Barstow U-47 Mod of Marshall MXL2001

[mtl777diy]

I have an old "Barstow U-47" mic which is a complete rebuild of a Marshall MXL2001 that Dave Royer made for me back in the time before he started Royer Labs:

http://recordinghacks.com/articles/one-tube-microphone-from-berlin/

I want to send this mic over to Shannon Rhoades at MicRehab.com who is known to do a great job in taking mics to the next level by reskinning the capsule and maybe doing other mods to the mic.  But before I send it, I'd like to know if it's a good idea to replace the body and headbasket first because the body and headbasket are too small compared to a Neumann U-47.  The diameter at the point where the body meets the headbasket is only 4.5 cm, and the headbasket is about 6 cm long.  The total length of the mic is 19 cm.  Here's a picture of the mic:

https://www.bhphotovideo.com/c/product/767066-REG/MXL_2001_2001A_Large_Diaphragm_Condenser.html

So my question is:  Is the body/headbasket size a critical factor in getting that big, Neumann U-47 sound -- so critical that you won't be able to get that sound no matter what mods you do unless you change the body/headbasket to the size of a U-47?

If your answer to my question is yes, could you please give me a link to where I can buy a replacement body/headbasket that will do the job well?

What do you think of this kit that I found?  Is it good? ...

http://www.aurycle.com/aurycle-a5500-diy-microphone-body-kit.html

Thanks very much for your much appreciated advice! 

 

[ln76d]

If royer mod circuit have anything to do with U47 (except the tube inside), we can assume that every  tube microphone is like u47...
Don't waste your time to adaptat that circuit in different body. Leave it as it is or potentially change capsule (chinese k47 could be good here). You can also damp some high frequencies of k67 using cap from plate to ground (100-470pF).
If you want anything at least in 50% similar to the U47, look for the body with similar headbasket (chinese from Chunger store, Aputis, Flea), M7 capsule (Thiersch, Poctop),  BV8 type transformer (ioaudio, haufe, ami).
There is few variants of tubes to use instead VF14.

 

[mtl777diy]

If royer mod circuit have anything to do with U47 (except the tube inside), we can assume that every  tube microphone is like u47...
Don't waste your time to adaptat that circuit in different body. Leave it as it is or potentially change capsule (chinese k47 could be good here). You can also damp some high frequencies of k67 using cap from plate to ground (100-470pF).
If you want anything at least in 50% similar to the U47, look for the body with similar headbasket (chinese from Chunger store, Aputis, Flea), M7 capsule (Thiersch, Poctop),  BV8 type transformer (ioaudio, haufe, ami).
There is few variants of tubes to use instead VF14.

Thanks In76d!

I'm still a little confused.  Let's say that my mic has a U-47 circuit, a M7 capsule, a BV8 type transformer, a VF14 tube, so everything is as close as possible to an original U-47 except the body/headbasket.  Will my mic not be able to sound like a U-47 because of the body/headbasket being different than that of a U-47?  Is the body/headbasket very important to get that U-47 sound?  Do you really have to change the body/headbasket to a U-47 design and size in order to get that sound?

In other words, I would like to know what role does the body and/or headbasket play in the sound quality of a mic?  Is the body/headbasket (size, shape, etc.) very important or not really?  On a level of 1 to 10, with 10 being the highest importance, how would you rate the importance of the body/headbasket in the sound quality of a mic?

Thanks again! 

 

[ln76d]

If you are not a tubes speculator or don't want to spend 2000$ for single tube, you can delete VF14 from the list

Body by itself not, if we exclude self resonance of the body (which is often in many microphones)
Headbasket? Yes!

I don't want to write about U47 headbasket because i didn't make too much tests and never made the test with original headbasket. Anyway, this is the one of these microphones where headbasket really matters.
You can even find opinion on gdiy that it's most important
I think this an exaggeration a little bit

Generally about headbaskets!
Every headbasket is acoustic filter.
Shape, diameter, mesh wire thickness and overall density, number of layers, capsule positioning (especially with u67 style headbaskets), resonance etc.
These are factors which affect response in that or other way.
Don't believe?
Try few diefferent with one microphone
Or!
Try microphone with headbasket and without it (circuit need to be without grounded capsule).
You will be surprised!

