DiY AMI U47

[Pip]

After another two days, I still have not been able to re-create the clipping, so everything appears ok for the time being. I am uneasy that I was not able to figure out what was causing the problem.

I did notice that when I turn the PSU off, the audio clips. Is that normal/expected?

There is a lot of handling noise when I hold the mic. I'm going to do some testing against other mics to see if it's out of the ordinary.

How important is it to connect the shielding in the Gotham cable to the Ground pin of the Binder connectors? Would this solve cable handling noise?

I am basically considering the mic done, except for the following list of items.

To-do list:
-Try more EF800 tubes
-Install internal true cardioid switch
-Further secure capsule mount (it tilts the tiniest bit when you tilt the mic, which you can hear as a tiny, tiny thud int he sound. Shouldn't be an issue at all unless you're singing with the mic in your hand and moving all around, though haha

In the meantime, check out the clips I posted in the post above!

And here's a nice little picture

PSU question answer is yes. True Cardioid switch is whatever. Handling noise is and always has been a problem with this mic not to worry about it. The capsule though should be mounted properly at some time. Not the end of the world but I myself would not leave it like that. Fixing this can only help the handling noise issue.

Now the shielding issue. I assume you mean the copper braid. Which in this application is the drain. Is it connected in the circuit at all now. Because it is not the ground but it is how the EMI and RFI  (electro magnetic and radio frequency interferance in other words inductive forces) are kept out of the cable so it must be connected to the ground scheme on at least the PSU side of the issue. No it will not stop handling noise much as that is more a function of the capacitance of the cable than other factors.

 

[Melodeath00]

After another two days, I still have not been able to re-create the clipping, so everything appears ok for the time being. I am uneasy that I was not able to figure out what was causing the problem.

I did notice that when I turn the PSU off, the audio clips. Is that normal/expected?

There is a lot of handling noise when I hold the mic. I'm going to do some testing against other mics to see if it's out of the ordinary.

How important is it to connect the shielding in the Gotham cable to the Ground pin of the Binder connectors? Would this solve cable handling noise?

I am basically considering the mic done, except for the following list of items.

To-do list:
-Try more EF800 tubes
-Install internal true cardioid switch
-Further secure capsule mount (it tilts the tiniest bit when you tilt the mic, which you can hear as a tiny, tiny thud int he sound. Shouldn't be an issue at all unless you're singing with the mic in your hand and moving all around, though haha

In the meantime, check out the clips I posted in the post above!

And here's a nice little picture

PSU question answer is yes. True Cardioid switch is whatever. Handling noise is and always has been a problem with this mic not to worry about it. The capsule though should be mounted properly at some time. Not the end of the world but I myself would not leave it like that. Fixing this can only help the handling noise issue.

Now the shielding issue. I assume you mean the copper braid. Which in this application is the drain. Is it connected in the circuit at all now. Because it is not the ground but it is how the EMI and RFI  (electro magnetic and radio frequency interferance in other words inductive forces) are kept out of the cable so it must be connected to the ground scheme on at least the PSU side of the issue. No it will not stop handling noise much as that is more a function of the capacitance of the cable than other factors.

Thanks for the reply Pip!

Regarding internal switch - I think this will be easy enough to mount a switch with hot glue onto the underside fo the acrylic deck. I might even be able to access it by only taking the headbasket off, since there is a very small gap in the metal and acrylic deck at the front of the mic. We'll see.

Regarding the mount: it's not bad, but I guess because the wooden dowel (which has two metal washers underneath it) is not PERFECTLY flat, it will always shift unless i fix it with glue or something. I will try to think of the best solution.

Yes, I am referring to the braid of copper (I think it's copper, at least). I have it connected to the housing of the binder connectors, but it is not in the circuit at all other than that. One person advised I should connect it to the Ground Pin 4, but I never did. Actually, if it's attached to the Binder connectors, it probably makes contact with ground in the PSU...

 

[Pip]

After another two days, I still have not been able to re-create the clipping, so everything appears ok for the time being. I am uneasy that I was not able to figure out what was causing the problem.

I did notice that when I turn the PSU off, the audio clips. Is that normal/expected?

There is a lot of handling noise when I hold the mic. I'm going to do some testing against other mics to see if it's out of the ordinary.

