M49c Build p2p in Flea body.

[SparkleBear]

Hey that looks great! Thanks a lot
I've wanted to build this one for a long time, I have the Flea body as well, and Beesneez's K47, and a 5840 tube. I'm not sure which POM to get, and wonder if you have any suggestion for a transformer?
Thank you!

I would get my transformer from Haufe via don-audio or from Srdjan at moby directly. I used the haufe in mine. AMI makes a nice transformer too... but I prefer moby and haufe.

Sounds like you have a nice build in the works. The flea body is top notch. I built the m49c so i just followed the neumann circuit. (6s6b-v rather than ac701 for now)

As for what BOM you should follow: look at this thread that talks about the B vs C choice. https://groupdiy.com/threads/should-i-build-the-m49b-or-c-version.55541/

or Klaus discussing it on his forum: https://repforums.prosoundweb.com/index.php?topic=5534.0

I didn't want to deal with the possible noise that comes from your PSU in the B version (being that its biased differently.)

Thanks for the kind words.

 

[Frank00]

SparkleBear, where did you get the Neumann capsule?

 

[SparkleBear]

Right now it has a vintage M7 thats been reskinned by thiersch. But originally I put in a neumann K47 that I bought directly from neumann back in 2018 when they still sold to the public.

 

[Frank00]

I understand, do you prefer one over the other? Just wondering.

 

[Frank00]

Such a shame Neumann don’t sell capsules to the public anymore btw…

 

[SparkleBear]

I understand, do you prefer one over the other? Just wondering.

TBH I think they are both useful but I prefer the k47 for my voice. But the m7 also sounds super great!! Might be a better choice to send down a chain that crisps up the signal like an la2a... or some vibey eq. Both capsules are definitely amazing.

 

[Frank00]

Damn…I might have to find a source for a genuine K49. They idea of fitting it in a Flea 47 or something is temping.

 

[Frank00]

Do you have experience with 47 builds of this level (the level of your 49 I mean)?

 

[gbruler]

I would get my transformer from Haufe via don-audio or from Srdjan at moby directly. I used the haufe in mine. AMI makes a nice transformer too... but I prefer moby and haufe.

Sounds like you have a nice build in the works. The flea body is top notch. I built the m49c so i just followed the neumann circuit. (6s6b-v rather than ac701 for now)

As for what BOM you should follow: look at this thread that talks about the B vs C choice. https://groupdiy.com/threads/should-i-build-the-m49b-or-c-version.55541/

or Klaus discussing it on his forum: https://repforums.prosoundweb.com/index.php?topic=5534.0

I didn't want to deal with the possible noise that comes from your PSU in the B version (being that its biased differently.)

Thanks for the kind words.

Well, I want to say the B version is the one for me based of what I read, although I would like to ask - what kind of noise are we talking about, is it that the B version needs constant maintenance in order to not be noisy, or does it just picks up more noise from bad power and such? In that case it will have to be C I guess.
Anyway, I'm concerned about the different tube I'm going to use in my build, a 5840, does anyone know if I need to change anything in schematic for that?
Thank you!

 

[SparkleBear]

Well, I want to say the B version is the one for me based of what I read, although I would like to ask - what kind of noise are we talking about, is it that the B version needs constant maintenance in order to not be noisy, or does it just picks up more noise from bad power and such? In that case it will have to be C I guess.
Anyway, I'm concerned about the different tube I'm going to use in my build, a 5840, does anyone know if I need to change anything in schematic for that?
Thank you!

Yeah, the B version is more susceptible to bad power noise if I understand correctly from what I have read.

RE the tube: you dont have to change the schematic. Just tie some of the legs together at the tube. 5 and 7 i believe.



Else is the same.

I am definitely curious about building a B circuit to hear the differences. I remember seeing a post about a mod that was best of both worlds between b and c that brian fox did research about.

 

[gbruler]

Yeah, the B version is more susceptible to bad power noise if I understand correctly from what I have read.

RE the tube: you dont have to change the schematic. Just tie some of the legs together at the tube. 5 and 7 i believe.

View attachment 122769

Else is the same.

I am definitely curious about building a B circuit to hear the differences. I remember seeing a post about a mod that was best of both worlds between b and c that brian fox did research about.

Thanks!
I believe it is somewhere in that link you've sent me -
https://groupdiy.com/threads/neuman...9b-tube-microphone-build-thread-sample.50834/
I'll try to find it and let you know.
So I believe that is where I take the BOM for the circuit?

 

[SparkleBear]

I think that dany's BOM do fine, I have not double checked I just looked at the schematic and picked the parts on mouser. Also, think about how you want to approach the cardioid pattern. Are you fine with the electrical cardioid pattern? Do you want to add a cardioid only switch to improve S/N? This can be done with a physical switch inside the mic or you can use a relay/reed switch inside the mic...

Good luck with your build

 

[doqmemory]

I remember seeing a post about a mod that was best of both worlds between b and c that brian fox did research about.

