MK-U47 - build thread

[Pip]

A quick question regarding the PSU - Max do you have a schematic for it specifically, or you are recommending the Zayance or a real Neumann PSU?

I'm tempted to go PTP on this one, as I want to mount the resistors off-board anyway; I'm not certain what value the Zayance PCB will provide with more than half the components not even mounted.

I do have a question regarding the LED that is on the Zayance PCB - how does this not get fried? I thought LED's were around 5V or such; I can't see how the voltage gets dropped to support it...or are there some high-power LEDs out there of 105V? I tried doing the math on it and can't figure this...any thoughts, anyone?

Thanks

Mike

There is a PSU schematic somewhere here. I love the PCB that Zayance sells. There is a drop down resistor incorporated in the Zayance PCB for the LED.

 

[Phrazemaster]

Thanks Pip. I have one coming, although I am probably going to go PTP on this one since I'm already going to mount the resistors off-board anyway.

EDIT: tried figuring the LED maths but I think I did it wrong; removing calculations...

 

[ioaudio]

Max, at one point you mentioned you were working on an M7 of your own, as well as a PSU for this kit.

Are those still in the offing?

By the way, I'm sure you have spent some time in Klaus' forum for microphones. He says no one has nailed a real M7 in years. He thinks it's because the PVC material has changed. Just wondering if you were going to continue this research, and also suggest you contact him as he might be willing to offer suggestions/guidance if you wanted it.

Hope this isn't too far OT; just wanting to make the best MK-U47 possible (hint, hint!)



Mike

Hey Mike,

indeed I'm working on my take on the M7 capsule, on and off since nearly three years now.
I'm experimenting with all kind of different PVC films in various thickness, often sourced from outside EU for regulation issues.
I have come close to what i want it to sound, a pristine original Berlin M7 i use as a reference, but there's still a small difference, and i want to get it 100% right.  Testing is done by myself and by three sound engineers who have a U47s with original M7 capsules.
I recently found a Swiss manufacturer for specialty films and they will send me a couple of samples next week, I'll make an appointment with the research lab for the gold evaporation after that. I have a good feeling with the new film but we'll see.

regarding the PSU:
Since the MK-U47 works like the original, just follow the original PSU plans. Additionally the schematics can be found in the MK47 thread (minus the switch). Most of my costumers build with Zayance's PCB.
I recommend the LED because it also shows if there's any current left in the capacitors after switching off (the LED fades as it drains)
Led current/voltage drop resistor is simply calculated by ohms law (google led resistor calculator)

-Max

 

[Phrazemaster]

Max this is so exciting! Thanks for the update!!

Yes of course I understand how to calculate for one LED; the issue is I don't know what the voltage is coming into that leg of the circuit. I guess I'll just trust Zayance's calculation for now.

I'm going to do a PTP using the MK47 schematic as you suggested.

Thanks much, and looking forward to the fruit of your labor!!

Best,

Mike

 

[Phrazemaster]

OK knowledgeable minds, show me the error in my calcs.

I'm trying to understand why the MK-47 specifies a 100K 1W resistor for the LED.

Let's assume the voltage is 105v. It's probably a bit higher in this leg of the circuit, but let's go with 105 for the moment. Actually since in parallel circuits all voltages are the same, it would be 105V, right? If the PSU is calibrated of course.

Let's assume a 5V, 20mA LED (pretty standard).

This means we need to drop 100V to give the LED it's requisite 5V. So far so good?

This gives us an R = V/I value of 100V/.02A = 5K.

Power rating would be = V*I = 100*.02 = 2W. Double it for safety, 4W, ~5W.

Now let's look at the stock 100K resistor.

Assuming the 100K resistor also dropped 100V, the current would be = V/R = 1mA. The power would be = V*I=100*.001=.1W

So basically this 100K resistor will work fine for very low current LEDs of around 1mA or so? In my case I have a 6V LED that uses 15mA, so I'll have to use a higher bigger resistor for my project instead. I'm using the Antek toroid, which puts out a bit more juice than the Triad, so I think I'll be ok in that regard.

In my exact case, I've done a simulation of the PSU using a link in this thread, and using a value of 470R instead of the 680/330 combo. Pot value at 220R gives 105.2V.

I drop 99V across my resistor, at 15mA.