How important is it to connect the shielding in the Gotham cable to the Ground pin of the Binder connectors? Would this solve cable handling noise?

I am basically considering the mic done, except for the following list of items.

To-do list:
-Try more EF800 tubes
-Install internal true cardioid switch
-Further secure capsule mount (it tilts the tiniest bit when you tilt the mic, which you can hear as a tiny, tiny thud int he sound. Shouldn't be an issue at all unless you're singing with the mic in your hand and moving all around, though haha

In the meantime, check out the clips I posted in the post above!

And here's a nice little picture

PSU question answer is yes. True Cardioid switch is whatever. Handling noise is and always has been a problem with this mic not to worry about it. The capsule though should be mounted properly at some time. Not the end of the world but I myself would not leave it like that. Fixing this can only help the handling noise issue.

Now the shielding issue. I assume you mean the copper braid. Which in this application is the drain. Is it connected in the circuit at all now. Because it is not the ground but it is how the EMI and RFI  (electro magnetic and radio frequency interferance in other words inductive forces) are kept out of the cable so it must be connected to the ground scheme on at least the PSU side of the issue. No it will not stop handling noise much as that is more a function of the capacitance of the cable than other factors.

Thanks for the reply Pip!

Regarding internal switch - I think this will be easy enough to mount a switch with hot glue onto the underside fo the acrylic deck. I might even be able to access it by only taking the headbasket off, since there is a very small gap in the metal and acrylic deck at the front of the mic. We'll see.

Regarding the mount: it's not bad, but I guess because the wooden dowel (which has two metal washers underneath it) is not PERFECTLY flat, it will always shift unless i fix it with glue or something. I will try to think of the best solution.

Yes, I am referring to the braid of copper (I think it's copper, at least). I have it connected to the housing of the binder connectors, but it is not in the circuit at all other than that. One person advised I should connect it to the Ground Pin 4, but I never did. Actually, if it's attached to the Binder connectors, it probably makes contact with ground in the PSU...

Yes if it is connected to the housing of the Binder Connector it should be well into the ground scheme of the mic. Check it though with your DMM using the continuity function just to be sure.

 

[Melodeath00]

Yes if it is connected to the housing of the Binder Connector it should be well into the ground scheme of the mic. Check it though with your DMM using the continuity function just to be sure.

Yes, continuity between ground and connector interior.

Did anyone check out the clips? I think they're pretty cool.

 

[Melodeath00]

My first actual production/mix with the U47, rather than just test clips. DiY 47 on acoustic guitar

https://soundcloud.com/damianherring/mourning-fields

 

[scott_humphrey]

Nice music!

 

[letterbeacon]

My first actual production/mix with the U47, rather than just test clips. DiY 47 on acoustic guitar

https://soundcloud.com/damianherring/mourning-fields

Sounds awesome! What was the signal chain and what did you use in the mix?

 

[Melodeath00]

Nice music!

Thanks! Sometimes I get so caught up with gear that I forget the whole purpose is to actually make music and record it!

Sounds awesome! What was the signal chain and what did you use in the mix?

Thanks! U47 in cardioid, Mogami Cable, Focusrite Liquid Saffire 56 (standard preamp), recorded in Reaper at 44.1kHz, 24bit.

In the mix I used a small amount of EQ (1dB boost in the highs, 1dB cut in the lows), Slate VTM, Slate VCC, ValhallaRoom (reverb), and Ozone 5 for Maximizer.

No compression, which is unusual for me. However, I did use Ozone 5 multiband dynamics in the most upper register to attenuate one string squeak. I set the processor threshold so that it isn't doing anything other than attenuating that one squeak.

The thunder was recorded about two years ago with an SM57 by an open window.

 

[fiveinfinity]

Long time lurker here...Im slowly figuring out (thanks to these forums) how I want to go about building my U47. I know everyone's mic is going to be different, but does anyone have a Mouser Project (BOM) set up? I know someone has a U47 FET BOM up there, and thought it would be a good place to start.  Also, what are you guys using for PCB's? Are you building your own, or.....?
Thanks for the help!

 

[AusTex64]

Long time lurker here...Im slowly figuring out (thanks to these forums) how I want to go about building my U47. I know everyone's mic is going to be different, but does anyone have a Mouser Project (BOM) set up? I know someone has a U47 FET BOM up there, and thought it would be a good place to start.  Also, what are you guys using for PCB's? Are you building your own, or.....?
Thanks for the help!

