Trying out Gus' VM1 circuit............

So while I was waiting for my ef800 tube to arrive, i thought I'd get some sort of circuit going with the EF86 tubes I have around here, so I could at least hear the beesneez K7, skylars U47 body, and cinemag 2461 in action, even if it wasn't a U47 type circuit.

So I looked at Gus' VM1 schematic and went with that, since it looked pretty straightforward and simple, and I had all the parts here. The only thing I did different was use 1gig resistors instead of 3gig resistors, coz that's what I had on hand.
I used the MK7 psu to get the voltages to where they needed to be.

I had my wife sing a few bits, and compared them to what we had orginally recorded. I wanted to post them, but she hated her performances (she was really tired) so I got a "no go" from her on that.
But Wow!! This thing sounds amazing!! Switching between the tracks, the VM1 circuit/U47 body had a depth that the others didn't.
Don't get me wrong, my royer mods and other goodies sounded great, but this had that 3d quality where the voice felt more real.

It's got a pretty hot output tho (i didn't include the pad), so the preamp can get a little clippy when belting or hitting those high notes. From the original thread Gus' estimated the transformer to be about a 6:1 so I'm guessing the cinemag 2461 is all good. Maybe a slightly higher ratio would help. (but then again I didn't build the pad on the mic)
The Tele EF86 isn't too noisy either, not the quietest I've ever heard but passable for now.

Whether it's the combination of the grill and the capsule giving me the magic, or not, I'm really liking this so far.
As soon as the EF800 arrives I'll whip everything out and change to U47ish circuit, and see how that sounds, but who knows, I might come back to the VM1 circuit........

pics ?

Circuit?

Yes, please post the circuit... I look through the META and so many links don't work and so many circuits are missing...  ???

Please post it

Thanks,
min

The VM1 I traced used a EF86 cathode biased circuit.  I traced it from the VM1 I owned.  If you look close the B+ and the plate voltages are close to the u67.   I forgot to measure the transformer ratio.

Here is a link someone posted in another thread at this forum

http://studiobeige.de/DL/VM1schem.gif

compare operation points

http://danalexanderaudio.com/Micpics/Neumann/U67Schematic.jpg
http://www.gyraf.dk/gy_pd/g7/u67.gif

Ok, here's some pics. Camera is just my iphone, so sorry for crappy quality of pics

One of the PIO caps isn't connected, it's just there for the U47 ish circuit.
I'm thinking I should really put the plasticy bit under the capsule mount for more isolation.

But this is how it sits in the basket. How high does the U47 capule sit, coz it was really high with the plastic bit

Here's it with the plastic/glass/perspex thingy in it. Looks closer to the wagner website pic. I need to center it more, as it has slight lean to the left.


I also have a phillips E80F that I'll try, but from reading I see it uses 300mA as opposed to the EF86 200mA. Now I know that the heater voltage will drop because of this, but I can adjust.
But what is the maximum current that the MK7 psu can handle on the heater side of things? I have 500mA on the transformer.

I'm doing something pretty similar right now. in general it's the mk7 circuit with higher plate voltage like  the brauner and 150k and 3gigs resistor. I'd like to have one really quiet mic


nicholas

i'll post pics

nicholas,

did you find the MK7 to be noisy stock?

I've got the E80F in there now, after a bit of adjusting with the MK7 psu. I'm sitting with the heater voltage at 5.4v which works out well as there's not much more to give on the voltage side, with the current being quite high.

It's definitely quieter than the telefunken EF86. The tele's I've got are old tho, so not exactly NOS.
Sonically the difference between the different tubes is minimal. Both sound great, and I'm sure a movement of millimetres of mouth to mic would change the tone more than the tube swap. The E80f is staying in for now, coz quiet is good.

My Royer mod with Dale M7, and cinemag 2480, sounds softer. Not duller or less bright, but softer. Maybe more forgiving on a hard sounding vocalist. The VM1/U47 seems to have some more definition in the mids. I hate describing sound........

It's now sitting in the studio, giving the tube a good burn in. How long is needed? 24-72 hours? I feel a little nervous about leaving it on overnight while I sleep....................

72 hours is normal for tube burn in, that's what I learned anyways.

So, if I may ask something... what do you think is the number 1 contributing factor that makes this microphone sound so great?  Are you saying it is the headbasket?  If it is perhaps you could explain why?  More info as to why this one sounds more detailed would be cool

Thanks,
min

My guess is it's the headbasket combined with a great capsule. I don't know a lot of the finer details, but there's been quite a bit of discussion in the U47 thread by people a lot smarter than me.

This article has some good info too.
http://mixguides.com/microphones/vintage_products/audio_vintage_microphones_part/

I can't comment on the U47 circuit as such, since I haven't built or heard it.

the mk7 is not very noisy but also not super quiet. With high value resistors you should get better SNR, it will also change the bass response.
I'll try it and tell you. I have mk7 mic

nicholas

e.oelberg said:

the mk7 is not very noisy but also not super quiet. With high value resistors you should get better SNR, it will also change the bass response.
I'll try it and tell you. I have mk7 mic

nicholas

Click to expand...

Are you sure it wasn't simply a bad tube? It can be very difficult and expensive to find a good EF86 tube these days. The high impedance part of the circuit is also a very happy antenna for static if you forgot to clean it with care or got careless with wiring.

I'm reluctant to believe MK7 design would somehow be more noisy than other similar historical alternatives, especially with the very brute force passive PSUs many people are using..

thats what I'm going to find out !


the tube is one out of ten nos telefunken and neuhaus. it's a neuhaus

I've built several mics, both FET and tube, with 60 meg resistors (like a U47) - they're pretty quiet. My U47 is very low noise, too (15 dB-A, as in original specs). So low value resistors don't automatically mean high noise.

So my EF800 arrived today, so I swapped out the VM1 circuit for the Olivers U47ish circuit.

A little different, but not by much. The VM1 sounded a fraction harder in the upper mids compared to the 47, but again I could change my distance to the mic and have more of a difference.
Output dropped a little with the 47 circuit too, which made it easier for the preamps to not distort on those loud high notes.

The tele EF800 I got was NOS/NIB and it's pretty quiet for straight out of the box. I"m running it at 105 B+ and 6.1v heater.
I'm sure it'll settle down even more after it's burn in time  ;D

I have to say tho, that I really liked the VM1 circuit. I'm going to try it out in my CT12 loaded mic, and see if I like it better than the Royer mid circuit I have in there at the moment.
At least I'll be able to make use of the other polar patterns with the VM1. Although, I'd have to join the two backplates together, which from what I can tell, raises the noise floor a bit when in cardioid mode.
Might be time for a new thread on that.

Also, where do I get relays for Hi Z circuits like in mics? The wrong type increases noise? I'd like to use one in the U47 so I can also use it in omni.

the original vm1 uses this relay

www.kiwistudio.gr/brauner_relay.pdf

Really nice! Thanks for sharing this.

A little different, but not by much.

Click to expand...

Sounds like you're hearing the capsule as the dominant factor, which is often the case.

noulou said:

the original vm1 uses this relay

www.kiwistudio.gr/brauner_relay.pdf

Click to expand...

thanks for that info !!