D-EF47 Tribute To Oliver Archut U47 Build Thread.

[McIrish]

If it isn't the tube or something in the supply, my guess is the capsule too. I have a Wunder CM7GS M7 and the capsule did that same sound. I baby my mics so I couldn't understand why it would go bad. At the time, I wasn't as experienced with fixing mics and I sent it back to Wunder for repair. Took them weeks to figure out it was the capsule and then even longer to get it replaced. It was gone for months. I believe it's a Thiersch red m7 type, which should be good. Anyway, I've had a K7 in a mic for years with no issues but something must have gone wrong on yours. If you have another capsule, even a cheap one, swap it and test. Is it possible the polarizing voltage is too high?
BTW, I may actually like the K7 more than the Thiersch. Wish I had a couple extra K7's to swap into other mics.

 

[wave]

My bet is that the leads are either loose at the center screws or the backplate connection. I would triple check all those connections and make sure everything is super clean. If you have an electrometer measure the bias voltages

 

[Minyshka]

Please tell me if I can use the 0.5W resistors (R1, R2, R3, R4, R5, R6) instead of the 0.25W that are listed in the specification on vintagemicrophonepcbkit.com?

And how to wiring the pattern switch? COM should be connected to OM in Omni, and to CRD in cardioid? Did I understand correctly

 

[wave]

Please tell me if I can use the 0.5W resistors (R1, R2, R3, R4, R5, R6) instead of the 0.25W that are listed in the specification on vintagemicrophonepcbkit.com?

And how to wiring the pattern switch? COM should be connected to OM in Omni, and to CRD in cardioid? Did I understand correctly

Yes you can use half watt resistors.
For the switch you seem to have it right. You take COM to the pole of the switch and use one position for Omni and one position for Cardioid.

 

[flatresponse]

Hi,
I´d recommend a close inspection of the capsules with magnifying glasses. I once had two fairly expensive capsules from the states enclosing metal particels.
Best
Manfred.

 

[dasnevestheo]

Thanks everyone for your advises ! I strongly suspect the capsule, no more noises since I bypassed it, I can only hear slight microphonics when tapping on the mic. I'm ordering a 3U M7 to test

 

[doqmemory]

Mic body for this project are now available here


http://store.studio939.com/category/microphones-and-parts
http://groupdiy.com/index.php?topic=50015.880
http://groupdiy.com/index.php?topic=58609.0

Does anyone know what the screw sizes are for the three screws holding the capsule basket to the body of the Alctron MK47? These are stripping out, but I do not seem to have any other sizes that fit. I may have to end up re-tapping the holes to fit other screws that I have.

 

[innercityman]

Hi there !

Did someone ever use this transformer from Beesneez ? Can't find any pinout, colour codes or informations except the ones on their site. I'd like to compare it with my AMI BV-08R.

Any help on how to wire it would be appreciated.

 

[mhelin]

There are four coils on the left and the right. On the left side probably red and pink are the primary, and the yellow and gray the secondary (may be the other way, too). Just measure the DC resistances so you will know. Lower resistance side is the secondary, and higher the primary. The right side is similar. Now because there are kind of two transformers working in humbucking configuration you have to figure out in which phase to connect the two primaries and secondaries in series (you will hear when they are out of phase). See this post:

https://groupdiy.com/threads/bv8-12-11-replica-support-thread.67743/#post-860859
So you should actually connect the right and the left side coils "out of phase" (electrically) meaning pink to blue and both grays together, so red and blue will be the inputs and the yellow wires are the outputs (please correct me anyone if you know better).

 

[Minyshka]

Can anyone suggest where to connect pin three of the seven-pin xlr in the microphone?
And where does the shield of the cable go, to pin three of the seven-pin xlr or to the connector housing?
Thank you.

 

[innercityman]

Thanks mhelin !

