Neumann M49 Clone : D-M49c and D-M49b Tube Microphone Build Thread. (+Sample)

[poctop]

Stuff for both version for 1 mic , note there is a 22K and a 2.2K as i could not be sure of the value of R7 in the C version

It´s a 2,2K. Let me know when the round 49c proto pcbs are there.

regards
Bernd

thanks for the info Bernd , i should some by next week.
Best,

Dan,

 

[micaddict]

;D

 

[Winetree]

I was told years ago to upgrade my Neumann M49 B's to the C versions.
It was just a resistor change or something. Never did. Left them orginal.
What's the "sound" difference between versions B and C?

 

[poctop]

I was told years ago to upgrade my Neumann M49 B's to the C versions.
It was just a resistor change or something. Never did. Left them orginal.
What's the "sound" difference between versions B and C?

I have no idea of what the sound difference is but i can tell b , c are not biased the same way , the self bias  on the c version isolate the heater from Katode,
it seems to give it another kind of sound but i hope i will find out soon. 
Best,
Dan,

 

[0dbfs]

The B version develops the cathode voltage ref'd to the h+ which is often referred to as fixed or stiffened bias. H+ needs to be well filtered or "stiffened" so as not to introduce any ac noise signal present in the h+ into the Vgk which would show up in the audio. The C version uses the 2k2 to elevate the cathode from ground and make the grid then negative wrt cathode. The C version also has the bypass cap from cathode to ground which shorts audio frequencies to gnd and therefore prevents NFB in that path. So the B version has NFB due to no bypass cap and thus lower output.

The 2k2 cathode resistor can be tweaked for "optimal" symmetrical bias although there is a wide range which "works fine" and the specific grid bias point can be tuned for desired results. That 2k2 also sets the current through the tube.

10uf cathode bypass cap is recommended with the 5840 instead of stock 20uf but experimentation and tuning is recommended.

5840 has a 6.3V heater and I used a 5.7V heater supply to slightly under heat.

Really looking forward to checking these out and experimenting a little. Thanks Dan!

Cheers,
jb

 

[poctop]

The B version develops the cathode voltage ref'd to the h+ which is often referred to as fixed or stiffened bias. H+ needs to be well filtered or "stiffened" so as not to introduce any ac noise signal present in the h+ into the Vgk which would show up in the audio. The C version uses the 2k2 to elevate the cathode from ground and make the grid then negative wrt cathode. The C version also has the bypass cap from cathode to ground which shorts audio frequencies to gnd and therefore prevents NFB in that path. So the B version has NFB due to no bypass cap and thus lower output.

The 2k2 cathode resistor can be tweaked for "optimal" symmetrical bias although there is a wide range which "works fine" and the specific grid bias point can be tuned for desired results. That 2k2 also sets the current through the tube.

10uf cathode bypass cap is recommended with the 5840 instead of stock 20uf but experimentation and tuning is recommended.

5840 has a 6.3V heater and I used a 5.7V heater supply to slightly under heat.

Really looking forward to checking these out and experimenting a little. Thanks Dan!

Cheers,
jb

Thanks JB, this is very well explained indeed ,
stay in touch,
Best ,
Dan,

 

[0dbfs]

Just a couple more notes here:

AMI Has a couple different BV11 "M49/50" style transformers:

------------ AMI TRAFO's ---------------
BV11A: Direct replacement for M49/50, historically correct -> AC701, AC701K -> $450
BV11R: BV11A with extended low and low-mid frequency response -> EC92, EF732, 5840, 6072a and 12AY7WA -> $450
T49: Similar to BV11, same ratio, can be used instead of T14, PCB mounted -> AC701, ECC81, EC92, 6072, 12AT7 and 12AY7 -> $85
------------ AMI TRAFO's ---------------

I have used the BV11R and T49 in this circuit (Olivers M49c conversion with some sections added back in from the original that are not in the AMI conversion) and I prefer the BV11r with 5840's although the T49 is also quite nice. I'm planning to use the BV11r's for this set so will need to wait for funds availability.

I may spring for a pair of AC701's one day but am completely happy with the results when pairing a 5840 with a BV11r.

The cool thing about the C version is that you can use a stock chinese PSU if you want (for example from a GT2B kit) and mod that with a couple zeners to drop B+ (and P+) from about 150V to 120V and insert a series standard diode into the heater supply (just before the connector) to drop the 6.3V heater down to about 5.6V.

