The Ultimate DIY U47 - Build Thread (And some PSU questions)

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StormsofVogue

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Hey all! I've been working on this U47 build for a while. My initial plans were just to get a cheap U47. As I've done research it's become more of an attempt at a holy grail clone than a cheap one. I do have a couple of questions I'd love to get some input on, but first a quick summary of my build.

The Mic


I'm sure you're all familiar with Dan's work. I purchased a mic body from him as well as some other parts. Much of my schematic information has come from him as well.

DSC01232.jpg

I don't think there's a more perfect U47 replica chassis in existence. Incredible work by Dan.

DSC01242.jpg

I was originally considering an EF-800 tube, but ended up going with the Phaedrus Audio VF-14M. The capsule is a BeesNeez K47. Transformer is a Cinemag CM-2461Nico, but I'll likely be switching it for an AMI BV8R.

The PSU


DSC01247.jpg

This is where things get a little uncertain. Since my original plans involved an EF-800 tube, Dan's PSU circuit for that tube was a no-brainer. I actually kind of liked the idea of having a separate line for the heater voltage rather than the big drop-down resistor. The problem is the Phaedrus requires 35vdc and the EF-800 circuit only supplies 5v.

The Dilemma


MQ-PSU-DIY_Bplus_02.jpg

This is kind of what I'm aiming for at the moment. I've done rivets on G-10 board before and I love the look of it. I might even go with turrets. The trick is coming up with an appropriate circuit.

2021-11-14 22_18_02-u47 PSU schematic.pdf - Personal - Microsoft Edge.png
This is Dan's EF-800 PSU schematic. I half-way thought I might be able to just use 105v side of this circuit and use the drop-down resistor to get my 35v to H+. However, I've noticed that the standard 105v PSU circuits that are used along with the pull-down resistor usually feature these beefy wire-wound ceramic resistors and a choke filter. I must be missing something.

I'm also concerned about sourcing the correct pull-down resistor. I think I'll need to get pretty close to that 35v to make the Phaedrus not-really-a-tube thing happy and I'm not sure I'm going to be able to source a resistor that's able to do that. If the schematic's I've found are correct, I need a heat-sinked resistor with somewhere around 1750ohms. I did some searching on Mouser, and these don't seem particularly easy to come by.


My Options

So I'm kind of stuck. Here's the basic summary of my options and concerns:
  • Build standard U47 PSU
    • I kinda' don't like the giant wire-wound resistors, and I'm not sure I'm going to be able to source the correct pull-down resistor.
  • Use the EF-800 105v circuit by itself along with the internal U47 pull-down resistor
    • I'm pretty sure this isn't going to work, plus it still leaves me with the issue of sourcing a pull-down resistor.
  • Use the EF-800 circuit concept, but redesign the 5v side for 35v operation
    • I don't mind this option, but redesigning the 5v side is currently outside of my skillset. I may research this option further if it seems to be the most ideal.

Any advice, assistance or opinions are welcome and very much appreciated. Thanks!​

 

moamps

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At the beginning I would like to praise your very organized first post and I would like to welcome you here.
The easiest way to complete the microphone is to use the EF800 and the pre-existing elements you already have. I think that is the best solution at the moment.
If you still want to use the VF14M PH, then you’ll need to pretty much redesign the power supply (and maybe use another mains transformer), according to the design of how the original U47 was made. I've never heard of a U47 mic with a VF14M PH, but I doubt it will sound better than the version with the EF800.

I wrote an article about U47 design that could be useful in deciding what to do next:
 

StormsofVogue

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At the beginning I would like to praise your very organized first post and I would like to welcome you here.
The easiest way to complete the microphone is to use the EF800 and the pre-existing elements you already have. I think that is the best solution at the moment.
If you still want to use the VF14M PH, then you’ll need to pretty much redesign the power supply (and maybe use another mains transformer), according to the design of how the original U47 was made. I've never heard of a U47 mic with a VF14M PH, but I doubt it will sound better than the version with the EF800.

I wrote an article about U47 design that could be useful in deciding what to do next:

I appreciate the response! I've actually visited and read through your website a few times since starting this project. Great information and amazing work!

Darn, I think you might be right about abandoning the VF14M PH. It wasn't a cheap purchase, but I too have some concerns that it might not even sound better than the EF800. I actually put some serious thought and research into designing a new PSU the last two days. I think I could do it, but what's the point if it's just to preserve the use of a solid-state device that's likely not going to benefit the final product.