There are four coils on the left and the right. On the left side probably red and pink are the primary, and the yellow and gray the secondary (may be the other way, too). Just measure the DC resistances so you will know. Lower resistance side is the secondary, and higher the primary. The right side is similar. Now because there are kind of two transformers working in humbucking configuration you have to figure out in which phase to connect the two primaries and secondaries in series (you will hear when they are out of phase)

The only configuration I've been able to get measurements is this one... From left to right... i've measued between red and yellow 403 Ohms, pink and gray 8.7 Ohms, black and yellow 405 Ohms, blue and gray 8,7 Ohms. Could someone interpret these results and help me to figure out on how to wire it... ?

If I follow this schematic, I should bridge yellow wires together and gray wires together. Please tell me if I'm wrong or right.

 

[mhelin]

Yes I think so, then your red (+) and black (-) will be the inputs (in 6.5:1 config) and purple (+) and blue (-) the outputs. Do you have any signal generator (output from audio interface) and DMM (or just use an audio interface input) to measure that the signal will attenuate in 6.5:1 relation?

 

[innercityman]

Yes I think so, then your red (+) and black (-) will be the inputs (in 6.5:1 config) and purple (+) and blue (-) the outputs. Do you have any signal generator (output from audio interface) and DMM (or just use an audio interface input) to measure that the signal will attenuate in 6.5:1 relation?

Yes, I'll try that, thanks for your help !

 

[innercityman]

I finally got those .47µF caps you recommended. I put one in C2, and swapped the EF80 for an EF800. I know, I should do one mod at a time, but nah, I hate opening the mic. lol

Anyway, it sounds great. Both ways sound very good, but this I think is more musical, a little more open, and less heavy on the lows (I assume changing the value of C2 shifted the EQ curve). I think the mic definitely cuts through better this way. I may get some better screws (the heads are already stripping, and I barely touched them), and then consider more tube swapping if I get bored or unhappy with the sound. I think this might be my favorite mic.

Thanks,
Josh

Hi,

I've got the chance to buy 10 pieces of NOS 0,5uf MGBO Russian capacitors. I've read somewhere that if you put such value cap in C2, you need to change the value of C1, is that true ? Did you do that, or did you just swapped C2 1uf cap with this 0.47uf ?

 

[Purplenoise]

Hi,

I've got the chance to buy 10 pieces of NOS 0,5uf MGBO Russian capacitors. I've read somewhere that if you put such value cap in C2, you need to change the value of C1, is that true ? Did you do that, or did you just swapped C2 1uf cap with this 0.47uf ?

Never heard that before. As far as I know c1 stayed the same value throughout all revisions.

 

[innercityman]

Never heard that before. As far as I know c1 stayed the same value throughout all revisions.

Ok thanks, I have the same kind of vintage NOS cap in my MK-47 but in 1uf value, do you think it's worth a try to test with one of these 0,5uf ? Different frequency response in lows I imagine. I've built an EF-47 for a friend, I'd be curious to try and compare with the one I put it on and this NOS Russian 0,5uf cap. Did you experiment ? Can you give your opinion ?

 

[Purplenoise]

Ok thanks, I have the same kind of vintage NOS cap in my MK-47 but in 1uf value, do you think it's worth a try to test with one of these 0,5uf ? Different frequency response in lows I imagine. I've built an EF-47 for a friend, I'd be curious to try and compare with the one I put it on and this NOS Russian 0,5uf cap. Did you experiment ? Can you give your opinion ?

I don’t hear a huge difference between 0.5 and 1uf, especially in vocals. Of course it’s tricky to choose the “right” value since the impedance relationship between current u47 clone tubes and current bv08s is different than the original vf14, bv08 combo. The type and brand of capacitor is also contributing in “coloration “. I have tried many different caps there and I have found metalized paper caps to work better for what my ears want to hear. Bosch s very nice if you can find one. Siemens is very nice also. I also liked aerovox a lot and Cornell doubilier super pups. The one that never worked for me is the green Russian k42…
Again though…it’s a synergy of parts. It’s hard to know beforehand how the whole system will behave with certain components. The output cap is an easy part to swap so I would suggest you experiment until you find what works best.

