DiY AMI U47

[o3misha]

Here's a simple line of reasoning: Neumann produced U47  until 1965. Very early U47 has 100M grid resistors and 1 uF coupling caps.
In 1960, Neumann already produced U67 microphones, which already used 400M grid resistors. Why  Neumann did not use 400M resistors in 1960-1965's U47s? Neumann, however,  did not increase100M value to 400M. Instead of that they reduce its value to 60M and they reduce also the value of coupling cap to 0.5uF . Think about it.  So I'm not just saying something, and have concrete facts. Increasing low end is not always good idea. More low end=less midrange.

 

[Pip]

Here's a simple line of reasoning: Neumann produced U47  until 1965. Very early U47 has 100M grid resistors and 1 uF coupling caps.
In 1960, Neumann already produced U67 microphones, which already used 400M grid resistors. Why  Neumann did not use 400M resistors in 1960-1965's U47s? Neumann, however,  did not increase100M value to 400M. Instead of that they reduce its value to 60M and they reduce also the value of coupling cap to 0.5uF . Think about it.  So I'm not just saying something, and have concrete facts. Increasing low end is not always good idea. More low end=less midrange.

Thus my comment about some feel this lends to "too much mic". Voicing a mic is something you can spend a lot of time on. Remember we are at the mercy of the designers who have come before us when we buy a mic or a pre. I will open myself up to some rash criticism here but I do so to prove a point. I have used Neve gear for most of my recording life. I have used the venerable 1073 mic pre/eq many times. It is not a mic pre I would go to for most things I do. I prefer the Neve 31102 if you must know.  But others will probably say "oh my whats his problem"! An API on the other hand is IMO a must for guitar, snare and kick drums, it just has that pop. Hold on I'm gonna go deep. I am not in love with the U87Ai but I am madly in love with the U87i. Again I can hear the gasps. The UM47 gained its reputation at a time when most of the other options really weren't very good and then Geoff Emerick started close micing with it and people went wow whats that. And a guy by the name of Frank Sinatra sang into one and people say it was the mic. PLEASE. Bono of U2 uses a SM57 into granted a nice signal chain. But I have noticed that a lot of people follow the group while some listen.

Try this! Grab any mic in your collection and put the shortest mic cable you can on it and still get it into the pre. I mean hang the pre on the mic stand right next to the mic if you can. Get that bad boys signal up to line level with as short a cable as possible. Record it and tell me that isn't the best that mic has ever sounded.

The point is this! This is where you remove the designer and bring in you, the DIY'er. If it don't work out read some more and make a change and listen. Change it back and listen. Talk to a more knowledgeable person and listen. Blow it up.... no don't do that!  Just build it! Keep in mind that you are working your way towards a U47 for about 7000 USD less than a vintage one that probably has problems and about 5000 less than a manufactured clone.

I realize this is a bit cathartic and off topic but please it is intended to spur you forward and say jump in the water is awesome! Not judge or criticize.

 

[o3misha]

I 'm not just agree with you,-  I have exactly the same views. Therefore, all my comments are the result of my experiments. If you keep in mind my references on the history of Neumann microphones, I just gave an explanation of the reasons for the use of small grid resistors.

 

[Pip]

I just do not agree with you, I have exactly the same views. Therefore, all my comments are the result of my experiments. If you keep in mind my references on the history of Neumann microphones, I just gave an explanation of the reasons for the use of small grid resistors.

I think I totally agree with you if you took it the other way I did not mean that at all. Check my comment about it here. http://www.groupdiy.com/index.php?topic=52022.msg673420#msg673420. The trend in 1G resistors is a thing and I think sometimes a wrong thing. My points were just that. I also think that people like what people like and a lot of people and designers use big resistors to make things sound the way they like. 

 

[AusTex64]

MDeath,

You wrote:

< I'd love to know more about the Lucas CS4. I've heard it's pretty much dead on to a U47 when you use the exact same capsule.>

This will be good news then - the AMI kit is VERY close to the CS4. Go find some pics on the net of CS4 insides and see if you recognize any parts. I think you might get pretty excited. That's why I used all of the parts Oliver sent!

I also used a Thiersch M7 PVC capsule, which is used in the CS4. Bought it from AMI with the kit.

 

[o3misha]

I just do not agree with you, I have exactly the same views. Therefore, all my comments are the result of my experiments. If you keep in mind my references on the history of Neumann microphones, I just gave an explanation of the reasons for the use of small grid resistors.