Thanks so much for your input. I think you've given me a good nudge in the right direction.
 

TLRT

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I build both(many pcs) and Phaedrus sounds better for vocals than ef800. But it needs lot of customization it is true.
 

StormsofVogue

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I build both(many pcs) and Phaedrus sounds better for vocals than ef800. But it needs lot of customization it is true.

Interesting. I've seen a lot of skepticism on the Phaedrus, and almost no one who's actually used it. It was originally called VF14ME by Grove Hill Audio. It stirred up quite a controversy because they originally priced it at around $950.
 

TLRT

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Interesting. I've seen a lot of skepticism on the Phaedrus, and almost no one who's actually used it. It was originally called VF14ME by Grove Hill Audio. It stirred up quite a controversy because they originally priced it at around $950.
Here is a quick test with the Phaedrus:
 

StormsofVogue

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Here is a quick test with the Phaedrus:

Beautifully captured vocal performance there! Certainly can't say the Phaedrus didn't hold up. Of course, without a direct a/b comparison, it's hard to say exactly how it affects the microphone's tone. In any case, I'd say you're likely more qualified than I to judge. I definitely appreciate your input.

I did notice that the schematic @moamps has on his website is probably pretty close to what I would need to get the Phaedrus working. We'll see what happens. I'm going to think about this for a bit.
 

TLRT

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Beautifully captured vocal performance there! Certainly can't say the Phaedrus didn't hold up. Of course, without a direct a/b comparison, it's hard to say exactly how it affects the microphone's tone. In any case, I'd say you're likely more qualified than I to judge. I definitely appreciate your input.

I did notice that the schematic @moamps has on his website is probably pretty close to what I would need to get the Phaedrus working. We'll see what happens. I'm going to think about this for a bit.
Actually the old u47 psu is very easy ,it has a rectifier,5caps,4resistors, no regulation so low noise. However you need some protection for phaedrus tube as it has lower max voltages as the real vf14.
 

StormsofVogue

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Actually the old u47 psu is very easy ,it has a rectifier,5caps,4resistors, no regulation so low noise. However you need some protection for phaedrus tube as it has lower max voltages as the real vf14.

Yeah, my concern with using a single voltage PSU was with getting the right voltage for the Phaedrus since the drop-down resistor required for that part of the circuit isn't easy to come by in the values I'd need. Dual voltage just makes more sense to me, but perhaps I'm overthinking it.

This is the schematic @moamps has on his site. I don't need the relay or the meter parts of the circuit, so I could just eliminate those. His site says that he's getting 120v for B+, and 40v for H+. I'm assuming that's under load. Other sources I've seen show u47 usually requires 105v for B+ and 35v for H+. I think I could get to those values by adjusting the pots and possibly changing the values of R201 and R205. Just trying to avoid having to design a circuit from scratch.

mU47_VF14_PS.jpg

And the component values:

2021-11-16 11_32_26-Journey into the Legend of the U47.png
 
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TLRT

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Check the original schematics, u47 is very simple in both the psu and the mic. The original mic has one 105v input only,there is one divider for anode / polarization voltage(low current apprx 1mA) and an internal 5w resistor to drop the 105v to 35v for vf14 heater(40mA) this is the tricky part as it will generate some heat inside the mic body.
 

StormsofVogue

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Check the original schematics, u47 is very simple in both the psu and the mic. The original mic has one 105v input only,there is one divider for anode / polarization voltage(low current apprx 1mA) and an internal 5w resistor to drop the 105v to 35v for vf14 heater(40mA) this is the tricky part as it will generate some heat inside the mic body.

I'll take a look. That would be the easiest way to go. I appreciate your input!
 

moamps

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Yeah, my concern with using a single voltage PSU was with getting the right voltage for the Phaedrus since the drop-down resistor required for that part of the circuit isn't easy to come by in the values I'd need. Dual voltage just makes more sense to me, but perhaps I'm overthinking it.

The VF14ME is a circuit that should have a long lifespan and should be less sensitive to supply voltage fluctuations, so I would recommend that you use either the original power supply circuit as suggested or the circuit used in the MAX IOaudio two-tube version.
The 1800 ohm resistor can be used instead of 1750ohm and can be obtained without any problems. If you need any additional information, PM me.
 

dmp

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I used a EF800 in a build and it is my favorite mic (out of about 10 builds)
What is inside the Phaedrus?

