D-47 Tube Mic Kit DIY Solution

[Delta Sigma]

As far as I had read someplace, I am accounting for the load of the microphone by a resistor at the output of the board that would go to the mic. The resistor I am using at the B+ output is a 270K resistor.

Quick calc from Dany's values on the mic schematic I got 213,333k ohms for a B+ dummy load resistor. A incorrect dummy load value may throw you for a loop. Maybe your 270k isn't enough load. If I had time, I'd measure mine with your  270k dummy load and see what mine does but unfortunately I'm busy. 17 ohms for H+ (2 watts!). Don't worry to get exact numbers here, just ballpark. Every tube will be different. I set up my PS with a load resistor to get close-ish but definitely not exact. If I can't dial H+ or B+ in precisely, I then change PS components to get where I need to be.

 

[prophei]

Quick calc from Dany's values on the mic schematic I got 213,333k ohms for a B+ dummy load resistor. A incorrect dummy load value may throw you for a loop. Maybe your 270k isn't enough load. If I had time, I'd measure mine with your  270k dummy load and see what mine does but unfortunately I'm busy. 17 ohms for H+ (2 watts!). Don't worry to get exact numbers here, just ballpark. Every tube will be different. I set up my PS with a load resistor to get close-ish but definitely not exact. If I can't dial H+ or B+ in precisely, I then change PS components to get where I need to be.

Thanks for the response!

Quick question, that calc is barely labeled, so I am not 100% certain I am using it right.
If you look at my pic from a few posts back where I labeled it for myself... am I correct?

Thank you so much.

 

[TillM]

When i build mine U47 with EF800 tube I used this dummy resistors loaded.
Heater: 22-47 ohm (above 2watt)
B+: 150k (above 0,25watt)
And don't forget to set a jumper between CRD and COM on the PSU pcb.

But like I said before, I had the same readings like you with my PSU.
When the mic is plugged, you will see, it will work. (requirement you don't make a mistake by soldering the mic parts)

 

[prophei]

When i build mine U47 with EF800 tube I used this dummy resistors loaded.
Heater: 22-47 ohm (above 2watt)
B+: 150k (above 0,25watt)
And don't forget to set a jumper between CRD and COM on the PSU pcb.

But like I said before, I had the same readings like you with my PSU.
When the mic is plugged, you will see, it will work. (requirement you don't make a mistake by soldering the mic parts)

Thanks... I will try your values to see if the loaded measurements make sense. So far nothing has.
Best,
Michael

 

[TillM]

If you have the PSU for the ef47 from Dan it’s important to jumper CRD and COM.
Otherwise you get false voltages.

 

[prophei]

If you have the PSU for the ef47 from Dan it’s important to jumper CRD and COM.
Otherwise you get false voltages.

How do I know that this PSU is for the ef47?

 

[prophei]

Never mind, it is. It was on the PCB. This may be my problem (jumping CRD/COM). Jumping these two did bring my readings down a bit, though I still had to mess significantly with R1. I got down to about 140V

 

[prophei]

Quick calc from Dany's values on the mic schematic I got 213,333k ohms for a B+ dummy load resistor. A incorrect dummy load value may throw you for a loop. Maybe your 270k isn't enough load. If I had time, I'd measure mine with your  270k dummy load and see what mine does but unfortunately I'm busy. 17 ohms for H+ (2 watts!). Don't worry to get exact numbers here, just ballpark. Every tube will be different. I set up my PS with a load resistor to get close-ish but definitely not exact. If I can't dial H+ or B+ in precisely, I then change PS components to get where I need to be.

How much voltage can I hit the mic with from the PSU before causing damage? From your response, it sounds like there is a bit of a range of voltages that I could get, and that I will have to fine tune to the pcb tube anyways... so what voltage is the point where I can actually damage the mic?

My desire to not kill the mic with a faulty PSU has kept me from completing that and connecting it, which would obviously give me the real load I am dealing with. 

Are there any guidelines? 

