0dbfs

Re: My M49 style mic
« Reply #40 on: July 30, 2012, 12:34:04 PM »
Question for anyone that would like to contribute:

If I have a B+ of 120V and a 100k plate resistor with about 45V at the plate and a 2k2 cathode resistor with about 1.5V at the cathode that gives me a tube impedance of about 65k.

The original M49c schematic calls for what appears to be a 600pF plate to ground cap which creates a 6dB/octave LPF with a -3dB @ about 4khz with similar voltages on the AC701k plate.

This sounds awfully extreme for use with what was originally an M7 capsule. Should that 600pf cap be much lower in value or am I off elsewhere in my numbers?

Thx,
jonathan
Music is everything!
Audio is everything else!


mata_haze

Re: My M49 style mic
« Reply #41 on: September 16, 2012, 02:03:45 PM »
Sorry for the perhaps silly question:
are the ac701 and the 5840 compatible? I mean did you use Tab's AC701 schematic and dropped in a 5840 instead?

Best,
Mattia.

0dbfs

Re: My M49 style mic
« Reply #42 on: September 16, 2012, 03:18:39 PM »
Mattia, yes. I used the 5840 in place of the ac701k. I brought H+ up to 5.65V, and used a 10uF cathode bypass cap. I also used one of Oliver's BV11r transformers intended for use with a 5840. With Tim's capsules and Oliver's bv11r's these are very nice and I feel that they are unique in a good way. As a matter of fact I just ordered a pair of thiersch m7's to make another more traditional pair. Low parts count, easy to perfboard or turret, stock Chinese psu mods are easy too with a couple 60v zeners and a series diode to drop stock h+.

Cheers,
jb
Music is everything!
Audio is everything else!

mata_haze

Re: My M49 style mic
« Reply #43 on: September 16, 2012, 03:25:22 PM »
thank you for the kind answer,
being not too familiar with this type of circuit, where did you add the 10uF?
I am planning to build it myself, I am just trying to find the body....
I'd love it to look as close to the original as possible!

Mattia.

0dbfs

Re: My M49 style mic
« Reply #44 on: September 16, 2012, 05:01:00 PM »
In Oliver's schematic it is C5. C5 is 25uF in his conversion schematic which connects the cathode to ground and bypasses the cathode resistor. Oliver recommended replacing with a 10uF when using a 5840 and I recommend trying it both ways and comparing while paying particular attention to low-end "depth and imaging" (not necessarily frequency response alone). For my next pair I am currently planning to use Nady 1050 style bodies. I highly recommend using the TAB BV11r's in any case... Especially if you are going with a nice high quality capsule These mic's started out with their T49's which were also very nice but swapped one of the T49's with the BV11r. I'll be swapping the next one very soon. I recommend saving a couple $'s and going with the bv11r's from the get-go.

All I can say regarding the transformers is that I will be using the BV11r's in my next pair. I didn't have any particular issues with the T49's and would recommend them to anyone. Advanced Audio, Peluso, and AMI/TAB all make a more budget priced BV11 or M49 style transformer. Maybe even Cinemag do too or perhaps even Sowter.

I rather enjoy experimenting with different transformers, capsules, parts, and circuit configurations but my experience so far with putting together several DIY mic's and comparing to high-end commercial mic's in critical applications is that Oliver at TAB and Max (ioaudio here on gdiy) both deliver the goods.

The AMI/TAB BV11r transformer along with a quality capsule makes the mic a little more expensive to build but well worth it in my opinion. There are some other budget options too if you want to get it going sooner and don't have funds for the costlier components right away. Plus then when you eventually upgrade the parts you'll have some spares to start another one :)

As far as a doner-body which is close to the original I don't know that there are any "budget" options but I would also be interested in any economical doner-body options.. The TLM49 lists for about 1k5 so add maybe close to another 1k on top of that for quality parts and you get something that not only sounds the part, but also looks the part.