For now i would say 4.
Not for sound quality but character!

 

[Pip]

I am sure you would agree that rooms have their own sonic character. When you put lets say a guitar in a certain room and put a mic up in that room a certain distance off the guitar so that the room comes into the equation. That guitar, in that room , has a sound that is unique to the interaction between the two as "heard" by the mic.

The head basket of each microphone is like a little room with many little windows that let the sound in but then those sound waves bounce around inside this little room and some leak back out. Well you get the idea.

So now lets compare two rooms U47 vs U67. The former has parallel room walls and is a cylinder with a domed ceiling. The latter is an non-parallel walled room with a sharp flat ceiling it is also a smaller room I think.

You begin to get the concept. It is all interrelated. 

 

[mtl777diy]

If you are not a tubes speculator or don't want to spend 2000$ for single tube, you can delete VF14 from the list

Body by itself not, if we exclude self resonance of the body (which is often in many microphones)
Headbasket? Yes!

I don't want to write about U47 headbasket because i didn't make too much tests and never made the test with original headbasket. Anyway, this is the one of these microphones where headbasket really matters.
You can even find opinion on gdiy that it's most important
I think this an exaggeration a little bit

Generally about headbaskets!
Every headbasket is acoustic filter.
Shape, diameter, mesh wire thickness and overall density, number of layers, capsule positioning (especially with u67 style headbaskets), resonance etc.
These are factors which affect response in that or other way.
Don't believe?
Try few diefferent with one microphone
Or!
Try microphone with headbasket and without it (circuit need to be without grounded capsule).
You will be surprised!

For now i would say 4.
Not for sound quality but character!

Thank you so much, In76d! 

What do you think of this mic body kit:

http://www.aurycle.com/aurycle-a5500-diy-microphone-body-kit.html

It is cheap but do you think it is good and will do the job well?

 

[ln76d]

Pip gave you really good explanation about headbasket

Auracycle body looks like t.bone sct800.
If it is - it's not the best option (ok i need to admit - i hate gold headbaskets ), works better without internall mesh.
If you compare it to U47 (i don't even compare mesh) you have difference  48-50mm diameter vs 60-63mm.
If you are from us, add 16 bucks and buy this one:
http://store.studio939.com/product/budget-47-body-kit

For example, pretty sh*tty cheap MXL 990/770 headbaskets sounds really great without double internal mesh.
If the outside mesh density would be lower it could be even much better. It also have 60mm diameter!

 

[mtl777diy]

I am sure you would agree that rooms have their own sonic character. When you put lets say a guitar in a certain room and put a mic up in that room a certain distance off the guitar so that the room comes into the equation. That guitar, in that room , has a sound that is unique to the interaction between the two as "heard" by the mic.

The head basket of each microphone is like a little room with many little windows that let the sound in but then those sound waves bounce around inside this little room and some leak back out. Well you get the idea.

So now lets compare two rooms U47 vs U67. The former has parallel room walls and is a cylinder with a domed ceiling. The latter is an non-parallel walled room with a sharp flat ceiling it is also a smaller room I think.

You begin to get the concept. It is all interrelated.

Thanks, Pip!  Good explanation.  So the headbasket is important also.

 

[mtl777diy]

Pip gave you really good explanation about headbasket

Auracycle body looks like t.bone sct800.
If it is - it's not the best option (ok i need to admit - i hate gold headbaskets ), works better without internall mesh.
If you compare it to U47 (i don't even compare mesh) you have difference  48-50mm diameter vs 60-63mm.
If you are from us, add 16 bucks and buy this one:
http://store.studio939.com/product/budget-47-body-kit

For example, pretty sh*tty cheap MXL 990/770 headbaskets sounds really great without double internal mesh.
If the outside mesh density would be lower it could be even much better. It also have 60mm diameter!

