Tube Mic Power Supply Upgrade Help

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kimothebeatmaker

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Hello fellow geeks! Would love to get some input/help for my tube mic's power supply.

I just bought a tube mic from Luke Audio. LA-Y59, it's fitted with a 12AT7WC and sounds fantastic.

I notice the PSU doesn't have any tubes, and a Chinese transformer in it. I would like to try and improve the noise floor.

Transformer Value is
175v 9.5v
115v 115v


I've written down the capacitor values:
C1-C6
22uF 400v

C7
.22uf 400V (Film Cap)

C8-C9
2200uF 25v

C10
10000uF 16v

C11
10uF 25v

attachment.php
 

rock soderstrom

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Hello, without knowing the exact circuit, the power supply looks pretty standard. The HT is passively filtered with plenty of RC stages, the filament is regulated, I think that's not your problem. (Tubes in mic PSUs are rare and this is not a disadvantage).

I would change the tube first as it is very important for the noise floor. At the moment there is a 12AT7 or ECC81 in it, here you could select with more 12AT7 tubes for low noise or take a better and also more expensive NOS 6072a or 12AY7.

PS: I bet C7 has no 22uF ;-)
 

RuudNL

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I am always surprised to see unscreened and untwisted wires connecting the microphone connector to the output, even if they are pretty close to the mains transformer.
 

kimothebeatmaker

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C7 capsule is one of these. 
Cbb22 caps
I attached a photo.


Ruud what do you mean by screen?  Rubber Shrink wrap?


Gus,
Yeah I posted on there as well. 
It’s like a slight very light sounding white noise.  I’m not sure if it’s the tube or the psu.  The mic is brand new so I’m guessing the tube is not the problem?  This is my first tube mic, sorry I’m still learning.  I just learned today to mount tube mics upside down. My friend just told me today to mount my mic upside down because the heat from the tube rises up and could damage the capsule.  I had no idea. 
 

kimothebeatmaker

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Yikes!  Sorry here is a better pic of the capacitor at c7. 

It reads
CBB22
224J400V
 

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rock soderstrom

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kimothebeatmaker said:
Oh!  Is that bad?

No, this is a standard size in this position. I only mentioned this because a 22uf/400V capacitor would be so big that it would be very cramped in the enclosure.

This capacitor does not play any role in your mentioned problem. I assume that the capsule is not contaminated or defective, so the only amplifying element, the tube, would be the main suspect for your noise problem.

So replace the tube or possibly send the mic back to the manufacturer if it does not meet the necessary technical specifications.

Cheers
 

Gus

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I would contact the manufacturer or do what rock soderstrom posted.

Take a picture of the area around the 3 terminal regulator for the filament if it has one. Is the reg marked 7806 and it there a 1N400_ diode by it?


Is it a NOS tube or a modern tube?
 

abbey road d enfer

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kimothebeatmaker said:
It’s like a slight very light sounding white noise.
So I would bet it's not the PSU that's at cause.

the mic is brand new so I’m guessing the tube is not the problem?
Every mic has some degree of noise. Tube mics are generally noisier than FET mics. Sopme tubes are noisier than others, even if they are the same type. Premium manufacturers select tubes for noise. It has a cost.

My friend just told me today to mount my mic upside down because the heat from the tube rises up and could damage the capsule.
That would be a concern if the diaphragm was PVC, that becomes brittle with age and temperature. I would bet yours is a mylar capsule. Unless there is a gross design error, the capsule should not be affected by teh heat produced by the tube.
 

Recording Engineer

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It’s a modern tube. My Y56 could use a better tube. It sounds small (though quiet) in comparison to most all my other tube mics using NOS tubes, including the Barbaric ones with Luke capsules. That’s not to say that it sounds small, just not as big. It sounds exactly as big as a U87Ai.
 

kimothebeatmaker

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Gus said:
I would contact the manufacturer or do what rock soderstrom posted.

Take a picture of the area around the 3 terminal regulator for the filament if it has one. Is the reg marked 7806 and it there a 1N400_ diode by it?


Is it a NOS tube or a modern tube?

The tube is a JAN 12AT7WC
The only 3 terminal regulator I see LM317T, and the diode number is not visible, only numbers I can read are the last 2 numbers which are 07. 


EDIT:
The diode says 1N4007
 

kimothebeatmaker

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It looks like Ac175 is bridged with a diode...

But the ac9.5 isn’t...
 

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Gus

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kimothebeatmaker said:
The tube is a JAN 12AT7WC
The only 3 terminal regulator I see LM317T, and the diode number is not visible, only numbers I can read are the last 2 numbers which are 07. 


EDIT:
The diode says 1N4007


Green printing on the tube?
 

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