Neumann M-147 modifications.

[colonel_sanders]

Hi guys,

I'm bit of a theory newb, so please bare with me.  I have a Neumann M-147 microphone which I dislike the sound of.  Selling it is not an option at the moment, but I was wondering if I could pull the old PCB and change the circuit, utilising the existing power supply (or with minimal mods) to change the sound to something more usable.

This is the only info I was able to gather from searches...

Capsule: K47
http://www.neumann.com/?lang=en&id=current_microphones&cid=m147_data
http://recordinghacks.com/microphones/Neumann/M-147

The K47 has dual diaphragms, but the rear diaphragm is not wired into the mic circuitry. The mic has a fixed Cardioid pickup pattern.
The tube in the amplifier circuit is used for impedance conversion. According to SoundOnSound, it is soldered to the circuit board.

The mic’s output is transformerless, which helps keep the mic’s self-noise to a very low 12dBA.

The manual for the M147 gives the pinout info as follows...

Pin1  -70V
Pin2  +5V
Pin3  audio signal +phase
Pin4  +70V
Pin5  sensor line
Pin6  +32V
Pin8  audio signal -phase

The mic body is quite small compared to something like a U47/67.  I also have 2 tubes compatible with the MXL 2001 'royer mod' circuit sitting around the workshop (bedroom ).

If any one can point me in the right direction, much appreciated!

Cheers,
Arie.

 

[Gus]

What is wrong with your 147?  It is not a bad microphone.  Selling it might be the best thing because there is a good chance it will have little worth if it is changed and you want to sell it.

I did see a schematic of it on the web.

 

[bluesbaz]

That mic has a terrible resale value. I tried to sell mine a few years ago the best I could get was 900. I just kept mine. The mic is totally lame it doesn't sound bad but it doesn't sound good either, just...... sort of lame.
-s

 

[zebra50]

ioaudio did something fun with one. Follow the link in this post to see photos.

http://www.groupdiy.com/index.php?topic=29859.msg361518#msg361518

 

[Andy Peters]

That mic has a terrible resale value. I tried to sell mine a few years ago the best I could get was 900. I just kept mine. The mic is totally lame it doesn't sound bad but it doesn't sound good either, just...... sort of lame.

There seems to be high correlation between "sounds lame" and "terrible resale value."

-a

 

[colonel_sanders]

It sounds average enough for me to continually not use it.  Not terrible, but average.

Selling it might be the best thing because there is a good chance it will have little worth if it is changed and you want to sell it.

I would like to be able to put the original circuit back without too much hassle.  I like what rascalseven did to his TLM49.  However, I'm not sure if theres enough room for a cinemag 2480 and new PCB?  I also have an MXL 2001 body.  What would it sound like with a K47 + royer mod I wonder?  ;D

The tubes I have are 5840.  The Royer mod schematic specifies a plate voltage of 93-100V.  Is it possible to achieve this with the existing power supply (70V)?  Am trying to track down the PS schematic...

ioaudio did something fun with one. Follow the link in this post to see photos.

  http://www.twin-x.com/groupdiy/displayimage.php?pid=2127&fullsize=1  Is that the mod?!  Wonder how it sounds.

 

[pucho812]

I have never known of any neumann mic that sounded lame or bad. The 147 sounds good it's possible something is wrong with yours,

 

[bluesbaz]

Ill say this, we had a great many experienced producers and engineers through the studio in the last 5 years and never, even once, did one of them grab that mic even in a pinch. My MXL/Royer SDC mics do get used all the time and you could build 4 of them for the price of the 147. :
-s

 

[colonel_sanders]

Ill say this, we had a great many experienced producers and engineers through the studio in the last 5 years and never, even once, did one of them grab that mic even in a pinch. My MXL/Royer SDC mics do get used all the time and you could build 4 of them for the price of the 147. Roll Eyes
-s

Hehe, pretty much.  It was the first condenser mic I ever bought.  Loved it back then, not so much now days.  Though I have heard them used well as overheads.

I'm going to go ahead and attempt to stick a royer mod in.  Will keep you guys updated...

 

[Gus]

You do know some transformerless microphones can have a different type of interaction with the preamp after it, if the input is a transformer.  If you search you might find a preamp spec sheet that has a transformerless microphone setting.

 

[strade]

The M147 is a very good microphone for achieving thick, full vocals. (It sounds round, warm and full, has no hissiness and all the hard letters like S, C, CK, SCH, T, P etc. NEVER sound sharp or hissy, but nice and rounded and musical (perfect for vocals). That's what it has No open top end, it sounds a bit duller in the highs than other mics, but that doesn't mean that you can't adjust the highs to your own taste with one or more EQs. The M147 is the thickest sounding mic next to Neumann's U47 . You just have to know how to mix the signal you get from the microphone. Listen to Sido's debut album "Mask" from 2003. Everything M147, including the aggro announcements 1-3 (possibly the 4th too). The vocals always sound professionally good.