This makes the mic pretty affordable to put together depending on your doner-body, capsule, and transformer choices. My other pair uses Tim Campbell CT12's and I've got a BV11r in one with a T49 in the other. They are slightly different circuit-wise too (really hard to keep stuff stock when tweak options also sound "good"). In any case these with M7's ought to provide some more sonic-options for my dirty little red-light-habit

Cheers,
jb

PS: I haven't used any of the other BV11 style trafo's from other sources but would certainly like to and maybe paired with some RK47/7/12 capsules could be very affordable.

 

[poctop]

D-M49c is Alive , sneek peek.  I will have few pcb left for sale, round and square version will post some pic soon there are minor silk error but thats it,  PSU, D-M49C- T49 Adator board all of this is in a gt-2B from Chunger , 
i am leaving the M49b option as of now, i will be offering the 49C version.  PM Me if interested i have about 15 set of each left ,

 

[dandeurloo]

I can't wait!

 

[wave]

Dany,
Once again you are proving yourself to be the Godfather of German microphone cloning! Looks great!

Dave

 

[micaddict]

Me likey!

Just in case, you never know etc.; would it fit in a gutted TLM49 (short and fat/wide, just like the M49)?

 

[poctop]

Me likey!

Just in case, you never know etc.; would it fit in a gutted TLM49 (short and fat/wide, just like the M49)?

the round pcb is 60mm diameter and should fit upcoming Riggler's M49 body or any other body that will accept this diamter ,  the square versions is the same size as fet47 pcb and they make it fantastic in the gt2b body , i will be installing an M7 in there tonight 
Let me know.
dany,

 

[micaddict]

the round pcb is 60mm diameter and should fit upcoming Riggler's M49

Yes, of course, there's the feeler thread about those.
Dany, so much has been happening here lately, sometimes I just forget things.  :-[

 

[poctop]

PCB D-49c added to online Store only 12 set left
Best, 
dan,

 

[riggler]

I have read a lot of opinion on B/C - fixed bias, etc. If you do a search on hear about it, there was a very good thread a few pages long about this. Klaus says that B is the way to go for the "real" sound. Who knows. I bet either way is going to sound great. C is certainly a safer, easier path.

Anyway, guy finally got back to me. Actively working on a price. We are going to make a couple test bodies in aluminum. Your 60mm boards will fit and holes are accounted for. Good times!!!!!!!!!!

:

 

[poctop]

I have read a lot of opinion on B/C - fixed bias, etc. If you do a search on hear about it, there was a very good thread a few pages long about this. Klaus says that B is the way to go for the "real" sound. Who knows. I bet either way is going to sound great. C is certainly a safer, easier path.

Anyway, guy finally got back to me. Actively working on a price. We are going to make a couple test bodies in aluminum. Your 60mm boards will fit and holes are accounted for. Good times!!!!!!!!!!

:

Dont worry i have all the version For the Round Body B, C just ask for it, even the M50B round, that it is just too much pcb  , I have both B, C square also , the issue is that the psu pcb is only working for the C version wich is not very picky about hummy-Supply not even sure about LM supply style either  , i am working on making another one specially for Filament Bias B version all passive.    Last Thing i need to work out as the coming M269 is fixed bias and the supply will work for both.

Best,
in developpment

 

[bkbirge]

What are capsule sources for this build? Anyone tuning for this circuit?

 

[poctop]

What are capsule sources for this build? Anyone tuning for this circuit?

the capsule are K47-M7 type as for tuning the stock value K bias 2.2K, and 100K plate  of the self biased c version get very very close to the spot as 52V for the plate and 1.55V for grid Bias for the 5840 ,  I also built a B version but i need to redo the power supply for this one as for the M269 wich will be a b version it did not work hum free ,
both installing a 1M pot i was able to tune the bias on spot . 
Let me know,
 
Best,

 

[micaddict]

What are capsule sources for this build?

M7 was in earlier M49; not in -c (which had K47/49). Regarding -b, it depends whom you ask.
But I wouldn't worry about that. Just get a nice M7 or K47 capsule (whichever is preferred).
For those who can't make up their minds (or regardless), there's the BeesnNeez K7 which is a crossbreed of the two.
Usual suspects for M7 are Thiersch (also in PVC), Dale Ulan, Beesneez again, Max/ioaudio (soon). Gefell (PVC) only as part of a microphone.
K47 can be had from quite a few more makers/suppliers.

Anyone tuning for this circuit?

Good question. A maker might chime in.
Of course, if necessary, tuning can also be done the other way around, if that makes sense.
And then there's personal taste.

 

[poctop]

All version are available so please do ask ,  the only thing is that the current pcb supply will support the c version.

I am not even sure if LM317 Style regulation will be enough in this b version.

This is going to be called Choke Time  ,

Dany,