Microphone Teaser

My Brauner VM1 is in small pieces. I am drawing up the circuit. ef86 150k plate load. Uses a reed relay to drop out the back side in cardiod from what I can tell so far. I will take pictures.

I think a large part of its good sound is the capsule/grill and other good parts used. None of my china capsule microphones seem to have as good as a capsule in the VM1.

Just got done tracing most of the VM1. I bought mine used. It is a cathode biased ef86 design.

The Magic of this microphone is the build, parts and CAPSULE. That capsule is different it might look like a k67 but it is not a K67.

Power Supply 184.4 B+
5.2 heater

Plate R 150K

Cathode R 2.2K bypassed with a 47uf electro

Plate V 79.8

All high value Rs are 3gig

1Uf wima polypro to a nice big transformer. I have not tested it but I would guess >6:1

pattern control is a little different than other microphones I have seen. I am going not post this part of the design.

I don't know if the ef86 is the one from the factory because I bought the microphone used. It looks to be a russian wing C tube with gold pointy pins it is marked MAL VALVE. Sounds good.

For the astute reader you will note it is a "standard" type tube microphone gain circuit kind of like a u67 without feedback.

Now if you read about the new VMA not VM1A. The VMA has a switch to make the microphone sound different than the VM1. My guess it is a VM1 with a circuit that drops the voltage and maybe remote switches a different cathode R in circuit or maybe just drops the B+.

Think G7 meets VM1 etc. For the G7 make the plate 150K up the B+ and use a transformer >6:1 make the last filter R switchable in the PS to adjust the B+

HAVE FUN!!!

How about some naked pics - (of the Mic I mean !!! :shock: !!!)


Regards
Steve

Gus
I could have sent you something that you needed so you would
not had to redraw that circuit.
But everytimne we talk you use the PM system.
I need your email. Please...............
I could have saved you time as I searched for 30 minutes
Saturday for a way to contact you. No go everytime you use the PM system.
So I sent my treat to Marik to forward to you.

My email is the little email icon below.

Can you tell us is that "nice big tx" lundahl or some custom?

Check the posts in Klaus heyne's forum at PSW for great info on underheating.

e.g.: http://recforums.prosoundweb.com/index.php/t/569/1517/

In short, it affects grid impedance.

I have had very good sound out of underheated tele PF86's - that are available at a fraction of the cost of tele EF86's

Jakob E.

Looking schematics the clean amp "sweet spot" voltages of the EF86 in a tube microphone appear on the u67 fixed bias and the above cathode bias. The minor voltage readings are due to the bias method fixed or cathode.

Just that schematic won't make a VM1. The body is thick brass the build is very good and the capsule is a different design. Its kind of a k47 mixed with a K67 capsule design. That capsule design and build is very nice. It seems to "hear" more "real" than any other capsule I have heard. I have compared it to a M7 capsule in a gefell microphone real k87 capsule in a u87, tlm103 lots of 3 and 6 micron china capsules in modded microphones. I would place the other microphones in stands and test at the same time. The next best capsule was the real k87 even with the stock u87 electronics something about the midrange sounding more real with the Brauner and Neumann.

When you realy start to understand and learn about microphones you learn there is a lot of things that make a good microphone. Neumann designers realy did their homework. Study all the schematics you can tube and SS it appears to me every part is there for a good reason.

Hi Gus
My observation:
With voltage divider formula here is about 67V on center electrode. I suppose must have patern from 0-134V (to got 0, 67 and 134 for all of three patern or from 1-134V varable patern like on VM1)?????
What is voltage before 470K on patern control?
Pad with 270p is same like on U67 (is it with switch on mike or internal).
What mains voltage was when you measure?.
Best
Duka

The pad is switched remote from the power supply. The microphone body has a 5v reed relay close to the capsule. The body has a transistor that drives the relay coil using the heater supply. I think this was done as to not have a current spike in the multi wire microphone cable.

I did not send out the supply schematic. The Important voltages are marked on the body schematic. The stock supply has an adjustable 3 term heater supply and a 5 cap 4 resistor well filtered HV supply not regulated.

One could voltage double 120 VAC (120 to 12, 12 to 120 transformers)to a few RCs use three 75V 1 watt zeners for about 225V then use a resistor and filter cap to bring it to about 185VDC adjust the last resistor for the correct B+.

The pattern control voltage should be adjusted for the capsule you will use. I did not see the point of showing the voltages because they were picked for the VM1 capsule. You should calculate the resistors for the capsule you want to build with.

the schematic was sent out kind of as a learning tool. There is nothing really new and different: however if you get a chance check out the VM1 it sounds very good. I think it is the capsule grill and good parts used to build it.

I Gus
Thanks for replay.
I dont want to build a VM1 (no capsule, no Pikantron). All I want is to learn to build some staff.
Am I all right when I am talking about (on VM1) 67V on center electrode and variable voltage from 1-134V. How I can determine adequate voltage for my capsule (AKG CK12-teflon, AKG CK12-brass and SKE106).
Does styroflex used for 0,01uF and 270p.?
Thanks in advance
Duka

Hi Gus
Probably you didnt read last reply.
Does styroflex used for 0,01uF and 270p.?
Thanks in advance
Duka

Can anyone tell me if Picatron still exist?

http://www.pikatron.de/

Why use a 3G resistor to bias the backplate ?

with my tests around DIY microphone, i found
that biasing the backplate directly after the voltage divider
resistors, is a way better, in term of noise and dynamics.
(like the C800G biasing)

Brauner is very serious about microphone, and i'm sure
there's a reason for this 3Gig resistor.... :roll:

any way of understanding ?

Great to read about the VM-1 internals.

I have used the Cite de la Musique's matched pair of VM-1s
to record a 18 piece french 'fanfare band' I was playing in.
The group was totally blown away with the recording.
I was quite pleased too.

I have a personal Valvet that I like very much too.
Used on everything from guitars and mandolins to tenor sax and upright bass.
Often with an Earthworks SR-71 as a distant mic.
Great mics in general and the VM-1 in particular.

They have a 5.1 surround ' grid 'mic of several VM-1s in a T frame,
and it is awesome for symphonic recording.