 

[JW]

The impedance relationship between tube and transformer I find curious w/ the dual 408a approach and always wanted to know more about that.

Purplenoise, do you remember when Max (ioaudio) sold the original MK47 kit with his custom transformer? I tried to ask some questions about that in the past but couldn't get much info. He subsequently came out with the MK-U47 kit, where the transformer was more 'accurate' I guess, but accurate to a U47?, not a dual 408a '47. So which was better for the impedance relationship? I tried to answer this myself by listening as I have both the MK47 transformer and Moby's U47 transformer, one with the 1uF and Moby's with .47uF cap. Mmmm. I couldn't tell the difference exactly. And it was in two different mics anyway, albeit identical otherwise. Then I sold one. It might have been that the one with Moby's transformer seemed to go deeper but the one with Max's transformer seemed to weigh in a little more heavy in the proximity regions. But subtle indeed if I truly did hear something.

But still, I wonder because I remember hearing you say you ordered a custom Xformer from Moby to take care of that impedance relationship when using (some other tube? Or was it the Nuvistor?)

 

[Purplenoise]

The impedance relationship between tube and transformer I find curious w/ the dual 408a approach and always wanted to know more about that.

Purplenoise, do you remember when Max (ioaudio) sold the original MK47 kit with his custom transformer? I tried to ask some questions about that in the past but couldn't get much info. He subsequently came out with the MK-U47 kit, where the transformer was more 'accurate' I guess, but accurate to a U47?, not a dual 408a '47. So which was better for the impedance relationship? I tried to answer this myself by listening as I have both the MK47 transformer and Moby's U47 transformer, one with the 1uF and Moby's with .47uF cap. Mmmm. I couldn't tell the difference exactly. And it was in two different mics anyway, albeit identical otherwise. Then I sold one. It might have been that the one with Moby's transformer seemed to go deeper but the one with Max's transformer seemed to weigh in a little more heavy in the proximity regions. But subtle indeed if I truly did hear something.

But still, I wonder because I remember hearing you say you ordered a custom Xformer from Moby to take care of that impedance relationship when using (some other tube? Or was it the Nuvistor?)

I don’t have any experience with Max’s kit. I have built a d-ef47 and a point to point 47. The point to point is built with a nuvistor and a mod suggested by Moby and Andreas Grosser to change the bias of the nuvistor. I am using a Neumann k47, Moby bv08 and a Bosch 0.5uf mp cap in this one and it sounds like…a u47 haha. I have put it against originals and I am not missing something. Also some very picky engineers have used this mic and they said the same thing…it’s a u47.
Now the d-ef47 is an interesting story. It’s a great sounding mic but I could never get that 3D juicy midrange with the ef800 tube. Don’t get me wrong, it’s an amazing mic and it became a favorite among singers here but I have found that it works best with an m7 capsule ( instead of a k47) for a smokier more vintage sound. On this I used the custom Moby transformer and indeed it gave it a little more heft in the low end but still the midrange was not exactly what I was looking for. Highly subjective of course because others preferred this mic even over my point to point one.
So I decided to go a different route and try a more modern approach. Modern components, no mods to Dans/Oliver’s circuit with the exception of the output cap ( nos aerovox mp 1uf). I swapped out the trafo to a terrapin 7.5:1 toroidal ( since higher ratio is recommended for ef800 by some for impedance matching) and a heiserman k47. The capsule will be here next week so I will let you guys know how it sounds. So far with Danny’s D7 it sounds really nice.

 

[Purplenoise]

So I finally got to try the heiserman hk47. Wow…wonderful capsule. Although not an exact Neumann clone it has that neumanesque 3D image that I don’t hear in other k47 clones. A little more tamed in the mids but beautiful sounding and smooth with a very nice but not shrill presence.
i need to do further testing but I believe that the synergy of hk47 and ef800 can bring you a lot closer to the k47/vf14 combo than k47 and ef800. I have a feeling that ef800 doesn’t have the sparkle of the vf14 so the hk47 with the touch of extra air works better.