 

[Tubetec]

Theres a few M49 style PCB's on sale here ,
Should fit the M147 body with plenty of room for a transformer ,
The M147 has a single membrane capsule , so you could delete the patern switching parts from the M49 board .

https://groupdiy.com/threads/neumann-m147-power-supply-m147-schem-added.23806/
Looks like the M147 psu isnt much good for a regular tube mic circuit ,

If you do decide to modify your 147 , think carefully about it , try and do it in a non destructive way , keep the original PCB's and PSU intact , build a new PSU from the ground up is my advice .

Ive built a few CF mics and I'm very happy with the sound , a little different to the Royer ,
Its a great project for a beginner because of its simplicity , you also dont need to put a transformer in the mic , or even use a transformer if you want an uncoloured sound .

 

[rock soderstrom]

Listen to Sido's debut album "Mask" from 2003. Everything M147, including the aggro announcements 1-3 (possibly the 4th too). The vocals always sound professionally good.

I would never have thought that Sido would make it in here as a professional production example, but tastes differ. Personally, I don't particularly like M147, but that's also a matter of taste. I would probably mod it...

Ive built a few CF mics and I'm very happy with the sound , a little different to the Royer ,
Its a great project for a beginner because of its simplicity , you also dont need to put a transformer in the mic , or even use a transformer if you want an uncoloured sound .

I am interested, schematic?

 

[Tubetec]

The Oktava MKL2500 is a really good sounding CF tube mic and well worth finding if you can get a hold of one cheap, they often develop noise problems because of the low quality foil screened cables , first step here is replacing that with Gotham Gac-7 , I lifted the usual one side of the heater supply from 0V in the microphone and made the connection with 2x100ohm resistors at the PSU output ,it lifts both ends of the heater from ground potential . Some extra cancelation of noise in the heater supply is possible this way , the success of this may depend on the heater having a helical structure , which the EF86 does ,EF37A and ECC83 LPS do as well .
The extra work allowed me to reduce the mics sensitivity to switching clicks on the incoming mains supply , things like a refridgerator switching on or off ,
The higher quality cable also helped reduce any spurious RF and gave much lower conductor resistance than foil screen and drain wire . Needless to say the higher gauge conductors in any tube mic cable are meant for the heaters .

The Bruel&Kjaer CF is also worth checking out , typically there mics were omni , circuit works very well with typical LDC capsules , although your biasing arrangements will need adjusting .

One interesting thing about the CF output is it doesnt need a transformer inside the mic to drive the cable , some of the Sonys do this and of course the Royer CF have the signal transformer in the PSU , if you want its very feasible to run the cathode follower unbalanced down coax cable into a HI-Z input , thats how the B&K does it ,

I have one ultra simple CF mic I made , it only has the grid resistance , the tube and a capsule in the mic itself , the grid voltage from the self biased CF provides the 50-60 volts for capsule polarisation , front membrane is connected to 0V , backplate directly onto the grid ,
The cathode follower is terminated in the usual way at the far end of the cable in a small diecast enclosure, this also contains a simple stepped HPF with 12 positions , PSU is seperate again
that module plugs directly into a tube preamp with 1Meg at the grid ,
Despite the high capacitance of the cable into a high load impedence the CF still provides low impedence drive and isnt bothered in the slightest by 15 feet of cable .
Cutting out the need for an input transformer makes a lot of sense , there costly things ,
The moneys way better spent on a lump of pig iron at the far end .

 

[terry setter]

The Oktava MKL2500 is a really good sounding CF tube mic and well worth finding if you can get a hold of one cheap, they often develop noise problems because of the low quality foil screened cables , first step here is replacing that with Gotham Gac-7 , I lifted the usual one...

A word of caution about the Oktava MKL2500 microphones: There are several "models" out there. Chinese counterfeits became common before the mics' availability ended. Guitar Center blew-out quite a few of these at $100/mic. If you find one that has the larger, British-made supply, you're probably good to go. If you find one that has the small, Chinese-made supply then pass on it, or only spend a SMALL amount of money on it. What's more, Russia made both Cahode Follower models and Plate Follower models. So, if your heart is set on a CF, you'll have to do some circuit tracing. The transformers in the two designs are quite different, so it's not as simple as just reconnecting the wires. Final caveat, the 2500s all use Russian versions of an EF95 which is soldered in and there is no room in the mic body for anything but a very small tube. In spite of all this, I've modded many of them, the capsules sound quite good, and an excellent microphone can result. Oh, OK, just one more caveat, The British-made power supply uses filter caps that are only rated for 160VDC. They run them at or above 160V....

 

[Forcemusicgroup]

Hi I'm interested in purchasing one of the m49 pcb kits. Can you point me in theb direction of purchasing one? Thanks

 

[Barry Hufker]

How about just trying a capsule replacement first with one from Soliloqueen? That would be easier than a major overhaul and she makes good capsules...

 

[jeremynothman]

How about just trying a capsule replacement first with one from Soliloqueen? That would be easier than a major overhaul and she makes good capsules...

Because the M147 already has a K49 there. Why replace the good part of this microphone?