DiY AMI U47

[o3misha]

I would never use resistors with value higher than 100M-200M for  U47-ish mics with old tubes. 60-100M is enough for me.

 

[Winetree]

So the local RadioShack has some 62/36 solder at 0.015". Is that too thin in your experience?

Yes, I use the 62/36/2  0.0015 Silver Bearing Soldier (64-035)
That's all I use with a Radio Shack 15 watt iron.
I have built over 80 DIY projects, rebuilt a 36 channel Harrison console, 12 mics
and many other projects with this combo.

 

[AusTex64]

MDeath,

I wired the mic to match the Binder pinout in the "U47 alternate tube with polarity switching" drawing from the AMI website. There are two ways you could go about this - wire the mic differently or wire the power supply differently. By the time I discovered this issue, the mic was already built. I felt it was easier to move a few wires around on the power supply Binder connector. Plus the mic and PSU voltages would them match the schematic and layout document I produced.

Here is what I changed on the Binder connector on the AMI PSU:

Pin 1 - no change (audio)

Pin 2 - no change (audio)

Move purple wire currently on pin 5 to pin 3 (120VDC to voltage divider)

Move green wire currently on pin 4 to pin 6 (+5.05VDC to tube heater)

Move white wire currently on pin 6 to pin 7 (0 - 120VDC for pattern control)

Move gray wire currently on pin 7 to pin 4 (ground)

Bridge pins 4 and 5 (ground)

I am not sure why the grounds are tied at the PSU and not in the mic, but I did as instructed (tied pins 4 and 5 at the PSU) and it worked fine.

 

[AusTex64]

I would never use resistors with value higher than 100M-200M for  U47-ish mics with old tubes. 60-100M is enough for me.

Misha,

I have seen many of your posts and obviously you know what you're doing. Why do you think Oliver supplies 1G ohm resistors with his kits, and also appears to use them in the Lucas design? I understand it has something to do with frequency response. I notice 797 Audio also used 1G ohm resistors with a Wima cap in my MXL V77's, along with Teflon PCB insulators and solid silver wire for the connectors from capsule to tube.  Looking to learn something here. Thank you.

Robert Mokry
Austin, Texas

 

[AusTex64]

MDeath,

Here is the correct component list to build "U47 alternate tube with remote polatrity switching", that will match the components you received from AMI:

R1 - 1G ohm, .5W
R2 - 100 ohm, .5W
R3 - 29 ohm, .5W
R4 - 100K ohm, .5W
R5 - 1G ohm, .5W
R6 - 1M ohm, .5W
R7 - 1M ohm, .5W
R8 - 51K ohm, .5W
R9 - 100M ohm, .25W
R10 - 1G ohm, .25W
C1 - 1uF, 250V (brown cap in AMI parts kit)
C2 - .01uF, 250V (green cap in AMI parts kit)
C3 - 1 uF, 250V (brown cap in AMI parts kit)
C4 - 1000pF, 250V (yellow cap in AMI parts kit)
C5 - 10 nF, 250V (green cap in AMI parts kit)

Note that .01uF and 10nF are the same green caps. I am not sure why he labeled them differently in the drawing.

I used all the parts Oliver supplied and my mic sounds ****in' GREAT!!! I didn't spend one minute searching for alternate components.

Good luck,

Robert Mokry
Austin, Texas

 

[AusTex64]

MDeath,

Regarding wire, I used standard 24AWG stranded copper wire with Teflon sheath (not even silver coated) for wiring everything but the tube heater and audio. I used regular vinyl sheathed copper wire (bigger gauge, 18 AWG I think, probably not neccesary, in hindsight) for +5VDC tube heater and heater ground, and 22 AWG solid silver with with FEP sheath from Homegrown Audio for all audio connections within the mic. I had no problem working with the solid core wire. It was easier actually, no little strands flopping around!

Robert Mokry
Austin, Texas

 

[Melodeath00]

MDeath,

Here is the correct component list to build "U47 alternate tube with remote polatrity switching", that will match the components you received from AMI:

R1 - 1G ohm, .5W
R2 - 100 ohm, .5W
R3 - 29 ohm, .5W
R4 - 100K ohm, .5W
R5 - 1G ohm, .5W
R6 - 1M ohm, .5W
R7 - 1M ohm, .5W
R8 - 51K ohm, .5W
R9 - 100M ohm, .25W
R10 - 1G ohm, .25W
C1 - 1uF, 250V (brown cap in AMI parts kit)
C2 - .01uF, 250V (green cap in AMI parts kit)
C3 - 1 uF, 250V (brown cap in AMI parts kit)
C4 - 1000pF, 250V (yellow cap in AMI parts kit)
C5 - 10 nF, 250V (green cap in AMI parts kit)

Note that .01uF and 10nF are the same green caps. I am not sure why he labeled them differently in the drawing.

