OPEN SOURCE DIY Mic Project - ORS 87 - Stripped Down u87

[mic test]

Lundahl LL1577 is installed in the brown valvet x​

 

[micolas]

Thanks for info about Lundahl being used in Stam.

Stam Audio SABV13, on the back-side of the mic, I see Lundahl 1935 being printed. Maybe rebranded was used?

https://www.lundahltransformers.com/wp-content/uploads/datasheets/1935.pdf

https://www.lundahltransformers.com/microphone/

What would be required to use this transformer instead in ORS build?

Or these below would be even a better choice? "Probably the best beer in the world..." - kinda statement.

View attachment 131205

1935 is ok.
Just configure it according to the scheme.
5 to the coupling capacitor
7 and E to GND
1 and 3 to Output

 

[micolas]

Lundahl LL1577 is installed in the brown valvet x​

1577 has a ratio of
7:1 or 14:1

The U87 topology usually uses a ratio transformer:
9.5 : 1 to 10 : 1

Moby BV-13 has ratio
9.23 : 1
https://www.mobytransformers.com/bv-13

 

[eso]

I've got some XML ribbon mics being upgraded with top quality ribbons and Lundahl transformers, but I didn't see anything in their offerings that looked right for the U87 builds.

I do have some of these on order for this project:

https://cinemag.biz/mic_output/PDF/CM-13113.pdf

 

[micolas]

Stam used a Lundahl output transformer
in the MK3 revision of SA-87
The MK1 and MK2 used a Sowter output transformer

​

Thanks for info about Lundahl being used in Stam.

Stam Audio SABV13, on the back-side of the mic, I see Lundahl 1935 being printed. Maybe rebranded was used?

The information was provided by Joshua himself (StamAudio)

 

[micolas]

I've got some XML ribbon mics being upgraded with top quality ribbons and Lundahl transformers, but I didn't see anything in their offerings that looked right for the U87 builds.

I do have some of these on order for this project:

https://cinemag.biz/mic_output/PDF/CM-13113.pdf

CM 13113 works perfectly in the circuit U87 i and ai.
It is also used in the Warm WA-87 R2, which I have and it sounds very good, very clean and with impressive headroom, but it has its own character quite different from the U87.
The difference is not due to the transformer.

 

[jeremynothman]

can you have this repaired somewhere ?

Hey Mic Test. I know it’s totally off this topic, but I’m pretty sure the old brauner capsules were designed by Haun/MBHO in Germany. Maybe get in touch with them to see if they’d fix the capsule?

 

[Sidebstudio]

Thank you very much I will do it but I have 5 PCBs I would like to use the Capsul again but it is from a 4000€ mic the membrane is defective I need a new gold foil is there anyone who can do that? Many greetings from Germany

Hi. In Italy we offer capsule reskin and repair in general.
If you want, you can contact me for a quotation.
Regards,
Alessandro

 

[micolas]

Hi. In Italy we offer capsule reskin and repair in general.
If you want, you can contact me for a quotation.
Regards,
Alessandro

Do you have an official website where we can see your work?

 

[Sidebstudio]

Do you have an official website where we can see your work?

https://sidebstudio.it/

Google "sidebstudio" , results are our webpages, social, youtube, customers reviews

 

[cello4u]

So this is what I came up with. No bueno. Probably because I had the other jfet with the brass knob pointing up, and stripped the circle when I tried to desolder it and put the other jfet in that fits the diagram. I get capacitors with longer positive side. That orange one fit in there pretty strangely. I will have another try with a new pcb.

 

[micolas]

So this is what I came up with. No bueno. Probably because I had the other jfet with the brass knob pointing up, and stripped the circle when I tried to desolder it and put the other jfet in that fits the diagram. I get capacitors with longer positive side. That orange one fit in there pretty strangely. I will have another try with a new pcb.

Better do the tests, the experiments, on this sacrificial PCB, even if you destroy it, and do all kinds of improvisations.
When everything is clear, you know exactly which components you will use in the end, you BIASed the jFET and it works perfectly, and you are satisfied, then mount everything on a new PCB. I usually do the initial experiments in a point-to-point build.
Often I end up with dozens of changes.
*
Can you post some clearer pictures of the entrance?
You have to be very careful with connecting the gate of the jFET and the capsule (I wouldn't put a connector)
*
Are you using an Ali... T-13 ASTDS transformer?