This means I need R=V/I = 99/.015A= 6.6K resistor. W=V*I = 99*.015 = 1.5W, double for safety and that gives me a 6.6K resistor at 3W.

Can anyone check me on this? Am I in the right ballpark?

Thanks,

Mike

 

[ioaudio]

Sorry for the late reply.
Yes, stock the LED works at a low current of 1mA, a little dimmed but still clearly visible.
15mA would be quite a waste of power.

 

[ioaudio]

I just read the thread over at Klaus' Forum.
I do not agree that the Thiersch blue line capsule is "project-studio quality".
Aside from the various great sounding MK-U47s, this capsule is/was used in high end builds from Wagner, Grosser, Wunder etc, hardly "project-studio quality" !

-Max

 

[Category 5]

I just read the thread over at Klaus' Forum.
I do not agree that the Thiersch blue line capsule is "project-studio quality".
Aside from the various great sounding MK-U47s, this capsule is/was used in high end builds from Wagner, Grosser, Wunder etc, hardly "project-studio quality" !

-Max

Agreed Max.  Klaus may have his own interests in mind when criticizing the works and products of others.  Both Blue and Redline capsules are premium performance products, just like the genuine Neumann capsules are (i.e. K49)

 

[Pip]

I just read the thread over at Klaus' Forum.
I do not agree that the Thiersch blue line capsule is "project-studio quality".
Aside from the various great sounding MK-U47s, this capsule is/was used in high end builds from Wagner, Grosser, Wunder etc, hardly "project-studio quality" !

-Max

I agree the  Thierch Elektroakustic (TE) capsule is not an amateur capsule. I also don't know who uses what in their mics as an example most of the companies say they make their own Wagner especially.  I also don't know what is meant by the phrase project studio quality? As most of the records recorded today are recorded in project studios. So maybe that's a good thing?!

I don't think Mr. Heyne is a big fan of the M7 capsule.  I haven't read his comments in a long time  but I distinctly remember getting the impression that he was more of a K47 guy. He also like the rest of us has a definite sonic character he has decided over years and years of listening that he sees as a Holy Grail sound. Which I think he will agree that not all original U47's share by any means.

There is something,  IMO that is more modern and relevant to today's production  desires  that is brought by the K47 over the M7 and there is also a definite difference between the East (Geffel) vs West (Neumann ,Berlin) M7 capsules.  As there is a  difference between the Dale M7 and the Cathedral Pipes M7 and the Beesneez M7 and the TE M7 both RED and Blue, etc...  I  also feel they each have their own use and shine in different ways on different things.

I have built all of my U47 copies with M7 design capsules and IMO I prefer the TE Blue Line for what I do. But that being said it is because of a definite sonic signature it is not because of its flat response curve or its truthiness to the source. If you want a more accurate U47 I think you do want one with a K47 or even a Stephen Paul or a Klaus Heyne mod.

To end I will say it again it always makes me giggle when anybody says "thats the mic The Beatles and Frank Sinatra used", because at the end of the session they where The Beatles and Frank Sinatra!

 

[Phrazemaster]

OK I  have requested a Blueline!!

Here's a question. WHY do we keep the dropping resistor inside the bottom bell of the microphone, heating up the microphone - just because Neumann did it?

Would it not make more sense to place this resistor in the PSU instead, keeping the microphone cool? Let the PSU heat up instead of the mic?  Or are we just deliberately trying to cook our precious capsules?

Would there be any sonic problem with mounting that dropping resistor inside the PSU instead of the mic? Has anybody tried this?

Thanks.

 

[Pip]

OK I  have requested a Blueline!!

Here's a question. WHY do we keep the dropping resistor inside the bottom bell of the microphone, heating up the microphone - just because Neumann did it?

Would it not make more sense to place this resistor in the PSU instead, keeping the microphone cool? Let the PSU heat up instead of the mic?  Or are we just deliberately trying to cook our precious capsules?

Would there be any sonic problem with mounting that dropping resistor inside the PSU instead of the mic? Has anybody tried this?

Thanks.

Proximity to the circuit is all and by that I mean where it is and what it is. If you were to do something different with the configuration you stray from the original design you also bring in a whole new set of variables including the voltage loss and capacitance of the cable length. Part of what makes this mic this mic is the single supply voltage concept for example there is voltage sag inherent in this design that comes into play as the SPL goes up. But why use a drop down resistor at all why not use a dedicated power supply for the necessary 40VDC for the filament no reason other than it would be a variant on the original design.