I used all the parts Oliver supplied and my mic sounds ****in' GREAT!!! I didn't spend one minute searching for alternate components.

Good luck,

Robert Mokry
Austin, Texas

Ok, now I am thoroughly confused. Those look like the values Oliver sent me, although I only got 9 resistors, not 10. I wasn't expecting any resistors or caps, so I just saw it as a bonus. And since most of the values did not match his schematic, once again I assumed Oliver just put some surplus parts in a baggy for me out of good will. But your telling me that's what his schematic is supposed to be? That's very divergent from a U47 schematic. I just don't understand...

 

[AusTex64]

MDeath,

You wrote:

<Ok, now I am thoroughly confused. Those look like the values Oliver sent me, although I only got 9 resistors, not 10. I wasn't expecting any resistors or caps, so I just saw it as a bonus. And since most of the values did not match his schematic, once again I assumed Oliver just put some surplus parts in a baggy for me out of good will. But your telling me that's what his schematic is supposed to be? That's very divergent from a U47 schematic. I just don't understand...>

I was confused too, don't feel bad. I was also pleasantly surprised to receive the components that were selected by Oliver. They are very high quality, IMHO. When I started measuring the included resistors and discovered they did not match the AMI schematic, I wigged out and called Oliver. He quickly set me straight. I'm just repeating what he told me AND it will be in writing for other builders to reference.

FWIW, the AMI kit is not intended for building a "dead stock" U47 clone - you're building a hybrid U47 style mic mic with U47 style capsule, output transformer, head basket and body, but with different preamp tube and remote polar pattern control (BIG difference). Far from a "stock" U47 with hard switched cardioid and omni pattern selection. Look at what Wunder Audio and Lucas are doing. That's the spirit of this build, I think. The remote pattern control/polarity inplementation is kinda similar to the M49 method. In this case specifically, to the UM92 link I posted yesterday.

I've attached my component layout/wiring diagram for "AMI U47 alternate tube schematic with remote polarity switching on the power supply unit". This is how my working AMI mic is assembled. BIG ASS DISCLAIMER - I am not a tube mic expert nor electrical engineer. Use this diagram at your own risk. Hope it helps.

Robert Mokry
Austin, Texas

 

[AusTex64]

MDeath,

Hole diameter for Keystone standoffs mounted to acrylite upper deck is .090 inches.

I gotta get back to work now!

Robert Mokry
Austin, Texas

 

[Melodeath00]

MDeath,

You wrote:

<Ok, now I am thoroughly confused. Those look like the values Oliver sent me, although I only got 9 resistors, not 10. I wasn't expecting any resistors or caps, so I just saw it as a bonus. And since most of the values did not match his schematic, once again I assumed Oliver just put some surplus parts in a baggy for me out of good will. But your telling me that's what his schematic is supposed to be? That's very divergent from a U47 schematic. I just don't understand...>

I was confused too, don't feel bad. I was also pleasantly surprised to receive the components that were selected by Oliver. They are very high quality, IMHO. When I started measuring the included resistors and discovered they did not match the AMI schematic, I wigged out and called Oliver. He quickly set me straight. I'm just repeating what he told me AND it will be in writing for other builders to reference.

FWIW, the AMI kit is not intended for building a "dead stock" U47 clone - you're building a hybrid U47 style mic mic with U47 style capsule, output transformer, head basket and body, but with different preamp tube and remote polar pattern control (BIG difference). Far from a "stock" U47 with hard switched cardioid and omni pattern selection. Look at what Wunder Audio and Lucas are doing. That's the spirit of this build, I think. The remote pattern control/polarity inplementation is kinda similar to the M49 method. In this case specifically, to the UM92 link I posted yesterday.

I've attached my component layout/wiring diagram for "AMI U47 alternate tube schematic with remote polarity switching on the power supply unit". This is how my working AMI mic is assembled. BIG ASS DISCLAIMER - I am not a tube mic expert nor electrical engineer. Use this diagram at your own risk. Hope it helps.

Robert Mokry
Austin, Texas

Many, many thanks for your layout, and the reply! It will be a huge help.