 

[TillM]

When you dummy load the PSU with the resistors, then calibrate the trimmer for B+ and H to the needed specs (or nearly in the range).
When you plug your mic in, then you can don the "real" calibration.
I always calibrate dummy loaded PSU's under voltage (If it works).
So lets say, I need 120v and with a dummy loaded resistor i can turn it to 110v, i trim it to 110v.
Sometimes with the dummy loaded resistor you can't get to the "real" specs. So you need 120v and the trimmer with dummy loaded resistor shows 130v with my DMM, then I take this.

 

[prophei]

When you dummy load the PSU with the resistors, then calibrate the trimmer for B+ and H to the needed specs (or nearly in the range).
When you plug your mic in, then you can don the "real" calibration.
I always calibrate dummy loaded PSU's under voltage (If it works).
So lets say, I need 120v and with a dummy loaded resistor i can turn it to 110v, i trim it to 110v.
Sometimes with the dummy loaded resistor you can't get to the "real" specs. So you need 120v and the trimmer with dummy loaded resistor shows 130v with my DMM, then I take this.

Even with the jumper in place now, I am going to need some major adjustment to my R1 to get anywhere near what I need. Makes me wonder if that implies an issue someplace else. Maybe it doesn't matter how I get there? I have some 2v resistors coming tomorrow, so I'll be able to dig in then. I have been having to do some crude serial resistor stringing to get to the test values I need.

 

[prophei]

I know this is a bit of a repeat, but does anyone know the answer to this?

"How much voltage can I hit the mic with from the PSU before causing damage? ...
...Are there any guidelines? "

 

[Delta Sigma]

I know this is a bit of a repeat, but does anyone know the answer to this?

"How much voltage can I hit the mic with from the PSU before causing damage? ...
...Are there any guidelines? "

Look at your component ratings. Filter caps. What are they rated for?

 

[jrasia]

Kudos to Dan for making a top notch U47 clone kit.  Very lovely sounding!
I used a Neumann K49, Phædrus VF14 gold dot, and Moby BV8 in my build.
Couldn't be happier

 

[Avgatzeblouz]

Kudos to Dan for making a top notch U47 clone kit.  Very lovely sounding!
I used a Neumann K49, Phædrus VF14 gold dot, and Moby BV8 in my build.
Couldn't be happier

Wow, man ! This is THE mic ! I am waiting for my Aputis body, but I have almost the exact same components waiting for it (I have the FAB transformer). Congrats !

 

[TLRT]

I know this is a bit of a repeat, but does anyone know the answer to this?

"How much voltage can I hit the mic with from the PSU before causing damage? ...
...Are there any guidelines? "

Depends on your capsule voltage divider, (2:3 or 3:3) the capsule will die if you hit above 80-100V. So above 140-150V output from PSU will be too much

 

[prophei]

Kudos to Dan for making a top notch U47 clone kit.  Very lovely sounding!
I used a Neumann K49, Phædrus VF14 gold dot, and Moby BV8 in my build.
Couldn't be happier

How do you like that Phædrus VF14 gold dot? Have there been any comparisons made between that and something like the EF800?

 

[poctop]

Kudos to Dan for making a top notch U47 clone kit.  Very lovely sounding!
I used a Neumann K49, Phædrus VF14 gold dot, and Moby BV8 in my build.
Couldn't be happier

CAps ?

 

[jrasia]

CAps ?

MKT1813 poly caps

If anyone one has NOS Bosch caps, I'll gladly take them

 

[jrasia]

How do you like that Phædrus VF14 gold dot? Have there been any comparisons made between that and something like the EF800?

I actually have a ef800 build as well, but it's difficult for me to compare because the ef800 has a m7 capsule, and the Phaedrus has a Neumann k47.  I don't have a real vf14 to compare, but I have no complaints about the gold dot.

The ef800 is VERY low noise, very smooth and 'big' sounding.

The k47 build is similar, but more mid forward, perhaps more compression  or something going on.

 

[Phrazemaster]

Wow, man ! This is THE mic ! I am waiting for my Aputis body, but I have almost the exact same components waiting for it (I have the FAB transformer). Congrats !

Wow - you are going to be waiting a LONG TIME! I ordered an M49 body from Aputis 3 years ago; never got it.

Good luck tho!

Mike