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

Simply say you like it, guys.
That's what I do.
I guess I'm too old for them buttons. 

Hey Phraze, Re: C4 omission

Don't jumper it, just leave it out.

Jumpering would connect plate directly to grid.... Applying the 43V plate voltage to the front capsule diaphragm and the grid as well as the full bandwidth plate signal.

I was tinkering with some different tube mic setups some time ago and when I removed this cap I got tons of distortion and an un-useable signal. May have been some other issue combined with removing that because I eventually scrapped that experiment and did something else.

Makes sense about tuning in an accurate gain stage but from a purist (do no harm to the signal) standpoint I agree with leaving it out to minimize phase issues that may be associated with capacitive pads. How often is the pad on the mic used anyway?

On the other hand I also don't mind stuffing it at all to have a more circuit accurate M49.

Cheers!
-jb

Thanks JB!

Informative and thoughtful as usual.

Here's a question.

I'm going to build a "load" switch into my PSU along with a digital multimeter so I can test voltages at various locations when I use the M49. I'm going to use a real AC701 and don't want any mishaps due to variances in wall line voltages since the PSU is a passive design with no regulators.

I want to add a load to both the heater and the B+, even though I know the heater is the more critical.

My issue is that most switches are not rated for 120v DC! I know in general switches don't handle DC very well compared to their AC counterparts.

My thinking is, since the current is only .8mA this shouldn't matter, and I can go ahead and use a switch that is rated only 20-30v DC. I found one at .4A.

What is the wisdom gents; am I courting trouble or is it OK to go ahead with a lower rated DC switch since the current is so tiny?

Thanks for your thoughts.

Best, Mike

**PS I should mention I did find a switch that will handle it but it's $34 and not to my taste! I'd rather use a better looking switch but it's not rated for more than 30V DC.

reading this thread I see everybody used Raytheon's 5840W Tubes but it's hard to find here in Europe,
I found Mullard on ebay :
http://www.ebay.fr/itm/310272371060?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

do you think there will be a huge difference?
should I rather buy directly Raytheons tubes in the US?

Don't think there is much difference. But buy several as noise is always the problem. You might get lucky but I built mine so I could play with tubes and change them easily. The only tube that I would say is in me experience superior to most is the RCA manufactured 5840. Sadly the rest of the world thinks so as well and has bought em up.

Agreed I bought 10 RCA's from Germany. They are much quieter then the Jan tube I had in the mic originally and the top end is a bit smoother as well.  The second RCA I tried was super quiet, low microphonics and sounds great. I have stuck with that tube and now have plenty of spares. I purchased these ones from ebay http://www.ebay.com.au/itm/5x-RCA-CV-3929-EF732-EF-732-Subminiatur-Rohre-NOS-/321105571871?pt=DE_TV_Video_Audio_Elektronenr%C3%B6hren_Valves&hash=item4ac362301f

OK!
I just ordered these RCA,
thanks a lot for the link,
when my mics will be finished I will try RCA and mullard tubes and let you know the differences,

what are people doing with the ground pin on the IEC inlet? i can see one of the 0V terminals connecting the chassis/box but i'm not 100% sure what to do with the IEC ground?

what are people doing with the ground pin on the IEC inlet? i can see one of the 0V terminals connecting the chassis/box but i'm not 100% sure what to do with the IEC ground. I'm guessing it will connect to the the other 0V terminal on the PCB?

jackinthebox said:

what are people doing with the ground pin on the IEC inlet? i can see one of the 0V terminals connecting the chassis/box but i'm not 100% sure what to do with the IEC ground. I'm guessing it will connect to the the other 0V terminal on the PCB?

Click to expand...

OV from PCB pad goes to chassis and from Chassis goes to IEC earth ground.
best,
DAn,

Upcoming Soon,
Microphone Body for this Project ,
http://groupdiy.com/index.php?topic=52563.0
Thanks To Riggler and TSKGUY,
Best,
Dan,

I want to use the larger transformer for the D-M49 Tr board ( Round Version )
It's indicated The MX BV11 will work.
Will the AMI BV 11r or any other P.S.B.  transformer soldier directly to the board?

Winetree said:

I want to use the larger transformer for the D-M49 Tr board ( Round Version )
It's indicated The MX BV11 will work.
Will the AMI BV 11r or any other P.S.B.  transformer soldier directly to the board?

Click to expand...

the transfo pcb pinout (pad correspondance) is one side for Max Bv11 and the other side for the AMI T49 only, you can use about any transformer as long as it fits sterically in the deck, you can then solder directly the wire from the transformer to the second deck,
Let me know if you need help with the second deck connection scheme ,
Hope this helps,
Best,
Dan,

Hello everyone,

While I was perfectly happy with my m49b, I've lend it to a friend who could not use it because of a "buzz". As he gave it back to me, it indeed has a gigantic buzz and muffled sound!

Voltages are very strange, and certainly not as I've set them previously. Just to make sure I got it right, I made a quick picture of what my voltmeter should read -- beware: colors are utterly ugly.

Is that right ?

Hi guys,

So voltages seem to be OK. I measured them through a 1 GOhms voltage divider and a cheap multimeter.

So if voltages are OK, what can make this buzz/sound (wave file here : https://goo.gl/G0BoqI) ?

Hugo.

Just building up my mic, 49b

For biasing the mic, do I have to have the capsule installed?

Also, the psu I can't adjust the H+ lower than 20V.
Should I just add a larger value pot?

Thanks
Neil

Le Roux said:

Just building up my mic, 49b

For biasing the mic, do I have to have the capsule installed?

Also, the psu I can't adjust the H+ lower than 20V.
Should I just add a larger value pot?

Thanks
Neil

Click to expand...

Capsule isn't  needed.
Try much larger.

Le Roux said:

Just building up my mic, 49b

For biasing the mic, do I have to have the capsule installed?

Also, the psu I can't adjust the H+ lower than 20V.
Should I just add a larger value pot?

Thanks
Neil

Click to expand...

is the PSU Loaded , ( Mic connected)
a Passive psu will need a load for adjustement ,
D.

For the Bias try to aim at the plate voltage ,
Dan,

Dan - question for you from the other topic - i'm courious

How is connected input in your circuit?
Did you make switchable option for cardioid only - according to original schematic C1 via S2?