I have to say I am very disappointed to learn this info. The whole reason I bought the AMI kit is because the schematic was for a mic that is basically the same as a U47, but with the addition of remote pattern switching (which in theory, shouldn't affect tone/sound). All the values on the schematic are the same as a real U47, it just uses a different tube, and the high impedance section resistors have been brought up to "modern values" at 1G for the best signal to noise response and a lower cut-off frequency in the bass. Now, I realize this is an alternate-tube U47, and will not be an exact replica, but at least the circuit, besides the tube, was the same as a U47. Now it turns out the schematic is wrong? If I had seen the schematic and saw these new, correct values, which are way different from a U47, I would not have bought this kit. The circuit is not the same. I would have built the MK47 which uses the exact U47 circuit other than the tube. Am I over-reacting here? It never would have occurred to me that the schematic (linked to from the kit product page) would be incorrect.

Did Oliver say why all those values were changed? I'm pretty sure other guys built his kit using an EF800 and the U47 circuit values.

 

[AusTex64]

You wrote:
<I have to say I am very disappointed to learn this info. The whole reason I bought the AMI kit is because the schematic was for a mic that is basically the same as a U47, but with the addition of remote pattern switching (which in theory, shouldn't affect tone/sound). All the values on the schematic are the same as a real U47, it just uses a different tube, and the high impedance section resistors have been brought up to "modern values" at 1G for the best signal to noise response and a lower cut-off frequency in the bass. Now, I realize this is an alternate-tube U47, and will not be an exact replica, but at least the circuit, besides the tube, was the same as a U47. Now it turns out the schematic is wrong? If I had seen the schematic and saw these new, correct values, which are way different from a U47, I would not have bought this kit. The circuit is not the same. I would have built the MK47 which uses the exact U47 circuit other than the tube. Am I over-reacting here? It never would have occurred to me that the schematic (linked to from the kit product page) would be incorrect.

Did Oliver say why all those values were changed? I'm pretty sure other guys built his kit using an EF800 and the U47 circuit values.>

I don't have the answers to what other people did with AMI kits, that would only be speculation on my part. I don't think Oliver needs to deceive anyone, his reputation speaks for itself (and no, I am not on the AMI payroll). Oliver has been over-the-top helpful with me, and allowed me to build a superb mic for 1/2 of what a comparable production model would cost. And I don't think he's getting rich selling kits to guys like us.

ANY deviation from the "original recipe" Neumann historical U47 - M7 capsule, VF14M metal tube, carbon comp resistors, Bosch filter caps, hard switching for omni/cardioid, etc will affect the sound in some way or another. How much? That's a great question. Klaus Heyne emphatically states over and over that using ANY tube besides VF14M (that includes the other Telefunken metal tubes like EF14) renders a U47 "not a real U47" - period. Yet people worldwide are raving about the "U47 inspired" mics being produced today by Lucas, Bock, Wunder, Telefunken, Wagner, AMI, Flea and others. Many of these mics deviate significantly from the "original recipe", but still sound great and make great recordings. Just like the AMI U47 kit. Almost everyone has to use a different tube now, as stated, VF14M's are just not available to mere mortals these days.

You state "the addition of remote pattern switching (which in theory, shouldn't affect tone/sound)". Really? Of course it will affect the sound. Is it a "bad" affect? I don't think so. I've owned and used original U47's, and the mic I built from the AMI kit sounds awesome and very much "in the ballpark". IMHO, most of the color of the U47 comes from the capsule, headbasket, tube and output transformer. Changing a few resistor values to accomodate remote pattern control is to be expected, if one knows they are building a mic with remote pattern control. It would be a good idea for Oliver to correct that drawing and I will most likely direct his attention to this thread. I truly think it comes down to minutes in the day for him.

Perhaps consider giving the kit a chance before rushing to judgement. I've saved you hours of figuring stuff out I had to figure out, and am happy to do so. These forums helped me a lot with my build. So I'll ask that you give AMI/Oliver a break, build the mic, listen and then render your opinion. I am curious to hear what you think of the finished product.

Robert Mokry
Austin, Texas

 

[Melodeath00]

Robert,

I have nothing against Oliver. He's a very nice guy, and has been helpful. I will say that in my experience, he is very hard to get a hold of - this is probably due to, as you say, lack of minutes in the day. And it took a few shipments before my order was completely correct, but Oliver was great and never asked me for more shipping money. I also greatly appreciate the opportunity he has given us to build mics with quality parts like this.