I use the Matador C12 p/s from Chunger for my M49s. On two of them, I use the bias wire set to -1.6V, as in the C12 schematic (30MΩ and 250MΩ in series to the grid with 5nF film capacitor from the resistor junction to ground). They both sound great, with no heater noise on the cathode to worry about. Note that I originally tried to use the heater to set the cathode bias, as in the M49b schematic, but it was not filtered enough in the C12 p/s. The Brian Fox mod inspired me to try the C12 bias scheme on the M49.

I have Poctop's D49b with choke-filtered p/s, which these "Fox" M49b's sound very close to.

I also have one M49c self bias with resistor and bypass capacitor. It sounds great, but is missing a slight bit of the smoothness of the fixed bias ones. On my last M49c, I can switch the bias between resistor/capacitor and a pair of UF4007 diodes with a small 100nF film bypass capacitor. I prefer the diode bias setting, but it is not _that_ different from the resistor/capacitor bias.

 

[doqmemory]

I just finished a U47 using this C12-style bias, adapting the Oliver Archut alternate schematic. I used the AA Flat K47, TAB V8, and an Amperex EF184 "Bugle Boy". Instead of R1 from grid to ground, take R1 to a 30MΩ resister going to the bias wire (XLR pin 4) and connect 10nF styroflex capacitor from that R1/30MΩ junction to ground. So far it sounds great, but still burning in the tube.

Last weekend I finished a U47 using two UF4007 diodes for the bias (as suggested by @terry setter) with a Telefunken EF184, Neumann K47 capsule, and AMI BV8R. It has a great sound, too. I hope to compare them soon to my @poctop D-EF47 with Telefunken EF802, D7 capsule, and Moby Bv08.

I suppose this should really be in a separate thread on tube biasing...

 

[tomas.borgstrom]

Well, I want to say the B version is the one for me based of what I read, although I would like to ask - what kind of noise are we talking about, is it that the B version needs constant maintenance in order to not be noisy, or does it just picks up more noise from bad power and such?

I generally like the tone of fixed bias more. I've built two M49b, but not with 6s6b-v. Once you get it right there no need for constant maintenance. I have never experienced any more issues with "bad" power lines / power grounding than other equipment including microphones with self bias.

If you build an M49b it's important with good filtering of the heater supply but grounding is the most critical part. Once the microphone is working you will typically have a slight hum, and adding loads of capacitance in the filtering does not help. I got rid of it by finding a specific spot in the PSU where ground connects to shield/chassis. This can be quite time consuming and frustrating. In the end you can always easily convert it to self bias if it's too noisy.

Damn…I might have to find a source for a genuine K49. They idea of fitting it in a Flea 47 or something is temping.

I'm not sure that it will be an upgrade. I like U47 (and Flea47) a lot better with M7. A genuine K49 in an M49 clone is a better alternative.

 

[JW]

Doqmemory,

Can you share where you got the perf board material from? If I'm seeing it right, there's no solder pads on either side right? I like this for ptp, cause there's less possibility for shorts.

But then I ask, maybe it's not appropriate for an M49b? Perhaps the extra insulation from acrylic boards is necessary?

 

[doqmemory]

Doqmemory,

Can you share where you got the perf board material from? If I'm seeing it right, there's no solder pads on either side right? I like this for ptp, cause there's less possibility for shorts.

But then I ask, maybe it's not appropriate for an M49b? Perhaps the extra insulation from acrylic boards is necessary?

It was something like this from Mouser: https://www.mouser.com/ProductDetail/589-7100-45

Correct, no solder pads. I still use teflon standoffs for the Hi-Z sections. You need to be careful with tube sockets, since there is nothing to solder to. I like to bolt the socket to the board, for mechanical stability.

 

[JW]

well, with the miniature tubes for M49 a different set of dampening circumstances. Thanks for the link. So, for the hi z section, I'd like to fabricate a disk. Hate to be pesky, but do you have the teflon part? I have two new Chinese M49 bodies that don't fit with any of the current round pcbs, so I'm hoping to possibly fabricate the lower boards to be attached to the rails and then that gives me a place to attach the 90 degree connector part, like in the pics for your first mic.

I'm starting to think it would be just as easy to fabricate a piece of acrylic and insert turrets for the hi z section. Check these disks out https://www.ebay.com/itm/1832640439...pjOJ1sy6YZ7pAf+cFL4i0gxYK3|tkp:Bk9SR6DD5uC5Yw

 

[doqmemory]

So, for the hi z section, I'd like to fabricate a disk. Hate to be pesky, but do you have the teflon part?

I had a bunch of teflon standoffs from the Poctop BOMs https://www.mouser.com/ProductDetail/534-11218

Acrylic is not too hard to work with, but you have to learn how to drill and cut without cracking or melting. I made my own connectors with bus wire.

 

[TLRT]

Damn…I might have to find a source for a genuine K49. They idea of fitting it in a Flea 47 or something is temping.

We bought a lot when it was available