As to cooking the capsule with heat, I don't think it has any bearing on the issue. Our capsules are more in danger from handling issues and humidity issues, the most devastating one being spit with food particles and other such niceties which then allows for gunk attachment bringing on frequency attenuation and decrepitude. The heat factor has more to do with the noise specs of the mic is my guess as resistance heat dissipation=noise. I know that when that drop down resistor is not right it becomes an audio artifact making machine! If you use Teflon coated wire you will have no heat problem there either.

 

[Phrazemaster]

Good points Pip!

Yes fidelity to the original design is a consideration of course. I have a PSU from a well-known mic builder and he uses a zener in his PSU. Mic is very quiet anyway!

I guess my concern stems from posts wherein people have stated, "be sure to hang your U47 upside down to avoid sending undue heat to the capsule." I know that heat is a killer when it comes to electronics. In fact I read somewhere that every 10 degree increase in heat halves the life of your components. Dunno if that's true, but makes sense.

Plus if one has the PVC capsule, that is already prone to aging and getting brittle, just seems a bit like spiting fate to use so much heat.

Thanks.

Mike

 

[Pip]

Good points Pip!

Yes fidelity to the original design is a consideration of course. I have a PSU from a well-known mic builder and he uses a zener in his PSU. Mic is very quiet anyway!

I guess my concern stems from posts wherein people have stated, "be sure to hang your U47 upside down to avoid sending undue heat to the capsule." I know that heat is a killer when it comes to electronics. In fact I read somewhere that every 10 degree increase in heat halves the life of your components. Dunno if that's true, but makes sense.

Plus if one has the PVC capsule, that is already prone to aging and getting brittle, just seems a bit like spiting fate to use so much heat.

Thanks.

Mike

Hanging the mic upside-down to avoid heat hurting capsule pure wives-tale stuff IMHO. The only reason to hang it that way is so it doesn't block the view of the music-stand or allows for a better placement. I also have noticed that there is something that psychologically aids singers when its that way they tend to sing in a more physically relaxed manor but that is not science and it is just my feeling.

 

[Phrazemaster]

Well...not to be contrary...but of course heat rises, and I'm sure the capsule could do without all that extra heat...

I loved your comment about singers being more relaxed with the mic upside down...

 

[Category 5]

Well...not to be contrary...but of course heat rises, and I'm sure the capsule could do without all that extra heat...

I loved your comment about singers being more relaxed with the mic upside down...

The capsule mount is isolated so really the only heat the capsule sees is the heat from the air that surrounds it.  Put your hand on the grill and you'll see there really isn't much heat up there at all.  Maybe it's a little warmer than ambient, but nothing that I would expect to significantly impact the performance or longevity of the capsule (even PVC).  If you want to preserve the longevity of the capsule, bag the mic before you disconnect power, and store it in a cool dry place.  The bell on the other hand will get almost too hot to touch, and I rather like it.  To me it says "I'm all warmed up and ready to impress"

You could also put the dropper in the PSU and wire the heater through one of the redundant ground pins (or use a 7 pin insert for the mic).  That would eliminate most of the heat from the mic side, but again I don't think there is really much benefit as far as longevity is concerned.

 

[stribor1]

Finally put my MKPSU together. Everything working fine I got it tuned to 105V, but it keeps popping fuses, apparently only when I turn it on or off. When I get it working it is stable, then I power it off and when I power it on the fuse is blown (doesn´t happen every time but very frequently, like  50% even more)
I have 220V power and use a slow blow 125mA fuse. The Mains transformer is is a 30VA toroidal one with a 200V output and 6,3V pilot light output purchased from TubeTown.de
I got the 220V leads connected to my euro-power connector which also contains a fuse holder.

I put a 200mA slow blow fuse in there and the problem is gone, but 200mA gives 44VA on 220V and I´m afraid that the mains transformer might die on me.
Any idea? Is it possible that this is caused by a bad mains transformer?
Thanks,
J.

 

[stelin]

I have built three PSUs for my MK-U47s. One of the PSUs has blown the (0.125 amp) fuse one time.