Have you looked at the AMI parts list? Oliver sure makes it easy....

 

[AusTex64]

Melodeath,

For true cardioid you can use a small relay to switch the back diaphragm in and out of the circuit. It will be mounted under the capsule deck, attached with E6000. You'll need a relay with 6V switching. Take 6V from the tube heater to the + side of the relay coil. Tie the heater and mic grounds together in the mic. This will free up a pin on the Binder. You'll wire up the ground from the relay coil to this now unused pin. Then add a DPDT toggle switch to the power supply. One side of the toggle switch will make and break ground - this will switch the relay on and off. Use the other side of the toggle switch to shunt the polarization voltage to ground via a resistor when the switch is in cardioid mode. When you switch the back diaphragm in and out of circuit, this will keep the polarization voltage from making loud thumps in the audio. It will ramp up and down nicely. Also wire the relay where the "normally open" position is the default (both diaphragms in circuit), that way the coil doesn't have to be energized all the time.

Good luck,

Robert

 

[micaddict]

Melodeath,

For true cardioid you can use a small relay to switch the back diaphragm in and out of the circuit. It will be mounted under the capsule deck, attached with E6000. You'll need a relay with 6V switching. Take 6V from the tube heater to the + side of the relay coil. Tie the heater and mic grounds together in the mic. This will free up a pin on the Binder. You'll wire up the ground from the relay coil to this now unused pin. Then add a DPDT toggle switch to the power supply. One side of the toggle switch will make and break ground - this will switch the relay on and off. Use the other side of the toggle switch to shunt the polarization voltage to ground via a resistor when the switch is in cardioid mode. When you switch the back diaphragm in and out of circuit, this will keep the polarization voltage from making loud thumps in the audio. It will ramp up and down nicely. Also wire the relay where the "normally open" position is the default (both diaphragms in circuit), that way the coil doesn't have to be energized all the time.

Good luck,

Robert

Thanks for this contribution, Robert!


Henk

 

[marcus4audio]

Excuse my ignorance but what is the "true cardoid"? I' familiar with :
Omnidirectional
Bi-directional or Figure of 8
Subcardioid
Cardioid
Hypercardioid
Supercardioid
Shotgun

Do I miss something?

 

[HellfireStudios]

Excuse my ignorance but what is the "true cardoid"? I' familiar with :
Omnidirectional
Bi-directional or Figure of 8
Subcardioid
Cardioid
Hypercardioid
Supercardioid
Shotgun

Do I miss something?

I believe true cardioid is when the back diaphragm is taken out of the circuit like a U-47. As oppossed to the C12 which sends voltage to the backplate to create it cardioid pattern.

-James-

 

[marcus4audio]

I believe true cardioid is when the back diaphragm is taken out of the circuit like a U-47. As oppossed to the C12 which sends voltage to the backplate to create it cardioid pattern.

-James-

So the "true cardoid" is cardoid but exclusively connected to U47 because of approach?

 

[HellfireStudios]

They are both cardioid. The main difference ends up being S/N. The U-47 and all of the other mics that use this type of pattern switching have a lower noise floor due to the fact that the back diaphragm isn't adding additional noise to the circuit in cardioid. The pattern switching is not exclusive to the U-47.

-James-

 

[marcus4audio]

Thanks 

 

[Melodeath00]

Melodeath,

For true cardioid you can use a small relay to switch the back diaphragm in and out of the circuit. It will be mounted under the capsule deck, attached with E6000. You'll need a relay with 6V switching. Take 6V from the tube heater to the + side of the relay coil. Tie the heater and mic grounds together in the mic. This will free up a pin on the Binder. You'll wire up the ground from the relay coil to this now unused pin. Then add a DPDT toggle switch to the power supply. One side of the toggle switch will make and break ground - this will switch the relay on and off. Use the other side of the toggle switch to shunt the polarization voltage to ground via a resistor when the switch is in cardioid mode. When you switch the back diaphragm in and out of circuit, this will keep the polarization voltage from making loud thumps in the audio. It will ramp up and down nicely. Also wire the relay where the "normally open" position is the default (both diaphragms in circuit), that way the coil doesn't have to be energized all the time.

