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 1 
 on: Today at 12:00:37 pm 
Started by MikeCheck - Last post by Jim Williams
Use an el cap to bypass the reference/adjust pin to ground on a LM317/337/LT1085, etc. It lowers the noise. I use 47 uf here, a Panasonic FR series tantalum replacement. Those have lower impedance specs than a tantalum cap.

 2 
 on: Today at 08:35:14 am 
Started by radardoug - Last post by boz6906
http://www.neumann.com/forums/view.php?bn=neumann_mictec&key=1236063072&v=f

 3 
 on: Yesterday at 10:33:16 pm 
Started by radardoug - Last post by gtoledo3
Yeah, that is something that in fact did exist. It was for an anniversary year.

 4 
 on: Yesterday at 08:00:24 pm 
Started by radardoug - Last post by radardoug
Klaus, theres this guy listing a gold U87 on Ebay. Wants lots for it! He says 300 of these gold ones were made.
Can you or anyone else confirm this?

 5 
 on: Yesterday at 06:25:08 pm 
Started by MikeCheck - Last post by uwe ret
As the filament current for a single AC701(k) is onlu 100 mA you will probably fine with your present arangement. If it is working satisfactorily without getting too hot to touch comfotably, there is no need to replace the regulator IC.

 6 
 on: Yesterday at 04:08:05 pm 
Started by MikeCheck - Last post by MikeCheck
Thanks Uwe for all your help and information!

I will change to the 220 package.

 7 
 on: Yesterday at 11:45:35 am 
Started by MikeCheck - Last post by uwe ret
Congratulations!
As I never considered this forum to be a DIY tutorial, I forgot to mention a recommendation to use a LM317-T in the TO220 package and mounting it to the metal chassis for proper heat dissipation.

As to the concerns about noise raised in previous posts to this thread:
a) the LM317 is an analog regulator with the reference far removed from the output path;
b) the filament is too sluggish to let its temperature follow mV noise variations in its supply;
c) to ameliorate any doubts, some data sheets suggest an additional capacitor of 1F or larger
    placed between the 'Adjust' terminal and ground (I never found it to make any difference);
d) anyone undertaking any equipment modifications should be qualified enough to possess a
    basic understanding about proper circuit layout and grounding principles.

 8 
 on: March 21, 2017, 09:34:26 pm 
Started by MikeCheck - Last post by MikeCheck
Update:
Built and installed Uwe's circuit. It's working great, and I was able to fit it in the original location of the Stabilyt cells.

 9 
 on: March 18, 2017, 04:43:42 pm 
Started by MikeCheck - Last post by Kai
In a good regulator design you will see around 1 mv of noise, that's a bit more than -60 db down, not bad. ...
In as this is for a DC heater design, most of the audio concerns can be eliminated.
Some tube microphones use the DC heater for grid biasing too.
In this case additional filtering by a large cap is desirable.
Even if this is not the case, noise current introduced into the common ground connection might creep into the audio path.
A 4700uF / 16V cap doesn't cost a fortune.

 10 
 on: March 18, 2017, 12:27:42 pm 
Started by MikeCheck - Last post by Jim Williams
In a good regulator design you will see around 1 mv of noise, that's a bit more than -60 db down, not bad. It's benign hiss, steadystate white noise. There are no switching artifacts as there is no switching. It shows more hiss than a quiet opamp does.

That hiss does not translate to the active element increasing it's noise as PSU filtering prevents that. With opamps you also get that PSRR ratio spec that nulls out that noise contribution another -80 db or more.

In as this is for a DC heater design, most of the audio concerns can be eliminated.

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