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 11 
 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.

 12 
 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.

 13 
 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.

 14 
 on: March 18, 2017, 06:04:53 am 
Started by MikeCheck - Last post by Kai
I was always under the impression that the constant voltage adjustment to regulate the constantly changing incoming voltage generates the audible noise in these regulators.
The key word is constantly. An analog, so called linear regulator does NOT wait for a change, then have a delay and then react.
Look at it as an analog amplifier (which in fact it is), and as every of such it regulates immediately, constantly, within its maximum speed range.
So there is no switching noise generated, because there is no switching or stepping going on. It greatly reduces the noise that is on the unregulated power supply side.
To get the best out of this a proper grounding scheme for the whole circuit is necessary. Regulation is in reference to its reference voltage input, this needs to be the center of the grounding starpoint.
A common mistake is to use a point at the unregulated side as grounding starpoint, where hum and noise currents are floating.
Further filtering (by caps) is best done close to the supplied circuit, to reduce supply impedance.

 15 
 on: March 18, 2017, 12:16:18 am 
Started by MikeCheck - Last post by klaus
Most of these older non-low dropout style regulators used a zener clamp diode with an opamp for the adjustable reference. That's where most of the internal hiss is generated.

So is this strictly the electron noise generated by the amount of (bad) components in a (bad) circuit implementation? Or is there switching noise involved?
I was always under the impression that the constant voltage adjustment to regulate the constantly changing incoming voltage generates the audible noise in these regulators. But I don't want to perpetuate that notion if it's wrong.


 16 
 on: March 17, 2017, 12:07:03 pm 
Started by MikeCheck - Last post by Jim Williams
Most of these older non-low dropout style regulators used a zener clamp diode with an opamp for the adjustable reference. That's where most of the internal hiss is generated.

The LT 1085/6 style low dropout regulators are much more precision and have lower output noise. I stil use a large el cap on their outputs to reduce that, 1000uf is a good starting point. Add a small film .01 uf to trap hf spikes and other noise.

Good heatsinking is equally important to reduce the noise. Cool semiconductors gererate less hiss than hot semiconductors.

Alternatively, one can add a transistor shunt after the regulator to further reduce ripple/noise. Feed the collector, run the base to ground with a cap and exit the emitter. Use a small 2k resistor from the collector to base. Observe polarity and don't let the smoke out.

 17 
 on: March 17, 2017, 10:23:29 am 
Started by MikeCheck - Last post by soapfoot
Good to know. Do you have a schematic for that chip? I am curious how it regulates.

page 3:

https://www.onsemi.com/pub/Collateral/LM317-D.PDF

 18 
 on: March 16, 2017, 08:12:43 pm 
Started by MikeCheck - Last post by klaus
Good to know. Do you have a schematic for that chip? I am curious how it regulates.

 19 
 on: March 16, 2017, 05:13:10 pm 
Started by MikeCheck - Last post by Kai
... biggest complaint when using IC chips for regulation: switching noise.
The LM317 is an analog linear regulator, no switching inside. It does not generate lots of noise. What's left is filtered out by the final R2-C2 combination, no further improvements necessary.

 20 
 on: March 16, 2017, 02:56:08 pm 
Started by MikeCheck - Last post by klaus
The 317 regulator design is the better choice of these.
Thanks, Jim.
That's my biggest complaint when using IC chips for regulation: switching noise. Good filtering plus your Zener suggestion needs to be implemented to avoid that.

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