D-EF47 Tribute To Oliver Archut U47 Build Thread.

[Robby1970]

Good morning Mr. Dan, unfortunately I can't get the D-EF47 to work, I had a technician look at it, but it doesn't work,
Could you please help me?
Thank you

 

[Delta Sigma]

Sorry, but a blank call for help isn't enough.

What doesn't work? Audio? Tube voltages out? Tube not heating?

Your doctor isn't gonna give you cream unless you show them your rash.

 

[EarthTone]

Is it OK to use 160V caps at C2 and C3? Obviously the BOM and layout/schemo call for 250V in both spots but I want to use vintage PIO caps like original Neumann and the only ones I have access to are 160V.

 

[rock soderstrom]

It depends on your PSU and B+. In the original u47 schematic C3 is rated for 160V and C2 for 250V, but I think even 160V for C2 would be enough in the original design. In the Ef800 version, the situation is slightly different because of the separate heating. If the voltage is briefly too high during switch-on, use a zener diode to clamp the voltage down. (or add a LED with resistor to the PSU as additional load)

 

[Robby1970]

Good morning Gentlemen, the D-EF47 works, but the output gein is very low, it could be the transformer the primary is 8ohm the secondary is 290ohm.
A thousand thanks

 

[Robby1970]

it was the 2 jumpers on the microphone that made it work

 

[Robby1970]

Now I will also look for the capacitors you recommended
Thank you

 

[EarthTone]

It depends on your PSU and B+. In the original u47 schematic C3 is rated for 160V and C2 for 250V, but I think even 160V for C2 would be enough in the original design. If the voltage is briefly too high during switch-on, use a zener diode to clamp the voltage down. (or add a LED with resistor to the PSU as additional load)

Hi Rock! Thank you so much for your response. Right, I always noticed that what you said about the original schemo- C3 is 160v and C2 is 250 but it seems like the voltages indicate 160V would be ok for C2 as well.

I think the zener idea as a voltage regulator sounds like a good move. So please excuse my lack of knowledge, but would the +/- of the zener diode go on this schemo? I assume it would go inside the mic and not the PSU.

https://cdn.imagearchive.com/groupdiy/u/39511/58d1402a0713c.pdf

 

[rock soderstrom]

Right, I always noticed that what you said about the original schemo- C3 is 160v and C2 is 250 but it seems like the voltages indicate 160V would be ok for C2 as well.

I think so too, but as I said, in the EF800 version the heating is separate, which can result in a different behaviour when mic is switched on.

In normal operation, the 160V for both capacitors in the EF800 version are sufficient. Only when switching on, when the tube is cold and no current is flowing, the B+ can become considerably higher. I don't have a suitable PSU here, otherwise I would measure it.

Long story short, I would install a Z-diode in the mic to ensure that B+ (in the mic) never exceeds a certain voltage (max. 160V with safety margin). So a zener diode with 120V looks good to me. In normal operation the zener diode would be out of circuit.



Edit: When everything is ready, I would take a closer look, especially during the start phase, and see if the Zener diode is really necessary. Please give me some feedback...

 

[rock soderstrom]

I think the zener idea as a voltage regulator sounds like a good move.

Of course, you could also use the Zener diode as a "regulator" ( or better stabilizer), but then you should also provide some extra filtering, as the Zener diodes tend to be noisy...

My suggestion does not require this (I hope so ), as the Zener is not active in normal operation.

 

[EarthTone]

Of course, you could also use the Zener diode as a "regulator" ( or better stabilizer), but then you should also provide some extra filtering, as the Zener diodes tend to be noisy...

My suggestion does not require this (I hope so ), as the Zener is not active in normal operation.

Awesome! This makes sense to me. Thank you so much for your helpful posts! I will indeed try this on my build and report back. It will be a little while- I think I will have the rest of the parts I need by mid February, but I will let you know. Thanks again.

 

[Robby1970]

I think so too, but as I said, in the EF800 version the heating is separate, which can result in a different behaviour when mic is switched on.

In normal operation, the 160V for both capacitors in the EF800 version are sufficient. Only when switching on, when the tube is cold and no current is flowing, the B+ can become considerably higher. I don't have a suitable PSU here, otherwise I would measure it.

Long story short, I would install a Z-diode in the mic to ensure that B+ (in the mic) never exceeds a certain voltage (max. 160V with safety margin). So a zener diode with 120V looks good to me. In normal operation the zener diode would be out of circuit.

View attachment 120860

Edit: When everything is ready, I would take a closer look, especially during the start phase, and see if the Zener diode is really necessary. Please give me some feedback...

Kindly, and referring to me, this change?

 

[rock soderstrom]

Kindly, and referring to me, this change?

No, sorry. I was talking to member EarthTone.

Cheers

 

[doqmemory]

Good morning Gentlemen, the D-EF47 works, but the output gein is very low, it could be the transformer the primary is 8ohm the secondary is 290ohm.
A thousand thanks

Have you wired the transformer backwards? The primary should have the higher resistance.

 

[Robby1970]

I tried turning it around, but it's worse

 

[Delta Sigma]

I tried turning it around, but it's worse

Worse as in lower out put? Or more noise? You could have more than one problem.

 

[terry setter]

Of course, you could also use the Zener diode as a "regulator" ( or better stabilizer), but then you should also provide some extra filtering, as the Zener diodes tend to be noisy...

I'm a fan of putting a zener on the B+ output of the supply that is rated for about 20V above the working B+ after stabilization. That way, it only passes current if someone fails to plug in the mic when the supply is switched on, or if they pull out the mic cord before shutting off the supply off. It does not add noise to the supply under any normal usage, it's just an emergency brake. I suppose that if the tube is to old to conduct properly, the zener might begin to conduct, but at that point the lousy tube is the real issue.

 

[EarthTone]

I'm a fan of putting a zener on the B+ output of the supply that is rated for about 20V above the working B+ after stabilization. That way, it only passes current if someone fails to plug in the mic when the supply is switched on, or if they pull out the mic cord before shutting off the supply off. It does not add noise to the supply under any normal usage, it's just an emergency brake. I suppose that if the tube is to old to conduct properly, the zener might begin to conduct, but at that point the lousy tube is the real issue.

Cool! This is a great idea I think. I will do this in my build as a safety net for my 160V vintage PIO caps. I’m so pumped- I just scored the whole lot of these for pretty cheap eBay! They’ll fit this PCB with some retrofitting, and maybe good for p2p builds later. But may I ask you this-

If you were to put the zener in the supply itself, would you stick it in between the B+/ground outputs of the supply’s PCB and the 7-pin connector on the supply case? Like right between the PCB and the 7-pin connector? Or would it be located somewhere else?

Sorry I know this is a basic question… I’m mainly only a musician & audio engineer. I have built a lot of mics and preamps though, which all eventually worked! I just need real specific guidance when it comes to mods of DIY projects, as I’m not a real tech, and this is medium high voltage so want to be sure I ask first…

Thanks!! Super cool.

Matt

 

[Migs 31]

I tried turning it around, but it's worse

Yeah,
Like @Delta Sigma said, what do you mean by «worse ». You are talking to Technical people, so you need to quantify: more noise & what type of noise or less volume, if there too much bass or not enough bass frequencies?
Then people can make a «diagnostic »
And help you
M

 

[Robby1970]

Yes Thank you, a low volume comes out, no low frequencies, only highs
Grazie