That mic body looks awesome. Is it the lighting or did you paint it?
 

StormsofVogue

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The VF14ME is a circuit that should have a long lifespan and should be less sensitive to supply voltage fluctuations, so I would recommend that you use either the original power supply circuit as suggested or the circuit used in the MAX IOaudio two-tube version.
The 1800 ohm resistor can be used instead of 1750ohm and can be obtained without any problems. If you need any additional information, PM me.

Thanks so much! I found the old thread for the IOAudio circuit. All the images are dead, but I came across the schematic in another forum, so I think that's good enough. After reading through the thread, the only thing I'm not clear on is the purpose of the 14k/12k 1w resistors at the end of the circuit. I know the 2.3k is for dummy load testing.

MK47 PSU schematic.JPG

I used a EF800 in a build and it is my favorite mic (out of about 10 builds)
What is inside the Phaedrus?

That mic body looks awesome. Is it the lighting or did you paint it?

The Phaedrus is a solid-state design. No idea what's in it. Some speculate it's just a FET circuit. Probably is. I've seem discussions about FET replacement circuits in u47's being actually kinda' difficult to distinguish. My ears are probably in the "can't distinguish" category, so... it's perfect. lol

http://www.phaedrus-audio.com/VF14M Phaedrus electronic tube.htm

The mic looks pretty much like that. No paint. That's the anodized flat silver finish that Dan puts on them. It's pretty dark, but that photo may be making it look just a tad darker than it is.
 

Henleyguitars

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I have the phadreus in a 47 build and it sounds amazing
 

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btown2009

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Where did you find that body? The only ones i can find don’t have the window for the polar pattern selector. Thank you, a link would be awesome to exactly where you found it
 

StormsofVogue

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I have the phadreus in a 47 build and it sounds amazing

Great to hear! Helps ease my skepticism a bit. I did pay $270 for the darn thing. It had better sound good. haha

Where did you find that body? The only ones i can find don’t have the window for the polar pattern selector. Thank you, a link would be awesome to exactly where you found it

Dan from vintagemicrophonepcbkit.com makes those, but they're not listed on his website. You'll have to email him and probably get on a waitlist for his next production run. They cost around $900.

[email protected]

Vintage Tube & Vintage FET Microphone PCB Kit For DIY & New D7 Custom Capsule
 
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moamps

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... but I came across the schematic in another forum, so I think that's good enough. After reading through the thread, the only thing I'm not clear on is the purpose of the 14k/12k 1w resistors at the end of the circuit. I know the 2.3k is for dummy load testing.

It is a switch for engaging relay in microphone body for pattern selection. The lower resistor (12k) mimics the same load that has a relay to the power supply.
 

Pip

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Yes Dan's AKA Poctop's bodies are the best I know of. The Phaedrus Audio tube solutions are excellent IMO and their customer service is quite good.

I have used the Phaedrus solution in multiple builds and I am quite happy with the result. The EF800 is IMO the best actual vacuum tube alternative to the VF14K. It was originally designed to be the replacement alternative to the VF tubes. The EF800 does require filament voltage and obviously is a totally different socket. One nice thing about the Phaedrus approach is that if you ever stumble across an actual usable (now unobtainium) VF14K you can just pop it in the mic.

The phaedrus is not the only FET based solution on the market for VF14 replacement. Andreas Grosser makes one but at last inquiry would not sell it unless you let him install it in the mic. Their are also Tube solutions by Telefunken, and Saturn sound I only mention them as they are there, IMO these are not the answer.

Two notes. In the PSU photo the resistors they are using in the filter circuit are they the right wattage they look rather small to me. They get very warm. I myself use metal clad wire wound types in this area and use a case that acts as a heat sink. The drop down resistor that gives the filament voltage gets warm and needs to be properly installed so that its heat is dissipated into the mic body. The Phaedrus VF14M does not like excessive heat. I built a copy that is overstuffed with vintage parts and had to move the drop down resistor into the PSU as I could no longer get the heat to a low enough level to not cause problems. My website has some info in the blog section. Some say that this can cause problems, I have noticed none.

Accopean power supplies makes a regulated UL listed PSU that I use and it works great. Yes I know part of the sound is down to the unregulated nature of the supply but I opted for safety and consistent voltage and I have not noticed a truly tangible sonic difference. If anything IMO the regulated supply makes for a bit more presence in the sound.

Lastly check out the Moxtone website if you want to really jump down the rabbit hole!



 
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