Good luck,

Robert

Robert, thanks so much for this info! It all made sense me up until the "other side of the toggle switch to shunt the polarization voltage to ground via a resistor when the switch is in cardioid mode." I'm not sure what that means in practice. I understand I'm running the 0V heater to ground, freeing up a Binder pin for a tap from the 6V heater, but that's about it.

One interesting point I've realized about true cardioid is that the U47 and U48 are different. Because the U47 is Omni and Cardioid, it always has 0V to the rear diaphragm. So when you switch it to cardioid, you are disconnecting the rear which has 0V. In a U48, it is Bi-Directional and Cardioid, so the rear diaphragm always gets about 105V (U48 gets about 52.5V polarization as opposed to 60V). When you switch the Cardioid, the rear diaphragm still gets 105V, but it is disconnected from the audio circuit. According to Oliver's post here on polarization, that affects the sound, and is why when you set the internal switch in an M49 to cardioid-only, you should be set to Omni mode on the power supply so that you have 0V on the rear diaphragm. Reply #27: http://repforums.prosoundweb.com/index.php/topic,33882.15.html

Even when set to Omni and disconnecting the rear, it's not exactly the same as a U47 due to a "capacitive leak via buffer resistors to ground" that influence sound.

So setting my PSU to Bi-Directional, and disconnecting the rear diaphragm from the circuit would yield the closest to U48 cardioid, while having the PSU on Omni would yield the closest to U47 cardioid. Granted, I bet the differences are subtle...

Is it bad to disconnect the rear diaphragm from the circuit pre-polarization? I guess you would just have up to 120V going no-where, which shouldn't really be a problem, versus polarizing the rear diaphragm, and having the resulting audio go no-where. It's a matter of putting the Relay between R10 and the rear diaphragm, or between the rear diaphragm and C4. http://www.tab-funkenwerk.com/id85.html

It is clear that the U48, M49, and Lucas mics have their disconnect switch post-polarization and pre-capacitor, but I am wondering why, since if you disconnect pre-polarization you would negate the effect of polarizing the rear diaphragm, and essentially make it more like a U47 true cardioid, since the rear diaphragm is not connected to any source of DC Voltage.

 

[AusTex64]

Sorry it took me so long to post this info, trying to finish up a CD and working all the time....

What I mean by "shunting the rear polarization voltage to ground" is this: Mount a DPDT toggle switch on the PSU. One side will make and break ground on the pin from the Binder that goes to the relay ground wire, which will open and close the relay inside the mic, as described in my earlier post. The other side of the DPDT switch will go in line with the rear diaphragm polarization voltage. When the toggle switch is OFF (both diaphragms in operation), the polarization voltage passes right through the switch to the mic. When the toggle switch is in the ON position (rear diaphragm disconnected from circuit by the relay, AKA "true cardioid") the polariation voltage will go to a 10K 1/2 watt resistor attached to ground. What this will do is pull the polarization voltage down to where the rear diaphragm is not polarized, thus avoiding the problem mentioned about the rear capsule polaization still affecting the sound of the front capsule. Another benefit is if/when you switch the mic hot from "true cardioid" to normal multipattern operation, you won't get a loud thump in the audio, the polarization voltage (now disconnected from the resistor that runs to ground) will rise up slowly. You can watch it with a meter, it takes a second or so to go from O VDC to 105 VDC. Nifty.

Note that the relay can be wired for open or closed with the coil not energized, depending on what pins you choose to use on the switch side of the relay. I chose to wire it for normally closed (rear diaphragm connected) with the coil not energized. This is what I would call the OFF position. When the ground is made, what I'm calling ON/true cardioid, the switch is open. I suppose how one uses the mic would determine how you wire this. I figured I would be using true cardioid only some of the time, and more with both diaphragms on, but would now challange that assumption. Might do it the other way around, if I had it do over again. Probably doesn't make any difference anyway.

Final bit of info - here's the relay I used: Mouser part # 769-DS2E-M-DC6V

And a link to make it easy: http://www.mouser.com/Search/ProductDetail.aspx?qs=YINDDaGsG3E%252beqT3zlaH1g%3D%3D

You guys can thank Oliver Archut for this approach, I'm only the messenger.....  8)

 

[scott_humphrey]

Excellent! I was just about to ask for a part number. Good timing! Thanks.