The size of the fuse does not change how much current the transformer draws. It only sets a limit: If the current is too high the fuse will blow. It’s a protection against a short circuit, when the 220 volts AC, 200 volts AC secondary or 105 volts DC gets connected directly to ground.

In Sweden we now have 230 Volts in the power outlets (it used to be 220 volts). If I remember right, there are three ways you can connect the transformer from TubeTown (I’m using the same one): 220, 230 and 240 volts.
I have used the 240 volts lead. That means that the voltage on the secondary side will be a little bit less than if you use the 220 or 230 volt lead.

When you turn on the PSU it will draw a lot more current for a short moment. That’s because the capacitors in the PSU are empty and they must be “filled up” with charge. Also, the microphone will draw a bit more current in the first five seconds or so because the heater in the tubes have very low resistance before they start to glow (the resistance increases when the wire in the heater warms up).

I suspect that the 0.125 amps recommendation is based on how much current the microphone draws when it is “warmed up and in operation”.

I changed the fuses in my PSUs to 0.3 amps. I have not had any blown fuses since I did that.

- Stefan

 

[stribor1]

Thanks Stefan,
I´m using the 200mA fuse now and no blown fuses so far.
I know that the fuse is not impacting the current draw, only limiting it and I also figured that the initial impulse when powering on is probably blowing the 125mA fuse. I was only concerned that the 200mA fuse is would limit the current past the power rating of the transformer (could reach 44VA with this fuse) but it is not likeley that a permanent 200mA current draw should occur.

The mic is working fine in cardio btw, but no omni, but I already know the reason and will fix this shortly.
Using Philips Miniwatt tubes and burn in is still ongoing. Have some Tungsols, they are next. Trying to get some WE´s.

 

[Pip]

Thanks Stefan,
I´m using the 200mA fuse now and no blown fuses so far.
I know that the fuse is not impacting the current draw, only limiting it and I also figured that the initial impulse when powering on is probably blowing the 125mA fuse. I was only concerned that the 200mA fuse is would limit the current past the power rating of the transformer (could reach 44VA with this fuse) but it is not likeley that a permanent 200mA current draw should occur.

The mic is working fine in cardio btw, but no omni, but I already know the reason and will fix this shortly.
Using Philips Miniwatt tubes and burn in is still ongoing. Have some Tungsols, they are next. Trying to get some WE´s.

Are your Philips Miniwatts microphonic? When you tap the mic body do they make a ping sound?

After much research my suggestion is you want to look for made in USA WE tubes with the large font. I believe these are older than the others available and there is no doubt in my mind anymore that they are the lowest noise of the WE's. If you can find some Ericsson 408a's they are the best noise to microphonic in my experience and sound great. The Philips TS62 Miniwatts sound the best out of all I have tested but they are the most microphonic.

 

[stribor1]

Thanks Stefan,
I´m using the 200mA fuse now and no blown fuses so far.
I know that the fuse is not impacting the current draw, only limiting it and I also figured that the initial impulse when powering on is probably blowing the 125mA fuse. I was only concerned that the 200mA fuse is would limit the current past the power rating of the transformer (could reach 44VA with this fuse) but it is not likeley that a permanent 200mA current draw should occur.

The mic is working fine in cardio btw, but no omni, but I already know the reason and will fix this shortly.
Using Philips Miniwatt tubes and burn in is still ongoing. Have some Tungsols, they are next. Trying to get some WE´s.

Are your Philips Miniwatts microphonic? When you tap the mic body do they make a ping sound?

After much research my suggestion is you want to look for made in USA WE tubes with the large font. I believe these are older than the others available and there is no doubt in my mind anymore that they are the lowest noise of the WE's. If you can find some Ericsson 408a's they are the best noise to microphonic in my experience and sound great. The Philips TS62 Miniwatts sound the best out of all I have tested but they are the most microphonic.

Yes, quite microphonic. They are cooking for some 10 hours so I´m still burning them in and hope this will improve. I´m very happy with the sound (classical guitar sounds magic, voice very natural and warm), but didn´t compare them yet to other tubes.
Found some 50ies WE 408A in nostubestore.com (got the miniwatts there as well, gold pins O-getter), the guy has just 4 left don´t know if they are paired still waiting for a reply.