I think I totally agree with you if you took it the other way I did not mean that at all. Check my comment about it here. http://www.groupdiy.com/index.php?topic=52022.msg673420#msg673420. The trend in 1G resistors is a thing and I think sometimes a wrong thing. My points were just that. I also think that people like what people like and a lot of people and designers use big resistors to make things sound the way they like. 

That's right, thank you.  Look at the first sentence of my previous posts, I corrected it.

 

[AusTex64]

Here's a simple line of reasoning: Neumann produced U47  until 1965. Very early U47 has 100M grid resistors and 1 uF coupling caps.
In 1960, Neumann already produced U67 microphones, which already used 400M grid resistors. Why  Neumann did not use 400M resistors in 1960-1965's U47s? Neumann, however,  did not increase100M value to 400M. Instead of that they reduce its value to 60M and they reduce also the value of coupling cap to 0.5uF . Think about it.  So I'm not just saying something, and have concrete facts. Increasing low end is not always good idea. More low end=less midrange.

This is a very interesting discussion on this topic: http://repforums.prosoundweb.com/index.php/topic,35368.0.html

Could it also be that Neumann did not want to change the sound of the "historical" U47? For example, so that current and older mics would be compatible as stereo pairs in frequency response? And why did Neumann choose to use 400Meg grid resistors in U67, if 60Meg or 100Meg sounded "the best"?

Since we can't ask the Neumann designers why they made those choices, we can only make educated guesses as to why.

 

[o3misha]

I can simply explaiin  why Neumann did not use 60M resistor in U67: k67 capsule produce less low frequencies than k47 or m7 capsules. I have, personally, tested it .

 

[Melodeath00]

MDeath,

You wrote:

< I'd love to know more about the Lucas CS4. I've heard it's pretty much dead on to a U47 when you use the exact same capsule.>

This will be good news then - the AMI kit is VERY close to the CS4. Go find some pics on the net of CS4 insides and see if you recognize any parts. I think you might get pretty excited. That's why I used all of the parts Oliver sent!

I also used a Thiersch M7 PVC capsule, which is used in the CS4. Bought it from AMI with the kit.

Now this is very interesting! I indeed recall being told that the AMI kit is a "simplification" of the Lucas CS-4. I would love a Thiersch M7 PVC. Perhaps if/when I build an M49, I will put my BeesNeez K7 in that, and get a Thiersch for the U47. Anyway, did you have any internal pics in mind specifically? All the ones I saw were very tiny and hard to see, and some were labelled "prototype."

Also, did you get one brown resistor with your kit? I haven't been able to figure out what its value is, and it only has 3 color bands. My multimeter seems incapable of reading it, which lead me to believe it was over 400Mohm.

I have read the Lucas CS-4 is "true cardioid" when in cardioid mode, despite the fact that it has remote pattern switching. How did they achieve this? The Lucas CS-1 is supposedly the same, and you can see a very small schematic here: http://recordinghacks.com/microphones/lucas/CS-1 - Unfortunately the "Enlarge" link is broken.

The sound changes because in the u47 the rear diaphragm is switched in/out of circuit which changes the noise floor by 6db with two capsules connected to the grid. With remote switching the rear capacitor (diaphragm) is in circuit with the bias voltage being changed so you don't get the benefit of disconnecting the rear.

It is DIY though so you can hook it up with both options if you like.

Cheers,
Jonathan

Hi Jonathan, please see my comments above. Any insights into how I could hook up both options? Without drilling up the mic body and installing a switch, that is. Thanks!

 

[AusTex64]

http://recordinghacks.com/microphones/lucas/CS-4

I strongly suggest using the parts Oliver sent. I was very happy with the results. You can't beat the price (came with the kit), and you can always experiment with coupling caps, etc later. 

I am guessing that brown resistor is 100Meg. Take the list of parts I posted here and use the process of elimination. That's how I figured out what was what. For example, there are 3 1Gig resitors, so they are easy to identify. Then label them.

The Lucas CS-4, Wunder CM7-GTS and a few others use a small relay located under the capsule to switch the back diaphragm on and off remotely.

 

[Melodeath00]

http://recordinghacks.com/microphones/lucas/CS-4

I strongly suggest using the parts Oliver sent. I was very happy with the results. You can't beat the price (came with the kit), and you can always experiment with coupling caps, etc later. 

I am guessing that brown resistor is 100Meg. Take the list of parts I posted here and use the process of elimination. That's how I figured out what was what. For example, there are 3 1Gig resitors, so they are easy to identify. Then label them.

The Lucas CS-4, Wunder CM7-GTS and a few others use a small relay located under the capsule to switch the back diaphragm on and off remotely.

Well, part of the problem is I received only 9 resistors, so I can't use the process of elimination, because I was supposed to receive 10. Interesting about the relay - I'm going to have to research how those work.