However, linking to an incorrect schematic on the page dedicated to selling a DiY kit seems like a pretty big oversight to me. As a result, I now have to rewire the PSU, and I wouldn't have even known if not for having this thread and your reply.

I'm no expert, but remote pattern switching is achieved by varying the voltage sent to the rear diaphragm of the capsule. I don't see why this would affect tone of the mic. In cardioid, the rear will get 0V, just like a real U47. In fact, one of the guys who works at AMI (or used to, at least) mentioned that it should not affect sound when I asked in an email about a year ago.

But also, I don't see why any resistor values need to be changed to achieve remote switching. You need to add some components to the circuit so you can apply a voltage to the rear diaphragm, but I don't see why you need to change the existing audio circuit. In other words, unless I'm very wrong, it seems you could leave the U47 portion of the circuit be. Maybe someone here can chime in? It's almost as if we were sent the component parts for the UM92 and not for the U47.

I'm not passing judgement on the kit or the mic. I'm sure your mic sounds awesome, is int he U47 ballpark, and that a mic is mostly its capsule anyway. I'm simply expressing that I feel a bit mislead here.

Thanks again so much for participating in the thread! Maybe I just need to call Oliver to get to the bottom of this.

 

[0dbfs]

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

 

[Pip]

Robert,

I have nothing against Oliver. He's a very nice guy, and has been helpful. I will say that in my experience, he is very hard to get a hold of - this is probably due to, as you say, lack of minutes in the day. And it took a few shipments before my order was completely correct, but Oliver was great and never asked me for more shipping money. I also greatly appreciate the opportunity he has given us to build mics with quality parts like this.

However, linking to an incorrect schematic on the page dedicated to selling a DiY kit seems like a pretty big oversight to me. As a result, I now have to rewire the PSU, and I wouldn't have even known if not for having this thread and your reply.

I'm no expert, but remote pattern switching is achieved by varying the voltage sent to the rear diaphragm of the capsule. I don't see why this would affect tone of the mic. In cardioid, the rear will get 0V, just like a real U47. In fact, one of the guys who works at AMI (or used to, at least) mentioned that it should not affect sound when I asked in an email about a year ago.

But also, I don't see why any resistor values need to be changed to achieve remote switching. You need to add some components to the circuit so you can apply a voltage to the rear diaphragm, but I don't see why you need to change the existing audio circuit. In other words, unless I'm very wrong, it seems you could leave the U47 portion of the circuit be. Maybe someone here can chime in? It's almost as if we were sent the component parts for the UM92 and not for the U47.

I'm not passing judgement on the kit or the mic. I'm sure your mic sounds awesome, is int he U47 ballpark, and that a mic is mostly its capsule anyway. I'm simply expressing that I feel a bit mislead here.

Thanks again so much for participating in the thread! Maybe I just need to call Oliver to get to the bottom of this.

Yes I think that is the answer. Call Oliver he knows what he is doing. He is also a small business that is doing a lot of OEM manufacturing for those big name clones at the same time he is dealing with us. Awesome isn't it. That is just an explanation he needs no defending by the likes of me.

That being said. The changes to the components in his "Alternate" schematics are because after years of research he feels that these components lead to a better sounding mic. The 1 gig resisitors give better low end and transient response. Some thing that some people believe to be too much mic. The fact that you went for the remotely switched version of a U47 means you already deviated from the path of the original. The original U47 had a totally different sonic character in cardioid because of the on the mic switching. I believe this is the only really famous mic of its type that did this by switching out the back capsule.

IMO we will never be able to build a true 47 again as the venerable VF14 tube BV8 transformer combo is no longer available to us unless someone comes up with a new microphone grade VF14.

The MK47 does try to stay close to the original concept in the fact that it uses the single voltage supply design. Resulting in a closer circuit response to that of a original U47.

Build it and you will be happy.

 

[Melodeath00]

Well, as I've stated, I'm not hugely concerned with having a replica as much as I am with having the sonic footprint of a U47, so I don't think the remote polar switching is that far of a departure. Actually, I got the remote switching simply based on the advice of Oliver, as he said it can be a headache to get the Telefunken switching part to fit his kit. It would be quite interesting to do a real scientific test to see if remote pattern switching sounds different from on-mic switching.

The real question though, is why were the 2M and 3M resistors changed to 1M each, and why was the 30k resistor changed to 51k? Maybe it's just so it can work with a more generic PSU that can also be sold to power other mics?

 

[tonycamp]

Ok I should have a very cheap BV8 and K67 on the way just for testing. They probably wont be necessary, but this is my first build so I want to be very careful.

