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Simple Zener Secondary Voltage Regulators
Simple Zener Secondary Voltage Regulators
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Old 1st January 2018, 12:54 PM   #1
Wavewhipper is offline Wavewhipper  United States
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Default Simple Zener Secondary Voltage Regulators

What chances are there that the cheap, easy, Zener, resistor, and capacitor used to make secondary voltages, say for a pre-amp or equalizer, being noisy as they are, would add overhead to the opamp's ability to reject noises and other undesired effects on it's ability to operate in micro-distortion performance. (what a sentence !)
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Old 1st January 2018, 02:05 PM   #2
Elvee is offline Elvee  Belgium
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The answer lies in computation, calculations and more computation: how much ripple is present in the first place, how much does the simple reg eliminates, and what is the opamp's PSRR.
If the result ends up being drowned in the native noise, then it's OK.

In the seventies, when the range of monolithic regulators was much more limited, this solution was very often used, when one would need, say +31V or any other non-standard voltage, and it posed no particular problem.

A typical open-loop, optimal simple reg + gyrator combo will typically provide 60 ~ 70dB rejection (limited by the Early effect).
If the opamp adds another 80dB, it's probably going to be sufficient, but you need to do the maths for each specific case.

Regarding "micro distortions", dunno....
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Old 1st January 2018, 02:22 PM   #3
Mark Johnson is offline Mark Johnson  United States
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Simple Zener Secondary Voltage Regulators
If some is good then more is (often) better.

In cases where calculation shows that "60 ~ 70dB rejection (limited by the Early effect)" is insufficient for your needs: connect two of them in cascade. Double the parts count and double the dBs of rejection.
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Old 2nd January 2018, 02:21 AM   #4
Wavewhipper is offline Wavewhipper  United States
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I worded that in a complex way. What I meant was can all the different types errors add together and make the opamp "too busy" to compensate for them all ?

I suppose those active constant current supplies that feed each section of a complex opamp might individually manage each type of distortion at the points they normally enter the signal. I was so happy to see such a simple zener regulator working well to feed a TL071 in a bass guitar amp, I'd toss that out to cyberworld and see what came back.
They may not do so well in hifi. Some music instrument amps are not hifi, they have intentional distortions to give a sonic personality to the instrument.

I don't think simple resistive long tails would do nearly as well.

Last edited by Wavewhipper; 2nd January 2018 at 02:27 AM.
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Old 2nd January 2018, 03:20 AM   #5
Wavewhipper is offline Wavewhipper  United States
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I suppose I'd really rather use a zener step-down and a 78LXX and 79LXX to clean the noise, just to be sure. Saves transformer money and space if the current demand is low enough. I always gave simple zener regulators the nose curl.

That's how I'll do it then.
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Old 2nd January 2018, 04:12 PM   #6
PRR is offline PRR  United States
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I think you are over-thinking this.

We have caps. Supply "noise" (unspecified!) can be reduced with caps.

Nearly all small-signal audio can be done with basic passive power supply and a few stages of R-C filtering.

Especially with opamp chips which are half regulators inside. (Nearly every gain stage works against a CCS.)

Regulators have a point when you must go right to the rating limit of your amplifier to make your desired signal voltage. Pro audio regulates to +/-15V or +/-18V so that it can meet the historical level of 6V6 line amps. Hi-Fi and instrument can be run 10dB lower and can use sloppy 20V-30V power without fear of overvoltage. (All the lamps in your house will explode before your TL072 does.)

Regulators "have a point" when the amplifier designer can't handle uncertain supply voltage. There are several classic designs which work OK at, say, 9V, but collapse at 6V and do not make use of higher supplies effectively. A ton of phono preamps were this way and for common wall-voltage variation and multi-stage R-C filtering they gave no trouble.

As Elvee says: C, C, and C!! Don't dizzy-tither, put numbers on it.
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Old 7th January 2018, 02:36 AM   #7
Wavewhipper is offline Wavewhipper  United States
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Well I can't hear anything wrong with line level signals powered by noisy 15v zener/resistor regulators. Again I just didn't know if it helps to reduce the everything thrown at it situation. They only say how it performs with reference to one adverse condition at a time, not all of them at once.
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Old 7th January 2018, 03:38 AM   #8
dotneck335 is offline dotneck335  United States
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Why use zeners when you can use this, for $7?
LM317 LM337 AC-DC Adjustable Dual Voltage Regulator Regulated Power Supply Board | eBay
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Old 7th January 2018, 02:32 PM   #9
Wavewhipper is offline Wavewhipper  United States
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Because I have a bin of assorted zeners, they cost a few cents, less board space, and I like the awesome graphics display of output geometry.
Capacitor couple the output to a small audio amp and it puts you to sleep without drugs.
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Old 7th January 2018, 02:48 PM   #10
globalplayer is offline globalplayer  Germany
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Fixed voltage regulators like the 78xx/79xx series will not really cost more and are a lot better.
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