Thanks, In76d!  If I understood the description correctly, I think this Studio939 body kit has two layers.  Does that mean it has double internal mesh?  What's the difference between mesh and layer?  Sorry for my ignorance. 

 

[ln76d]

Outside mesh with biggest holes is the first layer, every another inside is addtional layer of mesh.
This one have two layers, one  outside and one  inside.

 

[mtl777diy]

Outside mesh with biggest holes is the first layer, every another inside is addtional layer of mesh.
This one have two layers, one  outside and one  inside.

So when you say "double internal mesh", it means two inside layers plus one outside layer for a total of three layers?

As a rule, is it better to have less number of layers, so one layer is best?

 

[micaddict]

With a single layer (e.g. original C12) there's a chance you'll pick up RF or hum.

Unless a clone or copy is wanted, I'm a big fan of two layers total; one coarse, one fine.

A typical U47 headbasket would have three.

 

[ln76d]

Outside mesh with biggest holes is the first layer, every another inside is addtional layer of mesh.
This one have two layers, one  outside and one  inside.

So when you say "double internal mesh", it means two inside layers plus one outside layer for a total of three layers?

As a rule, is it better to have less number of layers, so one layer is best?

Yes, then it's three layer.
There's no general rule. For my own circuits or some mods usual i prefer single layer.
I never had problem with hum or RF due to single layer.
Each additionl layer change the sound, some not much, some significant.
If you want copy something - then it's best to use exact copy.
I truly don't know how big can be difference between double layer and three layer in U47.

 

[Gus]

Have you contacted Royer about changing the body?

Is there something wrong with the sound?

It might be worth more left alone

 

[mtl777diy]

Have you contacted Royer about changing the body?

Is there something wrong with the sound?

It might be worth more left alone

Other than a little bit of honkiness, there's nothing seriously bad about the sound.  But I want to send it over to Shannon at MicRehab who can reskin the capsule and tailor the sound to my voice and do further improvements.  I just wanted to know if I should change the body/headbasket first before I send it, because if the current headbasket which is relatively small (6 cm long and 4.5 cm diameter that tapers down as it is angled) is a big issue, then I might as well change it so that it won't get in the way of the mic becoming the best that Shannon can make it.

 

[ln76d]

Is it original mxl capsule in it?
If so, it's not worth in my opinion - a little waste of money.
You can adjust circuit by yourself (or not?) and do some other mods.
K67 reskin  doesn't change much, thicker mylar potentially little difference in transients, different diaphragm tension a little difference in response but still hi frequency bumped. For chinese k47 thicker mylar could make great difference but not for k67 (32mm here) in flat circuit.

Some ideas for mod:
- remove internal mesh
If i remember correctly there's double internal mesh, overall three layers.
Remove only front half (diphragm side), you can try first one layer, but probably both would be better.
Leave all layers at the back of the headbasket.

- install 5mm (M3 if i remember correctly) distance bolt between capsule saddle and existing distance bolt.
Cpsule  can't touch headbasket frame!

- change C2 for 470nF/680nF MKT or 0.5uF MP (my recommendation)

- replace R3 and R4 with trim potentiometer 1M to 5M and adjust polarisation voltage (newer set marginal position from both sides). Adjust pot during voice test and see what you like better.
Alternative:
* replace R4 with 3M resistor (if R3 is also 3M)
* replace R4 with 1M resistor - polarisation voltage should be circa 75V. These 32mm K67 usual sounds really good with such high voltage.

- replace R1 with 2k-3k trim potentiometer also make voice test and adjust

Other options:

- put capacitor across R1
* for original 750ohm try 47uF, 68uF, 100uF
* for higher resitor you can try values from 22uF

- put capacitor from plate to ground for HF damping
Try values from 100pF - 470pF and see what you like.