AMI kit is still on the way.

Can anyone let me know if this is a good soldering iron for mic building and PCB work? http://www.amazon.com/Weller-WLC100-40-Watt-Soldering-Station/dp/B000AS28UC/ref=sr_1_2?ie=UTF8&qid=1367888638&sr=8-2&keywords=soldering+iron+weller#productDetails

If it's not, could you suggest another? So far two people have mentioned that it doesn't have temperature control/feedback, so maybe this isn't so good? Much appreciated!

I burned through 2 of these irons in 2 months, the base still works?? :-\

 

[Melodeath00]

Ok I should have a very cheap BV8 and K67 on the way just for testing. They probably wont be necessary, but this is my first build so I want to be very careful.

AMI kit is still on the way.

Can anyone let me know if this is a good soldering iron for mic building and PCB work? http://www.amazon.com/Weller-WLC100-40-Watt-Soldering-Station/dp/B000AS28UC/ref=sr_1_2?ie=UTF8&qid=1367888638&sr=8-2&keywords=soldering+iron+weller#productDetails

If it's not, could you suggest another? So far two people have mentioned that it doesn't have temperature control/feedback, so maybe this isn't so good? Much appreciated!

I burned through 2 of these irons in 2 months, the base still works?? :-\

I wound up getting the WES51 Analog instead!

 

[micaddict]

It would be quite interesting to do a real scientific test to see if remote pattern switching sounds different from on-mic switching.

I don't know what kind of test you have in mind exactly, but AFAIK the noise difference is a fact and the tone difference (some mics have both, so it's easy to compare) is more than obvious IME (Horch RM2J).

Here's a U47 "clone" that has both:
http://www.wunderaudio.com/cm7-gt.html

 

[o3misha]

I would never use resistors with value higher than 100M-200M for  U47-ish mics with old tubes. 60-100M is enough for me.

Misha,

I have seen many of your posts and obviously you know what you're doing. Why do you think Oliver supplies 1G ohm resistors with his kits, and also appears to use them in the Lucas design? I understand it has something to do with frequency response. I notice 797 Audio also used 1G ohm resistors with a Wima cap in my MXL V77's, along with Teflon PCB insulators and solid silver wire for the connectors from capsule to tube.  Looking to learn something here. Thank you.

Robert Mokry
Austin, Texas

Oliver uses 1G for Lucas CS4. Andreas Grosser uses 100 M for Vox-o-rama, as far as I remember. Neumann used 60M-100M ( its not true that Neumann has not got possibility to use resititors with bigger value. They avoided to increase low end. First U47s has different grid resistors and coupling capacitors value) There are many other important things besides" low end". I personally don't like big grid resistors because of unpleasant stiffness in sound and excessive toughness, especially with old tubes.

 

[Melodeath00]

It would be quite interesting to do a real scientific test to see if remote pattern switching sounds different from on-mic switching.

I don't know what kind of test you have in mind exactly, but AFAIK the noise difference is a fact and the tone difference (some mics have both, so it's easy to compare) is more than obvious IME (Horch RM2J).

Here's a U47 "clone" that has both:
http://www.wunderaudio.com/cm7-gt.html

I'm not sure exactly what test I have in mind either. I know the noise difference is very real, but I'm having a hard time believing there's a difference tone-wise that you couldn't make up for with altering voltage on the capsule. Again, though, I'm no expert. What difference do you find in your Horch RM2J?

I would never use resistors with value higher than 100M-200M for  U47-ish mics with old tubes. 60-100M is enough for me.

Misha,

I have seen many of your posts and obviously you know what you're doing. Why do you think Oliver supplies 1G ohm resistors with his kits, and also appears to use them in the Lucas design? I understand it has something to do with frequency response. I notice 797 Audio also used 1G ohm resistors with a Wima cap in my MXL V77's, along with Teflon PCB insulators and solid silver wire for the connectors from capsule to tube.  Looking to learn something here. Thank you.

Robert Mokry
Austin, Texas

Oliver uses 1G for Lucas CS4. Andreas Grosser uses 100 M for Vox-o-rama, as far as I remember. Neumann used 60M-100M ( its not true that Neumann has not got possibility to use resititors with bigger value. They avoided to increase low end. First U47s has different grid resistors and coupling capacitors value) There are many other important things besides" low end". I personally don't like big grid resistors because of unpleasant stiffness in sound and excessive toughness, especially with old tubes.

You're saying they had access to larger than 100M resistors when the U47 was invented? 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.