I would say that it's probably worth it to go with an ac701k and a tlm49 body if you really want something as close to an original as you can get but I don't believe it's absolutely necessary to build a world class mic.

I do a ton of tracking and always need more mic's so my money is better spent on producing more mic's and planning to keep them working for a lifetime.

One positive thing I have to say about using the apex460 style bodies with this circuit (instead of something shorter and fatter like the original) is that the long/slender body lends itself to placement in tighter quarters and I like that.

Cheers,
And best of luck!

Ciao,
jonathan
Music is everything!
Audio is everything else!

mata_haze

Re: My M49 style mic
« Reply #45 on: September 16, 2012, 05:27:37 PM »
Again Jonathan,
thank you. I have definitely some food for thoughts here...and budget calculations to do....
I really would like it to look like the original, I hope someone here with more mechanical expertise than I have will be able to come up with something suitable.
I have built a couple of U47 replicas (with IOAudio kit.FAB!) and some others more DIY, but this time I'd love to get as close as possible to the original.
I am definitely going to get the BV11 and 5048..I don't think I can afford a 701 as yet,but you never know, once the mic is done and works well I might be lucky to find one on evil bay....and the modification needed to make it work with a 701 it's minimal...

I hope I will be able to start working on one as soon as possible (budget is always a priority unfortunately) and perhaps share some of this journey here !

Mattia.

dmp

Re: My M49 style mic
« Reply #46 on: September 17, 2012, 11:43:41 AM »
Quote
I also used one of Oliver's BV11r transformers intended for use with a 5840.
This transformer is $450?
Have you compared to the Cinemag 2480?

0dbfs

Re: My M49 style mic
« Reply #47 on: September 17, 2012, 12:04:12 PM »
I compared it to Oliver's T49 which is his budget version of an M49 trafo @ about $90.... I've gotta say that his BV11r results in a nicer mic... At least in my opinion.

I have not tried the 2480 though I certainly wouldn't mind trying it and may do so on my next set given that it's about 1/10th the cost of an historically correct BV11 version. The 2480's can be used for other mic's too so it would certainly be no loss.

Oliver's conversion schematic also has some different values and omits both a feedback cap/resistor and a plate-to-gnd cap... I have installed those missing components in one of my m49c's but have not developed an opinion yet on which I prefer except the one with the feedback network has less output signal. Sorry, still experimenting a little.

I think my next set of m49's with Thiersch M7's will use all original component values. I may check into ac701k pricing as well just to tempt myself...

Cheers,
jb
Music is everything!
Audio is everything else!

mata_haze

Re: My M49 style mic
« Reply #48 on: September 17, 2012, 01:13:04 PM »

....

I think my next set of m49's with Thiersch M7's will use all original component values. I may check into ac701k pricing as well just to tempt myself...

Cheers,
jb

can you still get them???

Mattia.

dmp

Re: My M49 style mic
« Reply #49 on: September 17, 2012, 01:27:10 PM »
on ebay, $400 - $500
Thanks for the info on the transformers.
I've used the Beyer 10:1 peanuts backwards in mics with 5840s and they sound really good as well.
I just bought a red and a blue Thiersch M7 to try...


0dbfs

Re: My M49 style mic
« Reply #50 on: September 17, 2012, 03:12:41 PM »
Yes. Ebay and such have ac701(k?)'s in the $500.- range and there are suppliers that can provide selected ones as well for a bit of an upcharge....

I don't know if they are that much better but I may end up renting an original m49 at some point to compare whenever I get the M7 versions together. They are quite nice with Tim's capsules and a 5840. Certainly acceptable for critical work and within the realm of economy depending primarily on capsules, transformers, tube, and of course bodies used..

Here are some #'s I came up with for budgeting:
Body/Case/PSU/Mount/Cable: $250 -to- $1,500+
Capsule: $100 -to- $400+
Transformer: $50 -to- $450+
Tube: $20 -to $500+
Parts/Components: $100

So, somewhere from maybe $600 - $3500... Depending...