 

[AusTex64]

<Well, part of the problem is I received only 9 resistors, so I can't use the process of elimination, because I was supposed to receive 10.>

Did you even try?

Guess you'll have to read the resistor codes then.

 

[0dbfs]

Yes. Relays can remotely switch the front/back connection. Max uses one in his mk47 here instead of a switch on the body. Then use a conductor on the cable to get the switched control voltage up to the relay.

Or an internal jumper if you don't plan to change it a bunch.

Cheers,
jb

 

[Melodeath00]

<Well, part of the problem is I received only 9 resistors, so I can't use the process of elimination, because I was supposed to receive 10.>

Did you even try?

Guess you'll have to read the resistor codes then.

I was just pointing out I can't use the process of elimination definitively, since I do not have the correct total amount of components. But yes, I do seem to have 3 identical 1G resistors. The brown resistor only has 3 bands, otherwise I would have read the code. How do you read the codes for 3 bands? I thought it needed 4 or 5. Regardless, all I'm missing according to your list is 100M and 100 ohm, so I would guess the brown resistor is 100M, since I should be able to read a 100 ohm resistor.

EDIT: Ok, woops! I was mistaken - My multimeter can only read up to 40M, not 400M, so the brown resistor is no doubt the 100M. Now, looks like I'm off to find a 100 ohm resistor. Do you think any local stores would carry that, or am I going to have to purchase online?

Thanks again to everybody for the help!

 

[AusTex64]

<Now, looks like I'm off to find a 100 ohm resistor. Do you think any local stores would carry that, or am I going to have to purchase online?>

Radio Shack

 

[Melodeath00]

<Now, looks like I'm off to find a 100 ohm resistor. Do you think any local stores would carry that, or am I going to have to purchase online?>

Radio Shack

Exactly what I did! I didn't think they carried stuff like that these days, but they had a 5 pack of (carbon film) 100 ohm, 1/2 Watt resistors. I'm not too worried that it's carbon film compared to all the other pieces. I'm just happy I have it all now. Thank you for your diagram again. I never would have figured out how to wire this thing without it. It's much easier to work backwards and see how it perfectly follows the schematic! haha

So I still plan to call Oliver, but I'm fairly certain at this point that all the values were changed just to work with his PSU. For example, the voltage divider with 2M and 3M only works properly if you are feeding it 105V, but the PSU is feeding 120, so you need a divider of 1M and 1M. From my new and limited understanding there's really nothing in the U47 circuit besides capsule to tube to coupling cap to transformer. The rest is just power-related.

I'm definitely going to need some help in terms of figuring out this relay mod, but for now, I can build the circuit decks at least.

Robert, how tight/hard was it to work inside of the PSU and rewire the Binder? I considered getting some heat-shrinkable connectors at RadioShack too, so that I could just use hookup wire on the Binder and give myself some slack. Good/bad idea?

Thanks

 

[AusTex64]

I was able to rewire the power supply Binder connector without doing anything but removing the metal PSU cover. There is plenty of room in there. Start with the part of the connector nearest the center of the PSU and work your way out towards the side. Be careful not to melt any wires.

 

[AusTex64]

Note that the voltage feeding the divider is 120VDC and the variable 0 - 120VDC for the back diaphragm for remote pattern control. Both 120VDC. Makes the supply a lot easier (and cheaper) to build. You are correct, nothing in the audio circuit is significantly different.

 

[Melodeath00]

I was able to rewire the power supply Binder connector without doing anything but removing the metal PSU cover. There is plenty of room in there. Start with the part of the connector nearest the center of the PSU and work your way out towards the side. Be careful not to melt any wires.

I'm going to open it up and take a look this weekend.

Yes. Relays can remotely switch the front/back connection. Max uses one in his mk47 here instead of a switch on the body. Then use a conductor on the cable to get the switched control voltage up to the relay.

Or an internal jumper if you don't plan to change it a bunch.

Cheers,
jb

JB, please excuse my ignorance, but I'm still confused. The idea is to have my 11-pattern remote switching, but have the cardioid mode be "true" with a switched out rear diaphragm.

Please tell me if my understanding is wrong: The relay would have to allow all voltages through, except 60V. At 60V, it needs to shut off, disconnecting the rear diaphragm. Does a relay exist that allows through 0-59V and 61-120V? Either it does, or my understanding is incorrect. Thanks

 

[0dbfs]

How about just having a relay in the mic controlled via a PSU switch that connects / disconnects the rear diaphragm regardless of the polarization voltage on the rear.

Cheers,
jb