

If it goes away when you shut off the PSU it is probably not the tube. Most likely there is insufficient filtering in the psu for either the heater or B+

 

[0dbfs]

Finally finished a couple of these end of last year with skylars first round bodies and dale's last round of M7's. Using them now in sessions quite regularly. Absolutely Amazing. Thanks Max! Thanks Dale! Thanks Skylar! It took me a minute or two to source all the parts and put them together but I played with the circuit quite a bit in other franken-mic's and have learned much.

I happen to use pf86's in mine without issue noted. Purchased five of those PF tubes and the first two worked fine without noise issues. Sounds great.

I am considering getting into a couple EF86's for these but they are obviously more expensive so would rather use the cash for something else if there is not a significant difference. If the diff is fairly significant I don't mind. Also, seems they are more susceptible to potential noise issues but I could be wrong on that.

I am wondering whether anyone has any observations to contribute regarding both / either qualitative and/or quantitative differences in sonic attributes between PF and EF 86's in these mic's.

Appreciate it!

Best,
jonathan

 

[loopermc5]

So I did a p2p of this and for some reason my heater voltage goes down to .5 v when I plug in the tube without tube it's where it should be.All else checks out I redid the circuit 3 times now with the same result what can I be missing!

 

[Kingston]

I am wondering whether anyone has any observations to contribute regarding both / either qualitative and/or quantitative differences in sonic attributes between PF and EF 86's in these mic's.

Well there's the fact that PF86 was only made in the golden age of tubes. While golden age EF86 are still available they are very expensive and chances are the good ones are already harvested and in use. It's used in too many famous "audiophile" projects and guitar amps and that always means an astronomical price hike.

From purely statistical point of view you have a better chance getting a brilliant PF86 than EF86, and they are still relatively cheap and you won't run into any rebranding bullshit.

Which is why I don't even bother hunting EF86's for mics.

Also, EF86 is still being manufactured as modern remakes, for better (at least they're available) and worse (not as high quality as the olden days) and these should be avoided if you don't want to gamble with noise and microphonics.

 

[Bri]

I just finished my second MK7...using a Beezneez K7 capsule.
My voltages are good.
Power supply is fine.

When I switch polar patterns, I get an extremely loud noise rush for around 7 seconds or so.
It sounds like a giant wave crashing onto a shore of pebbles, mixed with the sounds of frying with oil.

In my first MK7 build, which uses a Dale M7, there is only a faint hint of white noise when switching between polar patterns.

I'm using the same power supply for each mic.
I've tried different tubes...makes no difference.

Does anyone know off hand why this would occur?
I'm worried that it may be the Beezneez capsule.
Can a capsule cause this problem?

--Brian

 

[MagnetoSound]

When I switch polar patterns, I get an extremely loud noise rush for around 7 seconds or so.
It sounds like a giant wave crashing onto a shore of pebbles, mixed with the sounds of frying with oil.

In my first MK7 build, which uses a Dale M7, there is only a faint hint of white noise when switching between polar patterns.

Seven seconds sounds like a capacitor charge-up period for sure, but it could just be a noisy resistor. I would swap out the two resistors in the polarisation feed path (33M, 100M) and see if that helps. Check the values of the 47nF filter cap and the 1nF membrane coupling cap too.

Worst case scenario, I wonder if it might be the rear membrane audibly stiffening and relaxing when you change the voltage, due to insufficient tensioning.

 

[telefunk]

I have now finished one with MK7 PSU and the mic has EF80, so it's more like Oliver Archut's alternative U47 with polarity pattern in the PSU like in MK7. Very close, just bit diffrent resistor values because of the different tube.

Anyway, I tried to built it first with the generic stock PSU mod, no luck, unless I used it with self-bias. WAY too much hum.

So, I built the MK7 PSU with the choke. And STILL lot of hum that I eventually was able to track down to transformer being too close to the caps and wires of the heater circuit.

So what now? New transformer? Would it be enough to just get one for the heater supply?

 

[Bri]

Seven seconds sounds like a capacitor charge-up period for sure, but it could just be a noisy resistor. I would swap out the two resistors in the polarisation feed path (33M, 100M) and see if that helps. Check the values of the 47nF filter cap and the 1nF membrane coupling cap too.

Worst case scenario, I wonder if it might be the rear membrane audibly stiffening and relaxing when you change the voltage, due to insufficient tensioning.

Thank you for the helpful advice Dan.
After a couple days of "Burn in", the crackling and rushing sounds when switching polar patterns, subsided.
Unfortunatly, after the third day, it came back with a vengeance.

I just finished replacing the resistors and the 47nf cap, among other things.
Quite an ordeal relative to how I designed my mic body.

Hooked it all back up, and was very relieved to hear no more noise.
I'll leave it on for awhile to be sure.
I'm just glad it wasn't the capsule....
Although, my K7 capsule's behavior seems strange to me....
I'll pose a question in a separate post.

--Brian