Cheers,
jb
Music is everything!
Audio is everything else!

kpearsall

Re: My M49 style mic
« Reply #51 on: October 03, 2012, 10:15:05 PM »
Just came across the MXL 990XL and thought it would make a great donor mic for this and found the thread. Great to see other people working on this!


0dbfs

Re: My M49 style mic
« Reply #52 on: October 05, 2012, 11:22:23 AM »
Quote
so...ehm....PCB? KIT? ehm.... 
[quote/]

Well I am planning to make a couple more of these with M7's and the short-body-u47 style tube mic's out there.... Thing is that the 5840 tube is readily available, the circuit is very simple, and you can use a standard chinese PSU with easy mods... Also several trafo's are readily available and you can use any capsule intended for a "flat" circuit. This is basically a standard plate-out circuit so can be used with many tubes & trafo's outside of the m49 family.

The thing I don't like about my current build is the robustness of the the perfboard and subbing different components is a little bit of a hassle.

I was thinking of coming up with a couple PCB's that use the keystone teflon inserts for all circuit connections so it's essentially all P2P but very serviceable. May be a bit of overkill since the whole circuit isn't hi-z and doesn't need to be floating in teflon standoff's but I like the idea of being able to easily experiment with backplate dividers, bias resistors, grid resistors, different caps, etc.... Without destroying the pads and things... PCB would be fairly thick and the keystone standoff's would be the ones with connections on both sides to increase wiring options. Silkscreen layer would probably indicate the various sections and connections or layout.

Not sure whether anyone may be interested in such a beast and I don't currently have a particular schedule in mind for design/production but I have been thinking about the options and I find a very robust and serviceable implementation as being quite useful. I would also like to somehow engineer this to work with various body shapes and sizes. Long&skinny, short&fat, etc....

If you may be interested or have any particular thoughts please let me know.

Cheers,
jonathan
Music is everything!
Audio is everything else!

bernbrue

Re: My M49 style mic
« Reply #53 on: October 05, 2012, 01:32:46 PM »
Well I am planning to make a couple more of these with M7's and the short-body-u47 style tube mic's out there.... Thing is that the 5840 tube is readily available, the circuit is very simple, and you can use a standard chinese PSU with easy mods... Also several trafo's are readily available and you can use any capsule intended for a "flat" circuit. This is basically a standard plate-out circuit so can be used with many tubes & trafo's outside of the m49 family.

The thing I don't like about my current build is the robustness of the the perfboard and subbing different components is a little bit of a hassle.

I was thinking of coming up with a couple PCB's that use the keystone teflon inserts for all circuit connections so it's essentially all P2P but very serviceable. May be a bit of overkill since the whole circuit isn't hi-z and doesn't need to be floating in teflon standoff's but I like the idea of being able to easily experiment with backplate dividers, bias resistors, grid resistors, different caps, etc.... Without destroying the pads and things... PCB would be fairly thick and the keystone standoff's would be the ones with connections on both sides to increase wiring options. Silkscreen layer would probably indicate the various sections and connections or layout.

Not sure whether anyone may be interested in such a beast and I don't currently have a particular schedule in mind for design/production but I have been thinking about the options and I find a very robust and serviceable implementation as being quite useful. I would also like to somehow engineer this to work with various body shapes and sizes. Long&skinny, short&fat, etc....

If you may be interested or have any particular thoughts please let me know.

Cheers,
jonathan

Hi Jonathan,
I would be interested in a few pcbs with standoffs or standard pcbs. Since I have a nice M49 I could make some A/B comparison. Keep me informed about your plans, please.
kind regards
Bernd
« Last Edit: October 06, 2012, 05:14:47 AM by bernbrue »

bernbrue

Re: My M49 style mic
« Reply #54 on: October 06, 2012, 05:34:29 AM »
Hi Jonathan,
when I started to repair my M49, I took a few pictures that might be of interest.

schematic numbered components:



closeup:



sideview attached
regards
Bernd



 

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