 

[cello4u]

Better do the tests, the experiments, on this sacrificial PCB, even if you destroy it, and do all kinds of improvisations.
When everything is clear, you know exactly which components you will use in the end, you BIASed the jFET and it works perfectly, and you are satisfied, then mount everything on a new PCB. I usually do the initial experiments in a point-to-point build.
Often I end up with dozens of changes.
*
Can you post some clearer pictures of the entrance?
You have to be very careful with connecting the gate of the jFET and the capsule (I wouldn't put a connector)
*
Are you using an Ali... T-13 ASTDS transformer?

Better do the tests, the experiments, on this sacrificial PCB, even if you destroy it, and do all kinds of improvisations.
When everything is clear, you know exactly which components you will use in the end, you BIASed the jFET and it works perfectly, and you are satisfied, then mount everything on a new PCB. I usually do the initial experiments in a point-to-point build.
Often I end up with dozens of changes.
*
Can you post some clearer pictures of the entrance?
You have to be very careful with connecting the gate of the jFET and the capsule (I wouldn't put a connector)
*
Are you using an Ali... T-13 ASTDS transformer?

The idea was to have a working circuit, and then insert this one as a trial. Trying to be able to switch capsules ( and circuits) more easily. I see the merit of your method, I will look more closely at the thread to see what I can test. Yes Ali T-13.

 

[micolas]

@cello4u
I can't see clearly in the picture.
Are the gate of the jFET and the red wire from the capsule touching the surface of the PCB?
Careful! You melted the Wima capacitor housing.
Excessive heating (too high temperature or longer time) can compromise any components(even jFET) or the PCB.

 

[Khron]

The idea was to have a working circuit, and then insert this one as a trial. Trying to be able to switch capsules ( and circuits) more easily. I see the merit of your method, I will look more closely at the thread to see what I can test. Yes Ali T-13.

Y'know, you COULD zoom into whatever photos you take, and see just how blurry they are, BEFORE attaching them here Those are about as clear as mud...

 

[micolas]

@cello4u
Did you connect the Gate of the jFET and the wire from the capsule using a turret (ptfe insulated terminal), isolated from the PCB?
(the pictures are only examples)

 

[Khron]

So this is what I came up with. No bueno. Probably because I had the other jfet with the brass knob pointing up, and stripped the circle when I tried to desolder it and put the other jfet in that fits the diagram. I get capacitors with longer positive side. That orange one fit in there pretty strangely. I will have another try with a new pcb.

I see you don't have a trimpot installed in that 3-pin footprint in the middle, OR an R* in its footprint next to C8(?). So the JFET has no connection between its source pin and ground. That's gonna be AT LEAST part of the reason why this is "no bueno".

Circuits rarely work when they're incomplete, and as this has already been trimmed down from the original Neumann schematic, there's not all that much room (or need) for Muntzing anymore anyway...

https://en.wikipedia.org/wiki/Muntzing

 

[micolas]

I see you don't have a trimpot installed in that 3-pin footprint in the middle, OR an R* in its footprint next to C8(?). So the JFET has no connection between its source pin and ground. That's gonna be AT LEAST part of the reason why this is "no bueno".

Circuits rarely work when they're incomplete, and as this has already been trimmed down from the original Neumann schematic, there's not all that much room (or need) for Muntzing anymore anyway...

https://en.wikipedia.org/wiki/Muntzing

@Khron , in this case it is about the famous wireless BIAS, which we have all heard of)
(Sorry, couldn't resist)

 

[cello4u]

Y'know, you COULD zoom into whatever photos you take, and see just how blurry they are, BEFORE attaching them here Those are about as clear as mud...

Sorry, you should have seen the first one.

@Khron , in this case it is about the famous wireless BIAS, which we have all heard of)
(Sorry, couldn't resist)

@Khron , in this case it is about the famous wireless BIAS, which we have all heard of)
(Sorry, couldn't resist)

Yeah, I'm just throwing in parts from the BOM. That's why I need a step by step. And a picture of the 1.1, which until recently I had none. Not sure that helps.

 

[cello4u]

Sorry, you should have seen the first one.


Yeah, I'm just throwing in parts from the BOM. That's why I need a step by step. And a picture of the 1.1, which until recently I had none. Not sure that helps.

May stick to building cellos, that I'm not very good at either but know something about. Couldn't afford a Strad either. I'd rather be mixing.