 

[mtl777diy]

Is it original mxl capsule in it?
If so, it's not worth in my opinion - a little waste of money.
You can adjust circuit by yourself (or not?) and do some other mods.
K67 reskin  doesn't change much, thicker mylar potentially little difference in transients, different diaphragm tension a little difference in response but still hi frequency bumped. For chinese k47 thicker mylar could make great difference but not for k67 (32mm here) in flat circuit.

Some ideas for mod:
- remove internal mesh
If i remember correctly there's double internal mesh, overall three layers.
Remove only front half (diphragm side), you can try first one layer, but probably both would be better.
Leave all layers at the back of the headbasket.

- install 5mm (M3 if i remember correctly) distance bolt between capsule saddle and existing distance bolt.
Cpsule  can't touch headbasket frame!

- change C2 for 470nF/680nF MKT or 0.5uF MP (my recommendation)

- replace R3 and R4 with trim potentiometer 1M to 5M and adjust polarisation voltage (newer set marginal position from both sides). Adjust pot during voice test and see what you like better.
Alternative:
* replace R4 with 3M resistor (if R3 is also 3M)
* replace R4 with 1M resistor - polarisation voltage should be circa 75V. These 32mm K67 usual sounds really good with such high voltage.

- replace R1 with 2k-3k trim potentiometer also make voice test and adjust

Other options:

- put capacitor across R1
* for original 750ohm try 47uF, 68uF, 100uF
* for higher resitor you can try values from 22uF

- put capacitor from plate to ground for HF damping
Try values from 100pF - 470pF and see what you like.

Wow, In76d!  Thank you very much!

It has the original K67 capsule, but Shannon may replace the capsule if it's not worth reskinning it.

Remove only front half (diphragm side), you can try first one layer, but probably both would be better.

I understand this.  Remove one or both of the internal mesh of the headbasket.  Removing both would probably be better.

But then you say:

Leave all layers at the back of the headbasket.

I'm confused.  I thought you said to remove the internal layers but now you say to "leave all layers at the back of the headbasket".  Which layers are the ones that are "at the back of the headbasket"?

This is what I understand:

Internal Layer 1 (this is the one nearest the capsule) - remove this.  Is this what you call the "front" layer?
Internal Layer 2 (this is the one between Internal Layer 1 and the External Layer) - remove this.  Is this what you call a "back" layer?
External Layer - Keep this.  Is this what you call a "back" layer also?

With regards to "front" and "back", from what point of reference are you looking at?  Are you looking from the inside of the mic?

When I'm looking from the outside of the mic, I see only the external layer and this is what I would call the "front" layer. 

 

[Khron]

The original MXL 2001 capsule is a single-sided (cardioid-only) K67-clone.

"Front" of the microphone doesn't necessarily mean "outside layer of mesh" - there's an outside layer both on the front and the back of the microphone (duuuh ).

The idea was, i'm sure, to remove the internal mesh on the front side of the microphone (ie. the side where the gold-plated diaphragm is), but to leave it in on the rear side (ie. the back of the microphone, where the null of the cardioid capsule is).

Surely it's not THAT complicated

 

[ln76d]

Yeap, Khron is right.
When microphone is cardioid only there's no need to remove internal mesh from both sides of the capsule.
Front is front diaphragm (with gold surface), front of the microphone etc.

 

[Andriejus]

Outside mesh with biggest holes is the first layer, every another inside is addtional layer of mesh.
This one have two layers, one  outside and one  inside.

So when you say "double internal mesh", it means two inside layers plus one outside layer for a total of three layers?

As a rule, is it better to have less number of layers, so one layer is best?

Yes, then it's three layer.
There's no general rule. For my own circuits or some mods usual i prefer single layer.
I never had problem with hum or RF due to single layer.
Each additionl layer change the sound, some not much, some significant.
If you want copy something - then it's best to use exact copy.
I truly don't know how big can be difference between double layer and three layer in U47.

I had hum problems due to the single layer. I've placed additional fine layer inside the headbasket and it solved my problem...

Andrew